WO2020027688A1

WO2020027688A1 - A method of production of a superhard material and superhard material based on tungsten pentaboride

Info

Publication number: WO2020027688A1
Application number: PCT/RU2018/000777
Authority: WO
Inventors: Vadim Veniaminovich BRAZHKIN; Vasily Ivanovich BUGAKOV; Igor Petrovich ZIBROV; Vladimir Pavlovich FILONENKO; Artem Romaevich OGANOV; Alexandr Gennadievich KVASHNIN; Artem Yaudatovich ZAKIROV; Andrey Alexandrovich OSIPTSOV
Original assignee: Obschestvo S Ogranichennoi Otvetstvennostyu "Gaspromneft Nauchno-Tehnichesky Tsentr" (Ooo "Gaspromneft Ntc")
Priority date: 2018-08-01
Filing date: 2018-12-03
Publication date: 2020-02-06
Also published as: RU2698827C1

Abstract

The invention relates to the synthesis of new superhard materials. The method for production of a superhard material based on tungsten pentaboride includes sintering of the tungsten and boron powders at high temperatures and pressures. The source materials for this method are tungsten (particles size of 1-10 μm) and submicron boron (particles size of 0.1-0.5 μm) or the boron compound carborane. Sintering is carried out at pressures of 1-8 GPa, temperatures of 1000-1500°C, a holding time of 1-10 minutes, with the tungsten share in the mixture of 50-90% wt. The sintering process is performed in toroid or piston-cylinder chambers. The superhard material based on tungsten pentaboride consists of tungsten powder and boron compound. The tungsten powder has particle sizes of 1-10 μm, and the boron compound is represented by 1.7-di(oxymethyl) - M - carborane (M-carborane). The material has the following proportion of ingredients by weight: tungsten powder with particle sizes of 1-10 μm - 90-50% wt., and M-carborane - 10-50% wt.

Description

A METHOD OF PRODUCTION OF A SUPERHARD MATERIAL AND SUPERHARD MATERIAL BASED ON TUNGSTEN PENTABORIDE

FIELD OF THE INVENTION

The invention relates to synthesis of new materials and can be used for the following purposes:

mining of minerals, use in cutting inserts of rock-cutting tools (drill bits) and other structural elements and mechanisms requiring high wear resistance of working surfaces.

manufacturing (mechanical engineering and metalworking production): machines, tools, accessories (cutting, chipping, grinding, etc.), devices, consumer goods, defense products, application/formation of wear-resistant and superhard surfaces (seals, bearings, etc.) by different methods.

medical industry: cutting tools (scalpels, scissors, chisels).

BACKGROUND OF INVENATION

The developed material with improved properties and cheaper production technology makes it possible to replace conventional materials (including superhard materials and hard alloys) used for cutting, crushing, chipping, abrasion, application/formation of wear- resistant and superhard surfaces by various methods.

Currently, bits for rock cutting and crushing tools are mainly made of two types of superhard materials: synthetic polycrystalline diamond (PCD) and polycrystalline cubic boron nitride (PCBN), or their combination (patent RU2484888). Diamond is the most durable material (Vickers hardness up to 100 GPa). But the synthesis of diamond and production of PCD requires high pressure and temperature ensured by special equipment. The pressure range of 5-6 GPa (i.e., tens of thousands of atmospheres) which is most widely used in the modern production equipment limits the size of hard- surface products and increases their cost.

The vast majority of patents proposing various methods for synthesis of diamond composites are related to the application/formation of the working layer using diamond micropowder which is applied on a base surface of tungsten carbide basis containing cobalt (WC-Co) (patent US 20160289078A1). Such an ensemble undergoes thermobaric treatment in a high-pressure chamber. The working layer of the final product consists of the diamond particles that form a framework whose pores are filled with a cobalt-based binder. The biggest disadvantage of such composites is their susceptibility to thermal destruction. At temperatures above 700°C, in the presence of a metal binder, diamond tends to transform into metal carbides which leads to destruction of the composite in the course of operation.

One of the ways of solving the composite thermal degradation problem is to remove the binder metal by leaching it with an acid or by electrochemical methods (patents US4224380, US6544308). This procedure improves thermal stability of the composite but may have different effects on its other properties (which may either improve or deteriorate). Another way to solve the thermal degradation problem is disclosed in patent US5011514. A method is proposed in which the surface of the diamond powder first interacts with a carbide-forming element, for example tungsten, and then the pores between the diamond particles are filled with eutectic metal compositions.

Diamond composites with silicon carbide are known to have much higher thermal stability. These composites are produced by infiltrating liquid silicon into the diamond layer or by sintering a homogeneous powder mixture (patents US81681 15, RU2036779). Later ideas of using intermetallic compounds to ensure heat resistance coupled with high strength are reviewed in patent US7473287B2. In the proposed method, once the diamond coalescence is finished cobalt forms an intermetallic compound which makes it inert to the reverse transition of diamond into graphite.

