阅读说明：本技术 一种表面富粘结相层内wc晶粒形状呈规则排列的超细晶梯度硬质合金及其制备方法 (Superfine crystal gradient hard alloy with regularly arranged WC crystal grains in surface binding phase-rich layer and preparation method thereof ) 是由 周向葵 王艳 吴深 王凯 王强 李莹 樊江磊 于 2019-08-26 设计创作，主要内容包括：一种表面富粘结相层内WC晶粒形状呈规则排列的超细晶梯度硬质合金及其制备方法,本发明属于硬质合金制造领域,具体涉及一种表面富粘结相区域内WC晶粒呈规则排列取向分布的超细晶梯度硬质合金及其制备方法。所述梯度硬质合金表面为仅含有WC和Co的富粘结相层,厚度为40-80μm,富粘结相内的WC晶粒形状近似为长方形板状且呈规则有序排列分布；芯部均匀分布着WC、Co和立方相,WC晶粒形状不规则呈无序分布；制备方法是配料球磨后压成,先进行压力烧结,再在真空无氮气氛下进行梯度烧结热处理,获得表面富粘结相区域内WC晶粒呈取向分布的超细晶梯度硬质合金。本发明结构设计合理,制备工艺简单可控,生产成本较低,可大规模的工业化生产和应用。(the invention discloses an ultrafine grain gradient hard alloy with regularly arranged WC crystal grains in a surface binding phase-rich layer and a preparation method thereof, belongs to the field of hard alloy manufacturing, and particularly relates to an ultrafine grain gradient hard alloy with regularly arranged and oriented WC crystal grains in a surface binding phase-rich region and a preparation method thereof. The surface of the gradient hard alloy is a binding phase-rich layer only containing WC and Co, the thickness is 40-80 μm, and WC crystal grains in the binding phase-rich layer are approximately rectangular plate-shaped and are regularly and orderly arranged and distributed; WC, Co and cubic phases are uniformly distributed in the core part, and WC crystal grains are irregularly distributed in a disordered way; the preparation method comprises the steps of preparing materials, ball-milling, pressing, sintering under pressure, and performing gradient sintering heat treatment in a vacuum nitrogen-free atmosphere to obtain the superfine crystal gradient hard alloy with WC crystal grains in an oriented distribution in a bonding phase-rich region on the surface. The invention has reasonable structural design, simple and controllable preparation process and lower production cost, and can be industrially produced and applied on a large scale.)

1. An ultra-fine grain gradient hard alloy with WC crystal grains regularly arranged in a surface binding phase-rich layer is characterized in that: the components are prepared from the following raw materials in percentage by mass:

2-8% of Ti (C, N), 0-8% of W, Ti C, 4-15% of Co and the balance of WC.

2. The ultrafine grained gradient cemented carbide according to claim 1 with regularly arranged WC grain shapes in the binder phase-rich surface layer, characterized by the following:

the gradient hard alloy is a binding phase-rich layer with the surface only containing WC and Co phases and the Co content in gradient distribution and higher than that of the core part;

the thickness of the surface rich binder phase layer of the gradient hard alloy is 40 ~ 80 mu m;

The majority of WC crystal grains in the surface binding-rich phase layer are in the shape of a rectangular plate or similar plate and are regularly arranged;

the WC crystal grains are regularly arranged, namely the rectangular platy WC crystal grains are approximately arranged in parallel, and the arrangement direction is that the surface points to the core part along the long edge of the rectangle;

The core structure of the gradient hard alloy consists of WC, Co and a cubic phase, wherein the cubic phase is TiC and TiN, and WC crystal grains of the core are different in shape and are distributed randomly.

3. The method for preparing the ultrafine grain gradient hard alloy with the WC crystal grains regularly arranged in the surface binding phase-rich layer according to the claim 1 is characterized by comprising the following steps:

(1) the hard alloy raw material added with the carbonitride is adopted for mixing, and the hard alloy raw material comprises the following components in percentage by mass: 2-8% of Ti (C, N), 0-8% of (W, Ti) C and 4-15% of Co, and the balance of WC;

(2) Ball milling and drying the raw materials;

(3) loading the mixture into a die, and performing pressure sintering to prepare compact hard alloy;

(4) And carrying out gradient sintering heat treatment on the hard alloy block in a vacuum nitrogen-free atmosphere to prepare the superfine crystal gradient hard alloy with the surface rich in bonding phase layer and the shape of WC crystal grains regularly arranged.

