WC/Co粉体粒径匹配与放电等离子烧结致密化

对放电等离子烧结(SPS)不同粒径匹配的WC/Co混合粉末的收缩过程进行了系统分析.结果表明,SPS烧结不同WC粒径混合粉末时,烧结体开始收缩温度、收缩速率峰值温度和致密化完成温度基本相同;对不同Co粒径混合粉末,三种温度随Co粉初始粒径的减小而降低,即SPS烧结过程与WC粒径无关而与Co粒径密切相关.SPS致密化过程中收缩速率随温度的变化、收缩速率与相对密度的关系均与常规烧结不同,其开始收缩温度和收缩速率峰值温度均较常规烧结低,同时收缩速率峰值处所对应的相对密度也较常规烧结低.这说明在常规烧结中粉末在大量液相出现(即收缩速率出现峰值时)之前已完成很大程度的收缩致密化,而SPS烧结中大量液相出现之前粉末的收缩致密化程度较低.

MATCHING OF PARTICLE SIZES OF WC/Co POWDERS AND SPARK PLASMA SINTERING DENSIFICATION

The particle size of raw powders to prepare the cemented carbides plays a significant role not only in the properties of the resultant bulk material, but also in the sintering process. WC/Co composite powders with various size matches were prepared by spark plasma sintering (SPS), and the variations of shrinkage rate, which is an important factor describing SPS process, with the sintering temperature and the relationship between the shrinkage rate and the relative density of the sintered sample were analyzed. The results show that the temperature of shrinkage starting, the temperature corresponding to the peak of the shrinkage rate, and the temperature of full densification are almost the same for different sized WC particles, however, all of the above temperatures reduce with the decrease of the Co particle size. It indicates that the shrinkage process of SPS has a rather very weak relationship with the WC particle size, whereas has a close relationship with the Co particle size. As compared with the conventional sintering methods, the above temperatures and the relative density corresponding to the maximum of the shrinkage rate are all lowered. It implies that in the conventional process, at the stage with the maximum of the shrinkage rate, most of the shrinkage has been accomplished. However, in the SPS process, at the same stage the shrinkage degree is lower. Finally, he secial SPS mechanisms for comosite powders with various size matces were analyzed.