The discussed methods for production of PCD materials used in cutting and drilling tools turn to be very costly due to the expensive raw materials and the need for synthesis under pressure of not less than 5 GPa. The main disadvantage of cobalt-based PCDs is its low heat resistance, and that of silicon-based PCDs is its high brittleness.

For patents dealing with boride-based ceramics production methods, the main production method proposed in such patents is the high pressure sintering in graphite molds (US4292081 , US5571759, CN 10601 1586). For some compositions, it is also proposed to use the method of self-propagating high temperature synthesis.

For instance, patent RU2622276 describes a method for production of a boride ceramic consisting of 90% wt. of (Ti₀.9Cr₀.i)B₂ and 10% wt. of CrB.

Yet, at a small residual porosity of about 1.5%, the Vickers hardness of this ceramic does not exceed 26 GPa which is significantly lower than the conventional superhardness threshold which is normally considered to be 40 GPa.

The closest analog to the proposed method is a method for production of tungsten tetraboride with WB₄ stoichiometry (patent CN1061 16593), comprising the following stages:

1 ) tungsten powder and boron powder are mixed together; 2) the mixed powder is placed in a graphite mold, heated in a vacuum oven to 1200-1600°C and kept at these temperatures and pressures of 10-100 MPa for 30-180 minutes.

The synthesis process results in the formation of a soft compact substance which is ground to produce WB₄ in the form of a powder. That is, the proposed method is intended to production of tungsten tetraboride powder only, which requires further development of methods for its consolidation, i.e. additional high-temperature processing at high pressures (1-2 GPa) to produce a superhard material.

SUMMARY OF THE INVENTION

The proposed invention is intended to solve the task of replacing conventional superhard materials for cutting inserts of rockcutting tools (drill bits) with new materials having improved properties.

The technical result of the invention is the production of a new superhard material based on synthesized tungsten boride WB₅ with predicted properties which combines high hardness and thermal stability with high fracture toughness.

This material can be competitive as compared to composites based on diamond or diamond-like boron nitride, and can also be a better and more affordable replacement for hard alloys based on tungsten carbide (WC).

Theoretical calculations and studies of mechanical properties showed that in terms of hardness the tungsten pentaboride can be categorized as a superhard material.

This task is solved by the use of specific powder mixture components: tungsten powder with a particle size of 1-10 pm and submicron (0.1 -0.5 pm) boron powder or a boron compound (M-carborane) with the general formula of B10H16C4O2 (in the molecule of which two carbon atoms occupy the boron positions in the icosahedron).

The method for production of a superhard material was implemented by sintering the source mixtures at pressures of 1.5- 8 GPa and temperatures of 1000-1500°C with a holding time of 1 to 10 minutes.

Sintering of 1-10 pm tungsten powder with M-carborane was carried out in a toroid heating chamber (diameter of the center pit 15 mm) at pressures of up to 8 GPa. The toroid chamber consists of two coaxial hard-alloy shaped anvils fastened with steel rings. Between the anvils, a cell of lithographic stone is placed and compressed. Heating of the chamber is provided by passing electric current through the graphite heater inside the cell.

Sintering of tungsten powder (1-10 pm fraction) with M- carborane was also performed in a high pressure piston-cylinder chamber at a pressure of 1.5 GPa. The sintering technology using a piston-cylinder chamber is implemented on the basis of a hydraulic high pressure sintering unit with a capacity of 2,000 tnf. The high pressure is developed by applying force to a pair of pistons, one of which is movable and the other one is fixed. The use of a heat and electrical insulating shell of compacted calcite provides a reliable sealing and electrical insulation of the movable piston with a gap width of up to 0.5 mm.

A mixture of submicron and micron powders of tungsten and submicron powder of boron was also sintered in the toroid and piston- cylinder chambers. The source mixtures for a superhard material based on tungsten pentaboride include tungsten powder with a particle size of 1-10 pm, and M-carborane or submicron (0.1 -0.5 pm) boron at the following ingredients ratio, % wt.:

tungsten powder with a particle size of 1-10 pm

90 - 50 % wt.

boron or M-carborane powder

10 - 50 % wt.

High-strength WB₅ compacts were produced at moderate reactive sintering temperatures and without the application of high pressures (which are necessary for synthesis of diamonds and cubic boron nitride). Thanks to this factor, the cost of the material is significantly reduced, the production process scaling becomes much easier, and service life of working elements of drill bits used in some applications becomes much longer compared to PCD.

