Preparation method of cemented carbide modified by in-situ precipitation of nano wc on surface of nano y2o3

Abstract

The application discloses a preparation method of modified hard alloy based on in-situ precipitation of nano WC on the surface of nano Y2O3. 3 The abnormal growth of WC is effectively inhibited by increasing the migration resistance of the grain boundary through the Zener pinning effect. In addition, during the high-temperature sintering process, W and C atoms diffused into the Co phase are heterogeneously nucleated on the (211) and (123) surfaces of Y2O3, a large number of 10-30 nm spherical WC particles which are coherent with the matrix are in-situ precipitated, and the WC particles are dispersedly distributed in the Y2O3 phase. A significant synergistic effect is formed by using the deep crystallographic interface strengthening mechanism and the traditional physical pinning, the interface bonding strength is significantly enhanced, and the defects such as the easy interface deaggregation caused by the pure Y2O3 particle pinning of the existing hard alloy are solved.

Description

Technical Field

[0001] This invention relates to the field of Y2O3 modified cemented carbide preparation technology, and more specifically, to a method for preparing cemented carbide based on in-situ precipitation of nano-WC on the surface of nano-Y2O3. Background Technology

[0002] WC-Co cemented carbide, with its high hardness, excellent wear resistance, and good fracture toughness, has long been the preferred material in metal cutting, geological drilling, and precision mold manufacturing. However, during high-temperature sintering, WC exhibits high solubility in liquid Co, following a "dissolution-precipitation" mechanism. This makes it highly susceptible to the Ostwald ripening effect in localized areas, leading to abnormal growth of individual WC grains that engulf surrounding material, severely weakening the material's service reliability.

[0003] Existing technologies often suppress abnormal WC grain growth by adding grain inhibitors. Common grain inhibitors include carbides such as VC and Cr3C2, as well as rare earth oxides. For example, CN101967593A, "Ultra-fine Grained Hard Alloy Material Containing Rare Earth and Its Preparation Method," discloses that VC and Cr2O3 have good grain growth inhibition effects, primarily suppressing WC grain growth. Micro-alloying of (TaC+TiC+NbC) and Y2O3 further inhibits WC grain growth, improving the hardness, heat resistance, and wear resistance of the hard alloy. Y2O3 further refines the grains and increases hardness, improving the overall performance of the metal. This patent uses multiple grain inhibitors to suppress grain growth and refine the grains; however, carbides such as VC and Cr3C2 can cause solid solution embrittlement of the binder phase and lose their inhibitory effect under high-temperature service conditions. Rare earth oxides (especially Y2O3), on the other hand, possess high melting points, excellent thermal stability, and unique crystallographic characteristics. CN109652727A discloses that adding Y2O3 to a recycled WC-8Co cemented carbide can significantly improve the hardness and bending strength of the cemented carbide. Y2O3 can inhibit grain growth and abnormal growth during sintering, thereby enhancing the mechanical properties of the cemented carbide. The addition of Y2O3 increased the bending strength of the WC-8Co cemented carbide from 1780 MPa to 2120 MPa. This demonstrates that Y2O3 can maintain the stability of cemented carbide properties at high temperatures.

[0004] While the addition of Y₂O₃ can enhance the strength of cemented carbides, the strength obtained by simply mixing and sintering Y₂O₃ with WC and Co is limited and cannot meet the practical requirements of cemented carbides. In particular, when nanoscale Y₂O₃ is dispersed in a WC-Co matrix, the Y₂O₃ nanoparticles easily agglomerate, becoming defects in the material. CN111893339A describes a wet chemical method for preparing high-performance WC-8Co-Y₂O₃ cemented carbides. In this method, ammonium metatungstate (AMT) is used as the tungsten source, and yttrium nitrate hexahydrate (Y(NO₃)₃·6H₂O) is used as the yttrium source. W-Y₂O₃ powder is prepared according to the wet chemical principle, and then it is carbonized at high temperature and sintered with cobalt to prepare the WC-8Co-Y₂O₃ alloy. This patent adds Y₂O₃ by doping W, which can inhibit the growth and aggregation of WC particles during the carbonization stage and further refine the WC grains during sintering. Although doping with Y₂O₃ and W can prevent agglomeration and improve the hardness and bending strength of cemented carbide through dispersion strengthening, achieving values ​​of 89.2–90.3 HRA and 2320–2660 MPa respectively, this method requires high-temperature carbonization at 1850–1950℃ for 1–2 hours to generate WC-Y₂O₃ powder. The Y₂O₃ doping process is complex, and simply pinning Y₂O₃ particles can easily lead to interfacial depolymerization, thus limiting the performance improvement of cemented carbide. Summary of the Invention

[0005] The main technical problem to be solved by this invention is to address the shortcomings of existing cemented carbide, such as the tendency for interfacial depolymerization to be easily caused by simply pinning Y2O3 particles. This invention provides a method for preparing cemented carbide modified by in-situ precipitation of nano-WC on the surface of nano-Y2O3.

