硬质合金表面覆钴机理及其影响因素

Cobalt Capping Mechanisms on Cemented Carbide and its Influence Factors

本文综述了硬质合金表面覆钴机理、影响因素及其对合金性能的影响,重点阐述了硬质合金液相迁移力、毛细管力、表面张力和Co相挥发对表面覆钴层的形成的影响,并结合各种合金成分和烧结制度,阐明了影响表面覆钴的主要工艺因素和控制途径。结果表明,表面覆钴层形成于降温过程中某个非常短的时间段,合金成分钴含量高、晶粒度细,并且烧结过程中慢速降温和在脱碳气氛中降温,可以促进表面覆钴层的形成。表面覆钴层可以显著提高WC-Co硬质合金表面韧性和焊接性能。

In this paper, the research achievements of cobalt capping were summarized, including its mechanisms, the influence factors and its effect on the properties of the alloy. The effects of liquid migration pressure, capillarity pressure,liquid surface tension and Co evaporation on the formation of cobalt capping were described in detail. Combined with various alloy compositions and sintering schedules, the main process factors and controlling methods affecting surface cobalt capping were clarified. The results show that the cobalt capping forms during a specific narrow temperature interval during the cooling step. The cobalt layer formation can be promoted under the conditions that alloy composition with high cobalt content and fine grain size, slow cooling and cooling in decarburizing atmosphere. The fracture toughness and wettability by braze alloys of the surface of WC-Co articles are dramatically improved due to the presence of the cobalt capping.