The materials produced on the basis of WB₅ tungsten boride are characterized by high structural dispersion. The tungsten pentaboride crystals have the size of less than 1 micron and an equiaxed shape (Fig. 1 shows the microstructure of the WB₅ cleavage surface).

Phase analysis of samples produced by sintering showed that when M-carborane was used the material consisted of a mixture of WB₅ and WB₂ borides with the share of WB₂ being 20-30%. Compacts that do not contain WB₂ can be produced from mixtures of submicron tungsten and boron powders. Fig. 2 shows a diffractogram of the sintered materials where 1 is sintering of submicron tungsten and boron powders (1.5 GPa, 1200°C, 10 minutes), and 2 is sintering of micron tungsten powder with M-carborane (4.0 GPa, 1300°C, 1.5 minutes). According to hardness measurements, the VKe hard alloy has a Rockwell hardness of 86-88 HRA which corresponds to standard samples. Rockwell hardness of the material (compact) produced from tungsten pentaboride reached 93-95 HRA. If we compare the average area of the imprints made by a diamond cone, in the test sample it was 0.91 mm², and in the hard alloy it was 1.52 mm². This means that the area of the imprint in the tungsten pentaboride compact is almost 1.7 times smaller than that in the standard sample which evidences a very high hardness of the tungsten pentaboride compact.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

Tungsten with particle sizes of 1-10 pm and M-carborane are used as a source material for the synthesis process. The tungsten share in the mixture is 50% wt., and the M-carbon share is also 50% wt.

Tungsten is sintered with M-carborane in a toroid chamber at 7 GPa, 1500°C and a holding time of 1.0 minute.

The WB₅ tungsten boride crystallites have a size of about 1 pm and an equiaxed shape. The samples contain about 20% of the WB₂ boride.

Rockwell hardness of the tested sample was 88-90 HRA, and the wear spot area was 1.45 mm².

Thermal stability of the material is guaranteed by the fact that the material is synthesized at a temperature of 1500°C, i.e. in an inert environment the material will work at least up to this temperature.

The synthesized WB₅-based composition showed a lower wear rate compared to the industrial sample based on a hard alloy. Example 2

Submicron tungsten and boron powders are used as source materials for the synthesis process.

The 1-10 pm tungsten share in the mixture is 70% wt., and the submicron (0.1 -0.5 pm) boron share is 30% wt.

Tungsten is sintered with boron in a piston-cylinder chamber at 1.5 GPa, 1200°C and a holding time of 10 minutes.

The sample hardness was determined by the Rockwell method, the wear resistance was determined by the area of the wear spot caused by abrasion.

According to the measurements, the hardness of the sample is 93-95 HRA, the wear spot area is 0.91 mm².

A high thermal stability is guaranteed by the absence of components with a low melting point.

Example 3

The 1-10 pm tungsten share of in the mixture is 90% wt., and the submicron (0.1 -0.5 pm) boron share is 10% wt.

Tungsten is sintered with boron in a toroid chamber at 4.5 GPa,

1000°C and a holding time of 5 minutes.

The phase composition of the sample after sintering is 90% of WB₅ and 10% of WB₂.

Theoretical calculations show that the tungsten pentaboride is super hard and maintains outstanding mechanical properties up to temperatures of about 1700°C.

Table 1 shows the properties of the tungsten pentaboride samples. Table 1.

INDUSTRIAL APPLICABILITY

The materials produced on the basis of tungsten pentaboride can be used for the manufacture of:

tools used under conditions that require high hardness and corrosion resistance, as well as to apply wear-resistant coating on parts operating under intense abrasive wear with moderate impact loads; various cutters, abrasive and grinding tools or materials, drills, cutters, drill bits and other cutting tools;

end-face seals of shafts in mechanisms operating in highly abrasive or highly viscous media.

Claims

1. A method for production of a superhard material based on tungsten pentaboride, comprising sintering of the tungsten and boron powders at elevated temperatures and pressures, with the source materials being tungsten (particles size of 1 -10 pm) and submicron boron (particles size of 0.1 -0.5 pm) or the boron compound of carborane, and the sintering being performed under pressures of 1-8 GPa and temperatures of 1000-1500°C with a holding time of 1-10 minutes, with the share of tungsten in the mixture being

50-90% wt.

2. A method for production of a superhard material as described in Claim 1 , characterized in the sintering process being performed in a toroid or piston-cylinder chamber.

3. A SUPERHARD MATERIAL based on tungsten pentaboride, comprising tungsten and boron compound powders, characterized by the material consisting of tungsten powder with particle sizes of 1-10 pm and the boron compound being 1.7-di(oxymethyl) - M- carborane (M-carborane), with the following shares of the ingredients, % wt.:

tungsten powder with 1-10 pm particles sizes: 90-50% wt. M-carborane: 10-50% wt.