HRP20220467A1 - HARD METAL COMPOSITION WC-1.0Cr3C2-0.2Co AND ITS APPLICATION - Google Patents
HARD METAL COMPOSITION WC-1.0Cr3C2-0.2Co AND ITS APPLICATION Download PDFInfo
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- UFGZSIPAQKLCGR-UHFFFAOYSA-N chromium carbide Chemical compound [Cr]#C[Cr]C#[Cr] UFGZSIPAQKLCGR-UHFFFAOYSA-N 0.000 claims abstract description 30
- 229910017052 cobalt Inorganic materials 0.000 claims abstract description 20
- 239000010941 cobalt Substances 0.000 claims abstract description 20
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 claims abstract description 20
- UONOETXJSWQNOL-UHFFFAOYSA-N tungsten carbide Chemical compound [W+]#[C-] UONOETXJSWQNOL-UHFFFAOYSA-N 0.000 claims abstract description 19
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- INZDTEICWPZYJM-UHFFFAOYSA-N 1-(chloromethyl)-4-[4-(chloromethyl)phenyl]benzene Chemical compound C1=CC(CCl)=CC=C1C1=CC=C(CCl)C=C1 INZDTEICWPZYJM-UHFFFAOYSA-N 0.000 description 5
- 238000012360 testing method Methods 0.000 description 5
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- MTPVUVINMAGMJL-UHFFFAOYSA-N trimethyl(1,1,2,2,2-pentafluoroethyl)silane Chemical compound C[Si](C)(C)C(F)(F)C(F)(F)F MTPVUVINMAGMJL-UHFFFAOYSA-N 0.000 description 2
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Abstract
Predmetni izum otkriva postupak dobivanja proizvoda od tvrdog metala na bazi prahova volfram karbida (WC), krom karbida (Cr<SUB>3</SUB>C<SUB>2</SUB>) i kobalta (Co). Sastav je odabran na način da bude WC - 98,8 %. tež. sa srednjom veličinom zrna od oko 150 nm, Cr3C2 – 1,0 % tež. koji se koristi u smjesi kao inhibitor rasta zrna, te Co – 0,2 % tež. Spomenutim postupkom dobiva se tvrdi metal sastava WC-1.0Cr<SUB>3</SUB>C<SUB>2</SUB>-0.2Co<B> </B>uglavnom<B> </B>bez pora, gustoće 15,55 g/cm<SUP>3</SUP>, tvrdoće 2590 prema Vickers metodi, sinteriranjem vrućim izostatičkom prešanjem na temperaturi od 1600°C, što je za približno 200 °C niža temperatura sinteriranja nego je uobičajeno u stanju tehnike. Ovaj materijal izuzetno je pogodan za proizvodnju mlaznica koje se koristi za rezanje vodenim mlazom.The related invention discloses a process for obtaining hard metal products based on tungsten carbide (WC), chromium carbide (Cr<SUB>3</SUB>C<SUB>2</SUB>) and cobalt (Co) powders. The composition was chosen to be WC - 98.8%. wt. with an average grain size of about 150 nm, Cr3C2 – 1.0% wt. which is used in the mixture as a grain growth inhibitor, and Co – 0.2% wt. The mentioned process produces a hard metal with composition WC-1.0Cr<SUB>3</SUB>C<SUB>2</SUB>-0.2Co, mostly without pores, density 15.55 g/cm<SUP>3</SUP>, hardness 2590 according to the Vickers method, by sintering by hot isostatic pressing at a temperature of 1600°C, which is approximately 200°C lower sintering temperature than is usual in the state of the art. This material is extremely suitable for the production of nozzles used for water jet cutting.The subject invention discloses a process for obtaining hard metal products based on tungsten carbide (WC), chromium carbide (Cr<SUB>3</SUB>C<SUB>2) and cobalt (Co) powders. The composition was chosen to be WC - 98.8%. wt. with an average grain size of about 150 nm, Cr3C2 – 1.0% wt. which is used in the mixture as a grain growth inhibitor, and Co – 0.2% by weight. The mentioned process produces hard metal with composition WC-1.0Cr<SUB>3</SUB>C<SUB>2</SUB>-0.2Co<B> </B>mainly<B> </B>without pores, density 15.55 g/cm<SUP>3</SUP>, hardness 2590 according to the Vickers method, by sintering by hot isostatic pressing at a temperature of 1600°C, which is approximately 200°C lower sintering temperature than is usual in the state of the art. This material is extremely suitable for the production of nozzles used for water jet cutting. The related invention discloses a process for obtaining hard metal products based on tungsten carbide (WC), chromium carbide (Cr<SUB>3</SUB>C<SUB >2</SUB>) and cobalt (Co) powders. The composition was chosen to be WC - 98.8%. wt. with an average grain size of about 150 nm, Cr3C2 – 1.0% wt. which is used in the mixture as a grain growth inhibitor, and Co – 0.2% wt. The mentioned process produces a hard metal with composition WC-1.0Cr<SUB>3</SUB>C<SUB>2</SUB>-0.2Co, mostly without pores, density 15.55 g/cm<SUP>3</SUP >, hardness 2590 according to the Vickers method, by sintering by hot isostatic pressing at a temperature of 1600°C, which is approximately 200°C lower sintering temperature than is usual in the state of the art. This material is extremely suitable for the production of nozzles used for water jet cutting.
Description
Područje tehnike The field of technology
Ovaj izum otkriva specifičan postupak dobivanja tvrdog metala sastava WC-1.0Cr3C2-0.2Co kao i specifičnu upotrebu istog. S obzirom na sastav ovog tvrdog metala gdje je osnovni konstituent volfram karbid (WC), ovaj izum pripada području legura zasnovanih na karbidima, posebno na volframovu karbidu. S obzirom na specifičan način dobivanja, predmetni izum pripada području metalurgije praha, gdje su svi korišteni materijali inicijalno u praškastoj formi, a koji se postupkom sinteriranja konsolidiraju u željeni tvrdi metal. This invention discloses a specific process for obtaining hard metal composition WC-1.0Cr3C2-0.2Co as well as its specific use. Considering the composition of this hard metal where the main constituent is tungsten carbide (WC), this invention belongs to the field of alloys based on carbides, especially tungsten carbide. With regard to the specific method of obtaining, the subject invention belongs to the field of powder metallurgy, where all the materials used are initially in powder form, and which are consolidated into the desired hard metal by the sintering process.
Tehnički problem Technical problem
Proizvodnja volfram karbida datira od ranih 1920-ih kada je njemačka tvrtka za električne žarulje Osram tražila zamjenu za korištene skupe dijamantne mlaznice (alate) u proizvodnji volframove žice. Napori u zamjeni dijamanta doveli su do izuma tvrdog metala, kojeg su mnoge tvrtke ubrzo počele proizvoditi i plasirati na tržište za višestruke primjene. Njegova visoka otpornost na trošenje bila je presudna za široku primjenu. The production of tungsten carbide dates back to the early 1920s when the German electric light bulb company Osram was looking for a replacement for the expensive diamond nozzles (tools) used in the production of tungsten wire. Efforts to replace diamond led to the invention of carbide, which many companies soon began producing and marketing for multiple applications. Its high wear resistance was crucial for its wide application.
