激光熔覆ZrO_2／Ni合金复合涂层的凝固组织与分层机制

用激光束在４Ｃｒ１３钢基体上熔覆ＺｒＯ２与Ｎｉ合金的混合粉末，形成了分层结构的复合涂层，即表面为致密的ＺｒＯ２陶瓷层．介于陶瓷层与基体之间的是Ｎｉ基合金过渡层。组织分析表明，ＺｒＯ２层的上部为等轴晶，中下部为柱状晶，主要由ｔ＇－ＺｒＯ２相及少量沿ｔ＇晶界分布的ｍ－ＺｒＯ２相组成；Ｎｉ合金结合带呈现出树枝晶及其晶间共晶的单一凝固组织。该复合涂层的分层机制可解释为互不混溶的ＺｒＯ２与Ｎｉ合金熔珠在界面张力和浮力作用下发生离析重排，再各自重新凝固。

Solidification Microstructure and Stratification Mechanism of a Laser Clad ZrO_2/Ni-alloy Composite Coating

Using a laser to clad a mixture POwder of 60 V. -% ZrO2 plus 40 V.-% Nialloy preplaced on steel 4Cr13 substrate, a comPOSite coating that consists of a pure Zro2layer at the upper region and a Ni-alloy bonding zone adjacent to the substrate is formed. The microstructural analyses reveal that the ZrO2layer exhibits equiaxed grains at the upper part and a columnar structure at the lower part and is comPOsed of t-ZrO2 Phase and 2. 9% m-ZrO2 phase distributed along the t boundary. The bonding zone presents an even solidification microstructure comPOsed of Ni-based dendrites and interdendritic eutectics. The stratification mechaoism of the comPOSite coating is interpreted as that the insoluble meltS of ZrO2 and Ni-alloy POwders undergo a redistribution before solidification due to density difference and inter facial,tension between these two liquid Phases, and then rasolidify separately.