NL2031237B1 - “THERMAL-ELECTRIC” COUPLING PREPARATION METHOD OF TiAl ALLOY SHEET WITHOUT-CANNING - Google Patents

Abstract

The present disclosure relates to a “thermal-electric” coupling preparation method of a TiAl alloy sheet without-canning, and aims to solve the problems that an existing cast ingot metallurgy canning rolling method of the TiAl alloy sheet is complex in process, high in cost, poor in sheet shape and low in material utilization rate, and overcome the shortcomings that a powder metallurgy method is high in impurity content, high in cost, low in density and low in production efficiency. The “thermal- electric” coupling preparation method comprises the specific steps of: l, weighing all raw material components; 2, preparing a cast ingot through vacuum induction skull melting and metal mold casting, 3, performing first blank pretreatment, 4, performing second blank pretreatment, and 5, performing “thermal-electric” coupling non-canning rolling on the sheet, to obtain a TiAl alloy sheet.

Description

“THERMAL-ELECTRIC” COUPLING PREPARATION METHOD OF TiAl ALLOY

SHEET WITHOUT-CANNING

TECHNICAL FIELD

[DI] The present disclosure relates to the field of preparation of alloy materials, and particularly relates to a “thermal-electric” coupling preparation method of a TiAl alloy sheet without-canning.

BACKGROUND ART

[02] As a novel high-temperature structural material with light weight, high specific strength and good high-temperature oxidation resistance and creep resistance, the TiAl alloy sheet has great application prospects in the aerospace fields of thermal protection systems of space-ground reciprocating aircrafts, skins of supersonic aircrafts, etc.

However, due to the intrinsic brittleness of intermetallic compounds, the TiAl alloy is poor in high-temperature deformation capacity and narrow in hot working window, which limits the development and engineering application of its sheet.

[03] The existing preparation method of the TiAl alloy sheet mainly includes ingot metallurgy method, powder metallurgy method and foil metallurgy method. According to the ingot metallurgy method, the rolling of the TiAl alloy sheet is achieved through a series of procedures such as ingot cogging, hot isostatic pressing, forging cogging, cutting, surface treatment, canning blank making and rolling. The ingot metallurgy method is complex in procedure, high in canning cost, large in deformation resistance difference between canning and TiAl alloy, poor in deformation coordination and low in material utilization rate. According to the powder metallurgy method, the preparation of the TiAl alloy sheet is achieved through a series of procedures such as TiAl alloy powder making, canning blank making, degassing sealing, hot isostatic pressing and rolling. The powder metallurgy method is high in impurity content such as O and N impurity content, high in raw material cost, low in blank density and low in production efficiency.

According to the foil metallurgy method, Ti foil and Al foil serve as the raw materials and are alternately arranged to form a multi-layer structure, and the TiAl alloy sheet is prepared through rolling compounding and subsequent heat treatment. The foil metallurgy method is complex in procedure, weak in component design capacity and poor in plate uniformity and mechanical property. In summary, a large number of researches are carried out on the preparation methods, and certain achievements are obtained, but there are problems that need to be solved urgently.

SUMMARY

[04] The present disclosure provides a “thermal-electric” coupling preparation method of a TiAl alloy sheet without-canning, and aims at solving the problems that an ingot metallurgy canning rolling method is complex in procedure, high in canning cost, poor in deformation coordination and low in material utilization rate, and the challenges that a powder metallurgy method and a foil metallurgy method are difficult in component control and poor in plate uniformity and mechanical property.

[05] In order to solve the above technical problems, the technical solution adopted by the present disclosure is as follows: a “thermal-electric” coupling non-canning preparation method of a TiAl alloy sheet comprises the following steps:

[06] step 1, weighing of raw materials: respectively weighing high-purity sponge titanium, high-purity aluminum, high-purity chromium, aluminum-niobium alloy, aluminum-molybdenum alloy, aluminum-yttrium alloy, aluminum-vanadium alloy, high-purity nickel powder, boron powder and carbon powder as raw materials; alloy comprises the following components in atomic percent: 41-44% of Al, 0-9% of Nb, 0- 9% of V, 0-2% of Cr, 0-4% of Mo, 0-0.5% of X and the balance Ti and inevitable impurity elements, wherein X is one or more of B, Y, C and Ni elements;