[0006] The objective of this invention is achieved through the following technical solution: A method for preparing a cemented carbide modified with nano-WC based on in-situ precipitation of nano-Y₂O₃ on the surface, the raw materials including WC 90.5~91.8 wt.%, Co 8~9 wt.%, Y₂O₃ 0.2~0.5 wt.%. The preparation steps include: S1. Mix WC, Co and Y2O3, ball mill and dry to obtain dry powder; S2. Mix the dry powder and molding agent evenly, sieve to obtain mixed powder, press into shape and then put into a vacuum hot press furnace for sintering; S3. During the sintering process, the temperature is controlled as follows: First stage of heating: first heat up to 240℃ at a rate of 5~8℃ / min and hold for 45~90min, then heat up to 420℃ at a rate of 5~8℃ / min and hold for 45~75min; The second stage of heating: the temperature is increased to 1030℃ at a rate of 8~10℃ / min, held for 100~150min, argon gas is introduced and the Ar pressure is 5~10 MPa, then the temperature is increased to 1460℃, controlled and held for 90~120min. The third stage of cooling: first, the temperature is lowered to 1340℃ at a rate of 3~5℃ / min, and then cooled to room temperature at a rate of 8~10℃ / min to obtain the modified cemented carbide.

[0007] Furthermore, the raw materials are WC 90.7 wt.%, Co 9 wt.%, and Y2O3 0.3 wt.%.

[0008] Furthermore, the particle size of WC is 1~3 μm, the particle size of Co is 0.5~1 μm, and the particle size of Y2O3 is 30~50 nm.

[0009] Furthermore, the ball mill has a ball-to-material ratio of 5:1, uses ethanol as the grinding medium, a ball milling speed of 40 rpm, and a ball milling time of 24 h.

[0010] Furthermore, the amount of the molding agent added is 7.3~7.6% of the mass of the dried powder.

[0011] Furthermore, the sieving is done with a 100-mesh sieve.

[0012] Furthermore, the pressing force during the pressing process is 200 MPa.

[0013] Furthermore, the first stage of heating involves first heating at 5°C / min to 240°C and holding for 60 min, and then heating at 5°C / min to 420°C and holding for 60 min.

[0014] Furthermore, the second stage of heating involves raising the temperature to 1030°C at a rate of 8°C / min and holding it for 120 min, introducing argon gas and controlling the Ar pressure at 8 MPa, and then raising the temperature to 1460°C at a rate of 8°C / min and holding it for 120 min.

[0015] Furthermore, the third stage of cooling involves first cooling to 1340°C at a rate of 5°C / min, and then cooling to room temperature at a rate of 10°C / min.

[0016] Compared with existing technologies, the beneficial effects are: This invention utilizes nano-Y₂O₃ to induce heterogeneous nucleation of W and C atoms dissolved in the binder liquid phase on the surface of Y₂O₃ grains. Nano-Y₂O₃ significantly reduces interfacial energy through crystal plane matching and orbital hybridization with WC, inducing heterogeneous nucleation and self-limiting growth of WC atoms. This results in the in-situ precipitation of numerous 10–30 nm coherent spherical WC particles, dispersed throughout the Y₂O₃ phase. These multi-scale composite units effectively anchor the WC grain boundaries in the matrix through the Zener pinning effect, inhibiting their migration and coarsening at high temperatures. This invention reduces the agglomeration of nano-Y₂O₃, and the Y₂O₃ grains distributed within the grains provide dispersion strengthening. The high-coherence interface optimizes stress distribution and induces deflection and branching during crack propagation, thereby achieving overall refinement and toughening of the cemented carbide matrix microstructure. Attached Figure Description