Prvi sastavi na bazi volfram karbida i kobalta ubrzo su primijenjeni kao materijali u izradi alata za rezanje i mljevenje lijevanog željeza. Početkom 1930-ih, pionirske tvrtke za proizvodnju tvrdog metala uvele su sastave tvrdih metala u mlinove za mljevenje čelika a gdje su ti, tada novi i revolucionarni materijali, osim kobalta i volframova karbida, sadržavali i karbide tantala i titana. Nakon toga pojavili su se posebni rudarski alati s vrhovima od tvrdog metala koji su produžili vijek trajanja bušilica za stijene za faktor od najmanje 10 u usporedbi s konvencionalnim alatima za bušenje na bazi čelika. The first compositions based on tungsten carbide and cobalt were soon used as materials in the production of tools for cutting and grinding cast iron. In the early 1930s, pioneering hard metal production companies introduced hard metal compositions into steel mills, where these then new and revolutionary materials, in addition to cobalt and tungsten carbide, also contained tantalum and titanium carbides. This was followed by special carbide tipped mining tools that extended the life of rock drills by a factor of at least 10 compared to conventional steel-based drilling tools.
Vremenom slijede i druge primjene, kao što su npr. primjena za izrađivanje mlaznica za rezanje vodom. Rezanje vodenim mlazom spada među nestandardne postupke obrade metala i tvrdih materijala, koji se temelje na postupku mehaničkog odnošenja materijala. Abrazivni vodeni mlaz je tanak mlaz mješavine vode i kremenog pijeska pod visokim tlakom, koji djeluje na radni komad koji se obrađuje i erozijom odnosi osnovni materijal, te tako radi rez na spomenutom materijalu. Rezanje vodenim mlazom koristi se za rezanje metala (nehrđajući čelik, aluminijske legure, kaljeni čelik, bakar i mjed - sve do čak 150 mm debljine), tvrdog metala, stakla, kamena (npr. granit), polimera , gume, drva, itd. Vodeno rezanje ne zagrijava materijal, što je naročito korisno za čelike koji su namijenjeni za naknadnu toplinsku obradu. Prosječnom stručnjaku područja je jasno da mlaznica, koja se ponekada naziva i cijev za miješanje, mora biti otporna na trošenje kako bi efikasno obavljala svoj posao kroz određeno vrijeme upotrebe, nakon koje se naravno zamjenjuje radi potrošenosti. Over time, other applications followed, such as, for example, the application for making nozzles for water cutting. Water jet cutting is one of the non-standard methods of processing metals and hard materials, which are based on the process of mechanical material removal. Abrasive water jet is a thin jet of a mixture of water and flint sand under high pressure, which acts on the work piece being processed and removes the base material by erosion, thus making a cut on the mentioned material. Waterjet cutting is used for cutting metals (stainless steel, aluminum alloys, hardened steel, copper and brass - up to 150 mm thick), hard metal, glass, stone (e.g. granite), polymer, rubber, wood, etc. Water cutting does not heat the material, which is especially useful for steels that are intended for subsequent heat treatment. It is clear to the average expert in the field that the nozzle, which is sometimes called a mixing tube, must be resistant to wear in order to perform its job efficiently for a certain period of use, after which it is of course replaced due to wear and tear.
Osnovni tehnički problem koji se rješava predmetnim izumom odnosi se na konsolidaciju tvrdog metala sastava WC-1.0Cr3C2-0.2Co tzv. sinter-HIP postupkom (postupkom sinteriranja u vakuumu i naknadnim vrućim izostatičkim prešanjem, eng. sintering via Hot Isostatic Pressure) u jednom ciklusu, kod kojeg je korištena temperatura sinteriranja za oko 200°C manja od uobičajene temperature sinteriranja materijala sličnog sastava, a s tehnološkim rezultatom koji je barem jednako toliko dobar kao i onaj na povišenoj temperaturi, a očituje se u tvrdom metalu – proizvodu bez pora. Naime, poznato je da se sinter-HIP postupak koristi uglavnom kako bi se dobili karbidi sa malo ili gotovo ništa poroznosti te s gustoćom koja je blizu teorijske gustoće za dani sastav. Predmetni postupak dokazano, kao što ćemo vidjeti, daje jednaki rezultat uz signifikantno nižu temperaturu postupka. The basic technical problem that is solved by the present invention relates to the consolidation of hard metal composition WC-1.0Cr3C2-0.2Co, so called. sinter-HIP process (sintering via Hot Isostatic Pressure) in one cycle, where the sintering temperature is about 200°C lower than the usual sintering temperature of materials of similar composition, and with a technological result which is at least as good as the one at elevated temperature, and is manifested in hard metal - a product without pores. Namely, it is known that the sinter-HIP process is used mainly to obtain carbides with little or almost no porosity and with a density that is close to the theoretical density for the given composition. The procedure in question has been proven, as we will see, to give the same result with a significantly lower temperature of the procedure.
Drugi tehnički problem, a koji se simultano rješava s prvim problemom, odnosni se na faktičnu primjena tako dobivenog materijala WC-1.0Cr3C2-0.2Co za formiranje mlaznica za rezanje vodom. Rješenje za navedene tehničke probleme nalazi se u pripremi smjese za sinteriranje, kako ćemo vidjeti u detaljnom opisu ovog izuma koji slijedi niže. The second technical problem, which is solved simultaneously with the first problem, relates to the actual application of the thus obtained material WC-1.0Cr3C2-0.2Co for the formation of nozzles for water cutting. The solution to the mentioned technical problems is found in the preparation of the sintering mixture, as we will see in the detailed description of this invention that follows below.
Stanje tehnike State of the art
U stanju tehnike poznati su materijali bliskog sastava navedenog u ovom dokumentu. In the state of the art, materials close to the composition specified in this document are known.
Kineska prijava patenta objavljena kao CN113061764A za izum TUNGSTEN CARBIDE-BASED HARD ALLOY AND PREPARATION METHOD THEREOF poučava o dobivanju materijala gdje se volfram karbidu (WC) dodaje od 0-1,5 % tež. krom karbida (Cr3C2), 0,0-2,0 % tež. vanadij karbida (VC) ili titan karbida (TiC) i između 0-1,5 % tež. kobalta (Co) ili nikla (Ni). U primjeru 6 istoimenog dokumenta, naveden je sastav WC-0.8Cr3C2-0.5VC-0.2Co, gdje se kao inhibitor rasta zrna koristi smjesa Cr3C2 i VC, te se u postupku homogeniziranja koristi n-heksan ili aceton. Ovaj dokument pokazuje da se sinteriranje izvodi u dva koraka, prvi do 1540°C i drugi na oko 1800°C, uz tlak od 240 MPa. Razlika između predmetnog izuma i CN113061764A je u temperaturi sinteriranja, premda su materijali vrlo sličnog sastava uz već spomenutih 0,2 % tež. Co. The Chinese patent application published as CN113061764A for the invention TUNGSTEN CARBIDE-BASED HARD ALLOY AND PREPARATION METHOD THEREOF teaches the preparation of a material where tungsten carbide (WC) is added from 0-1.5% by weight. chromium carbide (Cr3C2), 0.0-2.0% by weight. vanadium carbide (VC) or titanium carbide (TiC) and between 0-1.5% by weight. cobalt (Co) or nickel (Ni). In example 6 of the document of the same name, the composition WC-0.8Cr3C2-0.5VC-0.2Co is specified, where a mixture of Cr3C2 and VC is used as a grain growth inhibitor, and n-hexane or acetone is used in the homogenization process. This document shows that sintering is performed in two steps, the first up to 1540°C and the second at about 1800°C, with a pressure of 240 MPa. The difference between the subject invention and CN113061764A is in the sintering temperature, although the materials are of very similar composition with the already mentioned 0.2% by weight. Co.
