基于粒子飞行特性及铺展行为的WC-10Co4Cr涂层孔隙形成机理研究

Pore Formation Mechanism of WC-10Co4Cr Coatings Based on Collected In-flight Particles and Individual Splat

采用超音速等离子喷涂设备制备WC-10Co4Cr涂层,通过调整喷涂功率得到了具有不同孔隙结构特征的涂层,以液氮为冷却介质收集不同熔化状态下的飞行粒子,并通过镜面钢收集熔滴撞击铺展之后所形成的扁平粒子,采用扫描电子显微镜观察涂层、收集的飞行粒子及扁平粒子形貌,采用透射电镜观察涂层显微组织结构。结果表明:随着喷涂功率的增大,涂层的大孔隙含量逐渐降低,而当喷涂功率上升到60kW时,涂层内部出现较多的热裂纹,涂层的显微硬度则随着功率的增加而先增大后减小,WC扁平粒子主要有四种类型,包括熔化不佳、破碎型、气泡型及花瓣型,孔隙的形成主要是由于"遮蔽效应"、微区气体作用、熔滴不充分润湿及气孔迁移等。

The supersonic plasma spray equipment was utilized to fabricate WC-10Co4Cr coatings. Four spraying parameters with different spraying powers were employed to obtain coatings with different porous structure. The liquid nitrogen was used to freezing in-flight particles with different molten status. The individual splat was deposited on mirror polished stainless steel at preheating temperature of about 200℃. The scanning electron microscopy（SEM） was used to observe the morphologies of coating, raw spraying powder, freezing particle, and individual splat. The field emission microscopy（FEM） was utilized to observe the microstructure of coating, while the energy dispersive spectrometer（EDS） was used to analyze the composition. The results show that with increment of spraying power, the large size pores kept decreasing. With 60 k W spraying power, a few thermal cracks appeared within the coating due to the heat accumulation. Micro hardness of the coatings increased firstly and then decreased with the increment of spraying power. Solidified morphologies of individual splat could be distinguishe as four types, namely, partially melted type, fragmented type, bubble-like type, as well as flower-like type. Pores within the WC-10Co4Cr were mainly formed by shadowing effect of solidified coatings and substrate, gas effect of the micro valley, insufficient wetting of droplet, as well as the pore migration within the liquid phase of the splat.