[0017] Figure 1 This is a process flow diagram of the present invention; Figure 2 This is a comparison diagram of the bending strength of Embodiment 1 and Comparative Example 1 of the present invention; Figure 3 This is a comparison diagram of the fracture toughness of Embodiment 1 and Comparative Example 1 of the present invention; Figure 4 This is a hardness comparison diagram between Example 1 and Comparative Example 1 of the present invention; Figure 5 SEM morphology and EDS surface scan images of the WC-Co-Y2O3 alloy; Figure 6 SEM images of the three-point bending fracture surface of the WC-Co-Y2O3 alloy; Figure 7 TEM image of WC-Co-Y2O3 alloy; Figure 8 TEM and HRTEM images of WC-9Co-0.3Y2O3; Figure 9 The microstructure characterization diagram of discrete nano-WC phases on Y2O3 grains; Figure 10 The images show the scanning electron microscope (SEM) images and XRD patterns of the Y2O3 grains in Comparative Example 2. Figure 11 This is a planar morphology characterization diagram of the cemented carbide in Comparative Example 2; Figure 12 The image shows the fracture morphology of the cemented carbide in Comparative Example 2. Detailed Implementation

[0018] The following examples further explain and clarify the invention, but the specific examples do not limit the invention in any way.

[0019] Example 1 This embodiment provides a method for preparing a nano-WC modified cemented carbide based on in-situ precipitation of nano-WC on the surface of nano-Y2O3. The raw material used is a WC-9Co-0.3Y2O3 alloy, and its parameters are as follows:

[0020] like Figure 1 As shown, the preparation steps include: S1. Place the mixed powder of WC, Co and Y2O3 into a tungsten carbide ball mill jar with a ball-to-powder ratio of 5:1. Use ethanol as the grinding medium. The slurry is ball-milled at 40 rpm for 24 h using an LC-PBM-12L planetary ball mill. Then, it is dried in a vacuum drying oven at 80℃ for 3 h to obtain dried powder. S2. Add 40ml of rubber to 500g of vacuum-dried powder, stir thoroughly, and dry in a vacuum drying oven at 80℃ for 15min. Sieve the mixed powder through a 100-mesh sieve, and press the resulting powder into a graphite mold with a pressing force of 200MPa. S3. The billet is sintered using a vacuum hot press furnace: The first stage of heating involves raising the temperature to 240℃ at a rate of 5℃ / min and holding it for 60 minutes, followed by raising the temperature to 420℃ at a rate of 5℃ / min and holding it for 60 minutes to remove molding agents and volatile impurities and prevent the blank from cracking.

[0021] The second stage of heating: the temperature is increased to 1030℃ at a rate of 8℃ / min and held for 120min. Argon gas is introduced and the Ar pressure is controlled at 8 MPa. Then the temperature is increased to 1460℃ at a rate of 8℃ / min and held for 120min. The third stage of cooling: first, the temperature is lowered to 1340℃ at a rate of 5℃ / min, and then cooled to room temperature at a rate of 10℃ / min to obtain the modified cemented carbide.

[0022] Comparative Example 1 The process of this comparative example is the same as that of Example 1, except that Y2O3 was not added in this comparative example.

[0023] Comparative Example 2 The process of this comparative example is the same as that of Example 1, except that the particle size of Y2O3 used in this comparative example is about 100nm.

[0024] Mechanical properties were tested on Example 1 and Comparative Example 1, such as... Figures 2-4As shown, the flexural strength of the WC-9Co-0.3Y2O3 alloy is significantly higher than that of the WC-9Co alloy, reaching a maximum flexural strength of 3938 MPa, which is 18.72% higher than the highest value of the undoped alloy (3317 MPa). Comparison of fracture toughness indicates that the addition of nano-Y2O3 particles greatly improves the toughness of the material, increasing its maximum fracture toughness to 15.26 MPa·m. 1 / 2 The highest value of the undoped alloy (13.46 MPa·m) 1 / 2 Compared to the previous year, the hardness increased by 12.95%. Hardness comparison shows that the addition of nano Y2O3 particles improved the Vickers hardness of the alloy, with a maximum hardness of 1389 Hv, which is 3.04% higher than the maximum hardness of the undoped alloy (1348 Hv).

[0025] like Figures 10-12 The planar morphology and fracture morphology images of the alloy show obvious agglomeration of Y₂O₃, with agglomerated particles approaching 2 μm in size, forming particles several times larger than their original size. No nano-WC formation was observed. Mechanical property testing showed that the comparative example achieved a flexural strength of 2769 MPa and a fracture toughness of 14.16 MPa·m. 1 / 2 The hardness reached 1272 Hv. Compared with the WC-9Co alloy, the alloy prepared by adding 100 nm Y2O3 in this comparative example has lower bending strength and hardness than the WC-9Co alloy without Y2O3 (3317 MPa and 1348 Hv). This shows that simply adding nano-yttrium oxide can easily lead to agglomeration, which can create material defects and reduce the performance of cemented carbide.

