Beta-layer-removed gradient hard alloy and preparation method thereof

Abstract

The invention belongs to the technical field of alloys, and provides a beta-layer-removed gradient hard alloy and a preparation method thereof. The preparation method comprises the following steps: 1) carrying out compression molding on a nitrogen-free raw material to obtain a pressed blank; the nitrogen-free raw material comprises a mixture and an optional forming agent, and the mixture is composed of WC, Co and alloy carbide; 2, the pressed blank is sequentially subjected to pre-sintering, first oscillation hot-pressing treatment and second oscillation hot-pressing treatment, and the beta-layer-removed gradient hard alloy is obtained.By means of the method, the hard alloy with the low beta-phase residual amount and the high beta-layer-removed thickness uniformity can be obtained.

Description

Technical Field

[0001] This application belongs to the field of alloy technology, specifically, it provides a de-β layer gradient hard alloy and its preparation method. Background Technology

[0002] Beta-degraded gradient carbide is a material with a gradient structure. Its surface layer is a tough, cubic-phase-degraded region, while the core is a cubic-phase-rich, deformation-resistant region. The surface layer, a high-toughness region, is free of the hard and brittle cubic phase (β phase) and is thus called the beta-degraded layer. This cubic-phase-free tough region (surface layer) effectively prevents the propagation of high-temperature stress cracks generated during the coating process into the matrix, while the core possesses high resistance to plastic deformation. This not only enhances the interfacial bonding strength but also reduces interfacial stress concentration, thereby jointly and effectively improving the service life of coated carbide tools, making them suitable for heavy-duty and interrupted cutting operations.

[0003] In aerospace and other fields, heavy or intermittent cutting of difficult-to-machine materials such as high-temperature alloys and titanium alloys not only exposes cutting tools to enormous cutting forces and high temperatures but also poses a high impact risk due to the low plasticity of the materials. This places extremely high demands on the toughness of the tool substrate, the adhesion stability of the coating, and its resistance to thermal shock. Therefore, it is necessary to strictly control the performance of the beta-removed layer in graded cemented carbide. Specifically, if there is a large amount of beta phase residue in the beta-removed layer, it will lead to increased brittleness of the substrate surface, making it prone to microcracks under high stress and high impact conditions, which in turn will cause coating or cutting edge chipping. If the beta-removed layer thickness is not uniform, on the one hand, it is not conducive to maintaining a smooth interface between the coating and the substrate, and the coating is prone to premature peeling due to insufficient bonding strength. On the other hand, it will cause significant differences in toughness in different areas of the cemented carbide surface, and local thin areas are prone to stress concentration points, ultimately causing local chipping of the cutting edge and affecting the machining accuracy of the parts. Based on the actual tool requirements, there is an urgent need to develop alloys with uniform beta-removed layer thickness and low beta phase residue in the beta-removed layer.

[0004] Traditional methods for preparing beta-layer-free gradient cemented carbides often involve adding a cubic nitrogen source to the alloy raw material to form the beta layer. However, this method has two disadvantages: firstly, the nitrogen source is unstable during sintering, and when process parameters are mismatched, nitrogen gas is difficult to escape, easily forming pores and leading to a decrease in alloy density and mechanical properties; secondly, the brittle nitrogen-containing cubic phase remaining in the core easily becomes a stress concentration point under stress, generating microcracks, which significantly reduces the alloy's toughness and bending strength. Therefore, the preparation of beta-layer-free gradient cemented carbides using nitrogen-free raw materials (i.e., raw materials without nitrogen elements) has gradually become a research focus. Currently, there are reports on beta-layer-free gradient cemented carbides prepared using nitrogen-free raw materials. These studies mainly focus on the raw material formulation and sintering process, but research on how to control the performance of the beta layer is still limited. For example, CN110512132A discloses a method for preparing a gradient cemented carbide with long rod-shaped WC grains on the surface and no cubic phase. This method involves preparing a billet by using a composite powder composed of TiC, VC, Cr3C2, Co, Mo, B, Y2O3 and WC in a certain ratio, and then sintering it through a multi-stage process to obtain the gradient cemented carbide. CN110387496A discloses a method for preparing a WC-TiC-Co based gradient cemented carbide without a TiC phase on the surface. The raw materials do not contain a nitrogen source. The billet is prepared by using a composite powder composed of TiC, VC, Cr3C2, Co and WC, and the gradient cemented carbide is obtained under a specific multi-stage vacuum sintering process. In addition, some literature (Shi Liuyong, Huang Jihua, Lin Bin, et al. Effect of sintering temperature on de-β layer gradient cemented carbide prepared from nitrogen-free raw materials [J]. Rare Metals and Cemented Carbide, 2015, 43(03):50-53+62.) proposes that a process of micro-pressure nitriding followed by gradient sintering is used to prepare de-β layer gradient cemented carbide. The thickness of the de-β layer increases with increasing sintering temperature, but compared with the direct addition of TiCN nitrogen source, the thickness of the de-β layer of the cemented carbide prepared by this method is significantly reduced under the same sintering process. At present, the method of preparing de-β layer gradient cemented carbide from nitrogen-free raw materials faces two major problems: First, the micro-pressure nitriding process has a narrow process window, which easily leads to uneven layer thickness or surface embrittlement; Second, the inherent low nitrogen activity of the matrix leads to insufficient nitrogen penetration driving force, resulting in a generally thin de-β layer, which is difficult to meet the requirements of use under harsh working conditions.

[0005] In summary, how to effectively reduce the residual amount of β phase in the β-layer and improve the uniformity of the β-layer thickness to comprehensively enhance the strength and toughness of gradient cemented carbide is an urgent problem to be solved in the preparation of nitrogen-free β-layer gradient cemented carbide. Summary of the Invention

[0006] This application aims to provide a novel β-phase removal gradient cemented carbide and its preparation method. This method can obtain cemented carbides with low β-phase residual content and high uniformity of β-phase removal thickness.

[0007] In a first aspect, this application provides a method for preparing a β-layer gradient hard alloy, comprising: 1) Press the nitrogen-free raw material into a compact; The nitrogen-free raw material includes a mixture and an optional molding agent, and the mixture consists of WC, Co and alloy carbides; 2) The compact is subjected to pre-sintering, a first oscillating hot pressing treatment, and a second oscillating hot pressing treatment in sequence to obtain a β-layer-removed gradient cemented carbide; wherein, The first oscillating hot pressing treatment is carried out in the presence of nitrogen gas at a pressure of 0.1~4 kPa, with a median oscillation pressure P1 of 50~85 MPa and an amplitude P. m1 The pressure is 5~20MPa, and the frequency f1 is 0.5~4Hz; The second oscillating hot pressing treatment is carried out under vacuum conditions, with a median oscillation pressure P2 of 25~50 MPa and an amplitude P m2 The pressure is 10~30MPa, and the frequency f2 is 2~10Hz; Furthermore, P1 and P2, P m1 With P m2 f1 and f2 must satisfy the following relationship: P1 > P2, P m1 <P m2 f1 < f2.

