A cemented carbide with acicular structure and a method of producing the same

Abstract

The application relates to a cemented carbide with needle-shaped structure and a preparation method thereof, and belongs to the technical field of cemented carbide additive manufacturing. The method comprises the following steps: WC-VC-Co spherical composite powder is prepared by taking WC, Co and VC powder with an average particle size of less than 1 mu m as raw materials; after heat treatment and particle size grading, the WC-VC-Co spherical composite powder is printed and formed by adopting a powder laying type selective laser melting device, so that WC and VC form VWC2 phases in situ under the action of laser; and the cemented carbide part obtained by printing is heat treated at 1410-1480 DEG C and 5-6 MPa in an argon atmosphere for 50-80 min, so that the VWC2 phases are decomposed into WC and V4WC5, and the formed WC is caused to grow in orientation. The cemented carbide with needle-shaped structure prepared by the application has a dense microstructure, needle-shaped WC is uniformly distributed in different directions in space, and the volume content of the needle-shaped structure is high.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of cemented carbide additive manufacturing, and particularly relates to a process method for preparing a cemented carbide with acicular structure by means of laser 3D printing and subsequent heat treatment. TECHNICAL BACKGROUND

[0002] The cemented carbide represented by WC-Co composition has high hardness, strength and wear resistance, and its Vickers hardness can reach 1000-2400 kgf / mm 2 , and the bending strength can reach more than 5000 MPa. Even in a high-temperature and high-pressure environment, it can also maintain excellent comprehensive mechanical properties, which makes the cemented carbide be widely used in many industrial fields as metal cutting tools, molds and wear-resistant parts.

[0003] Due to the difficulty of subsequent mechanical processing of cemented carbide, the powder metallurgy process is currently the main preparation method for various products. The cemented carbide prepared by this process is generally composed of equiaxed carbide (including WC, TiC, NbC, etc.) grain skeleton, and the gap between the skeleton is filled with Co, Ni, Fe or their alloys. The carbide in this metal ceramic composite material mainly provides high hardness and wear resistance for the alloy, and the metal binder phase provides plasticity and toughness, coordinates plastic deformation when the alloy bears external load, relieves stress concentration, thereby delaying fracture and improving the strength of the cemented carbide.

[0004] It has been found that by using a specific preparation process, WC grains with a hexagonal close-packed structure can be preferentially grown in the direction perpendicular to the prism face or basal plane, forming a plate-like or lath-like morphology. Since the basal plane and the prism face of WC have different hardness and wear resistance, this special oriented cemented carbide has obvious anisotropy in performance. By using this, the prepared cemented carbide products can have more outstanding performance in certain application scenarios, maximizing their advantages. However, the preparation of the above-mentioned special oriented cemented carbide often requires harsh process conditions, such as providing an oriented distribution of the initial powder by high-energy ball milling and filtration; applying a unidirectional pressure based on a special sintering equipment to make the WC grains grow in an oriented manner. Due to the difficulty in preparation, the practical application of such cemented carbide is limited. Especially, it is difficult to prepare cemented carbide parts with complex geometry and special crystal orientation by traditional methods.

[0005] In view of the above problems, the present application proposes a method for preparing a cemented carbide with acicular structure based on innovative design of composition and laser 3D printing process, which realizes the free design of the shape of the cemented carbide parts with special crystal orientation for the first time. SUMMARY

[0006] The preparation process and principle provided by the present invention are as follows: first, a WC-VC-Co composite powder with uniform dispersion of each phase is obtained by ball milling, and then spray granulation and heat treatment are performed to obtain a printable powder with high density. During the heat treatment, a certain amount of WC and VC react to form a V4WC5 phase; the powder is printed and formed using a selective laser melting device, so that the remaining WC and V4WC5 phases in the powder react in situ to form a metastable VWC2 phase during the melting and extremely rapid solidification of the powder; then, to improve the density of the printed part, it is subjected to heat treatment. At this time, a part of the metastable VWC2 phase is re-decomposed into WC and V4WC5 phases. Due to the aggregation and distribution of V atoms on the special crystal planes of the WC grains during this process, they undergo oriented growth, thereby obtaining a new WC-Co cemented carbide with a needle-like structure.

[0007] The present invention provides a cemented carbide having an acicular structure and a preparation method thereof, characterized in that the method comprises the following steps:

[0008] (1) Using WC, Co, and VC powders with an average particle size of less than 1 μm as raw materials, the WC-VC-Co composite powder is prepared so that the mass fraction of VC is 5%-22% and the mass fraction of Co is 10%-20%. The powders are thoroughly wet-milled using anhydrous ethanol to ensure that the three raw material powders are evenly mixed before drying. The dried powder is mixed with deionized water and polyethylene glycol to form a slurry, which is then agglomerated and granulated using a high-speed centrifugal atomization drying process to obtain a spherical WC-VC-Co composite powder.