[07] step 2, ingot casting: adding the raw materials weighed in the step 1 into a water-cooled copper crucible vacuum induction skull melting furnace and melting; and pouring a melt into a pre-heated metal casting mold to obtain a cylindrical TiAl alloy ingot, wherein the diameter of the ingot is greater than or equal to 100 mm, and the height of the ingot is greater than or equal to 180 mm;

[08] step 3, first blank pretreatment:

[09] a, removing a dead head of the TiAl alloy ingot and carrying out hot isostatic pressing; keeping the temperature for 3-4 h; cooling along with the furnace; and discharging from the furnace;

[10] b, carrying out homogenization treatment on the ingot and putting the ingot into a vacuum heat treatment furnace, keeping the temperature of 900-1,100 °C for 24- 48 h, and cooling along with the furnace;

[11] c‚ removing an oxide skin of the annealed ingot and flattening upper and lower end faces; processing the ingot into a standard cylindrical block through a wire cut electrical discharge machining, wherein the height-diameter ratio is 1.5: 1 to 2: 1; polishing the blank with abrasive paper, wherein the roughness RA is 1.6-0.8; then putting the ingot into an acetone solution and carrying out ultrasonic washing for 5-10 min; taking out the ingot and drying to obtain a TiAl alloy cylindrical blank;

[12] d, spraying high-temperature anti-oxidization coating on the circumferential surface, the upper end surface and the lower end surface of the TiAl alloy cylindrical blank; spraying the anti-oxidization coating for two layers, wherein each layer is 50 um in thickness; and after spraying each time, standing in a constant-temperature and constant-humidity chamber for 1 h;

[13] step 4, second blank pretreatment:

[14] a, wrapping the TiAl alloy cylindrical blank coated and sprayed with the high- temperature anti-oxidation using an asbestos felt with thickness of 8-10 mm; and keeping the temperature at 1,200-1,250°C for 60 min;

[15] b, heating an upper anvil and a lower anvil of a press machine to 600-700 °C by using a split cylindrical box type resistance furnace, clamping the blank that is subjected to heat keeping in the step a between the upper anvil and the lower anvil in a resistance furnace cavity, performing non-canning near-isothermal upsetting deformation on the TiAl alloy blank at a strain rate of 0.01-0.05 s™ wherein the total deformation is 70-80%; and then placing the blank that is subjected to upsetting in a vacuum heat treatment furnace, keeping the temperature at 900°C-1,000°C for 2 h, and cooling along with the furnace;

[16] c‚ removing oxide skin from the upset blank, flattening the surface, cutting a forging cake core part, processing the forging cake core part into a standard rectangular block, and processing a chamfer at the deformed front end of the blank; 17] d, polishing the rectangular blank with abrasive paper, wherein the roughness

Rais 1.6-0.8, placing the rectangular blank in an acetone solution, performing ultrasonic cleaning for 5-10 min, then taking out the rectangular blank, and drying the rectangular blank;

[18] step 5, “thermal-electric” coupling rolling:

[19] a, keeping the temperature of the dried TiAl alloy blank obtained in the step 4 in the vacuum box type heat treatment furnace under 1,150°C-1,200°C for 30-60 min;

[20] b, taking out the blank from the furnace, performing “thermal-electric” coupling rolling, wherein the surface temperature of a roller is 300°C-600°C; introducing pulse current from a blank far away from a rolling inlet through a copper conductive clamp with a graphite gasket, wherein the rolling speed is 0.5-1.5 m/s, and the pass reduction rate is 10-20%; and performing pass temperature keeping in the furnace again;

[21] c‚ keeping the temperature of the rolled sheet in the vacuum heat treatment furnace under 900°C-1,000°C for 2 h, and cooling along with the furnace to obtain the

TiAl alloy sheet.