[0008] In the preparation method provided in this application, the first oscillating hot pressing treatment is the oscillating hot pressing nitriding stage, and the second oscillating hot pressing treatment is the oscillating hot pressing gradient sintering stage (aimed at forming a gradient structure of the alloy phase). This method effectively solves the problems of high residual β phase and poor uniformity of β layer thickness that are common in traditional nitrogen-free β-layer de-bonded cemented carbides by optimizing the initial composition of the cemented carbide and combining the synergistic effect of oscillating hot pressing nitriding and oscillating hot pressing gradient sintering. Specifically, in the oscillating hot pressing nitriding stage, nitrogen atoms in the nitrogen atmosphere diffuse to the liquid phase on the surface of the alloy under the action of oscillating pressure, and react with the alloy carbides to generate a nitrogen-containing cubic phase. In this stage, the nitrogen equilibrium partial pressure inside the compact is kept lower than the atmosphere partial pressure to maintain the forward nitriding reaction. The oscillating pressure can enhance the diffusion of nitrogen atoms. Using medium-pressure median and low-frequency small-amplitude parameters is beneficial to improving the nitriding efficiency and promoting the uniform nucleation of the nitrogen-containing cubic phase on the surface. In the oscillating hot-pressing gradient sintering stage, vacuum denitrification causes the nitrogen-containing cubic phase already formed on the surface to undergo directional decomposition, resulting in a β-phase-free surface layer. This stage relies on the condition that the nitrogen equilibrium partial pressure of the nitrogen-containing cubic phase is much higher than the partial pressure of the vacuum environment. The oscillating pressure can accelerate the decomposition of the nitrogen-containing cubic phase and the desolvation of nitrogen atoms, promoting elemental diffusion and migration. Furthermore, the use of low-pressure median and high-frequency amplitude parameters can promote the uniform and thorough decomposition of the nitrogen-containing cubic phase, thereby reducing the residual amount of β phase and improving the uniformity of the β-phase layer thickness.

[0009] In some embodiments of this application, the alloy carbide is selected from a first metal carbide and optionally a second metal carbide, wherein the first metal carbide is a titanium-containing carbide, and the second metal carbide is at least one of NbC, TaC, and TaNbC. Further, the titanium-containing carbide is (Ti,W)C and / or TiC.

[0010] In some embodiments of this application, based on the total mass of the mixture, the mass content of WC is 70% to 90%, the mass content of Co is 5% to 20%, and the mass content of alloy carbides is 3% to 20%. Further, based on the total mass of the mixture, the mass content of the titanium-containing carbides is 1% to 5%.

[0011] In some embodiments of this application, the molding agent is selected from one or more of paraffin wax, microcrystalline wax, and polyethylene wax.

[0012] In some embodiments of this application, the mass content of the molding agent is 2% to 5% based on the total mass of the nitrogen-free raw materials.

[0013] In some embodiments of this application, the mixture is prepared by a method comprising the following steps: Tungsten carbide powder, cobalt powder, and alloy carbide powder are wet ball-milled to obtain a ball-milled slurry; The ball mill slurry is then vacuum dried.

[0014] Furthermore, the operating conditions for the wet ball milling include: using anhydrous ethanol as the medium, a ball-to-material ratio of (1.5~6):1, a rotation speed of 60~280 rpm, and a milling time of 8~76 h.

[0015] In some embodiments of this application, the pre-sintering process includes: 2-1) In an inert atmosphere, at 3~10 o Heating rate increased to 250~350 °C / min o C, keep warm for 30-60 minutes; then at 5-15 degrees Celsius... o Heating rate increased to 450~550 °C / min o C, keep warm for 30-100 minutes; finally, reduce to 5-15 degrees Celsius. o Heating rate increased to 700-900 °C / min o C, keep warm for 30~100 minutes; 2-2) Under vacuum conditions, at 5~10 o Heating rate increased to 950~1200 °C / min o C, keep warm for 30~100 minutes.

[0016] Furthermore, the inert gas is argon.

[0017] In some embodiments of this application, the temperature of the first oscillating hot pressing treatment is 1250~1400℃. o C, the heat preservation time is 20~60 min; the temperature of the second oscillating hot pressing treatment is 1420~1500 °C. o C, the heat preservation time is 30~90 minutes.

[0018] In some embodiments of this application, the first oscillating hot pressing process includes: 2-3) with 3~10 o The temperature is increased to 1250~1400 °C / min. o C. Switch to nitrogen atmosphere, apply oscillating pressure and maintain temperature.

[0019] In some embodiments of this application, the first oscillating hot pressing process includes: 2-4) with 5~10 o Increase the temperature by C / min to 1420~1500 o C. Switch to vacuum conditions, apply oscillating pressure, and maintain temperature.

[0020] In some embodiments of this application, in the first oscillating hot pressing process, the median oscillation pressure P1 is 50~80MPa, and the amplitude P m1 The pressure is 8~15MPa, and the frequency f1 is 1~2Hz; in the second oscillating hot pressing treatment, the median oscillation pressure P2 is 30~45MPa, and the amplitude P m2 The pressure is 18~30MPa, and the frequency f2 is 7~10Hz.

[0021] Secondly, this application provides a de-β layer gradient hard alloy prepared by the preparation method described in the first aspect of this application.

[0022] In some embodiments of this application, the average thickness of the beta-degraded gradient cemented carbide is ≥15 mm. Furthermore, the average thickness of the β-layer is 15~55 mm. .

[0023] In some embodiments of this application, the standard deviation of the thickness of the β-layer is <1.2. The residual β phase content in the β-layer is <0.5%.

[0024] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0025] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, wherein: Figure 1 SEM image of the vertical cross section of the nitrogen-free de-β-layer gradient cemented carbide prepared in Example 1; Figure 2 This is a SEM image of the vertical cross-section of the nitrogen-free de-β-layer gradient cemented carbide prepared in Example 5; Figure 3 SEM image of the vertical cross-section of the cemented carbide prepared in Comparative Example 1; Figure 4 SEM image of the vertical cross section of the nitrogen-free de-β-layer gradient cemented carbide prepared in Comparative Example 2; Figure 5 SEM image of the vertical cross section of the nitrogen-free β-layer gradient cemented carbide prepared in Comparative Example 3; Figure 6 The image shows a vertical cross-section of the nitrogen-free β-layer gradient cemented carbide prepared in Comparative Example 4. Detailed Implementation

[0026] The embodiments of this application are described in detail below. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0027] The "scope" disclosed in this application is defined in the form of a lower limit and / or an upper limit, whereby a given scope is defined by selecting a lower limit and / or an upper limit. This type of scope may or may not include endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form an undefined scope, and any lower limit can be combined with other lower limits to form an undefined scope, similarly, any upper limit can be combined with any other upper limit to form an undefined scope. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and can be combined with any other point or single value, or with other lower or upper limits, to form an undefined scope.

[0028] It should be noted that in this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated.

[0029] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0030] In the preparation of traditional nitrogen-free gradient cemented carbide with β-layer removal, the following key process problems exist: The process control of the micro-pressure nitriding stage is complex. Insufficient nitriding time leads to uneven nitrogen penetration into the matrix, causing fluctuations in the β-layer thickness; while excessive nitriding time causes excessive formation of nitrogen-containing cubic phases on the surface. If subsequent denitrification processes are not effectively matched, the residual β-phase content will increase, affecting the material's toughness. Simultaneously, because no nitrogen source is introduced into the initial raw materials, the nitrogen activity of the matrix is ​​low. Even after micro-pressure nitriding, the established nitrogen equilibrium partial pressure is still insufficient, limiting the penetration of nitrogen into the deeper layers of the material, ultimately resulting in a thin overall β-layer thickness.

[0031] Therefore, this application provides a method for preparing a β-layer gradient hard alloy, comprising: 1) Press the nitrogen-free raw material into a compact; The nitrogen-free raw material includes a mixture and an optional molding agent, and the mixture consists of WC, Co and alloy carbides; 2) The compact is subjected to pre-sintering, a first oscillating hot pressing treatment, and a second oscillating hot pressing treatment in sequence to obtain a β-layer-removed gradient cemented carbide; wherein, The first oscillating hot pressing treatment is carried out in the presence of nitrogen gas at a pressure of 0.1~4 kPa, with a median oscillation pressure P1 of 50~85 MPa and an amplitude P. m1 The pressure is 5~20MPa, and the frequency f1 is 0.5~4Hz; The second oscillating hot pressing treatment is carried out under vacuum conditions, with a median oscillation pressure P2 of 25~50 MPa and an amplitude P m2 The pressure is 10~30MPa, and the frequency f2 is 2~10Hz; Furthermore, P1 and P2, P m1 With P m2 f1 and f2 must satisfy the following relationship: P1 > P2, P m1 <P m2 f1 < f2.

