采用激光一步涂覆方法制备了梯度结构的TiC／（Ni合金）复合涂层.熔覆层的组织由TiC颗粒、γ－Ni枝状初晶及枝晶间的共晶组成。从熔覆层底部到顶部TiC颗粒呈现连续的梯度变化，即颗粒尺寸从0．8μm增长到4．5μm、体积含量从4％增加到33％；TiC颗粒的形貌也相应地从近似“球形”的细小粒子过渡到粗大的花瓣状粒子簇。TiC颗粒的快速长大主要来自颗粒的碰撞与粘结。凝固前沿对浮升速度相对较慢的TiC小颗粒优先捕获是导致熔覆层梯度结构原位生成的决定性因素。
A functionally gradient TiC/Ni alloy composite coating was produced by one step laser cladding with pre-placed mixture powder on 1045 steel substrate. The clad layer consists of TiC particles, γ-Ni primary dendrites and interdendritic eutectics. From the bottom to the top of the clad layer, TiC particles exhibit a continuous increase both in size (from 0.8μm to 4.5μm) and in volume fraction (from 4% to 33%), and their morphology changes correspondingly from small globe to coarse flower-like cluster. The rapid coarsening of TiC clusters during the solidification of laser pool results from the collision and sintering of particles. The preferntial engulfing to a small cluster moving at slower speed by liquid/solid front leads to in-situ formation of the gradient structure of the coating.
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