Study on Mechanical and Thermal Properties and Stresses of Functionally Gradient Materials Produced by Laser Splaying

采用激光和等离子喷涂的方法制备了低碳钢、不锈钢、氧化铝和氮化钛涂层，研究了涂层的残余应力状态。采用x射线应力测量法研究了沉积层、退火表面和磨削表面的残余应力。各种沉积层的残余应力均为拉应力，但应力值取决于沉积材料、基底材料和展布方式。沉积层中有无层状结构的最外表面残余应力差异不大。高温退火改变了金属涂层的残余应力状态，其最终状态可以用涂层与基体材料的热膨胀系数的差异来解释。而等离子喷涂沉积的陶瓷（氧化铝）层变化不大。在氧化铝涂层的情况下，应该研究x射线应力的物理意义。在二维轴对称问题条件下，采用有限元方法分析了单层和层合层的内应力。结果表明，层合对最外层的应力松弛作用不大，但与单层结构相比，层合界面的应力值差异变得非常小。

The present study investigated the residual stress state of the coating layers,of which the material was low carbon steel,stainless steel,alumina and titqnium nitride,deposited by laser-and plasma-spraying. X-ray stress measuring method was used to investigate residual stress on as-deposited layers, annealed surfaces and ground surfaces. Residual stress was tensile in all cases of various kind of deposited layers,but the stress value depended on depositing materials,substrate materials and splaying methods. There was little difference of the residual stress on the outermost surface between with and without a laminated structure in the deposited layer.Annealing at high temperature altered the residual stress state in metallic coating layer and the final state can be explained by the difference of the thermal expansion coefficient of the layer and the substrate materials. However,little change was observed in the case of ceramic(alumina)layer deposited by plasma spraying. The physical meaning of the X-ray stress should be investigated in the case of an alumina coating layer.Internal stress in a mono-layer and a laminated layer was analized by FEM calculation under the condition of a two-dimensional axi-symmetrical problem. It was found that the lamination does not largely contribute to a relaxation of the stress in the outermost layer but the difference of stress value through an interface of lamination becomes very mild in compering with the mono-layer structure.