[22] Preferably, in the step 2, the smelting atmosphere is argon atmosphere, the argon pressure is 0.95-1 MPa, the mass purity of argon is 99.99%, and a furnace chamber is washed for three times by adopting a “vacuumizing-argon filling-vacuumizing” mode before smelting; a casting mold material is low-carbon steel, the preheating temperature is 300-500°C, and a casting mold is pre-buried into Al20:3 or ZrO; sand; and furnace cooling is carried out after pouring.

[23] Preferably, in the step 3a, the hot isostatic pressing treatment process is carried out at 1,230-1,260 °C and 100-150 MPa, the argon atmosphere is used for protection, and the mass purity of argon 1s 99.99%; in the step 3b, the heat treatment atmosphere is argon atmosphere, the argon pressure is 0.95-1 MPa, and the mass purity of argon is

99.99%; and in the step 3d, the high-temperature anti-oxidation coating is a commercially available 1,500°C type finished product, the temperature during standing treatment is 50-55°C, and the humidity is 50-60% RH.

[24] Preferably, in the step 4b, the treatment atmosphere is argon atmosphere, the 5 argon pressure is 0.95-1 MPa, and the mass purity of argon is 99.99%; and in the step 4c, the chamfer is a fillet, the angle is 45 degrees, and the radius is 3-6 mm.

[25] Preferably, in the step 5, the heat treatment and annealing atmosphere 1s argon atmosphere, the argon pressure is 0.95-1 MPa, the mass purity of argon is 99.99%, and the inert atmosphere environment is guaranteed by introducing high-flow argon when a furnace door is opened and closed; in the step 5b, the roller temperature is realized by a resistance baking or electromagnetic induction surface heating method, the bearing temperature 1s guaranteed to be lower than 70°C by water-cooling transformation, the pulse current frequency is 300-800 Hz, the waveform is rectangular, the voltage is 120

V, the peak current is 100-200 A-mm'?, and the rolling mill rack insulation is realized by a bearing block ceramic insulating gasket.

[26] Preferably, in the step 5b, the heat keeping temperature is 1,150-1,200 °C, the heat preservation time is 10-15 min, and the total rolling deformation is 30-40%.

[27] Compared with the prior art, the present disclosure has the following beneficial effects:

[28] 1. The problem of segregation of high-melting-point B stable elements in deformed TiAl is successfully solved by adopting a vacuum induction melting and preheating metal mold casting mode.

[29] 2. An alloy solidification path is designed from the angle of alloy components, the phase composition of the TiAl alloy solidified by adopting the path at the room temperature and the high temperature is controlled, and the high-temperature deformation capacity of the alloy is improved.

[30] 3. Through large-deformation near-isothermal upsetting pretreatment, the structure form of the TiAl alloy ingot is effectively improved, as-cast dendritic crystals are crushed, grains are refined, and meanwhile, the problem that the components and the grain size in a blank are not uniform is further solved.

[31] 4. The “thermal-electric” coupling rolling method combining pulse current assistance and hot roller near-isothermal rolling is adopted, the promotion effect of the pure plastic effect in pulse current on the metal material dislocation and super- dislocation motion capacity is utilized, the material deformation resistance is reduced, and the plastic deformation capacity is improved, meanwhile, based on the high electrical resistivity of TiAl alloy, the joule heat effect of the pulse current is utilized, electric energy 1s converted into heat energy, the blank temperature is increased, and the temperature needed by thermal deformation is reduced; meanwhile, based on roller heating, the temperature drop of the blank in the rolling process is reduced, a near- isothermal rolling environment is provided, and a large number of body-centered cubic high-temperature B phases brought by component design are combined, thus high- temperature plastic deformation capacity of the TiAl alloy is improved from multiple aspects, and high-quality rolling of the TiAl alloy is achieved. [B2] 5. Non-canning assembly is adopted, the traditional blank canning treatment manner is broken through, the cost is reduced, the process is simplified, the problems that a canning material absorbs rolling deformation, and the compatibility with TiAl alloy deformation is poor are solved, and the rolling efficiency is improved.

[33] 6. The oxidation problem of the TiAl alloy in the heating and rolling process is solved by reducing the rolling temperature and conducting preheating and remelting under inert atmosphere protection, and the obtained sheet has good surface quality and is free of the obvious surface cracking phenomenon.

