WC-Co硬质合金疲劳断裂机制研究

On the fatigue and fracture features of WC-Co cemented carbides

疲劳和断裂是硬质合金失效的主要原因之一。主要对WC-Co硬质合金的高周疲劳性能和裂纹扩展行为进行了较为系统的研究。结果表明,WC-Co硬质合金材料表现出明显的疲劳效应,即应力水平的降低伴随着疲劳寿命的上升。在高应力区域,合金的疲劳寿命与强度有关;合金的强度越高,其疲劳寿命越长。随着应力幅值的降低,这种强度与疲劳寿命的联系越来越不明显,特别是进入高周疲劳区域后,高粘结剂含量的合金反而表现出更高的疲劳抗性。疲劳裂纹主要沿晶界和在粘结相中扩展;材料在承受疲劳载荷后,粘结相与WC硬质颗粒之间发生了剥离,这种脱粘造成WC颗粒之间相互错动形成孔隙和微裂纹,这些孔隙和微裂纹相互连接加速了裂纹的扩展并最终导致材料的断裂。粘结相在疲劳过程中产生了大量堆垛层错并发生相变,同时有析出物产生。

Fatigue and fracture are the major failure mechanisms for cemented carbides. The aim of the present work is to investigate the fatigue life and the microstructure properties of WC-Co hard metals under fatigue conditions. The result shows that the fatigue effect is strongly dependent on the stress amplitude. At high stress level, material＇ s fatigue life is more corresponding to its hardness, however, at low stress level, the fatigue life increases with increasing binder content. Fatigue cracks grow along grain boundaries and in binding phases. After cyclic loading, WC particles and binders separate, which causes pore and micro cracks forming. The pore and crackle connect to accelerate the crack growth and eventually lead to material fracture. In Co binders, stacking fault and phase transformation occur during fatigue process, precipitated phases are also found.