冷却介质对YG8硬质合金热疲劳性能的影响

Effect of Different Quenching Agent on the Thermal Fatigue Crack Propagation Behavior of WC-8Co Cemented Carbide

采用V型缺口试样,研究了YG8硬质合金在10~650℃热循环下冷却介质分别为pH=5.2的盐酸溶液、pH=7.4水、pH=8.8的氢氧化钠溶液的热疲劳行为.通过扫描电镜和变焦体显微镜观察疲劳断口形貌和疲劳裂纹形貌,研究热疲劳裂纹形成与扩展机制.结果表明：冷却介质对热疲劳性能影响显著,同样循环次数下在pH=5.2的盐酸中冷却先出现裂纹,且扩展速率较快;pH=8.8的氢氧化钠溶液次之,水（pH=7.4）是三者中抗热疲劳性能最好;在中性介质中,裂纹的扩展方式主要为WC相缺少Co粘结相的粘接作用而不断被剥落产生微孔洞,随着微孔洞尺寸不断变大,相邻的孔洞将相连形成微裂纹,沿WC/Co相界面扩展,在腐蚀介质中,疲劳裂纹形成过程变得十分复杂,扩展方式主要为裂纹穿过腐蚀疲劳坑和通过大尺寸的团聚物扩展.

The thermal fatigue crack propagation behavior of WC-8Co cemented carbide in different quenching agents was investigated.The pH of the aqueous solutions varied between 5.2,7.4 and 8.8.This study was in the temperature range of 650 ℃ to 10 ℃ by using V-notch plate specimens.The results have shown that a corrosive environment has a strong influence on the thermal fatigue crack propagation behavior of the material test.Acidic and alkali environment can reduce the thermal fatigue crack initial life and increase the crack propagation rate.In addition,in the neutral environment,the thermal fatigue crack propagates along the WC / Co phase boundary,and in acidic and alkali environment,the crack propagates through the pits and the large size of the reunion things.