4. the method for preparing the ultrafine grain gradient hard alloy with the surface rich in the binder phase layer and the regularly arranged WC crystal grains is characterized in that in the wet grinding in the step (2), the ball ~ to ~ material ratio is (5 ~ 15) to 1, the wet grinding medium is alcohol, the rotating speed is 30 ~ 100r/min, and the wet grinding time is 12 ~ 96 hours.

5. the method for preparing the superfine grain gradient hard alloy according to claim 3, wherein the step (3) of pressure sintering comprises the steps of placing a mold filled with the mixture in a pressure sintering furnace for presintering, vacuumizing to below 10Pa, heating to 350 ~ 650 ℃, keeping the temperature for 2 ~ 8h, continuing heating to the sintering temperature, keeping the temperature, applying the sintering pressure of 10 ~ 100MPa, keeping the sintering temperature of 1300 ~ 1500 ℃, keeping the temperature for 0.2 ~ 3h under the sintering pressure, and cooling to room temperature along with the furnace after the temperature is kept, so that the compact hard alloy is obtained.

6. the method for preparing the ultrafine grain gradient hard alloy with the surface rich in the binding phase layer and the regularly arranged WC crystal grains according to the claim 3, is characterized in that: the gradient sintering heat treatment in the vacuum nitrogen-free atmosphere in the step (4) comprises the following steps: placing the pre-sintered hard alloy in a vacuum nitrogen-free atmosphere furnace, and vacuumizing to 10 DEG^-1~10^-4and (3) starting heating below Pa, heating to 600 ~ 1000 ℃ and preserving heat for 0.1 ~ 1h, then continuing heating to 1300 ~ 1600 ℃ and preserving heat for 0.2 ~ 4h, and cooling to room temperature along with the furnace after heat preservation is finished.

Technical Field

the invention belongs to the field of hard alloy manufacturing, and particularly relates to an ultrafine grain gradient hard alloy with regularly arranged WC grains in a surface binding phase-rich layer and a preparation method thereof.

background

The hard alloy is an alloy material prepared by taking refractory metal compounds (WC, TiC, TaC, NbC and the like) as hard phases and transition group metals (Fe, Co, Ni) as bonding phases through a powder sintering method, has the advantages of high strength and hardness, good wear resistance and the like, is mainly used for manufacturing cutters or dies, and is widely applied to the fields of cutting machining and die manufacturing. In recent years, with the development of material science and machining industry, higher and higher requirements are provided for the wear resistance, strength, hardness, plastic deformation resistance and the like of hard alloy materials under complex working conditions such as high-speed and high-temperature continuous work and the like.

the ultrafine grain hard alloy shows very superior service performance in the field of mechanical processing due to fine grains and higher strength and hardness, can meet the requirements of modern processing industry on the material performance of the cutter for material processing, and is the development trend of future hard alloys.

with the development of coating technology, the cemented carbide tools currently in use are usually coated with one or more layers of metal or nonmetal compound coatings with higher hardness and better wear resistance by Chemical Vapor Deposition (CVD) or Physical Vapor Deposition (PVD), such as TiN, Al2O3, on the surface of the cemented carbide tool substrate, thereby improving the wear resistance and service life of the cemented carbide tool. However, due to the difference in thermal expansion coefficient between the coating and the substrate, thermal stresses developed between the coating and the substrate during cooling can cause some microcracking to occur and propagate into the substrate during use. In addition, the cutter bears larger cutting force in the cutting process, and the cutter base body is required to have higher strength, rigidity and plastic deformation resistance so as to prevent the rebound of the workpiece and improve the processing precision. At present, the cobalt-rich gradient hard alloy matrix with higher toughness on the surface is mainly adopted to prevent crack propagation, so that the performance and the service life of the hard alloy are improved and prolonged. However, the surface gradient layer has low hardness, low rigidity and poor resistance to plastic deformation, and is difficult to bear larger cutting force, so that the processing precision and the surface finish of the workpiece are poor.

