Binding-phase-free hard alloy preparation method

Abstract

The invention discloses a preparation method of a binding-phase-free hard alloy with high density. Comprising the following steps that S1, burdening is conducted, specifically, raw materials including 98.5 wt%-99.0 wt% of tungsten carbide are weighed according to the weight percentage, and the tungsten carbide is composed of 68.5 wt%-89.5 wt% of submicron tungsten carbide and 10 wt%-30 wt% of superfine tungsten carbide and further comprises 0 wt%-0.5 wt% of cobalt powder and 0.5 wt%-1 wt% of chromium carbide; s2, mixing: mixing the tungsten carbide with different granularities in a mixer for 2 hours; s3, ball milling and drying; s4, carrying out compression molding; s5, sintering; the sintering temperature is 1600 DEG C, the sintering pressure is 0.9 MPa, and the heat preservation time is 90 minutes; and S6, cooling is conducted, positive-pressure forced cooling is conducted, and the pressure is kept at 0.9 MPa. According to the method, the high-density binding-phase-free hard alloy can be prepared at the lower temperature and pressure, and the method is suitable for industrial popularization.

Description

Technical Field

[0001] The present invention relates to the field of manufacturing cemented carbides by powder metallurgy, and provides a method for preparing a binderless cemented carbide material with high density. Background Art

[0002] Binderless WC-based cemented carbides refer to cemented carbide materials that contain no or very little metal binder phase (<0.5 wt%). Compared with traditional WC-Co cemented carbides, binderless WC-based cemented carbides have more excellent wear resistance, corrosion resistance, polishing performance, and oxidation resistance, and are mostly used in fields such as precision optical molds, jet nozzles, electronic packaging materials, and nuclear industry seals. Due to the extremely low content of the binder phase, the self-diffusion coefficient of WC itself is very small and the melting point is as high as 2900 °C. The temperature required for sintering densification of binderless WC-based cemented carbides is usually 1800 - 2000 °C. It is very difficult to obtain a highly dense block by the sintering methods for preparing ordinary alloys. Advanced sintering technologies such as spark plasma sintering and hot isostatic pressing can reduce the sintering temperature to a certain extent and have a short sintering time, but currently they are only applicable to laboratories, and there are problems such as large equipment investment, low economic efficiency, and difficulty in expanding production scale.

[0003] A method for preparing a binderless cemented carbide in the prior art mainly includes the following steps: Mixing: Weigh WC powder, TiC powder, TaC powder, and a forming agent in a certain proportion, and carry out ball milling and drying; Mold pressing: Press the mixed powder through an automatic molding machine; Vacuum sintering: Carry out vacuum sintering at a certain temperature for pre-sintering; Hot isostatic pressing sintering: Put the pre-sintered blank into a hot isostatic pressing furnace for hot isostatic pressing sintering to promote densification. High-density or even fully dense binderless cemented carbide products can be obtained, and the material density can reach 99.9% of the theoretical density, which is beneficial to improving the material properties.

[0004] However, the densification sintering temperature of ordinary WC-Co cemented carbides in the above prior art is generally 1300 - 1500 °C, and the sintering pressure is about 3 - 5 MPa. However, the sintering densification of binderless cemented carbide materials requires higher temperature and pressure. For example, when preparing binderless cemented carbide materials by pressureless sintering, the sintering temperature is generally greater than 1800 °C, and the holding time is greater than 60 min; High-pressure sintering technology and SPS technology can reduce the sintering temperature to 1500 - 1600 °C to a certain extent, the sintering pressure > 50 MPa, and the sintering time is shortened to 2 - 3 min, which cannot be satisfied by the current low-pressure sintering process, and there are problems such as large equipment investment, low economic efficiency, and difficulty in expanding production scale. Moreover, in order to improve the sintering activity of raw WC powder in solid-phase sintering, binderless cemented carbide materials usually adopt a high ball-to-material ratio (8 - 10:1) and a long ball milling time (more than 64 h), which do not conform to the conventional cemented carbide production process. Summary of the Invention

[0005] In view of the deficiencies of the above-mentioned existing process technologies, the present invention provides a method for preparing a binderless cemented carbide with high density. This material is prepared by means of low-temperature and low-pressure sintering.

[0006] In order to achieve the above invention object, the present invention includes the following steps:

[0007] S1: Batching: Weigh raw materials according to weight percentages, including 98.5 - 99.0 wt% tungsten carbide, where the tungsten carbide consists of 68.5 - 89.5 wt% submicron tungsten carbide and 10 - 30 wt% ultrafine tungsten carbide, and also includes 0 - 0.5 wt% cobalt powder and 0.5 - 1 wt% chromium carbide;

[0008] S2: Mixing, mixing tungsten carbides with different particle sizes in a mixer for 2 h;

[0009] S3: Ball milling and drying;

[0010] S4: Compression molding;

[0011] S5: Sintering; the sintering temperature is 1600 °C, the sintering pressure is 0.9 MPa, and the heat preservation time is 90 min;

[0012] S6: Cooling, cooling under positive pressure, and maintaining the pressure at 0.9 MPa.

