超高压烧结对WC-8Co硬质合金微观组织及力学性能的影响

Effect of Ultra-High Pressure Sintering on Microstructure and Mechanical Properties of WC-8Co Cemented Carbide

使用六面顶压机在相同温度(1 400℃)和保温时间(6 min)条件下,研究了不同烧结压力(4.0~6.0 GPa)对WC-8Co硬质合金试样微观组织及力学性能的影响。结果表明:在1 400℃、4.0~6.0 GPa超高压条件下,WC-8Co硬质合金试样可在6 min内完成烧结;随着烧结压力的增加,WC-8Co硬质合金试样中WC晶粒的平均尺寸逐渐增大,甚至出现局部WC晶粒异常长大的情况,进而导致硬质合金试样的矫顽磁力、维氏硬度和断裂韧性随之逐渐减小。在考察压力范围内,烧结压力为4.0 GPa时,WC-8Co硬质合金试样的力学性能最好,在载荷为30 kgf(294 N)、保持时间为10 s的检测条件下,试样的维氏硬度为15.2 GPa,断裂韧性为14.9 MPa·m^(1/2),与相同检测条件下的商用YG8硬质合金的力学性能(维氏硬度15.6 GPa,断裂韧性15.9 MPa·m^(1/2))接近。随着烧结压力的增加,硬质合金试样的断裂形式从沿晶断裂占主导逐渐过渡到沿晶断裂与穿晶断裂共存,且穿晶断裂所占的比例逐渐增大。

The effects of different sintering pressures(4.0~6.0 GPa) on the microstructure and mechanical properties of WC-8Co cemented carbide samples were studied by using a cubic press at identical temperature(1 400 ℃) and holding time(6 min).The results show that the sintering of the WC-8Co cemented carbide samples can be completed within 6 min at 1 400 ℃ and ultra-high pressure of 4.0~6.0 GPa.As the sintering pressure increases,the average size of WC grains in WC-8Co cemented carbide samples gradually increases with local WC grains even growing abnormally,resulting in a gradual decrease in the coercivity,Vickers hardness and fracture toughness of the cemented carbide samples.Within the investigated pressure range,the mechanical properties of the WC-8Co cemented carbide samples reach the best at a sintering pressure of 4.0 GPa.And under the testing conditions of a load of 30 kgf(294 N) and a holding time of 10 s,the Vickers hardness and fracture toughness of the sample are 15.2 GPa and 14.9 MPa·m^(1/2),being very close to the mechanical properties of commercial YG8 cemented carbide(Vickers hardness of 15.6 GPa and fracture toughness of 15.9 MPa·m^(1/2)) under the same testing conditions.As the sintering pressure increases,the fracture forms of the cemented carbide samples gradually transition from the dominant intergranular fracture to a combination of intergranular fracture and transgranular fracture,with an increasing proportion of transgranular fracture.