the current technique for making such gradient cemented carbides is known as gradient sintering, as in us 4277283 and 4610931, using nitrogen-containing additives sintered in vacuum, while us 4548786 adds nitrogen to the gas phase, both of which result in surface binder-rich phase regions that are substantially free of cubic phases. Us 4830930 discloses decarburizing a sintered product to obtain a binder phase rich region on the surface. The sintering processes all adopt a two-step sintering method (pre-sintering and gradient sintering are completed in two steps), and the sintering atmosphere is nitrogen-free vacuum. The WC crystal grains in the gradient hard alloy prepared by the two-step sintering method have larger size, and particularly the WC crystal grains in the surface gradient layer are distributed in a disordered way and have lower performance.

the Chinese invention patents ZL 201410011294.8 and CN1900331 adopt one-step sintering to prepare the superfine grain gradient hard alloy with the surface rich in binding phase, the surface of the patents is a cobalt-rich layer and does not contain cubic phase, and the core part of the patents is a uniform structure containing WC, Co and cubic phase. However, the WC grains in the surface cobalt-rich layer are randomly distributed, so that the hardness and strength are weak under working conditions such as impact or use as a drill, and the function of the surface cobalt-rich gradient cemented carbide cannot be fully exerted. The WC crystal grains in the binding phase layer-rich surface of the invention are regularly arranged, and can bear larger mechanical action without exercise deformation when being used as a drill bit or being used under the condition of an impact working condition. In addition, the alloy of the patent has complex components, and the addition of the raw material powder with higher price increases the production cost.

The Chinese patent CN 106048360A adopts a two-stage sintering method to prepare the hard alloy with a double-layer gradient structure on the surface, the hard alloy comprises a first gradient layer, a second gradient layer and a core layer from outside to inside, the first gradient layer does not contain a cubic phase, and the second gradient layer consists of WC, Co and a cubic phase; the content of the bonding phase in the first gradient layer and the second gradient layer is respectively higher and lower than that of the hard alloy, the content of Ti in the second gradient layer is higher than the average content of Ti in the hard alloy, and the content of Co and Zr/Hf is respectively lower than the average content of Co and Zr/Hf in the hard alloy. And the grain size belongs to coarse grain hard alloy, and the strength and the hardness are lower. In addition, the WC crystal grains in the surface gradient layer of the gradient hard alloy with the structure are distributed randomly, the cobalt content is high, the hardness is low, and the gradient hard alloy cannot bear a large impact effect, otherwise deformation or cracking easily occurs. The alloy has a relatively simple structure, is easier to obtain by controlling components and sintering process, and can obtain better alloy performance on the basis of not increasing the cost.

in conclusion, in the application with high requirements for high-speed cutting and processing of workpieces, the ultrafine grain cemented carbide with ultrafine grains has higher strength, the coated cutter has higher wear resistance, and the prepared gradient coated cemented carbide cutter with ultrafine grains has great significance for improving the performance of cemented carbide and expanding the application of cemented carbide, so the invention provides the ultrafine grain gradient cemented carbide with the shape of WC grains regularly arranged in the surface rich bonding phase layer.

Disclosure of Invention

The invention aims to solve the defects of large grain size, low strength and hardness, low hardness in a hard layer under a binder-rich phase gradient layer with higher toughness, poor rigidity and plastic deformation resistance, and complicated and difficult control of the adopted two-stage sintering process in the prior gradient structure hard alloy grain size. Aiming at the existing problems, the invention provides an ultrafine grain gradient hard alloy with regularly arranged WC crystal grains in a surface binding phase-rich layer and a preparation method thereof, and the alloy is suitable for being used for mining high-toughness wear-resistant hard alloy workpieces.

The alloy uses WC and cubic phase carbonitride as hard phases and cobalt as a binder phase, adopts hot-pressing sintering to obtain hard alloy with compact structure through regulating and controlling the alloy components, and then carries out gradient sintering heat treatment in a vacuum nitrogen-free atmosphere to prepare the ultrafine-grained gradient hard alloy with the surface rich in the binder phase layer and the WC crystal grains regularly arranged.