[34] 7. The obtained sheet is uniform and fine in grain and good in comprehensive mechanical property and can be directly used or subjected to secondary forming.

BRIEF DESCRIPTION OF THE DRAWINGS

[35] FIG. 1 is a TiAl alloy sheet obtained in step 5 in Example 1;

[36] FIG. 2 is a SEM image of a TiAl alloy sheet obtained in step 5 in Example 2.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[37] The present disclosure will be further described in conjunction with specific embodiments.

[38] Example 1

[39] A “thermal-electric” coupling non-canning preparation method of a TiAl alloy sheet comprises the following steps:

[40] step 1, weighing of raw materials:

[41] respectively weighing high-purity sponge titanium, high-purity aluminum, aluminum-niobium alloy (Nb content of 54.56%), aluminum-yttrium alloy (Y content of 87.3%), and boron powder totaling 10 Kg as raw materials; the alloy comprises the following components in atomic percent: 44% of Al, 8% of Nb, 0.1% of X (X is a combination of B and Y) and the balance Ti and inevitable impurity elements.

[42] step 2, ingot casting:

[43] adding the high-purity sponge titanium, high-purity aluminum, aluminum- niobium alloy, aluminum-yttrium alloy, and boron powder weighed in the step 1 into a water-cooled copper crucible vacuum induction skull melting furnace for melting, wherein the melting atmosphere is argon atmosphere and the argon pressure is 0.95- 1MPa, the mass purity of argon gas is 99.99%, flushing the furnace chamber three times by the method of “vacuuming-argon filling-vacuuming” before melting; and pouring a melt into a 500°C pre-heated metal casting mold to obtain a cylindrical alloy ingot, wherein the diameter of the ingot is 100 mm, and the height of the ingot is 185 mm. The casting mold is pre-embedded in Al:Os sand; after pouring, cooled along with the furnace.

[44] step 3, first blank pretreatment:

[45] a, removing a dead head of the TiAl alloy ingot and carrying out hot isostatic pressing, wherein the treatment process is 1250°C, 150MPa, with argon protection, and the mass purity of argon is 99.99%; keeping the temperature for 4 h; cooling along with the furnace; and discharging from the furnace;

[46] b, carrying out homogenization treatment on the ingot and putting the ingot into a vacuum heat treatment furnace; keeping the temperature of 1,000 °C for 24 h, and cooling along with the furnace; wherein the heat treatment atmosphere is argon, the argon pressure is 0.95-1MPa, and the mass purity of argon is 99.99%;

[47] c‚ removing an oxide skin of the annealed ingot and flattening upper and lower end faces; processing the ingot into a standard cylindrical block through a wire cut electrical discharge machining, wherein the height-diameter ratio is 1.5: 1; polishing the blank with abrasive paper, wherein the roughness RA is 1.6; then putting the ingot into an acetone solution and carrying out ultrasonic washing for 5 min; taking out the ingot and drying;

[48] d, spraying high-temperature anti-oxidization coating on the circumferential surface, the upper end surface and the lower end surface of the TiAl alloy cylindrical blank; spraying the anti-oxidization coating for two layers, wherein each layer is 50 um in thickness; and after spraying each time, standing in a constant-temperature and constant-humidity chamber for 1 h; wherein the standing temperature is 50°C, and the humidity is 50%RH.

[49] step 4, second blank pretreatment:

[50] a, wrapping the TiAl alloy cylindrical blank using an asbestos felt with thickness of 8 mm; and keeping the temperature at 1,250°C for 30 min;

[51] b, heating an upper anvil and a lower anvil of a press machine to 600°C by using a split cylindrical box type resistance furnace, clamping the blank that is subjected to heat keeping in the step 1 between the upper anvil and the lower anvil in a resistance furnace cavity, performing non-canning near-isothermal upsetting deformation on the

TiAl alloy blank at a strain rate of 0.01 s™, wherein the total deformation is 70%; and then placing the blank that is subjected to upsetting in a vacuum heat treatment furnace, keeping the temperature at 900°C for 2 h, and cooling along with the furnace;

[52] c‚ removing oxide skin from the upset blank, flattening the surface, cutting a forging cake core part, processing the forging cake core part into a standard rectangular block, and processing a chamfer at the deformed front end of the blank; wherein the chamfer is round, the angle is 45°, the radius is Smm;

[53] d, polishing the rectangular blank with abrasive paper, wherein the roughness

Ra is 1.6, placing the rectangular blank in an acetone solution, performing ultrasonic cleaning for 5 min, then taking out the rectangular blank, and drying the rectangular blank.