US prijava patenta objavljena kao US2014072469A1 za izum INERT HIGH HARDNESS MATERIAL FOR TOOL LENS PRODUCTION poučava o materijalu čiji sastav se može zapisati kao WC-0.16%Co-0.95%Cr, a u smjesi se nalazi ugljik u opsegu od 5,85-6,13 % tež. Količinski udio Co je blizu onog iz izuma gdje je udio kobalta specificiran kao 0,2 % tež. Kako piše u opisu navedenog dokumenta stanja tehnike, tipične temperature sinteriranja za spomenute materijale kreću se od 1300°C-1850°C, no kvalitetna densifikacija dobije se tek u opsegu od 1600°C-1700°C. Uglavnom, ovaj dokument specificira, za dani težinski sastav, temperature koje su uglavnom bitno iznad 1600°C. The US patent application published as US2014072469A1 for the invention INERT HIGH HARDNESS MATERIAL FOR TOOL LENS PRODUCTION teaches about a material whose composition can be written as WC-0.16%Co-0.95%Cr, and the mixture contains carbon in the range of 5.85-6.13 % wt. The amount of Co is close to that of the invention where the cobalt content is specified as 0.2% by weight. As written in the description of the mentioned state of the art document, typical sintering temperatures for the mentioned materials range from 1300°C-1850°C, but quality densification is obtained only in the range of 1600°C-1700°C. Basically, this document specifies, for a given weight composition, temperatures that are generally substantially above 1600°C.
Dokument iz 2017. godine, Ma, R., Ju, S., Chen, H., & Shu, C.: „Effect of Cobalt Content on Microstructures and Wear Resistance of Tungsten Carbide–Cobalt-Cemented Carbides Fabricated by Spark Plasma Sintering“, IOP Conference Series; Materials Science and Engineering, 207, 012019. doi:10.1088/1757-899x/207/1/012019; poučava o WC-Co karbidima sa malo ili nimalo veziva u formi kobalta (Co), tj. 0 % tež., 0,2 % tež., 0.5 % tež. i 0,8 % tež., i ekvivalentnim postupcima sinteriranja, posebno kroz SPS (spark plasma sinthering). U navedenom dokumentu u tablici 2 nalaze se procesni parametri koji za sastav WC-0,2 % tež. Co pokazuju i dalje temperaturu koja je veća od 1600 °C, konkretno za 5%, te iznose oko 1680°C. Ovaj rad je značajan jer ukazuje na činjenicu da povećavanje udjela Co u WC-Co materijalima smanjuje potrebnu temperaturu sinteriranja. No, ovaj dokument ne govori o provedenoj densifikaciji i odsutnosti pora u dobivenim uzorcima prema otkrivenom postupku, što je izuzetno bitna karakteristika ukoliko se spomenuti materijal želi koristiti za formiranje mlaznica za rezanje vodenim mlazom. 2017 paper, Ma, R., Ju, S., Chen, H., & Shu, C.: “Effect of Cobalt Content on Microstructures and Wear Resistance of Tungsten Carbide–Cobalt-Cemented Carbides Fabricated by Spark Plasma Sintering ", IOP Conference Series; Materials Science and Engineering, 207, 012019. doi:10.1088/1757-899x/207/1/012019; teaches about WC-Co carbides with little or no binder in the form of cobalt (Co), i.e. 0% wt., 0.2% wt., 0.5% wt. and 0.8% by weight, and equivalent sintering procedures, especially through SPS (spark plasma sintering). In the mentioned document in table 2 there are process parameters which for the composition of WC-0.2 % wt. Co still show a temperature that is higher than 1600 °C, specifically by 5%, and is around 1680 °C. This work is significant because it indicates the fact that increasing the proportion of Co in WC-Co materials reduces the required sintering temperature. However, this document does not talk about densification and the absence of pores in the obtained samples according to the disclosed procedure, which is an extremely important characteristic if the mentioned material is to be used to form nozzles for water jet cutting.
Rad iz 2012. godine, Poetschke, J., Richter, V., & Holke, R.: „Influence and effectivity of VC and Cr3C2 grain growth inhibitors on sintering of binderless tungsten carbide. International Journal of Refractory Metals and Hard Materials“, 31, 218–223. doi:10.1016/j.ijrmhm.2011.11.006; ispituje utjecaj VC ili Cr3C2 kao inhibitora rasta zrna na mikrostrukturne karakteristike WC materijala. Iz tablice 1 istog rada može se deducirati da preferiran udio Cr3C2 od 1% tež. daje 100% desnifikaciju, bez abnormalnih zrna u proizvodu, što isti čini pogodnim za različite primjene. Paper from 2012, Poetschke, J., Richter, V., & Holke, R.: "Influence and effectiveness of VC and Cr3C2 grain growth inhibitors on sintering of binderless tungsten carbide." International Journal of Refractory Metals and Hard Materials", 31, 218–223. doi:10.1016/j.ijrmhm.2011.11.006; examines the influence of VC or Cr3C2 as a grain growth inhibitor on the microstructural characteristics of WC materials. From table 1 of the same work, it can be deduced that the preferred proportion of Cr3C2 of 1% by weight. gives 100% desnification, without abnormal grains in the product, which makes it suitable for various applications.
Rad iz 2020. godine, autora Lay, S., Antoni-Zdziobek, A., Pötschke, J., & Herrmann, M.: „Microstructural investigations in binderless tungsten carbide with grain growth inhibitors“, International Journal of Refractory Metals and Hard Materials, 93, 105340. doi:10.1016/j.ijrmhm.2020.105340; opisuje WC bez udjela Co, no sa 1% tež. Cr3C2. Treba reći da u opisu metode, posebno kod postupka mljevenja sastojaka, naknadno nađena kontaminacija prahova kobaltom (Co) od oko 0,05 % tež. koja potječe od korištenih kugličnih mlinova. Takva „kontaminirana“ smjesa sa udjelom Co koji je četiri puta manji od onoga prema izumu, sinterirana je na temperaturama od oko 1900°C te su dobiveni uzorci koji su 100% densificirani. 2020 paper by Lay, S., Antoni-Zdziobek, A., Pötschke, J., & Herrmann, M.: "Microstructural investigations in binderless tungsten carbide with grain growth inhibitors", International Journal of Refractory Metals and Hard Materials, 93, 105340. doi:10.1016/j.ijrmhm.2020.105340; describes WC without Co content, but with 1% wt. Cr3C2. It should be said that in the description of the method, especially in the process of grinding the ingredients, contamination of powders with cobalt (Co) of about 0.05% by weight was subsequently found. which comes from used ball mills. Such a "contaminated" mixture with a proportion of Co which is four times lower than that according to the invention, was sintered at temperatures of around 1900°C and 100% densified samples were obtained.
Niti jedan od gore navedenih dokumenata stanja tehnike ne otkriva izrijekom materijal sastava WC-1.0Cr3C2-0.2Co, koji se sinterira na relativno niskoj temperaturi od 1600°C, te koji je u cijelosti bez pora. Rješenje za ovaj tehnički problem detaljno će biti dano u opisu izuma. None of the above-mentioned state-of-the-art documents explicitly discloses the WC-1.0Cr3C2-0.2Co material, which is sintered at a relatively low temperature of 1600°C, and which is completely pore-free. The solution to this technical problem will be given in detail in the description of the invention.