[0032] The method of this application systematically solves the problems of high β-phase residue and poor uniformity of the de-β layer by optimizing the initial composition and combining the processes of oscillating hot-pressing nitriding and oscillating hot-pressing gradient sintering: In the oscillating hot-pressing nitriding stage, the medium-pressure median and low-frequency small-amplitude oscillation pressure helps to enhance nitrogen atom diffusion, promote uniform nucleation of nitrogen-containing cubic phase, and maintain the nitrogen equilibrium partial pressure inside the green body lower than the atmospheric partial pressure, ensuring that the nitriding reaction proceeds fully; In the subsequent oscillating hot-pressing gradient sintering stage, the use of low-pressure median and high-frequency large-amplitude oscillation parameters, combined with a vacuum environment, can accelerate the decomposition of nitrogen-containing cubic phase and nitrogen atom desolvation, and utilize element diffusion and migration to form a de-β layer with uniform thickness and low β-phase residue.

[0033] In this application, the nitrogen-free raw material refers to the solid raw material used that excludes nitrogen-containing components, which may include a mixture and an optional molding agent, preferably composed of the mixture and the molding agent.

[0034] In some embodiments, based on the total weight of the mixture, the mass content of WC is 70% to 90%, for example 70%, 75%, 80%, 82%, 85%, 87%, 90%, etc.; the mass content of Co is 5% to 20%, for example 5%, 7%, 9%, 10%, 11%, 13%, 15%, 18%, etc.; and the mass content of the alloy carbides is 3% to 20%, for example 3%, 5%, 9%, 10%, 12%, 15%, etc.

[0035] In this application, the alloy carbide may be selected from a first metal carbide and optionally a second metal carbide, wherein the first metal carbide is a titanium-containing carbide, preferably (Ti,W)C and / or TiC; the second metal carbide is at least one of NbC, TaC, and TaNbC. Specific examples of (Ti,W)C include, but are not limited to, (Ti... 0.8 W 0.2 C、(Ti) 0.5 W 0.5 C、(Ti) 0.2 W 0.8 C、(Ti) 0.5 W 0.5 C 0.9 In some embodiments, the mass content of the titanium carbide is 1% to 5% based on the total mass of the mixture, for example, 1%, 1.5%, 2%, 3%, 4%, 5%, etc.

[0036] In this application, the molding agent may be selected from organic binders commonly used in cemented carbide molding processes. As some preferred examples, the molding agent is selected from one or more of paraffin wax, microcrystalline wax, and polyethylene wax.

[0037] In some embodiments, the molding agent accounts for 2% to 5% of the total mass of the nitrogen-free raw materials, for example, 2%, 2.5%, 3%, 4%, 5%, etc.

[0038] In some embodiments, the mixture can be prepared by the following steps: a) Tungsten carbide powder, cobalt powder, and alloy carbide powder are wet ball-milled to obtain a ball-milled slurry; b) The ball-milled slurry is vacuum dried to obtain the mixture.

[0039] In step a), the Fisher particle size of each of the tungsten carbide powder, cobalt powder, and additive powder can be 0.5~10. For example, 0.5 0.6 1 1.5 2 5 6 Etc. As some examples, the Fisher particle size of tungsten carbide powder and cobalt powder is 0.5~5. The Fisher particle size of the titanium carbide powder is 1~2. The Fisher particle size of the second metal carbide is 1~5. .

[0040] In step a), the operating conditions for the wet ball milling may include: using anhydrous ethanol as the medium; a ball-to-material ratio (i.e., ball-to-material ratio) of (1.5~6):1, such as 1.5:1, 2:1, 3:1, 4:1, 5:1, 6:1, etc., preferably (3~5):1; and a rotational speed of 60~280 rpm, such as 80 rpm, 100 rpm, 150 rpm, 180 rpm, 190 rpm, 210 rpm, 220 rpm, 230 rpm, 270 rpm, etc., preferably 100~220 rpm. Furthermore, the total amount of solid raw material is the total mass of tungsten carbide powder, cobalt powder, and alloy carbides.

[0041] In step a), the wet ball milling time can be 8 to 76 hours, such as 12 hours, 15 hours, 24 hours, 30 hours, 36 hours, 42 hours, 50 hours, 55 hours, 60 hours, 67 hours, etc., preferably 24 to 60 hours.

[0042] This application does not impose any special restrictions on the ball milling equipment; for example, a planetary ball mill can be used.

[0043] In step b), the vacuum drying temperature can be, for example, 50~65°C. o C.

[0044] Optionally, the step of preparing the mixture further includes the following step c): c) Sieving: Pass the product obtained after vacuum drying through a 50-250 mesh sieve (e.g., 50 mesh, 60 mesh or 80 mesh).

[0045] In step 1), the mixture and the molding agent can be mixed evenly in a mixer, and then granulated by sieving. Specifically, the evenly mixed material is poured into the feed inlet of a sieve. With the reciprocating vibration of the vibrating screen, fine particles smaller than the sieve opening (50-250 mesh) pass through the sieve and are collected in a container to obtain the powder to be pressed (i.e., the nitrogen-free raw material). The pressed compact can be a tool blank (also called a "blade blank") or other geometric shapes. The pressing method can be, for example, compression molding. Compression molding can include: adding the powder to be pressed into the mold cavity, applying bidirectional pressure through a press to press and form a sample or compact blade. Additionally, the amount of nitrogen-free raw material can be selected according to the mold specifications. As some specific examples, the mold specifications used can be a×b×c, where a can be 5-30 mm, b can be 5-30 mm, and c can be 5-30 mm.

[0046] Each stage of sintering treatment in step 2) can be carried out in an oscillating hot pressing sintering furnace. The pre-sintering is intended to remove the forming agent in the pressed compact and reduce trace oxides on the surface of the raw material and remove adsorbed oxygen.

[0047] In some embodiments, the pre-sintering process includes steps 2-1) and 2-2).

[0048] 2-1) In an inert atmosphere, at 3~10 o Heating rate increased to 250~350 °C / min o C, keep warm for 30-60 minutes; then at 5-15 degrees Celsius... o Heating rate increased to 450~550 °C / min o C, keep warm for 30-100 minutes; finally, reduce to 5-15 degrees Celsius. o Heating rate increased to 700-900 °C / min o C, keep warm for 30~100 minutes. The preferred inert atmosphere is argon.

[0049] 2-2) Under vacuum conditions, at 5~10 o Heating rate increased to 950~1200 °C / min o C, keep warm for 30~100min. The vacuum level in this step can be controlled to <5Pa.

[0050] In step 2), the first oscillating hot pressing treatment belongs to the oscillating hot pressing nitriding stage. The core is to promote the rapid, efficient and uniform diffusion of nitrogen atoms in nitrogen gas to the liquid phase on the surface of the alloy, and to react with the alloy carbides to generate a uniformly distributed nitrogen-containing cubic phase (such as TiCN).

[0051] In some embodiments, the temperature of the first oscillating hot pressing treatment can be 1250~1400℃. o C, for example, 1250 o C, 1280 o C, 1300 o C, 1350 o C, 1380 o C, 1400 o For example, the heat preservation time can be 20~60min, such as 20min, 30min, 40min, 45min, 50min, 60min, etc. In order to improve the thickness of the β layer, the heat preservation time is preferably 35~60min.

[0052] In the first oscillating hot pressing treatment, the nitrogen pressure (gauge pressure) is controlled at 0.1~4 kPa to avoid excessive pressure damaging the alloy surface layer while ensuring a sufficient nitrogen concentration gradient is formed on the surface to maintain the diffusion rate of nitrogen atoms. Preferably, the nitrogen pressure is 0.3~4 kPa, such as 0.3 kPa, 0.5 kPa, 1 kPa, 1.5 kPa, 2 kPa, 2.5 kPa, 3 kPa, 4 kPa, etc. To increase the thickness of the β-layer, a nitrogen pressure of 1~4 kPa is more preferred.