[54] step 5, “thermal-electric” coupling rolling:

[55] a, keeping the temperature of the TiAl alloy blank obtained in the step 4 in the vacuum box type heat treatment furnace under 1,200°C for 30 min;

[56] b, taking out the TiAl alloy blank from the furnace, performing “thermal- electric” coupling rolling, wherein the surface temperature of a roller is 600°C, the pulse current frequency is 800Hz, the waveform is rectangular, the voltage is 120V, the peak current is 200A-mm™, the rolling speed is 0.5m/s, the pass reduction rate is 15%; and performing pass temperature keeping in the furnace again, wherein the holding temperature is 1200°C, the holding time is 10min, and the total rolling deformation is 30%;

[57] c‚ keeping the temperature of the rolled sheet in the vacuum heat treatment furnace under 900°C for 2 h, and cooling along with the furnace to obtain the TiAl alloy sheet.

[58] The TiAl alloy sheet obtained in the step 5 in the above Example 1 has a good surface quality, without obvious cracks, as shown in FIG.1.

Claims (1)

ConclusiesConclusions 1. Werkwijze voor het bereiden van een TiAl-legeringvel zonder welving middels thermo-elektrische koppeling, waarbij de werkwijze de volgende stappen omvat: stap 1, het wegen van grondstoffen: het respectievelijk wegen van grondstoffen volgens het atomische percentage van elke component; stap 2, het gieten van een staaf: het in een watergekoelde vacuüminductieskullsmeltoven met koperen kroes toevoegen van de grondstoffen die in de stap 1 gewogen zijn en het smelten; en het schenken van een smelt in een voorverwarmde metalen gietmal om een cilindrische staaf van TiAl-legering te verkrijgen; stap 3, eerste blancovoorbehandeling a, het verwijderen van een dode kop van de staaf van TiAl-legering en het uitvoeren van warme isostatische persing; en het behouden van de temperatuur gedurende 4 uur en het samen met de oven afkoelen; b, het op de staaf uitvoeren van homogenisatiebehandeling en het in een warmtebehandelingsvacuümoven plaatsen van de staaf; en het behouden van de temperatuur gedurende 48 uur en het samen met de oven afkoelen; c, het verwijderen van een oxidehuid van de gegloeide staaf en het afvlakken van boven- en onderuiteindevlakken; het bewerken van de staaf tot een standaard cilindrisch blok; na het polijsten, het in een acetonoplossing plaatsen van de staaf en het uitvoeren van ultrasoon wassen; het uitnemen van de staaf en het drogen om een cilindrische blanco van TiAl-legering te verkrijgen; d, het sproeien van een antioxidatie bekleding met hoge temperatuur op elk vlak van de cilindrische blanco; het sproeien van de antioxidatie bekleding gedurende twee lagen; en het elke keer na het sproeien het gedurende 1 uur laten staan in een kamer met constante temperatuur en constante vochtigheid; stap 4, tweede blancovoorbehandeling a, het gedurende 60 min behouden van de temperatuur van de blanco die bekleed en besproeid is met de antioxidatie bekleding bij hoge temperatuur van 1.250 °C; b, het tot 700 °C verwarmen van een bovenste aambeeld en een onderste aambeeld van een persmachine door middel van een weerstandsoven van het type met gesplitste cilindrische doos, het tussen het bovenste aambeeld en het onderste aambeeld in eenA method of preparing a TiAl alloy sheet without camber by thermoelectric coupling, the method comprising the following steps: step 1, weighing raw materials: respectively weighing raw materials according to the atomic percentage of each component; step 2, casting an ingot: adding the raw materials weighed in step 1 into a water-cooled vacuum induction skull melting furnace with copper crucible and melting; and pouring a melt into a preheated metal casting mold to obtain a cylindrical TiAl alloy rod; step 3, first blank pretreatment a, removing a dead head from the TiAl alloy rod and performing hot isostatic pressing; and maintaining the temperature for 4 hours and cooling it together with the