Bit izuma The essence of invention
Predmetni izum odnosi se na novi postupak dobivanja proizvoda od tvrdog metala na bazi prahova volfram karbida (WC), krom karbida (Cr3C2) i kobalta (Co). Sastav je odabran tako da bude WC - 98,8 %. tež. sa srednjom veličinom zrna od oko 150 nm, Cr3C2 – 1,0 % tež. koji se koristi u smjesi kao inhibitor rasta zrna, te ostatak čini Co – 0,2 % tež. Ovaj postupak sastoji od sljedećih koraka: The present invention relates to a new process for obtaining hard metal products based on tungsten carbide (WC), chromium carbide (Cr3C2) and cobalt (Co) powders. The composition was chosen to be WC - 98.8%. wt. with an average grain size of about 150 nm, Cr3C2 – 1.0% wt. which is used in the mixture as a grain growth inhibitor, and the rest is Co – 0.2% by weight. This procedure consists of the following steps:
A. priprema mješavine polaznih prahova, A. preparation of the mixture of starting powders,
B. miješanja i homogenizacije bez kontaminacije u cilju stvaranja homogene mikrostrukture, uz dodatak heptana (CH3(CH2)5CH3) te opcijski parafinskog voska do najviše 0,5% tež. omjera smjese, u kugličnom mlinu, B. mixing and homogenization without contamination in order to create a homogeneous microstructure, with the addition of heptane (CH3(CH2)5CH3) and optionally paraffin wax up to a maximum of 0.5% by weight. mixture ratio, in a ball mill,
C. sušenja mješavine radi eliminacije tekuće faze heptana vakuumskom destilacijom, C. drying the mixture in order to eliminate the liquid phase of heptane by vacuum distillation,
D. granulacije uz pomoću sita, koja za cilj ima dovođenje smjese prahova u svojstvo tečenja, te D. granulation using a sieve, which aims to bring the mixture of powders into a flowable state, and
E. oblikovanja prešanjem ili ekstruzijom koje definira konačan oblik proizvoda, a provodi se na temperaturi od 15-30°C. E. molding by pressing or extrusion, which defines the final shape of the product, and is carried out at a temperature of 15-30°C.
F. predsinteriranje – uklanjanje prethodno opcijski dodatnog parafinskog voska, te koraka zagrijavanja proizvoda do 800°C u vakuumu ili atmosferi vodika, F. pre-sintering – removal of previously optionally additional paraffin wax, and the step of heating the product up to 800°C in a vacuum or hydrogen atmosphere,
Tako oblikovan proizvod podvrgava se postupku sinteriranja u nekoliko koraka: The product formed in this way is subjected to the sintering process in several steps:
G. zagrijavanja proizvoda do 1200°C u vakuumu, G. heating the product up to 1200°C in a vacuum,
H. zagrijavanja od 1200°C do 1600°C u atmosferi argona (Ar) pri tlaku od 10 mbar u trajanju od 30 minuta, te H. heating from 1200°C to 1600°C in an atmosphere of argon (Ar) at a pressure of 10 mbar for 30 minutes, and
I. sinteriranjem vrućim izostatičkom prešanjem na temperaturi od 1600°C te tlaku 80-100 bar u trajanju od barem 45 minuta. I. sintering by hot isostatic pressing at a temperature of 1600°C and a pressure of 80-100 bar for at least 45 minutes.
Kao rezultat postupka dobije se tvrdi metal sastava WC-1.0Cr3C2-0.2Co uglavnom bez pora, gustoće 15,55 g/cm3 i tvrdoće od oko 2590 HV određenoj prema Vickers metodi. As a result of the process, a hard metal of composition WC-1.0Cr3C2-0.2Co is obtained, mostly without pores, density 15.55 g/cm3 and hardness of about 2590 HV determined according to the Vickers method.
Poželjno je da se korak B. provodi u trajanju od barem 72 sata. Nadalje, poželjno je da se korak C. provodi na temperaturi od oko 80°C, a korak D sitom veličine okâ od približno 315 μm. Korak E. provodi se na sobnoj temperaturi pod tlakom od oko 200 MPa ukoliko se radi o prešanju. It is preferable that step B. is carried out for at least 72 hours. Furthermore, it is preferable that step C. is carried out at a temperature of about 80°C, and step D with a sieve of approximately 315 μm. Step E. is carried out at room temperature under a pressure of about 200 MPa if it is about pressing.
Dobiveni proizvod prema predmetnom postupku može se, među ostalim, oblikovati kao mlaznica koja se koristi za rezanje vodenim mlazom u koraku E. samog postupka. The product obtained according to the process in question can, among other things, be shaped as a nozzle used for cutting with a water jet in step E. of the process itself.
Opis crteža Description of the drawing
Slika 1 prikazuje mikrostrukturu uzorka PL38-02 uzorak sastava WC-1.0Cr3C2-0.2Co dobiven postupkom prema predmetnom izumu uz temperaturu sinteriranja od 1600°C, gdje je karakterizacija provedena FESEM tehnikom. Figure 1 shows the microstructure of sample PL38-02, a sample of composition WC-1.0Cr3C2-0.2Co obtained by the process according to the subject invention with a sintering temperature of 1600°C, where the characterization was carried out using the FESEM technique.
Slika 1A prikazuje uzorak PL38-02 dobiven postupkom prema predmetnom izumu uz temperaturu sinteriranja od 1600°C, gdje je karakterizacija provedena optičkim mikroskopom, te gdje se vidi odsutnost pora na uzorku. Figure 1A shows the sample PL38-02 obtained by the process according to the subject invention with a sintering temperature of 1600°C, where the characterization was carried out with an optical microscope, and where the absence of pores on the sample can be seen.
Slika 2 prikazuje uzorak PK109-01 dobiven uz temperaturu sinteriranja od 1600°C, gdje je karakterizacija provedena optičkim mikroskopom, te gdje se jasno vidi prisutnost pora na uzorku. Uzorak je ulaznog sastava identičnog s uzorkom PL38-02, ali je postupak u koraku B. trajao po prilici 3x kraće, oko 24 sata. Figure 2 shows the PK109-01 sample obtained with a sintering temperature of 1600°C, where the characterization was performed with an optical microscope, and where the presence of pores on the sample is clearly visible. The sample's input composition is identical to that of sample PL38-02, but the procedure in step B. took about 3 times less time, about 24 hours.
Slika 3 prikazuje uzorak PK111-01 dobiven uz temperaturu sinteriranja od 1600°C, gdje je karakterizacija provedena optičkim mikroskopom, te gdje se vidi još veća prisutnost pora na uzorku u odnosu na uzorke PL38-02 i PK109-01. Uzorak je ulaznog sastava identičnog s uzorkom PL38-02, ali je postupak u koraku B. trajao po prilici 3x kraće, oko 24 sata i korišteni prah WC šarže bio je inicijalno manjih dimenzija čestica i veće specifične površine. Figure 3 shows the sample PK111-01 obtained with a sintering temperature of 1600°C, where the characterization was carried out with an optical microscope, and where one can see an even greater presence of pores on the sample compared to the samples PL38-02 and PK109-01. The sample's input composition is identical to that of sample PL38-02, but the procedure in step B. lasted about 3x shorter, about 24 hours, and the powder used in the WC batch was initially of smaller particle size and larger specific surface area.
Slike 4, 4A; 5, 5A te 6 i 6A prikazuju uzorke PL38-01, PK109-02 i PK111-02, sastava jednakog kao na slikama 1-3, istih prahova i jednakog postupanja/tretmana u koraku B. No, temperatura sinteriranja ove kontrolne skupine iznosila je 1800°C. Slike jasno pokazuju odsutnost pora - slike 4A, 5A i 6A, i kvalitetnu densifikaciju uzoraka dodatno karakteriziranih FESEM tehnikom, slike 4, 5 i 6. Figures 4, 4A; 5, 5A and 6 and 6A show samples PL38-01, PK109-02 and PK111-02, the same composition as in Figures 1-3, the same powders and the same procedure/treatment in step B. However, the sintering temperature of this control group was 1800°C. The images clearly show the absence of pores - Figures 4A, 5A and 6A, and the quality densification of the samples additionally characterized by the FESEM technique, Figures 4, 5 and 6.