[0053] In the first oscillating hot pressing treatment, the median oscillation pressure P1 is 50~85MPa, preferably 50~80MPa, such as 55MPa, 60MPa, 70MPa, 75MPa, 80MPa, etc.; the amplitude P m1 The pressure is 5~20MPa, preferably 8~15MPa, such as 8MPa, 9MPa, 10MPa, 12MPa, 15MPa, etc.; the frequency f1 is 0.5~4Hz, preferably 1~2Hz, such as 1Hz, 1.5Hz, 2Hz, etc.

[0054] In some embodiments, the first oscillating hot pressing process may include: 2-3) with 3~10 o The temperature is increased to 1250~1400 °C / min. o C. Switch to nitrogen atmosphere, apply oscillating pressure and maintain temperature.

[0055] In step 2), the second oscillating hot pressing treatment belongs to the oscillating hot pressing gradient sintering stage, which aims to denitrify and decompose the nitrogen-containing cubic phase that has been formed on the surface under high vacuum to form a β-free surface layer.

[0056] In some embodiments, the temperature of the second oscillating hot pressing treatment can be 1420~1500℃. o C, for example, 1420 o C, 1450 oC, 1470 o C, 1500 o For grade C, the heat preservation time can be 30~90 minutes, such as 30 minutes, 35 minutes, 45 minutes, 50 minutes, 60 minutes, 70 minutes, 80 minutes, 90 minutes, etc.

[0057] In the second oscillating hot pressing process, the median oscillation pressure P2 is 25~50MPa, preferably 30~45MPa, such as 30MPa, 35MPa, 37MPa, 40MPa, 45MPa, etc.; the amplitude P m2 The pressure is 10~30MPa, preferably 18~30MPa, such as 18MPa, 20MPa, 22MPa, 25MPa, 30MPa, etc.; the frequency f2 is 2~10Hz, preferably 7~10Hz, such as 7Hz, 7.5Hz, 8Hz, 9Hz, 10Hz, etc.

[0058] In some embodiments, the second oscillating hot pressing process includes: 2-4) with 5~10 o Increase the temperature by C / min to 1420~1500 o C. Switch to vacuum conditions, apply an oscillating pressure with a median value of P2, and maintain the temperature. The vacuum level in this step can be controlled to be <5 Pa.

[0059] According to some specific implementation methods, the method for preparing β-layer gradient cemented carbide of this application includes the following steps: 1) Tungsten carbide powder, cobalt powder, titanium-containing carbide powder and optional second metal carbide powder are wet ball-milled to obtain ball-milled slurry; the ball-milled slurry is then vacuum-dried and sieved to obtain the mixture.

[0060] Subsequently, the mixture and molding agent are mixed evenly, and then granulated by sieving to obtain the powder to be pressed.

[0061] The powder to be pressed is added into the mold cavity and pressed into shape to obtain a pressed blank.

[0062] 2) The pressed billet is placed in a vibrating hot pressing sintering furnace for sintering. The specific sintering procedure is as follows: 2-1) Under an argon atmosphere, at 3~10 o Heating rate increased to 250~350 °C / min o C, keep warm for 30-60 minutes; then at 5-15 degrees Celsius... o Heating rate increased to 450~550 °C / min o C, keep warm for 30-100 minutes; finally, reduce to 5-15 degrees Celsius. o Heating rate increased to 700-900 °C / min oC, keep warm for 30~100 minutes; 2-2) Switch to vacuum conditions (control vacuum level < 5 Pa), with a speed of 5~10 o Heating rate increased to 950~1200 °C / min o C, keep warm for 30~100 minutes; 2-3) with 3~10 o The temperature is increased to 1250~1400 °C / min. o C, switch to nitrogen atmosphere, apply an oscillating pressure with a median value of P1, and maintain the temperature; 2-4) with 5~10 o Increase the temperature by C / min to 1420~1500 o C. Switch to a vacuum atmosphere (control the vacuum level < 5 Pa), apply an oscillating pressure with a median value of P2, and maintain the temperature.

[0063] Subsequently, the sample was cooled in the furnace or subjected to positive pressure cooling to room temperature to obtain a nitrogen-free de-β-layer gradient cemented carbide.

[0064] The second aspect of this application provides a de-β layer gradient cemented carbide prepared by the preparation method described in the first aspect of this application.

[0065] The β-layer-removed gradient cemented carbide prepared in this application belongs to the nitrogen-free β-layer-removed gradient cemented carbide category. It typically consists of WC, Co, and cubic carbide phases (β phase), with a surface layer of WC+Co representing a ductile β-layer-removed region, and a core of WC+Co+β phase. As a typical example, such as... Figure 2 As shown in the SEM image of the vertical section of the beta-layered gradient cemented carbide, the alloy exhibits a uniform microstructure, free of metallurgical defects, and a typical gradient structure: a beta-layered surface with only WC and Co phases (upper right enlarged image), and a beta-rich structure in the interior (core) (lower right enlarged image). Furthermore, the surface toughness region of the nitrogen-free beta-layered gradient cemented carbide in this application is also a Co-rich region. Electron probe X-ray micro-area analysis revealed the Co element distribution from the surface to the core: from the surface to the interior, the Co content decreases and tends to stabilize.

[0066] In some embodiments, the prepared gradient cemented carbide is a cutting tool.

[0067] In particular, the de-β layer has virtually no cubic phase residue and its thickness uniformity is significantly improved.

[0068] In some embodiments, the average thickness of the beta-removed layer is ≥15. Preferably 15~55 .

[0069] In some embodiments, the standard deviation of the thickness of the beta-removed layer is <1.2. The residual β phase content in the β-layer is <0.5%.

[0070] In this application, the average thickness and thickness uniformity of the beta-depleted layer can be determined by the following method: At least three different regions of the alloy's vertical cross-section are selected, and five backscattered electron scanning electron microscope (SEM) images with a magnification of 1000× are acquired for each region. Thickness measurements are performed three times for each image using ImageJ image analysis software, with a total of no less than 45 measurements for a single sample. The arithmetic mean of all measurement results is taken as the average thickness of the beta-depleted phase region (denoted as "..."). Meanwhile, based on all the measurement results, the standard deviation of the thickness of the β-layer is calculated. This standard deviation can reflect the uniformity of the thickness of the β-layer. The smaller the value, the higher the thickness uniformity.

[0071] In this application, the content of the β phase within the β-layer was determined as follows: At least four different regions of the surface layer of the cemented carbide vertical cross-section were selected, and five backscattered SEM images with a magnification of 1000× were acquired for each region. ImageJ software was used for image analysis, with the average thickness of the β-layer ( Based on this, in each image, along a direction parallel to the sample surface, a width of [missing information] is defined. μ A rectangular region is used as the analysis unit. At least 20 unit regions are analyzed for each sample. The ratio of the total area of ​​the β phase within the β-layer to the total area of ​​the β-layer region is measured and calculated for each image. i Based on all the obtained ratios ( i Calculate the average value (%), which represents the degree of residual β phase within the β-layer. 。

[0072] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0073] The following examples illustrate the β-phase-removed hard metal alloy and its preparation method of this application. Unless otherwise stated, all percentages are by mass. All (Ti,W)C used is (Ti 0.5 W 0.5 The Fisher particle sizes of the powder raw materials WC, Co, (Ti,W)C, TiC, NbC and TaC are 2 μm, 0.8 μm, 1 μm, 1 μm, 1 μm and 1 μm, respectively.

[0074] Example 1 1) Weigh the powder raw materials according to the following mass ratio: 85% WC, 10% Co, 2% (Ti,W)C, 2% NbC, and 1% TaC. Place the weighed powder raw materials in a planetary ball mill and perform wet ball milling with anhydrous ethanol as the medium. Set the ball-to-material ratio to 5:1, the rotation speed to 150 rpm, and the milling time to 50 h. After ball milling, the resulting suspension is cooled to 60 °C. o Vacuum drying at C and passing through a 60-mesh sieve yields a mixture. Subsequently, 3% paraffin wax (by mass of the total pressed powder) is added to the mixture, and after thorough mixing, it is granulated by sieving (passing through a 60-mesh sieve) to obtain the powder to be pressed (i.e., nitrogen-free raw material).

