Effects of HfC Particles on Crack Initiation and Propagation Behavior of WC/Co Composites

HfC颗粒对WC/Co复合材料裂纹萌生和扩展行为的影响

School of Mechanical Engineering, Jinan University, Jinan 250022, China

Received: 15 July 2018

Abstract

Tungsten carbide composites were prepared by cold-pressing and hot-pressing sintering; fracture toughness and bending strength of the specimens were tested. The microstructures of HfC/WC/Co composites were observed with the SEM. The mathematical models were established to investigate the relationship between stress intensity factors of crack straight-through, crack deflection, and crack bifurcation with crack length, based on the crack propagation energy release rate. The simulation software ABAQUS was used to verify the four crack propagation methods of crack straight-through, crack deflection, crack bifurcation and crack pinning. The simulation results show that adding appropriate amount of HfC can effectively improve the fracture toughness and bending strength of the composites. The homogeneous distribution of HfC and Co in the matrix has a significant effect on the improvement of the strength and toughness of the composites, and the improvement mechanism is to disperse or transfer the stress at the crack tip to HfC by crack deflection, crack bifurcation, crack pinning, transcrystalline fracture, etc. As a result, the stress concentration at the crack tip in the matrix is reduced, and the toughness of the composites is improved.

摘要

以提高材料的韧性为目的，通过冷压、热压工艺制备出碳化钨基复合材料，对其断裂韧性、弯曲强度进行测试；利用SEM对HfC/WC/Co复合材料的微观形貌进行观察；基于裂纹扩展能量释放公式，构建了裂纹直行、裂纹偏转和裂纹分叉的应力强度因子与裂纹长度的数学模型；借助仿真软件ABAQUS对裂纹直行、裂纹偏转、裂纹分叉、裂纹钉扎4种裂纹扩展方式进行了仿真验证；结果表明：添加适量的HfC可以有效改善复合材料的断裂韧性和弯曲强度；HfC和Co在基体中均匀分布，对复合材料强度和韧性的提高具有明显作用，改善机制为裂纹偏转、裂纹分叉、裂纹钉扎、穿晶断裂等协同作用将裂纹扩展尖端的应力分散或转移到HfC上，从而降低基体中裂纹尖端的应力集中，提高复合材料的韧性。