Detaljan opis izuma Detailed description of the invention
Kako je već prije spomenuto, osnovni tehnički problem koji se rješava predmetnim izumom odnosi se na formiranje tvrdog metala sastava WC-1.0Cr3C2-0.2Co tzv. sinter-HIP postupkom (postupkom sinteriranja vrućim izostatičkim prešanjem u jednom ciklusu, eng. sintering via Hot Isostatic Pressure) kod kojeg je korištena temperatura sinteriranja za oko 200°C manja od uobičajene temperature sinteriranja istih ili sličnih uzoraka koja, prema stanju tehnike, iznosi oko 1800°C. Tehnološki rezultat prema predmetnom postupku izvedenom na 1600°C pokazuje se jednako dobar kao i onaj na povišenoj temperaturi sinteriranja od 1800°C i očituje se u dobivanju tvrdog metala kao proizvoda bez pora. As already mentioned before, the basic technical problem that is solved by the present invention relates to the formation of a hard metal with the composition WC-1.0Cr3C2-0.2Co, the so-called sinter-HIP process (sintering via Hot Isostatic Pressure) in which the sintering temperature used is about 200°C lower than the usual sintering temperature of the same or similar samples, which, according to the state of the art, is about 1800°C. The technological result according to the process in question performed at 1600°C is as good as that at the elevated sintering temperature of 1800°C and is manifested in obtaining hard metal as a product without pores.
Prema priloženim dokumentima stanja tehnike, sinteriranje prahova inicijalnog sastava WC-1.0Cr3C2-0.2Co na 1600°C ne daje dovoljnu densifikaciju, tj. proizvode koji su bez pora, a što je neobično važno ukoliko se namjeravaju proizvesti proizvodi kao što su mlaznice za rezanje vodenim mlazom. U praksi metalurgije praha, ovom problemu se može pristupiti sa dvije strane; jedna je svakako podizanje temperature sinteriranja na cca. 1800°C što je dobro poznato u stanju tehnike, a druga inventivna - da se posveti veća pažnja ulaznim parametrima pripreme smjese, npr. da se poveća vrijeme homogenizacije u mlinu i poveća brzina istog – o čemu nema podataka u stanju tehnike. According to the attached state-of-the-art documents, the sintering of powders with the initial composition of WC-1.0Cr3C2-0.2Co at 1600°C does not give sufficient densification, i.e. products that are without pores, which is unusually important if it is intended to produce products such as cutting nozzles water jet. In the practice of powder metallurgy, this problem can be approached from two sides; one is certainly raising the sintering temperature to approx. 1800°C which is well known in the state of the art, and the other inventive - to pay more attention to the input parameters of the preparation of the mixture, for example to increase the time of homogenization in the mill and increase its speed - about which there is no information in the state of the art.
Pokusi u vezi s predmetnim izumom zamišljeni su na način da se određeni procesni parametri variraju, te da se formiraju dvije serije po tri uzorka koji će proći isti postupak konsolidacije/sinteriranja pri različitim temperaturama; jednom na 1600°C, a drugi puta na 1800°C. Svim uzorcima zajednički sastav je WC-1.0Cr3C2-0.2Co uz alternaciju ulaznih prahova za WC – DN2.5 i/ili DN3, kako je to prikazano u Tabeli 1: Experiments related to the present invention are designed in such a way that certain process parameters are varied, and that two batches of three samples are formed that will undergo the same consolidation/sintering procedure at different temperatures; once at 1600°C and the second time at 1800°C. The common composition of all samples is WC-1.0Cr3C2-0.2Co with the alternation of input powders for WC – DN2.5 and/or DN3, as shown in Table 1:
[image] [image]
A. Priprema mješavine A. Preparation of the mixture
U ovom dijelu opisat ćemo korištene prahove. Kako je vidljivo iz tabele 1, za uzorke su korišteni prahovi volfram karbida (WC), srednje veličine WC zrna približno 150 nm, oznaka praha WC DN 2.5 i WC DN3.0, proizvođač, H.C. Starck Tungsten GmbH, Njemačka. Ove prahove karakterizira ekstremno mali sadržaj nečistoća, gdje su prahovi nano- do ultrafinih veličina zrna, od 90 nm do 200 nm, s različitom BET specifičnom površinom, za DN 2.5 od 2,4-2,7 m2/g, a za prah oznake DN 3.0 od 2,8-3,2 m2/g. In this part, we will describe the powders used. As can be seen from Table 1, tungsten carbide (WC) powders were used for the samples, average WC grain size approximately 150 nm, powder designation WC DN 2.5 and WC DN3.0, manufacturer, H.C. Starck Tungsten GmbH, Germany. These powders are characterized by an extremely low content of impurities, where the powders are of nano- to ultrafine grain sizes, from 90 nm to 200 nm, with a different BET specific surface area, for DN 2.5 of 2.4-2.7 m2/g, and for the powder marks DN 3.0 of 2.8-3.2 m2/year.
Detaljniji podaci mogu se dobiti na poveznici: More detailed information can be obtained at the link:
https://www.hcstarck.com/wp-content/uploads/2021/12/PD-1406_5-WC-DN.pdf https://www.hcstarck.com/wp-content/uploads/2021/12/PD-1406_5-WC-DN.pdf
Kao inhibitor rasta zrna, korišten je prah krom karbida (Cr3C2) težinskog udjela od 1% u smjesi. Uz spomenuto, korišten je i prah kobalta (Co), težinskog udjela 0,2 %, oznaka praha HMP Co, veličine čestica od 0,5 μm, belgijskog proizvođača Umicore. U svim navedenim uzorcima iz Tabele 1, odvagana je smjesa konstituenata WC-1.0Cr3C2-0.2Co na način da se dobije smjesa prahova težine 200 g. As a grain growth inhibitor, chromium carbide (Cr3C2) powder of 1% by weight was used in the mixture. In addition to the above, cobalt (Co) powder, 0.2% by weight, brand name HMP Co, particle size 0.5 μm, from the Belgian manufacturer Umicore was also used. In all the mentioned samples from Table 1, the mixture of constituents WC-1.0Cr3C2-0.2Co was weighed in such a way as to obtain a mixture of powders weighing 200 g.
B. Miješanje i homogenizacija B. Mixing and homogenization
Priprema mješavine polaznih prahova provedena je u horizontalnom kugličnom mlinu u spremniku od nehrđajućeg čelika s tvrdo-metalnim kuglicama. Primani cilj postupka je provođenje miješanja i homogenizacija prahova. Kako je već spomenuto, u mlin se stavljalo 200 g. smjese prahova, opcijski je dodavan parafin do maksimalnog udjela od 0,5 % tež., a korištene kuglice su bile promjera 4,5 mm uz omjer masa kuglica i mase smjese prahova 10:1, odnosno ukupna masa kuglica iznosila je 2 kg. Volumen komore mlina gdje se provodilo miješanje iznosio je približno 1 dm3, a korišten je bio laboratorijski kuglični mlin tvrtke ZOZ GmbH, Njemačka. Treba napomenuti da tvrdo-metalne kuglice korištene u samom kugličnom mlinu moraju biti takove da ne kontaminiraju ili tek minimalno kontaminiraju smjesu u procesu miješanja i homogenizacije, na način kako je to opisano u sekciji stanje tehnike, u radu autora Lay, S. i drugi, gdje se pojavio kobalt (Co) u smjesi koja je inicijalno zamišljena bez kobalta. The preparation of the starting powder mixture was carried out in a horizontal ball mill in a stainless steel container with hard metal balls. The primary goal of the procedure is to mix and homogenize the powders. As already mentioned, 200 g of the powder mixture was put into the mill, paraffin was optionally added up to a maximum proportion of 0.5% by weight, and the balls used were 4.5 mm in diameter with a ratio of the mass of the balls to the mass of the powder mixture of 10: 1, that is, the total mass of the balls was 2 kg. The volume of the mill chamber where the mixing was carried out was approximately 1 dm3, and the laboratory ball mill of the company ZOZ GmbH, Germany, was used. It should be noted that the hard metal balls used in the ball mill itself must be such that they do not contaminate or only minimally contaminate the mixture in the mixing and homogenization process, as described in the state of the art section, in the work by Lay, S. and others. where cobalt (Co) appeared in a mixture that was initially conceived without cobalt.