[0075] Take 20g of the powder to be pressed and add it to the mold cavity (20mm×7mm×6mm). Press it into shape on an automatic pressing press to obtain a rectangular blank.

[0076] 2) The billet is placed in a vibrating hot pressing sintering furnace for sintering. The specific sintering procedure is as follows: 2-1) Under an argon atmosphere, at 5 o Temperature increased to 300 °C / min o C, keep warm for 45 minutes; continue at 10 o Heat up to 500 °C / min o C, keep warm for 60 minutes; then add 10 o Heat up to 800 °C / min o C, keep warm for 60 minutes; 2-2) Switch to a vacuum atmosphere, control the vacuum level < 5 Pa, and use 10 o Heat to 1000 C / min o C, keep warm for 60 minutes; 2-3) with 5 o Temperature increased to 1300 °C / min o C, then switch to a nitrogen atmosphere for oscillatory hot-press nitriding, maintaining a nitrogen pressure of 2 kPa, applying an oscillatory pressure with a median pressure of 60 MPa, an amplitude of 10 MPa, and a frequency of 2 Hz, and at 1300 o Keep warm at C for 35 minutes; 2-4) Continue with 5 o Temperature increased to 1450 °C / min o C, then switch to a vacuum atmosphere, controlling the vacuum level <5Pa, to perform oscillating hot-pressing gradient sintering: adjust the oscillation pressure parameters to the median of 40MPa, amplitude of 20MPa, and frequency of 8Hz, and at 1450 o Keep warm at C for 60 minutes.

[0077] Subsequently, the sample was cooled to room temperature in the furnace to obtain a nitrogen-free de-β-layer gradient cemented carbide. Figure 1The SEM characterization results of the vertical cross section of the alloy are shown, revealing that its microstructure is intact and free of defects such as pores, decarburization, and cracks, with the surface layer being a decubic phase layer.

[0078] Example 2 1) Weigh the powder raw materials according to the following mass ratio: 80% WC, 12% Co, 5% TiC, and 3% NbC. Place the weighed powder raw materials in a planetary ball mill and perform wet ball milling with anhydrous ethanol as the medium. Set the ball-to-material ratio to 3:1, the rotation speed to 200 rpm, and the milling time to 48 hours. After ball milling, the resulting suspension is cooled to 60 °C. o Vacuum drying at C and passing through an 80-mesh sieve yields a mixture. Subsequently, paraffin wax, accounting for 2% of the total mass of the pressed powder, is added to the mixture. After thorough mixing, the mixture is granulated by sieving (passing through an 80-mesh sieve) to obtain the powder to be pressed.

[0079] Take 30g of the powder to be pressed and add it to the mold cavity (10mm×10mm×10mm). Press it into shape on an automatic pressing press to obtain a cube blank.

[0080] 2) The billet is placed in a vibrating hot pressing sintering furnace for sintering. The specific sintering procedure is as follows: 2-1) Under an argon atmosphere, at 8 o Temperature increased to 300 °C / min o C, keep warm for 50 minutes; continue at 10 o Heat up to 500 °C / min o C, keep warm for 80 minutes; then at 12 o Heat up to 800 °C / min o C, keep warm for 45 minutes; 2-2) Switch to a vacuum atmosphere, control the vacuum level < 5 Pa, and use 6 o Heat to 1000 C / min o C, keep warm for 70 minutes; 2-3) with 6 o Temperature increased to 1300 °C / min o C, then switch to a nitrogen atmosphere for oscillatory hot-press nitriding, controlling the nitrogen pressure at 4 kPa, applying an oscillation pressure with a median pressure of 80 MPa, an amplitude of 15 MPa, and a frequency of 1 Hz, and at 1300 o Keep warm at C for 45 minutes; 2-4) Continue with 10 o Temperature increased to 1450 °C / min o C. Subsequently, the atmosphere was switched to vacuum, with the vacuum level controlled to <5 Pa, and oscillating hot-pressing gradient sintering was performed: the oscillation pressure parameters were adjusted to a median of 30 MPa, amplitude of 20 MPa, and frequency of 10 Hz, and then sintered at 1450 °C. oKeep warm at C for 60 minutes.

[0081] Subsequently, the sample was cooled to room temperature under positive pressure to obtain a nitrogen-free de-β-layer gradient cemented carbide.

[0082] Example 3 The β-layer gradient cemented carbide was prepared according to the method of Example 1, except that in steps 2-3), the nitrogen pressure was controlled at 0.3 kPa, an oscillating pressure was applied with a median pressure of 70 MPa, an amplitude of 10 MPa, and a frequency of 1 Hz, and the oscillation was performed at 1300... o Keep warm at C for 20 minutes.

[0083] Example 4 The β-layer gradient cemented carbide was prepared according to the method in Example 1, except that the operating conditions in steps 2-3) and 2-4) were adjusted. Specifically, 2-3) with 5 o Temperature increased to 1300 °C / min o C, then switch to a nitrogen atmosphere for oscillating hot-press nitriding, controlling the nitrogen pressure at 3 kPa, applying an oscillation pressure with a median pressure of 60 MPa, an amplitude of 9 MPa, and a frequency of 1.5 Hz, and at 1300 o Keep warm at C for 60 minutes.

[0084] 2-4) Continue with 10 o Temperature increased to 1450 °C / min o C, then switch to a vacuum atmosphere, controlling the vacuum level <5Pa, to perform oscillating hot-pressing gradient sintering: adjust the oscillation pressure parameters to a median of 45MPa, amplitude of 30MPa, and frequency of 10Hz, and at 1450 o Keep warm at C for 80 minutes.

[0085] Example 5 The β-layer gradient cemented carbide was prepared according to the method in Example 2, except that the operating conditions in steps 2-3) and 2-4) were adjusted. Specifically, 2-3) with 6 o Temperature increased to 1300 °C / min o C, then switch to a nitrogen atmosphere, maintain a nitrogen pressure of 1 kPa, apply an oscillating pressure with a median pressure of 55 MPa, an amplitude of 8 MPa, and a frequency of 1 Hz, and then at 1300 o Keep warm at C for 40 minutes.

[0086] 2-4) Continue with 10 o Temperature increased to 1450 °C / min oC, then switch to a vacuum atmosphere, controlling the vacuum level <5Pa, to perform oscillating hot-pressing gradient sintering: adjust the oscillation pressure parameters to a median of 35MPa, amplitude of 25MPa, and frequency of 8Hz, and at 1450 o Keep warm at C for 50 minutes. Figure 2 The SEM characterization results of the vertical cross section of the alloy are shown, revealing that its microstructure is intact and free of defects such as pores, decarburization, and cracks, with the surface layer being a decubic phase layer.

[0087] Comparative Example 1 The cemented carbide was prepared according to the method in Example 1, except that oscillating hot pressing nitriding was not performed during the sintering process. The specific sintering procedure is as follows: 2-1) Under an argon atmosphere, at 5 o Temperature increased to 300 °C / min o C, keep warm for 45 minutes; continue at 10 o Heat up to 500 °C / min o C, keep warm for 60 minutes; then add 10 o Heat up to 800 °C / min o C, keep warm for 60 minutes; 2-2) Switch to a vacuum atmosphere, control the vacuum level < 5 Pa, and use 10 o Heat to 1000 C / min o C, keep warm for 60 minutes; 2-3) with 5 o Temperature increased to 1300 °C / min o C, and at 1300 o Keep warm at C for 35 minutes; 2-4) Continue with 5 o Temperature increased to 1450 °C / min o C, to perform oscillating hot-pressing gradient sintering: adjust the median oscillation pressure parameters to 40 MPa, amplitude to 20 MPa, and frequency to 8 Hz, and at 1450 o Keep warm at C for 60 minutes.