[0009] (2) The spherical composite powder obtained in the above steps is heat-treated to remove polyethylene glycol while allowing the agglomerated particles to obtain a certain cohesive strength, high density and fluidity, and at the same time causing some WC and VC to react to form a V4WC5 phase. The heat treatment temperature is 1180-1250°C, and the holding time is 90-120 minutes. Then, airflow classification is used to remove particles of excessively large and undersized particle size in the heat-treated powder, obtaining a WC-V4WC5-Co spherical composite powder with a particle size distribution of 10-30 μm required for printing.

[0010] (3) Using the powders graded in the above steps as raw materials, a powder-spreading selective laser melting device was used for printing and forming, so that WC and V4WC5 formed the VWC2 phase in situ under the action of the laser. The laser printing process parameters used were: laser power 100-140W, scanning rate 800-1000mm / s, scanning pitch 0.04mm, and powder layer thickness 0.03mm.

[0011] (4) The printed parts are subjected to atmosphere protection heat treatment at a temperature of 1410-1480°C. When the temperature reaches the target temperature, 5-6 MPa of argon is introduced and kept at this pressure for 50-80 minutes to decompose the VWC2 phase into WC and V4WC5, and promote the oriented growth of the formed WC. After cooling to room temperature, a cemented carbide part with a needle-like structure and freely designable shape is obtained.

[0012] In the further step (3), the phases of the parts formed by the powder under the action of laser include: VWC2 and relatively small amounts of WC, W2C, and Co3W3C.

[0013] Further, in step (4), the phases of the parts after heat treatment include: WC, V4WC5, VWC2 and Co.

[0014] Furthermore, the volume content of the needle-like structure in the part is finally obtained to be 40%-70%, the average length of the needle-like WC grains is 1.0-2.2 μm, and the average diameter range is 0.1-0.3 μm.

[0015] The technical features and advantages of the method of the present invention are mainly as follows: (1) The present invention introduces an appropriate amount of VC into traditional WC-Co powder, and then combines it with a selective laser melting process to realize the preparation of cemented carbide parts with needle-like structure and freely designable shape. The method is simple and easy to implement and has great industrial application prospects; (2) The present invention cleverly utilizes the metastable VWC2 phase. Through its in-situ formation under the action of laser and decomposition during heat treatment, V atoms are segregated at a special WC / Co interface, thereby realizing the oriented growth of the WC phase under conventional heat treatment process conditions, and obtaining WC grains with a one-dimensional needle-like structure. Compared with the lath-like WC obtained by the traditional process, the aspect ratio of the needle-like WC grains (which can reach more than 7) is significantly increased; (3) The cemented carbide with needle-like structure prepared by the present invention has a dense microstructure, and the needle-like WC is uniformly distributed in different directions in space, so that it has high hardness and excellent wear resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The scanning electron microscope morphology and particle size distribution of the spherical WC-VC-Co composite powder prepared in the present invention; wherein, (a) is the scanning electron microscope morphology and particle size distribution of WC-5VC-12Co powder, (b) is the scanning electron microscope morphology and particle size distribution of WC-10VC-12Co powder, and (c) is the scanning electron microscope morphology and particle size distribution of WC-15VC-12Co powder;

[0017] Figure 2Phase analysis results of the WC-V4WC5-Co spherical composite powder prepared in the present invention, and the laser-printed and heat-treated cemented carbide parts; (a) is the phase composition of the spherical composite powder, (b) is the phase composition of the laser-printed cemented carbide, and (c) is the phase composition of the laser-printed and heat-treated cemented carbide.

[0018] Figure 3 Figure 2 shows the microstructure of the cemented carbide sample after laser printing and heat treatment at 1410°C observed under a scanning electron microscope. (a) shows the microstructure of the WC-5VC-12Co sample after laser printing and heat treatment at 1410°C, (b) shows the microstructure of the WC-10VC-12Co sample after laser printing and heat treatment at 1410°C, and (c) shows the microstructure of the WC-15VC-12Co sample after laser printing and heat treatment at 1410°C. DETAILED DESCRIPTION

[0019] The present invention is further described below with reference to Example 1, Example 2 and Example 3, but the present invention is not limited to the following examples.