[0026] like Figure 5 As shown in (a), the sintered alloy has a dense microstructure, with the binder phase Co continuously filling the WC grain boundaries to form a network framework, indicating that the sintering process achieved good wettability of liquid Co on WC. Figure 5 (b) Grain size analysis revealed that WC grains exhibited a near-normal distribution, with uniform size concentrated between 2 and 4 μm. This indicates that nano-Y₂O₃ particles increased the grain boundary migration resistance of WC through grain boundary segregation and the Zener pinning effect, effectively suppressing abnormal grain growth during sintering. Figure 5 (c) The EDS surface scan results showed that the distribution of Y and O elements highly overlapped and were locally enriched in a point-like manner, confirming that the nano-Y2O3 particles were dispersed in the matrix as an independent oxide phase.

[0027] Depend on Figure 6 It can be seen that a large number of nanospheres with a size of 10–30 nm were observed on the surface and edges of the Y2O3 particles. Figure 6 a, b). Micro-area EDS spot scan comparison confirms that, compared to Y2O3 particles ( Figure 6c), the W content of the nanospheres increased from 5.2 wt% to 36.8 wt%, and the C content increased from 9.5% to 18%. Figure 6 d). This indicates that the nanospheres are rich in W and C.

[0028] TEM morphology of WC-Co-Y2O3 alloy as follows Figures 7-9 As shown in the figure, the nano-Y2O3 particles tend to be distributed at the WC / Co two-phase interface or at the triangular grain boundaries. Figure 7 a) Y₂O₃ increases grain boundary migration resistance through the Zener pinning effect, effectively suppressing the abnormal growth of WC grains. The interplanar spacings d of cubic Y₂O₃ (200), (222), and (123) are 0.5304 nm, 0.3062 nm, and 0.28351 nm, respectively. Figure 7 b). By Figure 7 (c) It can be seen that the interface between Y2O3 and the W and C rich nanospheres is a coherent interface, with continuous lattice fringes at the interface between the two phases, and no amorphous transition layer or microcrack defects were observed. It can be seen that in the early stage of liquid phase sintering, W and C atoms dissolved in the binder phase tend to undergo heterogeneous nucleation on the surface of Y2O3 grains, inducing 3-5 nm discrete WC clusters to preferentially germinate at active sites on the oxide surface. During high-temperature sintering, W and C atoms diffused into the Co phase undergo heterogeneous nucleation on the (211) and (123) planes of Y2O3, and a large number of 10-30 nm coherent spherical WC particles are precipitated in situ, which are dispersed in the Y2O3 phase. This multi-scale composite unit effectively anchors the WC grain boundaries of the matrix through the Zener pinning effect, inhibiting their migration and coarsening at high temperatures. In addition, the Y2O3 grains distributed within the crystals play a dispersion strengthening role, and the stress distribution is optimized through a highly coherent interface, thereby achieving overall refinement and toughening of the cemented carbide matrix structure.

[0029] This invention, based on the Zener pinning effect of Y₂O₃ to increase grain boundary migration resistance and effectively suppress abnormal growth of WC grains, further endows the material with extremely high interfacial bonding strength through a robust covalently bonded interface formed by heterogeneous nucleation and template effects. This fundamentally overcomes the defect of simple particle pinning easily leading to interfacial deagglomeration. Under stress and deformation, this strong bonding interface not only effectively passivates microcracks and hinders their propagation, but also ensures efficient and smooth stress transfer between grains.

[0030] Example 2 The process in this embodiment is the same as that in the previous embodiment, except that the sintering temperature is controlled as follows: First stage of heating: first heat up to 240℃ at 8℃ / min and hold for 90min, then heat up to 420℃ at 8℃ / min and hold for 75min; The second stage of heating: the temperature is increased to 1030℃ at a rate of 10℃ / min, held for 150min, argon gas is introduced and the Ar pressure is 5Mpa, then the temperature is increased to 1460℃, controlled, and held for 120min. The third stage of cooling: first, the temperature is lowered to 1340℃ at a rate of 3℃ / min, and then cooled to room temperature at a rate of 10℃ / min to obtain the modified cemented carbide.