[0088] Subsequently, the sample was cooled to room temperature in the furnace to obtain cemented carbide.

[0089] In this comparative example, the cemented carbide raw material itself does not contain a cubic nitrogen source, and there is no oscillating micro-pressure nitriding stage during sintering. Neither the surface nor the interior of the cemented carbide contains any decomposable nitrogen-containing cubic phases, thus failing to induce a nitrogen activity gradient and elemental diffusion. Therefore, a de-β layer cannot form on the surface (see...). Figure 3 ).

[0090] Comparative Example 2 The β-layer-removed gradient cemented carbide was prepared according to the method in Example 1, except that oscillating hot pressing was not used in either the nitriding stage or the gradient sintering stage during the sintering process. The specific sintering procedure is as follows: 2-1) Under an argon atmosphere, at 5 o Temperature increased to 300 °C / min o C, keep warm for 45 minutes; continue at 10 o Heat up to 500 °C / min o C, hold at that temperature for 60 minutes; then increase the temperature to 800°C at a rate of 10°C / min. o C, keep warm for 60 minutes; 2-2) Switch to a vacuum atmosphere, control the vacuum level < 5 Pa, and use 10 o Heat to 1000 C / min o C, keep warm for 60 minutes; 2-3) with 5 o Temperature increased to 1300 °C / min o C, then switch to a nitrogen atmosphere, maintain a nitrogen pressure of 2 kPa, and at 1300 o Keep warm at C for 35 minutes; 2-4) Continue with 5 o Temperature increased to 1450 °C / min o C, then switch to a vacuum atmosphere, control the vacuum level <5Pa, and at 1450 o Keep warm at C for 60 minutes.

[0091] Subsequently, the sample was cooled to room temperature in the furnace to obtain a gradient cemented carbide.

[0092] In this comparative example, no oscillatory hot pressing was applied. The uniformity of the β-layer thickness on the surface of the gradient cemented carbide was poor, and there were many β-phase remnants within the β-layer (see [link]). Figure 4 ).

[0093] Comparative Example 3 The β-layer gradient cemented carbide was prepared according to the method in Example 1, except that no oscillating hot pressing was performed during the nitriding stage of the sintering process. The specific sintering procedure is as follows: 2-1) Under an argon atmosphere, at 5 o Temperature increased to 300 °C / min o C, keep warm for 45 minutes; continue at 10 o Heat up to 500 °C / min o C, keep warm for 60 minutes; then add 10 o Heat up to 800 °C / min o C, keep warm for 60 minutes; 2-2) Switch to a vacuum atmosphere, control the vacuum level < 5 Pa, and use 10 oHeat to 1000 C / min o C, keep warm for 60 minutes; 2-3) with 5 o Temperature increased to 1300 °C / min o C, then switch to a nitrogen atmosphere, maintain a nitrogen pressure of 2 kPa, and at 1300 o Keep warm at C for 35 minutes; 2-4) Continue with 5 o Temperature increased to 1450 °C / min o C, then switch to a vacuum atmosphere, control the vacuum level <5Pa, apply oscillating hot pressure, with a median pressure of 40MPa, an amplitude of 20MPa, and a frequency of 8Hz, and at 1450 o Keep warm at C for 60 minutes.

[0094] Subsequently, the sample was cooled to room temperature in the furnace to obtain a gradient cemented carbide.

[0095] In this comparative example, no oscillating hot pressing was applied during the nitriding stage, resulting in the inability to form a uniform nitrogen-containing cubic phase on the alloy surface. Consequently, the resulting gradient cemented carbide surface layer exhibited poor uniformity in β-layer thickness and contained some β-phase residue (see [link to relevant documentation]). Figure 5 ).

[0096] Comparative Example 4 The β-layer-removed gradient cemented carbide was prepared according to the method in Example 1, except that no oscillating hot pressing was performed during the gradient sintering stage. The specific sintering procedure is as follows: 2-1) Under an argon atmosphere, at 5 o Temperature increased to 300 °C / min o C, keep warm for 45 minutes; continue at 10 o Heat up to 500 °C / min o C, keep warm for 60 minutes; then add 10 o Heat up to 800 °C / min o C, keep warm for 60 minutes; 2-2) Switch to a vacuum atmosphere, control the vacuum level < 5 Pa, and use 10 o Heat to 1000 C / min o C, keep warm for 60 minutes; 2-3) with 5 o Temperature increased to 1300 °C / min o C, then switch to a nitrogen atmosphere for oscillatory hot-press nitriding, maintaining a nitrogen pressure of 2 kPa, applying an oscillatory pressure with a median pressure of 60 MPa, an amplitude of 10 MPa, and a frequency of 2 Hz, and at 1300 o Keep warm at C for 35 minutes; 2-4) Continue with 5 oTemperature increased to 1450 °C / min o C, switch to a vacuum atmosphere, control the vacuum level <5Pa, and at 1450 o Keep warm at C for 60 minutes.

[0097] Subsequently, the sample was cooled to room temperature in the furnace to obtain a gradient cemented carbide.

[0098] In this comparative example, no oscillating hot pressing was applied during the gradient sintering stage, which prevented the nitrogen-containing cubic phase from fully and uniformly decomposing, resulting in the observation of obvious β-phase residue on the surface of the prepared gradient hard alloy (see [link to relevant documentation]). Figure 6 ).

[0099] Comparative Example 5 The method for preparing β-layer gradient cemented carbide was the same as in Example 1, except that in steps 2-3), the nitrogen pressure was controlled at 5 kPa, and an oscillation pressure was applied with a median pressure of 60 MPa, an amplitude of 10 MPa, and a frequency of 2 Hz, and the oscillation was performed at 1300°C. o Keep warm at C for 35 minutes.

[0100] In this comparative example, the use of high nitrogen pressure during the oscillating hot-pressing nitriding stage led to an imbalance between the nitrogen penetration rate and the alloy's relaxation ability. Ultimately, the high-pressure nitrogen gas caused defects on the alloy surface through mechanisms such as diffusion disorder, mechanical stress, and liquid phase instability. Although a β-phase was formed on the surface, its uniformity was poor.

[0101] Comparative Example 6 The β-layer gradient cemented carbide was prepared according to the method of Example 1, except that in steps 2-4), 10 o Temperature increased to 1450 °C / min o C, then switch to a vacuum atmosphere, controlling the vacuum level <5Pa, to perform oscillating hot-pressing gradient sintering: adjust the oscillation pressure parameters to the median 70MPa, amplitude 5MPa, and frequency 1Hz, and at 1450 o 60 minutes at C.

[0102] In this comparative example, the median pressure during the oscillating hot-pressing gradient sintering stage was set relatively high, while the amplitude and frequency were set relatively low. These inappropriate sintering process parameters resulted in a low degree of denitrification and a weak effect of oscillating hot pressing in promoting decomposition. The nitrogen-containing cubic phase formed on the surface of the cemented carbide during the nitriding stage could not be fully decomposed, leaving residual β-phase on the surface.

[0103] Example 6 1) Weigh the powder raw materials according to the following mass ratio: 82% WC, 12% Co, 3% (Ti,W)C, and 3% NbC. Place the weighed powder raw materials in a planetary ball mill and perform wet ball milling with anhydrous ethanol as the medium. Set the ball-to-material ratio to 5:1, the rotation speed to 150 rpm, and the milling time to 50 h. After ball milling, the resulting suspension is cooled to 60 °C. o Vacuum drying at C and passing through an 80-mesh sieve yields a mixture. Subsequently, paraffin wax, accounting for 2% of the total mass of the pressed powder, is added to the mixture. After thorough mixing, the mixture is granulated by sieving (passing through an 80-mesh sieve) to obtain the powder to be pressed.

[0104] Take 20g of the powder to be pressed and add it to the mold cavity (20mm×7mm×6mm). Press it into shape on an automatic pressing press to obtain a rectangular blank.