[0020] Example 1

[0021] WC, Co and VC powders with an average particle size of less than 1 μm are used as raw materials. The mass fraction of VC in the obtained WC-VC-Co composite powder is 5%, and the mass fraction of Co is 12%. The powder is fully wet-milled with anhydrous ethanol as the medium to ensure that the three raw material powders are evenly mixed and then dried. The dried powder is mixed with deionized water and polyethylene glycol in proportion to form a slurry, and agglomerated and granulated by a high-speed centrifugal atomization drying process to obtain WC-VC-Co spherical composite powder. The spherical composite powder obtained in the above steps is heat-treated to remove polyethylene glycol while allowing the agglomerated particles to obtain a certain cohesive strength, high density and fluidity, and at the same time allowing part of WC and VC to react to form V4WC5 phase. The heat treatment temperature is 1250°C, and the holding time is 90 minutes. Then, the particles with too large and too small particle sizes in the heat-treated powder are removed by airflow classification to obtain the WC-V4WC5-Co spherical composite powder with a particle size distribution of 10-30 μm required for printing, and its morphology is as follows. Figure 1 (a) Phase detection results are as follows Figure 2 (a) As shown. The powder after classification in the above steps is used as raw material, and a powder-spreading selective laser melting device is used for printing and forming, so that WC and V4WC5 form VWC2 phase in situ under the action of laser. The laser printing process parameters used are: laser power 100W, scanning rate 800mm / s, scanning spacing 0.04mm, and powder layer thickness 0.03mm. The phase detection results of laser printed cemented carbide are shown in Figure 2(b) The printed part was subjected to atmosphere heat treatment at 1410°C. When the temperature reached the target temperature, 5MPa of argon was introduced and maintained at this pressure for 50 minutes. This decomposed the VWC2 phase into WC and V4WC5, and promoted the oriented growth of the formed WC. After cooling to room temperature, a cemented carbide part with an acicular structure and freely designable shape was obtained. Figure 2 (c) and Figure 3 (a) shows the phase detection results of cemented carbide after laser printing and heat treatment, and the microstructure of cemented carbide with needle-like structure. The volume content of needle-like structure is about 40.59%, the average length of needle-like WC phase is 1.02μm, and the diameter is 0.13μm.

[0022] Example 2

[0023] WC, Co and VC powders with an average particle size of less than 1 μm are used as raw materials. The mass fraction of VC in the obtained WC-VC-Co composite powder is 10% and the mass fraction of Co is 12%. The powder is fully wet-milled with anhydrous ethanol as the medium to ensure that the three raw material powders are evenly mixed and then dried. The dried powder is mixed with deionized water and polyethylene glycol in proportion to form a slurry, and agglomerated and granulated by a high-speed centrifugal atomization drying process to obtain WC-VC-Co spherical composite powder. The spherical composite powder obtained in the above steps is heat-treated to remove polyethylene glycol while allowing the agglomerated particles to obtain a certain cohesive strength, high density and fluidity, and at the same time allowing part of WC and VC to react to form V4WC5 phase. The heat treatment temperature is 1185°C and the holding time is 90 minutes. Then, the particles with too large and too small particle sizes in the heat-treated powder are removed by airflow classification to obtain the WC-V4WC5-Co spherical composite powder with a particle size distribution of 10-30 μm required for printing. Its morphology is as follows. Figure 1 (b) The results of physical phase detection are as follows Figure 2 As shown in (a). The powder after classification in the above steps is used as raw material, and a powder-spreading selective laser melting device is used for printing and forming, so that WC and V4WC5 form VWC2 phase in situ under the action of laser. The laser printing process parameters used are: laser power 120W, scanning rate 900mm / s, scanning spacing 0.04mm, and powder layer thickness 0.03mm. The phase detection results of laser printed cemented carbide are shown in Figure 2 (b) The printed WC-VC-Co part was subjected to atmosphere heat treatment at 1410°C. When the temperature reached the target temperature, 5MPa of argon was introduced and maintained at this pressure for 50 minutes. This decomposed the VWC2 phase into WC and V4WC5, and promoted the oriented growth of the formed WC. After cooling to room temperature, a cemented carbide part with an acicular structure and freely designable shape was obtained. Figure 2 (c) and Figure 3 (b) shows the phase detection results of cemented carbide after laser printing and heat treatment, and the microstructure of cemented carbide with needle-like structure. The volume content of needle-like structure is about 51%, the average length of needle-like WC phase is 1.89 μm, and the diameter is 0.28 μm.