The binder phase-rich gradient layer of the alloy is a binder phase-rich layer on the surface of the alloy, only consists of WC and Co phases, has the cobalt content higher than the nominal content of the core of the alloy, and has the thickness of 40-80 mu m. The core is composed of WC, Co and cubic phase.

the WC crystal grains in the binder-rich phase on the surface of the alloy are regularly arranged, which means that most or almost all of the shapes of the WC crystal grains in the binder-rich phase are similar to rectangular plates, and the WC crystal grains are regularly and orderly arranged, wherein the arrangement direction is that the long sides of the rectangles point to the core part from the surface.

The WC crystal grains in the binder-rich phase on the surface of the alloy are regularly arranged, namely the WC crystal grains in the binder-rich phase are regularly and orderly arranged, and the WC crystal grains in the core are irregularly arranged and are distributed in a disordered way.

The superfine crystal gradient hard alloy with the shape of WC crystal grains regularly arranged in the surface binding phase-rich layer adopts a two-step sintering process combining pressure sintering and gradient sintering, and is carried out according to the following steps:

(1) The raw materials are mixed according to the mass percentage: 2-8% of Ti (C, N), 0-8% of W, Ti C, 4-15% of Co and the balance of WC, wherein the sum of the mass percentages of the components is 100%;

(2) The raw materials are blended, wet milled, dried and pressed into a blank;

(3) Presintering the blank under pressure to prepare a compact ultrafine-grained hard alloy block;

(4) And performing gradient sintering treatment on the pre-sintered hard alloy to prepare the superfine crystal gradient hard alloy with the shape of WC grains regularly arranged in the surface binding phase-rich layer.

in the above technical means, it is preferable that the WC powder is added in an average particle size of 0.2 ~ 0.5. mu.m, the Ti (C, N) powder is added in an average particle size of 0.4 ~ 1.5. mu.m, and the W, Ti) C powder is added in an average particle size of 0.4 ~ 1.5. mu.m.

in the technical scheme, the ball milling process in the step (2) is preferably that the ball ~ material ratio is (12 ~ 16): 1, the wet milling medium is alcohol, the rotation speed is 0 ~ 300r/min, and the wet milling time is 10 ~ 80 h.

in the technical scheme, the pressure sintering specific method in the step (3) is preferably carried out by placing the blank in a hot ~ pressing sintering furnace for presintering, vacuumizing to below 10Pa, heating, keeping the temperature for 2 ~ 8h when the temperature reaches 350 ~ 650 ℃, keeping the temperature when the temperature is continuously raised to the sintering temperature, applying the sintering pressure of 10 ~ 100MPa, keeping the sintering temperature at 1300 ~ 1500 ℃, keeping the temperature for 0.2 ~ 3h under the sintering pressure, and cooling to room temperature along with the furnace after the heat preservation is finished to obtain the compact ultrafine ~ grained hard alloy.

In the above technical solution, preferably, the gradient sintering treatment in the step (4) is performed by the following specific steps: placing the pre-sintered hard alloy in a vacuum nitrogen-free atmosphere furnace for gradient sintering heat treatment, and vacuumizing the vacuum furnace to 10 DEG C^-1~10^-4and (3) starting heating below Pa, heating to 600 ~ 1000 ℃ and preserving heat for 0.1 ~ 1h, then continuing heating to 1300 ~ 1600 ℃ and preserving heat for 0.2 ~ 4h, and cooling to room temperature along with the furnace after heat preservation is finished.

in the technical scheme, the thickness of the binder phase-rich gradient layer on the outer side of the superfine crystal gradient hard alloy with the shape of the WC crystal grains in the binder phase-rich layer regularly arranged on the surface is 40-80 μm.

compared with the prior art, the invention has the advantages that:

the invention prepares the superfine crystal gradient hard alloy with the shape of the WC crystal grains regularly arranged in the surface binding phase-rich layer for the first time, and enhances the impact resistance of the surface and obviously improves the performance of the hard alloy while improving the surface toughness of the alloy through the combined action of the structure and the components.

