含添加剂Cr_(3)C_(2)/VC超粗晶WC-Co硬质合金的疲劳行为及失效机理

Fatigue Performance and Failure Mechanism of the Ultra-coarse Cemented Carbides with Cr_(3)C_(2)/VC Additives

利用三点弯曲疲劳实验,研究了Cr_(3)C_(2)和VC添加对超粗晶硬质合金疲劳性能的影响规律和机理。超粗晶硬质合金的疲劳寿命随着循环载荷的增加呈指数型下降,随应力比的增加明显增加;少量Cr_(3)C_(2)的添加可有效提高超粗晶硬质合金的抗弯强度和抗疲劳性能,其原因是少量Cr_(3)C_(2)的添加可实现Cr原子对Co相的固溶强化、抑制fccCo向hcp-Co的相转变、使WC晶粒边角圆化缓解应力集中;而VC的添加则降低了合金的抗弯强度和疲劳断裂时的最大循环次数,是VC的添加易于在界面处形成脆性的层状组织(W,V)C_(x)降低界面结合强度、使WC晶粒边界呈锯齿状易于产生应力集中所致。

The fatigue performance and mechanism of the ultra-coarse cemented carbides with Cr_(3)C_(2)and VC addition were studied using three-point bending fatigue experiments.The fatigue life of the ultra-coarse cemented carbides decreased exponentially with the increase of the cyclic loading and the decrease of the stress ratio.Adding a small amount of Cr_(3)C_(2)can effectively improve the fatigue resistance of the ultra-coarse cemented carbide,which increases with the transverse rupture fracture.For the sample with Cr_(3)C_(2),the fatigue resistance was improved by solid solution strengthening Co phase,inhibition of the Co phase transition from fcc to hcp structure,and decrease of stress concentration in WC grains with round corner.While the cemented carbide with VC addition has a lower cycle number as fractured by compared with the WC-Co cemented carbide.The brittle(W,V)C_(x)film layer at interface and WC grains with serrated boundary,which decreased the interface bonding strength and resulted the stress concentration were the key factors to deteriorate the fatigue resistance of the sample with VC addition.