低功率超高速激光熔覆FeCr合金薄涂层微观结构与表面形貌演化

Microstructure and surface morphology evolution of FeCr alloy thin coatings deposited by ultra-high speed laser cladding with low laser power

超高速激光熔覆涂层易出现表面粗糙的缺陷,熔覆后需精磨处理。明确涂层表面形貌演化机制,控制涂层表面粗糙度,是制备高质量涂层的关键。本文采用自行设计的超高速激光熔覆头,聚焦熔覆态涂层表面形貌演化,在1.5 kW激光功率,线速度147 mm/s下,制备了稀释率<2%,表面粗糙度Ra<10μm的FeCr合金薄涂层,分析了粉末粒度、基体形貌、搭接率以及重熔激光功率对涂层表面形貌的影响。结果表明,受快速冷却影响,超高速激光熔覆涂层表面颗粒状特征明显,粉末粒径影响涂层表面质量;由于熔覆涂层稀释率低、过渡区小,基体表面形貌具有一定遗传特性,基体越粗糙,涂层表面粗糙度越大;提高搭接率可降低熔覆涂层表面高度差、改善涂层表面质量,搭接率超过70%,表面质量趋于平稳;在激光重熔作用下,熔覆涂层表面颗粒状特征逐渐消失,表面粗糙度值降低,重熔功率达0.7 kW后,变化不再显著。

The coating deposited by the ultra-high speed laser cladding process could produce a rough surface and, therefore, subsequent fine grinding becomes a necessary procedure. To prepare high quality coatings, it is critical to clarify the evolution mechanism of surface morphology to control the coating surface roughness. Focusing on surface morphology, FeCr alloy thin coating with dilution less than 2% and surface roughness Ra<μ10 m is deposited by ultra-high speed laser cladding process with home-designed powder feeding nozzle at 1.5 kW laser power and 147 mm/s linear speed. The effects of powder size, substrate morphology, overlapping ratio and remelting laser power on the surface morphology of the coatings are analyzed. The result shows that the coating has obvious granular characteristics due to the rapid cooling rate of the melting pool and, powder particle size markedly affects surface quality of the coating. Due to the low dilution, small transition zone, and memory effects of the substrate surface morphology, the rougher the substrate corresponds to the greater roughness of the coating surface. Increasing overlapping ratio can reduce height difference of the coating and improve its surface quality, while the surface roughness tends to be stable if the overlapping ratio exceeds 70%. Using laser remelting, the granular characteristics of the coating disappear gradually and the surface roughness reduces. No remarkable difference is observed when the remelting laser power is over 0.7 kW.