on the basis of the components of the traditional gradient hard alloy rich in bonding phase, a proper amount of (W, Ti) C cubic phase solid solution powder is added, pressure sintering and gradient sintering heat treatment are adopted to prepare the superfine crystal gradient hard alloy with the surface rich in bonding phase and the shape of WC crystal grains regularly arranged, the thickness of the gradient layer rich in bonding phase is about 40-80 mu m, the shape of the WC crystal grains of the gradient layer rich in bonding phase is rectangular plate-shaped, the WC crystal grains of each rectangular plate-shaped are approximately parallel and regularly arranged, and the arrangement direction is from the surface layer to the core part along the long sides of the rectangle. In the application with high requirements on surface toughness and impact resistance, the gradient hard alloy with the shape of WC grains regularly arranged in the surface binding phase layer has higher impact resistance and the capability of resisting crack propagation, and has important significance for prolonging the service life of the mining wear-resistant spherical tooth and expanding the application of the hard alloy.

Firstly, the method comprises four steps of raw material preparation, ball milling, molding and sintering treatment, wherein the sintering step sequentially comprises presintering and gradient sintering heat treatment, namely, the ultrafine grain hard alloy with compact structure is prepared by hot-pressing sintering under certain pressure, and then the ultrafine grain gradient hard alloy with the WC crystal grains regularly arranged in the surface rich bonding phase layer is obtained by the gradient sintering heat treatment under the vacuum nitrogen-free atmosphere, so that the production process is simplified, and the production cost is reduced.

The pressure sintering can apply larger pressure in the liquid phase stage, so that the flow of the liquid phase is accelerated, the distribution of a bonding phase is improved, the bonding phase is fully filled in gaps among WC powder particles, the hard alloy with compact structure is obtained, and simultaneously, a diffusion channel of cubic phase elements is added, thereby being beneficial to obtaining an alloy structure with WC crystal grains in regular arrangement in the vacuum gradient sintering heat treatment process; in the vacuum gradient sintering heat treatment process, the binder phase is uniformly distributed, the number of channels for atomic diffusion is obviously increased, the atomic diffusion efficiency is accelerated, a thicker binder phase-rich layer is favorably formed on the surface, and meanwhile, in the binder phase-rich area, WC in a dissolved binder phase can be separated out on large-size WC grains along the atomic diffusion direction to form rectangular plate-shaped grains, and finally, the superfine crystal gradient hard alloy with the shape of the WC grains in the binder phase-rich layer on the surface in regular arrangement is obtained.

Secondly, the cobalt content of the binder-rich phase layer of the superfine crystal gradient hard alloy with the regularly arranged WC crystal grains in the binder-rich phase layer on the surface is high, and the superfine crystal gradient hard alloy does not contain cubic phase, so that the hard alloy has good surface toughness, and the crack can be effectively prevented from expanding; the WC crystal grains in the binding phase-rich layer are rectangular plate-shaped and regularly arranged, point to the core from the surface, have higher shock resistance, and are beneficial to improving the shock resistance of the hard alloy.

The invention comprises the superfine crystal gradient hard alloy with the shape of WC crystal grains regularly arranged in a surface binding phase-rich layer, wherein WC is mainly used as a hard phase, cobalt is used as a metal binding phase, and one or more carbonitride solid solutions are added. The obtained superfine crystal gradient hard alloy with the shape of WC crystal grains regularly arranged in the surface rich binding phase layer is obtained by combining the pressure sintering with the vacuum heat treatment process, wherein the thickness of the surface rich binding phase layer is about 40-80 mu m, cubic phase carbide is not contained, and the WC crystal grains in the surface rich binding phase layer are rectangular plates and regularly arranged and point to the core part from the surface. The core part is uniformly distributed WC, Co and cubic phase, and WC crystal grains are different in shape and are randomly distributed.

Drawings

FIG. 1 is a metallographic structure diagram of a gradient cemented carbide prepared in example 1 of the present invention and having WC grains regularly arranged in the shape of a binder-rich phase layer on the surface;

FIG. 2 is a metallographic structure diagram of a gradient cemented carbide prepared in example 2 of the present invention and having WC grains regularly arranged in the shape of a binder-rich phase layer on the surface;

FIG. 3 is a metallographic structure diagram of a gradient cemented carbide prepared in example 3 of the present invention and having WC grains regularly arranged in the shape of a binder-rich phase layer on the surface;

Detailed Description