WC-25%Co硬质合金淬火热处理孔隙的微观特征及其形成机理

Microscopic Characteristics and Formation Mechanism of Pores in Quenched WC-25%Co Cemented Carbide

本文采用了金相显微镜、SEM、离子束抛光等分析手段,对冷镦模用WC-25%Co硬质合金烧结态、高温淬火热处理、低温淬火热处理的孔隙的微观特征及其分布进行了研究,并探讨了淬火热处理孔隙的分布特征与形成原因。结果表明,WC-25%Co硬质合金经淬火热处理后产生大量孔隙,孔隙呈圆弧形和不规则形,产生于WC晶粒桥接严重的部位、WC/Co的边界处以及Co层较薄处。淬火热处理合金的孔隙呈现由外表面向中心区域逐渐增多增大的分布特点,外边缘存在几十到几百微米厚的无孔隙区域,高温淬火热处理较低温淬火热处理而言,外边缘无孔隙区域更小而内部孔隙较多较大。淬火热处理孔隙的梯度分布是由于冷却过程中合金外表与内部刚性的梯度变化以及收缩内应力共同作用而引起的。

The microscopic characteristics and distribution of the pores in the WC-25%Co cemented carbides treated in different ways（sintered state, quenched at high temperature and quenched at low temperature） were studied in this paper by using metallographic microscope, SEM and ion beam polishing, and the reasons of the distribution characteristics of the pores in the alloys were also discussed. The results show that a large number of pores appear in WC-25%Co cemented carbides after quenching. Pores are circular and irregular, produced in the area of serious bridging of WC grains, the boundary of WC/Co and the thinner Co layer. The porosity of quenched alloy increases gradually from outer surface to the center region, and there exists no pore area in the outer edge of tens to hundreds micrometer. Compared with low temperature quenching heat treatment, the alloy quenched at high temperature has narrower no pore area in the outer edge and larger pores in centre region. The gradient distribution of pores in quenched alloy is due to the gradient of the rigidity of the alloy from outer surface to internal during the cooling procedure and internal stress caused by contraction during the cooling procedure.