Characteristics of residual stress generated by MoSi2 plasma thermal spraying

Abstract

Summary This paper describes an investigation of plasma thermal spraying of MoSi2 offering a high melting point together with excellent high-temperature oxidation resistance. MoSi2 powder was deposited by low-pressure plasma thermal spraying on the surfaces of blasted SS400 substrate specimens precoated with 50%Ni-50%Cr. The residual stress generated in the specimens was then determined. Compressive stress is generated in the MoSi2 sprayed deposit. Tensile stress is generated in the 50%Ni-50%Cr sprayed deposit except at the SS400 substrate surface. A series of experiments was conducted to clarify the validity of the residual stress distribution obtained. These results suggest the following: 1. When only blasting treatment is performed, compressive stress is generated from the upper surface to 0.3 mm inside. Minor tensile stress is also generated inside. 2. When 50%Ni-50%Cr is deposited after blasting treatment, the residual stress is tensile in the 50%Ni-50%Cr layer and compressive on the substrate upper surface. Tensile stress is found inside. This is due to the fact that the substrate restrains the contraction of the sprayed deposit with a high thermal shrinkage. The validity of this result is also supported by the fact that the compressive stress near the substrate upper surface is greater than when only blasting treatment is performed. 3. When MoSi2 is deposited after blasting treatment, compressive stress is generated in the MoSi2 layer. This is due to the fact that, despite the MoSi2 layer having a higher temperature than the substrate, the linear thermal expansion coefficient of MoSi2 is much smaller than that of the substrate, so that the MoSi2 layer restrains the contraction of the substrate. 4. During estimation of the residual stress in materials deposited by plasma thermal spraying, it is important to ensure that the modulus of elasticity of the sprayed deposit is measured separately for each set of thermal spraying conditions.