[0105] 2) The billet is placed in a vacuum sintering furnace for sintering. The specific sintering procedure is as follows: 2-1) Under an argon atmosphere, at 5 o Temperature increased to 300 °C / min o C, keep warm for 45 minutes; continue at 10 o Heat up to 500 °C / min o C, keep warm for 60 minutes; then add 10 o Temperature increased to 700 °C / min o C, keep warm for 50 minutes; 2-2) Switch to a vacuum atmosphere, control the vacuum level < 5 Pa, and use 10 o Temperature increased to 900 °C / min o C, keep warm for 70 minutes; 2-3) with 5 o Temperature increased to 1250 °C / min o C. After reaching the target temperature, switch to a nitrogen atmosphere for oscillating hot-press nitriding. Maintain the nitrogen pressure at 2 kPa, apply oscillation pressure with a median pressure of 65 MPa, an amplitude of 12 MPa, and a frequency of 1 Hz, and maintain the oscillation at 1250°C. o Keep warm at C for 60 minutes; 2-4) Continue with 5 o Heat to 1500 °C / min o C. Upon reaching the target temperature, simultaneously switch to a vacuum atmosphere, controlling the vacuum level <5 Pa, to perform oscillating hot-pressing gradient sintering: adjust the oscillation pressure parameters to the median of 35 MPa, amplitude of 20 MPa, and frequency of 9 Hz, and at 1500... o Keep warm at C for 45 minutes.

[0106] Subsequently, the sample was cooled to room temperature in the furnace to obtain a nitrogen-free de-β-layer gradient cemented carbide.

[0107] Example 7 1) Weigh the powder raw materials according to the following mass ratio: 85% WC, 10% Co, 2% (Ti,W)C, and 1% NbC. Place the weighed powder raw materials in a planetary ball mill and perform wet ball milling with anhydrous ethanol as the medium. Set the ball-to-material ratio to 5:1, the rotation speed to 150 rpm, and the milling time to 50 h. After ball milling, the resulting suspension is cooled to 60 °C. o Vacuum drying at C and passing through a 70-mesh sieve yields a mixture. Subsequently, paraffin wax, accounting for 2% of the total mass of the pressed powder, is added to the mixture. After thorough mixing, the mixture is granulated by sieving (passing through a 70-mesh sieve) to obtain the powder to be pressed.

[0108] Take 20g of the powder to be pressed and add it to the mold cavity (20mm×7mm×6mm). Press it into shape on an automatic pressing press to obtain a rectangular blank.

[0109] 2) The billet is placed in a vacuum sintering furnace for sintering. The specific sintering procedure is as follows: 2-1) Under an argon atmosphere, at 5 o Temperature increased to 300 °C / min o C, keep warm for 45 minutes; continue at 10 o Heat up to 500 °C / min o C, keep warm for 60 minutes; then add 10 o Heat up to 800 °C / min o C, keep warm for 60 minutes; 2-2) Switch to a vacuum atmosphere, control the vacuum level < 5 Pa, and use 10 o Heat to 1000 C / min o C, keep warm for 60 minutes; 2-3) with 5 o Temperature increased to 1300 °C / min o C, then switch to a nitrogen atmosphere for oscillatory hot-press nitriding, maintaining a nitrogen pressure of 2 kPa, applying an oscillatory pressure with a median pressure of 50 MPa, an amplitude of 15 MPa, and a frequency of 4 Hz, and at 1300 o Keep warm at C for 35 minutes; 2-4) Continue with 5 o Temperature increased to 1450 °C / min o C, then switch to a vacuum atmosphere, controlling the vacuum level <5Pa, to perform oscillating hot-pressing gradient sintering: adjust the oscillation pressure parameters to the median 45MPa, amplitude 20MPa, frequency 6Hz, and at 1450 o Keep warm at C for 60 minutes.

[0110] Subsequently, the sample was cooled to room temperature in the furnace to obtain a nitrogen-free de-β-layer gradient cemented carbide.

[0111] Example 8 1) Weigh the powder raw materials according to the following mass ratio: 81% WC, 12% Co, 5% (Ti,W)C, 1% NbC, and 1% TaC. Place the weighed powder raw materials in a planetary ball mill and perform wet ball milling with anhydrous ethanol as the medium. Set the ball-to-material ratio to 5:1, the rotation speed to 150 rpm, and the milling time to 50 h. After ball milling, the resulting suspension is cooled to 60 °C. o Vacuum drying at C and passing through a 60-mesh sieve yields a mixture. Subsequently, 4% paraffin wax (by mass of the total pressed powder) is added to the mixture, and after thorough mixing, it is granulated by sieving (passing through a 60-mesh sieve) to obtain the powder to be pressed.

[0112] Take 20g of the powder to be pressed and add it to the mold cavity (20mm×7mm×6mm). Press it into shape on an automatic pressing press to obtain a rectangular blank.

[0113] 2) The billet is placed in a vacuum sintering furnace for sintering. The specific sintering procedure is as follows: 2-1) Under an argon atmosphere, at 5 o Temperature increased to 300 °C / min o C, keep warm for 45 minutes; continue at 10 o Heat up to 500 °C / min o C, keep warm for 60 minutes; then add 10 o Heat up to 800 °C / min o C, keep warm for 45 minutes; 2-2) Switch to a vacuum atmosphere, control the vacuum level < 5 Pa, and use 10 o Temperature increased to 1100 °C / min o C, keep warm for 60 minutes; 2-3) with 5 o Temperature increased to 1350 °C / min o C, then switch to a nitrogen atmosphere for oscillatory hot-press nitriding, maintaining a nitrogen pressure of 4 kPa, applying an oscillatory pressure with a median pressure of 70 MPa, an amplitude of 8 MPa, and a frequency of 1 Hz, and at 1350 o Keep warm at C for 60 minutes; 2-4) Continue with 5 o Temperature increased to 1480 °C / min o C, then switch to a vacuum atmosphere, controlling the vacuum level <5Pa, to perform oscillating hot-pressing gradient sintering: adjust the oscillation pressure parameters to a median of 30MPa, amplitude of 25MPa, and frequency of 10Hz, and at 1480 o Keep warm at C for 85 minutes.

[0114] Subsequently, the sample was cooled to room temperature in the furnace to obtain a nitrogen-free de-β-layer gradient cemented carbide.

[0115] Test case The test examples are used to characterize and test the performance of the cemented carbides prepared in the above embodiments and comparative examples.

[0116] 1. Microscopic morphology characterization and quantitative analysis (1) Morphological characteristics After grinding and polishing the cemented carbide, the microstructure of the vertical cross-section of the polished sample was characterized by scanning electron microscopy (SEM), and backscattered SEM images were acquired.

[0117] (2) Average thickness and uniformity of the β-layer Three different regions were randomly selected from the vertical cross-section of the cemented carbide, and five SEM images were acquired for each region at a magnification of 1000×. ImageJ image analysis software was used to perform three thickness measurements on each image, for a total of 45 measurements per sample. Based on all measurement results, the average thickness of the β-layer was calculated. The standard deviation is used to reflect the uniformity of the β-layer thickness.

[0118] (3) Degree of β-phase residue after β-layer removal Four different regions of the alloy's vertical cross-section were randomly selected, and five SEM images were acquired for each region at a magnification of 1000×. ImageJ software was used for image analysis, and a section with a width of [missing information] was defined in each image. μ The rectangular region (beta-depleted layer) is used as the analysis unit. The ratio of the total area of ​​the beta phase within the beta-depleted layer to the total area of ​​the beta-depleted layer region in each image is measured and calculated. i For each sample, 20 data points were collected, based on all obtained ratios ( i ) Calculate the average value to reflect the residual amount of β phase within the de-β layer.

[0119] 2. Fracture toughness test The fracture toughness of cemented carbide was determined in accordance with the industry standard JB / T 12616-2016 Test Method for Fracture Toughness of Matrix Material for Cemented Carbide Tools.