[0013] According to the Horsfield dense packing theory and the particle size grading technology theory, a discontinuous particle size system is more likely to form the densest packing. In the theory of hexagonal close packing of spheres with different diameters, the porosity is 25.94% when there is only the first type of sphere, 20.7% after adding the second type of sphere, and 19.0% after adding the third type of sphere. That is, smaller-sized particles are filled in the voids of the system of large-sized particle packing, and then even smaller-sized particles are filled in the voids between the large and small particles until the porosity between particles reaches the minimum. The present invention adds a certain proportion (10 - 30 wt%) of / ultrafine / nano WC powder (Fischer particle size < 0.6 μm) to the submicron WC powder (Fischer particle size 0.6 - 1.0 μm), obtains a mixed powder through mixing in a double-motion mixer, then adds ultrafine cobalt powder and chromium carbide powder for wet milling, and obtains a binderless cemented carbide with a relative density greater than 98% after drying, granulating, compression molding, and low-temperature and low-pressure sintering. The low-temperature and low-pressure sintering process has a sintering temperature of 1500 - 1700 °C, a sintering pressure of 0.9 - 10 MPa, and a sintering time of 60 - 90 min. At the same time, the ball milling process of fine-grained WC powder is simplified, avoiding the increase of powder distortion energy due to long-term ball milling, thus causing abnormal growth of WC grains during sintering.

[0014] A further improvement is that in step S1, raw materials are weighed according to weight percentages, including 98.5 wt% tungsten carbide, where the tungsten carbide consists of 69 wt% submicron tungsten carbide, 29.5 wt% ultrafine tungsten carbide, 0.5 wt% cobalt powder, and 1 wt% chromium carbide;

[0015] A further improvement is that in step S1: raw materials are weighed according to weight percentages, including 98.5 wt% tungsten carbide, where the tungsten carbide consists of 69 wt% submicron tungsten carbide, 10 wt% ultrafine tungsten carbide, 19.5 wt% ultrafine tungsten carbide, 0.5 wt% cobalt powder, and 1 wt% chromium carbide; <>

[0016] A further improvement is that the wet grinding process parameters are as follows: the rotational speed of the ball mill is 72 r / min, the grinding media are WC-6 wt% Co cemented carbide balls with a diameter of , the ball-to-material ratio is 4 - 5:1, the wet grinding medium is hexane, the addition amount of hexane is (410 - 460) ml / Kg, the addition amount of the forming agent (paraffin) is 2.0 ± 0.2 wt%, and the ball milling time is 36 - 48 h.

[0017] A further improvement is that in step 4, the prepared mixture is molded by die pressing to obtain a green compact with corresponding dimensional requirements, and the pressing pressure is 3 MPa; the green compact is cold isostatically pressed at 110 MPa for 30 s to obtain a preform;

[0018] The present invention can prepare a high-density binderless cemented carbide at lower temperatures and pressures, with its porosity reaching A02B00C00, the density > 98%, and HV10 > 2400 kgf / mm 2 . Description of the Drawings

[0019] The following will clearly and completely describe the technical solution in conjunction with the drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them.

[0020] Figure 1 is the metallographic photograph of the cemented carbide in Example 1 of the present invention;

[0021] <00> Figure 2 is the metallographic photograph of the cemented carbide in Example 2 of the present invention. Detailed Embodiments <00>

[0022] The following further elaborates on the above content of the present invention in detail in conjunction with the specific embodiments of the examples. However, this should not be construed as limiting the scope of the above subject matter of the present invention to the following examples. Without departing from the above technical idea of the present invention, various substitutions or changes made according to common technical knowledge and customary means in the art should be included within the scope of the present invention.

[0023] Example 1:

[0024] A method for preparing a high-density cemented carbide without binder phase includes the following steps:

[0025] 1. Raw material ratio: Weigh the raw materials by weight percentage. The raw materials include 98.5 wt% tungsten carbide, and the tungsten carbide consists of two particle sizes, 69 wt% WC08 (Fsss particle size is 0.7 μm) and 29.5% WC02 (Fsss particle size is 0.2 μm). It also includes 0.5 wt% ultrafine Co powder (FSSS particle size is 1.0 - 2.0 μm) and 1 wt% Cr3C2 powder. The sum of the proportions of each component is 100%;

[0026] 2. Mixing: Mix WC with different particle sizes in a bench-top double-motion mixer for 2 h;