oven; b, performing homogenization treatment on the billet and placing the billet in a heat treatment vacuum oven; and maintaining the temperature for 48 hours and cooling it together with the oven; c, removing an oxide skin from the annealed rod and flattening top and bottom end surfaces; machining the rod into a standard cylindrical block; after polishing, placing the rod in an acetone solution and carrying out ultrasonic washing; taking out the rod and drying it to obtain a cylindrical blank of TiAl alloy; d, spraying a high temperature anti-oxidation coating on each face of the cylindrical blank; spraying the anti-oxidation coating for two coats; and each time after spraying, leave it for 1 hour in a room with constant temperature and constant humidity; step 4, second blank pretreatment a, maintaining the temperature of the blank coated and sprayed with the anti-oxidation coating at a high temperature of 1,250 °C for 60 minutes; b, heating an upper anvil and a lower anvil of a pressing machine to 700°C by means of a resistance furnace of the split cylindrical box type, between the upper anvil and the lower anvil in a S11 - weerstandsovenholte klemmen van de blanco die onderworpen is aan het behouden van warmte in de stap a, het uitvoeren van niet-welvende nabij isotherme opstuikende vervorming , vervolgens het plaatsen van de blanco in de warmtebehandelingsvacuümoven, het behouden van de temperatuur gedurende 2 uur en het samen met de oven afkoelen;S11 - resistance furnace cavity clamping the blank subjected to heat preservation in the step a, carrying out non-cambering near isothermal upsetting deformation, then placing the blank into the heat treatment vacuum furnace, maintaining the temperature for 2 hours and cool it together with the oven; c, het verwijderen van de oxidehuid van de opgestuikte blanco, het afvlakken van het oppervlak, het snijden van een smeedcakekerndeel, het bewerken van het smeedcakekerndeel tot een standaard rechthoekig blok en het bewerken van een afschuining bij het vervormde vooruiteinde;c, removing the oxide skin from the upset blank, flattening the surface, cutting a forging cake core part, machining the forging cake core part into a standard rectangular block and machining a chamfer at the deformed front end; d, het polijsten van de rechthoekige blanco, het plaatsen van de rechthoekige blanco in een acetonoplossing, het uitvoeren van ultrasoon reinigen, vervolgens het uitnemen van de rechthoekige blanco en het drogen van de rechthoekige blanco; stap 5, “thermo-elektrische”-koppelingsrollen a, het gedurende 30 — 60 min behouden van de temperatuur van de blanco in de stap 4 in de warmtebehandelingsoven van het vacuümdoostype;d, polishing the rectangular blank, placing the rectangular blank in an acetone solution, carrying out ultrasonic cleaning, then taking out the rectangular blank and drying the rectangular blank; step 5, “thermoelectric” coupling rollers a, maintaining the temperature of the blank for 30 — 60 min in the step 4 in the vacuum box type heat treatment furnace; b, het uit de oven nemen van de blanco, het uitvoeren van “thermo-elektrische”- koppelingsrollen, het inbrengen van pulsstroom van de blanco ver van een rolinlaat vandaan door een geleidende koperklem met een pakking van grafiet, en het uitvoeren van het behouden van passeerwarmte in de oven;b, removing the blank from the oven, performing “thermoelectric” coupling rolls, introducing pulse current from the blank far from a roll inlet through a conductive copper clamp with a graphite gasket, and performing retaining from passing heat in the oven; c, het gedurende 2 uur behouden van de temperatuur van de gerolde plaat in de warmtebehandelingsvacuümoven en het samen met de oven afkoelen om een TiAl- legeringsplaat te verkrijgen.c, maintaining the temperature of the rolled sheet in the heat treatment vacuum furnace for 2 hours and cooling it together with the furnace to obtain TiAl alloy sheet.