U samu smjesu , kako je to uobičajeno u stanju tehnike, dodan je medij za miješanje i homogenizaciju - heptan (CH3(CH2)5CH3), u količini od otprilike 200 mL, što uz gustoću od 0,683 g/cm3 daje oko 135 g nove tekuće faze u mlinu, uz sve ostale pobrojane konstituente. In the mixture itself, as is usual in the state of the art, a medium for mixing and homogenization was added - heptane (CH3(CH2)5CH3), in an amount of approximately 200 mL, which with a density of 0.683 g/cm3 gives about 135 g of new liquid stages in the mill, along with all other listed constituents.
U Tabeli 1 dana su procesna vremena i brzine kugličnog mlina korištenog u samom postupku. Uzorci PK109 i PK111 tretirani su u trajanju 24 sata uz 70 okretaja u minuti (rpm - rotation per minute). Uzorci oznake PL38 tretirani su 72 sata uz 90 rpm. Prilikom formiranja uzoraka iz serije PL38, izostavljen je parafin iz smjese, no naknadna ispitivanja i ponavljanja ovih pokusa pokazala su da dodavanje parafina gotovo da ne proizvodi mjerljiv učinak, ukoliko se isti dodaje u količinama od 0,5 % tež. Naravno, dodavanje parafina zahtijeva i njegovo naknadno uklanjanje postupkom predsinteriranja kako je opisano niže u koraku F Table 1 shows the process times and speeds of the ball mill used in the process itself. Samples PK109 and PK111 were treated for 24 hours at 70 revolutions per minute (rpm - rotation per minute). PL38 samples were treated for 72 hours at 90 rpm. During the formation of samples from the PL38 series, paraffin was omitted from the mixture, but subsequent tests and repetitions of these experiments showed that the addition of paraffin almost does not produce a measurable effect, if it is added in amounts of 0.5% by weight. Of course, the addition of paraffin requires its subsequent removal by the pre-sintering process as described below in step F
C. Sušenje mješavine C. Drying of the mixture
Nakon koraka B. i provedenog miješanja i homogenizacije, potrebno je ukloniti tekuću fazu iz smjese, odnosno provesti uklanjanje heptana. Uklanjanje heptana vrši se vakuumskom destilacijom, tj. zagrijavanjem smjese na temperaturu iznad temperature ključanja u vakuumu, a koja je oko 80°C. Radi reference navodimo da je temperatura ključanja heptana pri normalnom tlaku oko 98°C. Postupak se vrši sve dok postoji „tlak“ koji ukazuje na isparavanje heptana iz smjese, ili pak kroz empirijski određeno vrijeme procesa sušenja, npr. kroz 8 sati sušenja u predmetnom slučaju. After step B. and mixing and homogenization, it is necessary to remove the liquid phase from the mixture, i.e. remove heptane. The removal of heptane is done by vacuum distillation, i.e. by heating the mixture to a temperature above the boiling temperature in a vacuum, which is around 80°C. For reference, we state that the boiling point of heptane at normal pressure is about 98°C. The procedure is carried out as long as there is a "pressure" that indicates the evaporation of heptane from the mixture, or else through an empirically determined time of the drying process, for example through 8 hours of drying in the case in question.
D. Granuliranje D. Granulation
Postupak granuliranja provodi se uz pomoću sita. Postupak granulacije ima za cilj odvajanje kuglica za mljevenje od mješavine prahova i dovođenje smjese prahova u svojstvo tečenja. Za postupak granulacije prema predmetnom izumu, koristilo se sito promjera okâ od oko 315 μm čime se postigla ujednačenost veličine granula u smjesi i već prethodno spomenuto svojstvo tečenja. The granulation process is carried out using a sieve. The purpose of the granulation process is to separate the grinding balls from the powder mixture and bring the powder mixture into a flowable state. For the granulation process according to the subject invention, a sieve with a mesh diameter of about 315 μm was used, which achieved the uniformity of the size of the granules in the mixture and the previously mentioned flow property.
E. Oblikovanje E. Shaping
Oblikovanja smjese u formu željenog proizvoda vrši se prešanjem gdje se smjesa kompaktira u kalup koji definira oblik proizvoda. Uobičajeno se kompaktiranje provodi na temperaturi od 15-30°C i tlakom od 150-350 MPa, najbolje na sobnoj temperaturi i tlaku od otprilike 200 MPa. Forming the mixture into the form of the desired product is done by pressing, where the mixture is compacted into a mold that defines the shape of the product. Compacting is usually carried out at a temperature of 15-30°C and a pressure of 150-350 MPa, preferably at room temperature and a pressure of approximately 200 MPa.
Za potrebe eksperimenta i provedenih mjerenja u ovoj prijavi patenta korišteni su kalupi dimenzija 60,8 mm x 8,8 mm s debljinom kompaktiranog sloja od oko 7,5 mm što je davalo uzorke mase od oko 35 g. Provedeno kompaktiranje bilo je jednoosno. For the purposes of the experiment and the measurements carried out in this patent application, molds with dimensions of 60.8 mm x 8.8 mm were used with a thickness of the compacted layer of about 7.5 mm, which gave samples weighing about 35 g. The compaction carried out was uniaxial.
Uzorci iz serije PL38 kod kojih nije korišten parafin, pokazivali su izrazitu lomljivost – što je bilo i za očekivati radi nedostatka parafinskog voska koji se dodaje polaznim mješavinama zbog bolje oblikovljivosti i tečenja prilikom popunjavanja kalupa. Zbog lomljivosti nije bilo moguće provjeriti tzv. srednju gustoću zelene faze, za koju vjerujemo da je bila iznad 50% teorijske gustoće, komparirajući ostale testirane uzorke kod kojih je korišten parafinski vosak. Samples from the PL38 series, in which paraffin was not used, showed marked brittleness - which was to be expected due to the lack of paraffin wax added to the initial mixtures due to better formability and flow when filling the mold. Due to fragility, it was not possible to check the so-called mean density of the green phase, which we believe was above 50% of the theoretical density, comparing the other tested samples where paraffin wax was used.
Naravno, proizvodnja malaznica za rezanje vodenim mlazom, na način kako je gore opisana, bilo bi nepraktična. Ekstruzijski postupak, koji je često korišteni postupak u stanju tehnike, zadovoljava sve potrebe za oblikovanje složenijih oblika predmeta prije konačnih postupaka predsinteiranja i sinteriranja opisanih niže. Uobičajeno je u praksi koristiti standardno dostupne ekstrudere u svrhu oblikovanja proizvoda. Of course, producing nozzles for waterjet cutting in the manner described above would be impractical. The extrusion process, which is a frequently used process in the state of the art, meets all the needs for forming more complex object shapes before the final presintering and sintering processes described below. It is usual in practice to use standard available extruders for the purpose of shaping the product.