[0031] Example 3 The process in this embodiment is the same as that in the previous embodiment, except that the sintering temperature is controlled as follows: First stage of heating: first heat up to 240℃ at 5℃ / min and hold for 45min, then heat up to 420℃ at 8℃ / min and hold for 45min. The second stage of heating: the temperature is increased to 1030℃ at a rate of 8℃ / min, held for 150min, argon gas is introduced and the Ar pressure is 10Mpa, then the temperature is increased to 1460℃, controlled, and held for 90min. The third stage of cooling: first, the temperature is lowered to 1340℃ at a rate of 5℃ / min, and then cooled to room temperature at a rate of 8℃ / min to obtain the modified cemented carbide.

[0032] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing cemented carbide modified by in-situ precipitation of nano-WC on the surface of nano-Y2O3, characterized in that, The raw materials include WC 90.5~91.8 wt.%, Co 8~9 wt.%, and Y2O3 0.2~0.5 wt.%, and the preparation steps include: S1. Mix WC, Co and Y2O3, ball mill and dry to obtain dry powder; S2. Mix the dry powder and molding agent evenly, sieve to obtain mixed powder, press into shape and then put into a vacuum hot press furnace for sintering; S3. During the sintering process, the temperature is controlled as follows: First stage of heating: first heat up to 240℃ at a rate of 5~8℃ / min and hold for 45~90min, then heat up to 420℃ at a rate of 5~8℃ / min and hold for 45~75min; The second stage of heating: the temperature is increased to 1030℃ at a rate of 8~10℃ / min, held for 100~150min, argon gas is introduced and the Ar pressure is 5~10 MPa, then the temperature is increased to 1460℃, controlled and held for 90~120min. The third stage of cooling: first, the temperature is lowered to 1340℃ at a rate of 3~5℃ / min, and then cooled to room temperature at a rate of 8~10℃ / min to obtain the modified cemented carbide.

2. The preparation method of modified cemented carbide based on in-situ precipitation of nano-WC on the surface of nano-Y₂O₃ according to claim 1, characterized in that, The raw materials are WC 90.7wt.%, Co 9wt.%, and Y2O3 0.3wt.%.

3. The preparation method of modified cemented carbide based on in-situ precipitation of nano-WC on the surface of nano-Y₂O₃ according to claim 1, characterized in that, The particle size of WC is 1~3 μm, the particle size of Co is 0.5~1 μm, and the particle size of Y2O3 is 30~50 nm.

4. The preparation method of modified cemented carbide based on in-situ precipitation of nano-WC on the surface of nano-Y₂O₃ according to claim 1, characterized in that, The ball mill uses a ball-to-material ratio of 5:1, ethanol as the grinding medium, a ball milling speed of 40 rpm, and a ball milling time of 24 hours.

5. The preparation method of modified cemented carbide based on in-situ precipitation of nano-WC on the surface of nano-Y₂O₃ according to claim 1, characterized in that, The amount of the molding agent added is 7.3~7.6% of the mass of the dry powder.

6. The preparation method of modified cemented carbide based on in-situ precipitation of nano-WC on the surface of nano-Y₂O₃ according to claim 1, characterized in that, The sieve used is a 100-mesh sieve.

7. The preparation method of modified cemented carbide based on in-situ precipitation of nano-WC on the surface of nano-Y₂O₃ according to claim 1, characterized in that, The sub-pressure required for the pressing process is 200 MPa.

8. The preparation method of modified cemented carbide based on in-situ precipitation of nano-WC on the surface of nano-Y₂O₃ according to claim 1, characterized in that, The first stage of heating involves first heating at 5℃ / min to 240℃ and holding for 60min, then heating at 5℃ / min to 420℃ and holding for 60min.

9. The preparation method of the cemented carbide based on in-situ precipitation of nano-WC on the surface of nano-Y₂O₃ according to claim 1, characterized in that, The second stage of heating involves raising the temperature to 1030℃ at a rate of 8℃ / min and holding it for 120min, then introducing argon gas and controlling the Ar pressure at 8 MPa, followed by raising the temperature to 1460℃ at a rate of 8℃ / min and holding it for 120min.

10. The preparation method of modified cemented carbide based on in-situ precipitation of nano-WC on the surface of nano-Y₂O₃ according to claim 1, characterized in that, The third stage of cooling involves first cooling to 1340°C at a rate of 5°C / min, and then cooling back to room temperature at a rate of 10°C / min.

Images