[0024] Example 3

[0025] WC, Co and VC powders with an average particle size of less than 1 μm are used as raw materials. The mass fraction of VC in the prepared WC-VC-Co composite powder is 15%, and the mass fraction of Co is 12%. The powder is fully wet-milled with anhydrous ethanol as the medium to ensure that the three raw material powders are evenly mixed and then dried. The dried powder is mixed with deionized water and polyethylene glycol in proportion to form a slurry, and agglomerated and granulated by a high-speed centrifugal atomization drying process to obtain WC-VC-Co spherical composite powder. The spherical composite powder obtained in the above steps is heat-treated to remove polyethylene glycol while allowing the agglomerated particles to obtain a certain cohesive strength, high density and fluidity, and at the same time allowing part of the WC and VC to react to form a V4WC5 phase. The heat treatment temperature is 1185°C, and the holding time is 90 minutes. Then, the particles with excessively large and small particle sizes in the heat-treated powder are removed by airflow classification to obtain the WC-V4WC5-Co spherical composite powder with a particle size distribution of 10-30 μm required for printing, and its morphology is as follows. Figure 1 (c) Phase detection results are as follows Figure 2 (a) As shown. The powder after classification in the above steps is used as raw material, and a powder-spreading selective laser melting device is used for printing and forming, so that WC and V4WC5 form VWC2 phase in situ under the action of laser. The laser printing process parameters used are: laser power 130W, scanning rate 800mm / s, scanning spacing 0.04mm, and powder layer thickness 0.03mm. The phase detection results of laser printed cemented carbide are shown in Figure 2 (b) The printed WC-VC-Co part was subjected to atmosphere heat treatment at 1410°C. When the temperature reached the target temperature, 5MPa of argon was introduced and maintained at this pressure for 50 minutes. This decomposed the VWC2 phase into WC and V4WC5, and promoted the oriented growth of the formed WC. After cooling to room temperature, a cemented carbide part with an acicular structure and freely designable shape was obtained. Figure 2 (c) and Figure 3 (c) The phase detection results of the cemented carbide after laser printing and heat treatment, and the microstructure of the obtained cemented carbide with acicular structure, respectively. The volume content of the acicular structure is about 60%, the average length of the acicular WC phase is 2.14 μm, and the diameter is 0.3 μm.

Claims

1. A method for preparing a cemented carbide having a needle-like structure, characterized in that: The following steps are involved: (1) Using WC, Co and VC powders with an average particle size of less than 1 μm as raw materials, the WC-VC-Co composite powder is prepared so that the mass fraction of VC is 5%-22% and the mass fraction of Co is 10%-20%. The powders are fully wet-milled with anhydrous ethanol as a medium to ensure that the three raw material powders are evenly mixed and then dried. The dried powders are mixed with deionized water and polyethylene glycol to form a slurry, and agglomerated and granulated by a high-speed centrifugal atomization drying process to obtain a WC-VC-Co spherical composite powder. (2) The spherical composite powder obtained in the above steps is heat-treated to remove polyethylene glycol while allowing the agglomerated particles to obtain a certain cohesive strength, high density and fluidity, and at the same time allowing part of the WC and VC to react to form a V4WC5 phase; the heat treatment temperature is 1180-1250°C, and the holding time is 90-120 minutes; then, the particles with excessively large and undersized particle sizes in the heat-treated powder are removed by airflow classification to obtain a WC-V4WC5-Co spherical composite powder with a particle size distribution of 10-30 μm required for printing; (3) The powder after classification in the above steps was used as raw material and printed by powder spreading selective laser melting equipment, so that WC and V4WC5 formed VWC2 phase in situ under the action of laser. The laser printing process parameters used were: laser power 100-140W, scanning rate 800-1000mm / s, scanning spacing 0.04mm, and powder spreading layer thickness 0.03mm. (4) The WC-VC-Co parts obtained by printing are subjected to atmosphere protection heat treatment at a temperature of 1410-1480°C. When the temperature rises to the target temperature, 5-6 MPa of argon gas is introduced and kept at this pressure for 50-80 minutes to decompose the VWC2 phase into WC and V4WC5, and promote the oriented growth of the formed WC. After cooling to room temperature, a cemented carbide part with a needle-like structure and freely designable shape is obtained.

2. The method according to claim 1, characterized in that In step (3), the phases of the parts formed by the powder under the action of laser include: VWC2 and a relatively small amount of WC, W2C, and Co3W3C.

3. The method according to claim 1, characterized in that The phases of the parts after heat treatment in step (4) include: WC, V4WC5, VWC2 and Co.

4. The method according to claim 1, characterized in that The volume content of the needle-like structure in the final part is 40%-70%, the average length of the needle-like WC grains is 1.0-2.2μm, and the average diameter ranges from 0.1-0.3μm.

5. A cemented carbide having an acicular structure prepared according to the method of any one of claims 1 to 4.

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