Ova faza, bez obzira radi li se o ekstruzijskom postupku ili pak o jednostavnom postupku kompaktiranja rezultira materijalom koji se u praksi naziva - sirovac. Uobičajeno je istovremeno u postupku obrade imati više sirovaca što pojeftinjuje izradu jediničnog proizvoda. This phase, regardless of whether it is an extrusion process or a simple compacting process, results in a material that in practice is called raw material. It is common to have several raw materials at the same time in the processing process, which makes the production of a unit product cheaper.
F. Predsinteriranje F. Pre-sintering
Ukoliko je uzorak bio formiran uz korištenje parafinskog voska, prije samog postupka sinteriranja vosak se mora ukloniti postupkom predsinteriranja. Postupak poznat kao „debindering“ ili „vacuum dewax for hardmetals“ proveden je na način da se kod malog vakuuma od približno 30 mbara u atmosferi vodika i temperaturi cca. 800°C u trajanju od 60 minuta uzorci „ocijede“ i „odpare“ od voska. If the sample was formed with the use of paraffin wax, before the actual sintering process, the wax must be removed by the pre-sintering process. The procedure known as "debindering" or "vacuum dewax for hardmetals" was carried out in such a way that at a low vacuum of approximately 30 mbar in a hydrogen atmosphere and a temperature of approx. 800°C for 60 minutes samples "drain" and "evaporate" the wax.
Za sam postupak dobro je pogledati referencu: https://vacuum-furnaces.com/images/debindingand%20sinteringofmetalsceramics_062001.pdf For the procedure itself, it is good to see the reference: https://vacuum-furnaces.com/images/debindingand%20sinteringofmetalsceramics_062001.pdf
Alternativno, može se provesti postupak zagrijavanja sirovaca na cca 400°C u atmosferi vodika (H2), brzina grijanja 1°C/min (približno 7 sati) i naknadno ugrijavanje do 800°C uz veću brzinu ugrijavanja u vakuumu, s vremenom zadržavanja sirovaca u tim uvjetima u trajanju od 60 minuta, čime se postiže isti ili sličan tehnički efekt kao i u naprijed opisanim postupcima. Alternatively, the raw material can be heated to approx. 400°C in a hydrogen (H2) atmosphere, heating rate 1°C/min (approximately 7 hours) and subsequent heating up to 800°C with a higher heating rate in a vacuum, with a retention time for the raw materials in these conditions for 60 minutes, which achieves the same or similar technical effect as in the procedures described above.
G. - I. Sinteriranje G. - I. Sintering
Nakon toga se proizvod bez voska iz korak F. ili pak oblikovan u koraku E. podvrgava postupku sinteriranja u nekoliko koraka: After that, the wax-free product from step F. or molded in step E. is subjected to a sintering procedure in several steps:
G. zagrijavanja proizvoda do 1200°C u vakuumu, G. heating the product up to 1200°C in a vacuum,
H. zagrijavanja od 1200°C do 1600°C u atmosferi argona (Ar) pri tlaku od 10 mbar u trajanju od 30 minuta, te H. heating from 1200°C to 1600°C in an atmosphere of argon (Ar) at a pressure of 10 mbar for 30 minutes, and
I. sinteriranje vrućim izostatičkim prešanjem na temperaturi od 1600°C te tlaku 80-100 bar u trajanju od barem 45 minuta. I. sintering by hot isostatic pressing at a temperature of 1600°C and a pressure of 80-100 bar for at least 45 minutes.
Po završetku koraka I. dobiven je tvrdi metal, željenog oblika, te sastava WC-1.0Cr3C2-0.2Co o čijoj karakterizaciji će biti više riječi u nastavku. At the end of step I, a hard metal of the desired shape and composition WC-1.0Cr3C2-0.2Co was obtained, the characterization of which will be discussed further below.
Karakterizacija uzorka Characterization of the sample
Uzorci navedeni u Tabeli 1, karakterizirani su metodama koje su standardne u području. Određivanje gustoće konsolidiranih uzoraka provedeno je neposredno nakon postupka dobivanja. Gustoća ispitnih uzoraka određena je vaganjem ispitnih uzoraka na zraku i u tekućini sukladno normi HRN EN ISO 3369:2016, a rezultati su prikazani u već spomenutoj Tabeli 1. The samples listed in Table 1 were characterized by methods that are standard in the field. Determination of the density of the consolidated samples was carried out immediately after the obtaining procedure. The density of the test samples was determined by weighing the test samples in air and in liquid in accordance with HRN EN ISO 3369:2016, and the results are shown in the already mentioned Table 1.
Kako bi se provela analiza određivanja poroziteta i nevezanog ugljika, površine dobivenih uzoraka su polirane, očišćene i nagrižene sukladno važećoj normi HRN EN ISO 4499-1:2011. Karakterizacija mikrostrukture zasnivala se na različitim reakcijama Murakamijeve otopine s različitim fazama mikrostrukture. Dosadašnja istraživanja s nagrizanjem dovela su do klasifikacije reakcija nagrizanja konstituenta uporabom Murakamijeve otopine. Murakamijeva otopina se sastoji od 10 g K3Fe(CN)6, 10 g KOH i 100 ml H2O sukladno normi ISO 4499-4:2016. Uobičajeno se provodi više ciklusa nagrizanja, ispiranja vodom i čišćenja površine pomoću 96%-tne otopine etanola. Kako je poznato u stanju tehnike, takav postupak čini mikrostrukturu bolje vidljivom pod optičkim mikroskopom. In order to carry out the analysis of determination of porosity and unbound carbon, the surfaces of the obtained samples were polished, cleaned and etched in accordance with the current standard HRN EN ISO 4499-1:2011. The characterization of the microstructure was based on different reactions of Murakami's solution with different phases of the microstructure. Etching research so far has led to the classification of constituent etching reactions using the Murakami solution. Murakami's solution consists of 10 g of K3Fe(CN)6, 10 g of KOH and 100 ml of H2O in accordance with ISO 4499-4:2016. Usually, several cycles of etching, rinsing with water and cleaning the surface using a 96% ethanol solution are carried out. As is known in the state of the art, such a procedure makes the microstructure more visible under an optical microscope.
Mikrostrukture dobivenih uzoraka su analizirane na optičkome mikroskopu, kao i na elektronskom mikroskopu s emisijom polja FESEM. The microstructures of the obtained samples were analyzed on an optical microscope, as well as on an electron microscope with field emission FESEM.
Ovako priređene površine fotografirane su optičkim mikroskopom i rezultati su vidljivi na slikama 1A, 2, 3, 4A, 5A i 6A. The surfaces prepared in this way were photographed with an optical microscope and the results are visible in Figures 1A, 2, 3, 4A, 5A and 6A.
Na slici 1A vidimo da je polirana površina uzorka PL38-02, sinteriranog na 1600°C, u cijelosti bez poroziteta. Stupanj poroziteta može se klasificirati kao manji od A02 ili A00, nema nevezanog ugljika ili bilo koje druge nepravilnosti. Isto tako je vidljivo da nema većih pora ili pukotina, kao niti nevezanog ugljika, te se stoga uzorak također označava kao B00 i C00, sukladno gore navedenoj normi. Slike 2 i 3 pokazuju uzorke PK109-01 i PK111-01, istog sastava i sinterirane na 1600°C, sa po prilici 3x kraćim tretmanom u koraku B. - no s evidentno znatno izraženom poroznošću uzoraka. In Figure 1A, we can see that the polished surface of sample PL38-02, sintered at 1600°C, is completely free of porosity. The degree of porosity can be classified as less than A02 or A00, no unbound carbon or any other irregularities. It is also evident that there are no large pores or cracks, as well as no unbound carbon, and therefore the sample is also marked as B00 and C00, in accordance with the above-mentioned norm. Figures 2 and 3 show samples PK109-01 and PK111-01, of the same composition and sintered at 1600°C, with possibly 3x shorter treatment in step B. - but with evidently significantly pronounced porosity of the samples.