[0120] 3. Hardness Measurement The hardness of cemented carbide was determined in accordance with the national standard GB / T 7997-2014 Vickers Hardness Test Method for Cemented Carbide.

[0121] 4. Bending strength measurement The bending strength of cemented carbide was determined in accordance with the national standard GB / T 3851-2015 "Determination of transverse fracture strength of cemented carbide".

[0122] The test results are shown in Table 1.

[0123] Table 1

[0124] As can be seen from the data in Table 1, compared with Comparative Examples 1 to 6, the cemented carbide samples prepared in Examples 1 to 8 are superior in terms of uniformity of β-layer thickness and β-phase residue. While maintaining high hardness, they also improve fracture toughness and bending strength, resulting in superior overall mechanical properties.

[0125] A comparison of Example 1 and Comparative Example 1 shows that, because Comparative Example 1 did not employ oscillating hot pressing nitriding treatment, no decomposable nitrogen-containing cubic phase was formed on the surface or inside of the alloy, resulting in the inability to form a β-layer.

[0126] A comparison of Example 1 and Comparative Example 2 shows that, due to the absence of oscillating hot pressing, Comparative Example 2 exhibits poor uniformity in the thickness of the β-layer, with a standard deviation of 4.31. This is significantly higher than the 0.67 in Example 1. .

[0127] A comparison of Example 1 and Comparative Example 3 shows that Comparative Example 3 did not apply oscillating hot pressing during the nitriding stage, resulting in a larger standard deviation of the β-layer thickness and uneven distribution of its nitrogen-containing cubic phase.

[0128] Comparing Example 1 with Comparative Example 4, it can be seen that Comparative Example 4 did not apply oscillating hot pressing during the gradient sintering stage, resulting in a higher residual amount of β phase on the surface, and a significant decrease in the fracture toughness and bending strength of the alloy.

[0129] Comparing Example 1 with Comparative Examples 5-6, it can be seen that in Comparative Example 5, due to excessively high nitrogen pressure, defects appeared on the alloy surface, with a β-phase residue of 1.14% and a thickness standard deviation of 5.56%. The inability to form a uniform β-phase layer is a significant problem. In Comparative Example 6, the median pressing value during the oscillating hot-pressing gradient sintering stage was relatively large, and the amplitude and frequency settings were too low. This resulted in insufficient denitrification reaction, limited promoting effect of oscillating hot pressing on decomposition, leading to a high residual β-phase content, poor uniformity of the β-phase layer, and unsatisfactory overall mechanical properties. Furthermore, compared with Comparative Examples 2-6, the two-stage oscillating pressure sintering process in Example 1 not only ensured high uniformity and low β phase residue in the de-β layer, but also achieved a significant increase in the thickness of the de-β layer.

[0130] In summary, this application, through the process parameters of the coordinated oscillating hot-pressing nitriding stage and the oscillating hot-pressing gradient sintering stage, can generate a cemented carbide surface layer with a thickness standard deviation of <1.2. The process of removing the β-phase with a residual β-phase content of <0.5% allows for control over the microstructure and mechanical properties of the β-layer-free gradient cemented carbide. The prepared nitrogen-free β-layer-free gradient cemented carbide exhibits high fracture toughness, hardness, and bending strength.

[0131] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for preparing a β-layer gradient cemented carbide, characterized in that, include: 1) Press the nitrogen-free raw material into a compact; The nitrogen-free raw material includes a mixture and an optional molding agent, and the mixture consists of WC, Co and alloy carbides; 2) The compact is subjected to pre-sintering, a first oscillating hot pressing treatment, and a second oscillating hot pressing treatment in sequence to obtain a β-layer-removed gradient cemented carbide; wherein, The first oscillating hot pressing treatment is carried out in the presence of nitrogen gas at a pressure of 0.1~4 kPa, with a median oscillation pressure P1 of 50~85 MPa and an amplitude P. m1 The pressure is 5~20MPa, and the frequency f1 is 0.5~4Hz; The second oscillating hot pressing treatment is carried out under vacuum conditions, with a median oscillation pressure P2 of 25~50 MPa and an amplitude P m2 The pressure is 10~30MPa, and the frequency f2 is 2~10Hz; Furthermore, P1 and P2, P m1 With P m2 f1 and f2 must satisfy the following relationship: P1>P2,P m1 <P m2 ,f1<f2。 2. The preparation method according to claim 1, characterized in that, The alloy carbide is selected from a first metal carbide and an optional second metal carbide, wherein... The first metal carbide is a titanium-containing carbide, preferably (Ti,W)C and / or TiC; The second metal carbide is at least one of NbC, TaC, and TaNbC.

3. The preparation method according to claim 2, characterized in that, Based on the total mass of the mixture, the mass content of WC is 70%~90%, the mass content of Co is 5%~20%, and the mass content of alloy carbides is 3%~20%; Preferably, the mass content of the titanium carbide is 1% to 5% based on the total mass of the mixture.

4. The preparation method according to any one of claims 1-3, characterized in that, The molding agent is selected from one or more of paraffin wax, microcrystalline wax and polyethylene wax; Preferably, the mass content of the molding agent is 2% to 5% based on the total mass of the nitrogen-free raw materials.

5. The preparation method according to any one of claims 1-4, characterized in that, The mixture is prepared by a method comprising the following steps: Tungsten carbide powder, cobalt powder, and alloy carbide powder are wet ball-milled to obtain a ball-milled slurry; The ball-milled slurry was vacuum dried. Preferably, the operating conditions for the wet ball milling include: using anhydrous ethanol as the medium, a ball-to-material ratio of (1.5~6):1, a rotation speed of 60~280 rpm, and a milling time of 8~76 h.

6. The preparation method according to any one of claims 1-5, characterized in that, The pre-sintering process includes: 2-1) In an inert atmosphere, at 3~10 o Heating rate increased to 250~350 °C / min o C, keep warm for 30-60 minutes; then at 5-15 degrees Celsius... o Heating rate increased to 450~550 °C / min o C, keep warm for 30-100 minutes; finally, reduce to 5-15 degrees Celsius. o Heating rate increased to 700-900 °C / min o C, keep warm for 30~100 minutes; 2-2) Under vacuum conditions, at 5~10 o Heating rate increased to 950~1200 °C / min o C, keep warm for 30~100 minutes; Preferably, the inert gas is argon.

7. The preparation method according to any one of claims 1-6, characterized in that, The temperature of the first oscillating hot pressing treatment is 1250~1400℃ o C, the heat preservation time is 20~60 min; the temperature of the second oscillating hot pressing treatment is 1420~1500 °C. o C, the heat preservation time is 30~90 minutes; Preferably, the first oscillating hot pressing process includes: 2-3) with 3~10 o The temperature is increased to 1250~1400 °C / min. o C. Switch to nitrogen atmosphere, apply oscillating pressure and maintain temperature; Preferably, the second oscillating hot pressing process includes: 2-4) with 5~10 o Increase the temperature by C / min to 1420~1500 o C. Switch to vacuum conditions, apply oscillating pressure, and maintain temperature.

8. The preparation method according to any one of claims 1-7, characterized in that, In the first oscillating hot pressing process, the median oscillation pressure P1 is 50~80MPa, and the amplitude P m1 The pressure is 8~15MPa, and the frequency f1 is 1~2Hz; in the second oscillating hot pressing treatment, the median oscillation pressure P2 is 30~45MPa, and the amplitude P m2 The pressure is 18~30MPa, and the frequency f2 is 7~10Hz.

9. A de-β-layer gradient cemented carbide prepared by the preparation method according to any one of claims 1-8.

10. The β-layer gradient cemented carbide according to claim 9, characterized in that, The average thickness of the β-layer is ≥15 Preferably 15~55 ; Preferably, the standard deviation of the thickness of the β-layer is <1.

2. The residual β phase content in the β-layer is <0.5%.

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