热应力作用下碳化钨基钢结硬质合金梯形裂纹的形成机理

Formation mechanism of trapezoid crack in WC steel bonded carbide under action of thermal stress

在自约束型热疲劳试验机上对碳化钨含量不同的钢结硬质合金进行了热疲劳试验 ,用金相显微镜和扫描电镜对热疲劳裂纹扩展行为进行了研究。结果表明 :在热应力作用下 ,不仅在合金的表面 ,在合金的内部都形成了“梯形”裂纹。这种形态的裂纹是由试样缺口处的热疲劳裂纹扩展而引起的 ,合金中的钢基体相阻碍裂纹扩展 ,而WC硬质相诱导裂纹扩展 ,这两种因素的综合作用促使热疲劳裂纹成“梯形”扩展。分析认为 :使WC粒子在钢基体中均匀分布 ,提高钢基体的热疲劳抗力 ,从而来阻止梯形裂纹的形成 ,是提高碳化钨钢结硬质合金抗热疲劳性能的有效途径。

Thermal fatigue test of two kinds of WC steel bonded carbides with different WC contents was examined on self-strained thermal fatigue testing machines, and thermal fatigue crack propagation process was investigated by optical microscopy and SEM. The results show that a kind of trapezoid crack forms not only on the surface but also in the alloy, and the forming process of this kind of crack is the propagation process of the thermal fatigue crack that forms at the sample notch. Steel matrix prevents the crack from propagating, and WC hard phase induces the crack to propagate. The comprehensive effects of these two factors make thermal fatigue crack form trapezoid crack shape .It is pointed out by analyzing that making WC particles distribute uniformly in the steel matrix and increasing thermal fatigue resistance of the matrix to prevent trapezoid crack from forming are effective methods to increase the thermal fatigue resistance of WC steel bonded carbides.