Slike 4A, 5A i 6A jesu slike kontrolne skupine za uzorke (PL38-01, PK109-02, PK111-02). Ove slike napravljene su također optičkim mikroskopom, gdje su spomenuti uzorci prethodno sinterirani na 1800°C. Uočava se da kontrolna skupina nema izraženih pora uzoraka, bez obzira na trajanje tretmana provedenog u koraku B. ovog postupka. Figures 4A, 5A and 6A are images of the control group for the samples (PL38-01, PK109-02, PK111-02). These pictures were also made with an optical microscope, where the mentioned samples were previously sintered at 1800°C. It is observed that the control group does not have pronounced pores of the samples, regardless of the duration of the treatment carried out in step B. of this procedure.
Slika 1 pak prikazuje površinu uzorka PL38-02 snimljenu elektronskim skenirajućim mikroskopom s emisijom polja FESEM (Field Emission Scanning Electron Microscopy). Druga dva uzorka nisu nakon sinteriranja na temperaturi od 1600°C (PK109-01, PK111-02) bila u cijelosti densificirana pa nije niti rađena FESEM slika istih. Slike 4, 5, 6 pak pokazuju FESEM karakterizaciju površine kontrolne skupine za uzorke (PL38-01, PK109-02, PK111-02) koji su u cijelosti bili adekvatno densificirani. Figure 1 shows the surface of sample PL38-02 taken with a Field Emission Scanning Electron Microscopy (FESEM). The other two samples were not fully densified after sintering at a temperature of 1600°C (PK109-01, PK111-02), so no FESEM image was taken of them. Figures 4, 5, 6 show the FESEM surface characterization of the control group for samples (PL38-01, PK109-02, PK111-02) that were adequately densified throughout.
Analiza ovih slika ukazuje na neočekivan utjecaj trajanja postupka u koraku B. koja direktno utječe na kvalitetu uzoraka i sniženje temperature sinteriranja za oko 200°C, što svakako nije očekivan rezultat za stručnjaka područja. The analysis of these images indicates an unexpected impact of the duration of the procedure in step B, which directly affects the quality of the samples and the lowering of the sintering temperature by about 200°C, which is certainly not an expected result for an expert in the field.
Određivanje drugih mehaničkih svojstava provedeno je na svim uzorcima kako bi se ispitao utjecaj odabranih parametara i primijenjenih postupaka metalurgije praha, posebice temperature sinteriranja. The determination of other mechanical properties was carried out on all samples in order to examine the influence of the selected parameters and applied powder metallurgy procedures, especially the sintering temperature.
Određivanje mehaničkih svojstava sastojalo se od mjerenja tvrdoće i žilavosti. Ispitivanje tvrdoće provedeno je po Vickers metodi koja se sastoji od utiskivanja dijamantnog indentora oblika pravilne četverostrane piramide u površinu ispitnih uzoraka primjenom propisane sile F (N) sukladno HRN EN ISO 6507-1:2018. Determination of mechanical properties consisted of hardness and toughness measurements. The hardness test was carried out according to the Vickers method, which consists of pressing a diamond indenter in the shape of a regular four-sided pyramid into the surface of the test samples by applying the prescribed force F (N) in accordance with HRN EN ISO 6507-1:2018.
U svrhu određivanja žilavosti primijenjena je metoda po Palmqvistu kojom je istovremeno moguće odrediti vrijednost tvrdoće i žilavosti uzorka na temelju analize otiska indentacije. In order to determine the toughness, the method according to Palmqvist was applied, by which it is possible to simultaneously determine the value of the hardness and toughness of the sample based on the analysis of the indentation impression.
Mjerenje je provedeno sukladno ISO 28079:2009. Vrijednosti žilavosti određene su mjerenjem duljine pukotina - l1, l2, l3 i l4 -nastalih na vrhovima Vickersova otiska. Rezultati su sumirani u Tabeli 2, koja se nalazi niže: The measurement was carried out in accordance with ISO 28079:2009. The toughness values were determined by measuring the length of the cracks - l1, l2, l3 and l4 - formed at the tips of the Vickers imprint. The results are summarized in Table 2 below:
[image] [image]
Iz gornjih podataka iz Tabele 2 jednostavno je zaključiti da su mehanička svojstva proizvoda sinteriranog na 1600°C (uzorak PL38-02) usporediva sa kontrolnom skupinom (PL38-01, PK109-02, PK111-02) u okviru pogrešaka metode, gdje je kontrolna skupina uzoraka sinterirana na 1800°C – iz čega se vidi da je predmetni tehnički problem u cijelosti riješen. Izmjerene tvrdoće uzoraka PK109-1 i PK111-01 kod kojih nije postignuta 100% gustoća i s višim stupnjem poroziteta izmjere vrijednosti tvrdoće nešto su niže u usporedbi s tvrdoćom uzoraka PL38-01, PK109-02, PK111-02. From the above data from Table 2, it is easy to conclude that the mechanical properties of the product sintered at 1600°C (sample PL38-02) are comparable to the control group (PL38-01, PK109-02, PK111-02) within the errors of the method, where the control a group of samples sintered at 1800°C – which shows that the technical problem in question has been completely solved. The measured hardness of samples PK109-1 and PK111-01, where 100% density was not achieved and with a higher degree of porosity, the measured hardness values are slightly lower compared to the hardness of samples PL38-01, PK109-02, PK111-02.
Industrijska primjenjivost Industrial applicability
Predmetni izum otkriva postupak dobivanja proizvoda od tvrdog metala na bazi prahova volfram karbida (WC), krom karbida (Cr3C2) i kobalta (Co). Sastav je odabran na način da bude WC - 98,8 %. tež. sa srednjom veličinom zrna od oko 150 nm, Cr3C2 – 1,0 % tež koji se koristi u smjesi kao inhibitor rasta zrna, te Co – 0,2 % tež. Spomenutim postupkom dobiva se tvrdi metal sastava WC-1.0Cr3C2-0.2Co uglavnom bez pora, gustoće 15,55 g/cm3, tvrdoće približno 2590 HV. Zbog svojih karakteristika i odlične otpornosti na trošenje, ovaj materijal izuzetno je pogodan za proizvodnju mlaznica koje se korist za rezanje vodenim mlazom. Stoga je industrijska primjenjivost ovog postupka i proizvoda koji iz istoga proizlaze – očigledna. The subject invention discloses a process for obtaining hard metal products based on tungsten carbide (WC), chromium carbide (Cr3C2) and cobalt (Co) powders. The composition was chosen to be WC - 98.8%. wt. with an average grain size of about 150 nm, Cr3C2 – 1.0% by weight, which is used in the mixture as a grain growth inhibitor, and Co – 0.2% by weight. The mentioned process produces a hard metal with composition WC-1.0Cr3C2-0.2Co, mostly without pores, density 15.55 g/cm3, hardness approximately 2590 HV. Due to its characteristics and excellent wear resistance, this material is extremely suitable for the production of nozzles used for water jet cutting. Therefore, the industrial applicability of this procedure and the products resulting from it is obvious.
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