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

研究了低碳钢、不锈钢、氧化铝和氮化钛等材料激光和等离子喷涂涂层的残余应力状态。采用X射线应力测量方法研究了沉积态、退火态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，但其大小与沉积材料、基体材料和扩径方式有关。涂层最外表面的残余应力在有无层状结构时差别不大，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。然而，在通过等离子喷涂沉积的陶瓷（氧化铝）层的情况下观察到很少的变化。在氧化铝涂层的情况下，应研究X射线应力的物理意义，在二维轴对称问题的条件下，通过有限元计算分析了单层和叠层的内应力。结果发现，层压对最外层中的应力松弛没有很大贡献，但是与单层结构相比，通过层压界面的应力值的差异变得非常温和。

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.