[0027] 3. Ball milling and drying: Add the mixed powder in step 2 and the Co powder in step 1 into a 1.0 L ball milling cylinder, add hexane, paraffin, and stearic acid, and then place it on a cantilever ball mill for rolling ball milling. The rotational speed of the ball mill is 72 r / min; the addition amount of hexane is 400 ml / kg, the addition amount of paraffin is 2 wt% of the raw materials, and the addition amount of stearic acid is 0.04 wt% of the raw materials. The grinding media are WC-6wt% Co cemented carbide balls with a diameter of, the ball-to-material ratio is 5:1, and the ball milling time is 48 h; Place the slurry in a drying cabinet and vacuum dry it at 75 °C to granulate and obtain the mixed material.

[0028] 4. Pressing: Press the prepared mixed material by die pressing to obtain a green compact with the corresponding size requirements. The pressing pressure is 3 MPa; The green compact is cold isostatically pressed at 110 MPa for 30 s to obtain a preform;

[0029] 5. Sintering: Sinter the preform. The sintering temperature is 1600 °C, the sintering pressure is 0.9 MPa, and the holding time is 90 min;

[0030] 6. Cooling: After sintering, perform positive pressure cold cooling with a blower for rapid cooling. The cooling rate is about 20 °C / min, and the pressure is maintained at 0.9 MPa. After the temperature in the furnace is lower than 50 °C, take it out of the furnace.

[0031] Obtain the high-density cemented carbide without binder phase. The relative density of the alloy is 98.6%, HV10 is 2560 kgf / mm 2 , the fracture toughness is 8.1 MPa·m 1 / 2 , and the average grain size of WC is 0.6 μm.

[0032] Example 2

[0033] A method for preparing a high-density cemented carbide without binder phase is the same as Example 1 except for the following process steps.

[0034] 1. Raw material ratio: The raw materials include 69 wt% WC10 (Fsss particle size is 1.0 μm), 10% WC04 (Fsss particle size is 0.4 μm), and 19.5 wt% WC02 (Fsss particle size is 0.2 μm);

[0035] The relative density of the alloy is 99.2%, HV10 is 2440 kgf / mm 2 , and the fracture toughness is 8.9 MPa·m 1 / 2 , and the average grain size of WC is 0.8 μm.

[0036] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Any simple modifications and equivalent changes made to the above embodiments based on the technical essence of the present invention all fall within the protection scope of the present invention.

Claims

1. A method for preparing a cemented carbide without a binder phase, characterized in that, It includes the following steps: S1: Batching: Weigh the raw materials by weight percentage, including 98.5 - 99.0 wt% tungsten carbide, where the tungsten carbide consists of 68.5 - 89.5 wt% submicron tungsten carbide and 10 - 30 wt% ultrafine tungsten carbide, and also includes 0 - 0.5 wt% cobalt powder and 0.5 - 1 wt% chromium carbide; S2: Mixing, mix tungsten carbides with different particle sizes in a mixer for 2 h; S3: Ball milling and drying; S4: Compression molding; S5: Sintering; The sintering temperature is 1600 °C, the sintering pressure is 0.9 MPa, and the heat preservation time is 90 min; S6: Cooling, cooling under positive pressure, and the pressure is maintained at 0.9 MPa.

2. The method according to claim 1, characterized in that, In the step S1, weigh the raw materials by weight percentage, including 98.5 wt% tungsten carbide, where the tungsten carbide consists of 69 wt% submicron tungsten carbide, 29.5 wt% ultrafine tungsten carbide, 0.5 wt% cobalt powder, and 1 wt% chromium carbide.

3. The method according to claim 1, wherein In the step S1, weigh the raw materials by weight percentage, including 98.5 wt% tungsten carbide, where the tungsten carbide consists of 69 wt% submicron tungsten carbide, 10 wt% ultrafine tungsten carbide, 19.5 wt% ultrafine tungsten carbide, 0.5 wt% cobalt powder, and 1 wt% chromium carbide.

4. The method according to claim 1, characterized in that In the step S3, the ball milling process parameters are as follows: the rotational speed of the ball mill is 72 r / min, the grinding medium is WC - 6 wt% Co cemented carbide balls with a diameter of φ6.35 mm, the ball - to - material ratio is 4 - 5:1, the wet - milling medium is hexane, the addition amount of hexane is (410 - 460) ml / Kg, the addition amount of the molding agent (paraffin) is 2.0 ± 0.2 wt%, and the ball milling time is 36 - 48 h.

5. The method according to claim 1, characterized in that In the step 4, press the prepared mixture through die pressing to obtain a green compact with corresponding dimensional requirements, and the pressing pressure is 3 MPa; the green compact is cold isostatically pressed at 110 MPa for 30 s to obtain a preform.

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