Characteristics of Residual Stress Produced by MoSi2 Plasma Spraying and Its Production Mechanism

Abstract

Abstract MoSi2 powder was deposited by low pressure plasma spraying on the specimen with 50%Ni-50%Cr based coat after blasted SS400 substrate. Compressive stress was generated in MoSi2 spray deposit. Tensile stress was generated in 50%Ni-50%Cr spray deposit. Large compressive stress was generated in SS400 substrate adjacent to the interface. Investigating the production mechanism of residual stress and the validity of provided residual stress, a series of the experiments were done. Blasting on the substrate, residual stress near the surface of the substrate was compressive and that of the inner part of the substrate was tensile. After the blast treatment on SS400 substrate, depositing on the substrate with 50%Ni50% Cr, residual stress of the spray deposit was tensile. This is because SS400 substrate restricts the contraction of 50%Ni-50%Cr spray deposit which has large thermal shrinkage. Depositing MoSi2 after the blast treatment, compressive stress was generated in the spray deposit. This is because the linear expansion thermal coefficient of MoSi2 is extremely small comparing with that of SS400 substrate nevertheless the temperature of the spray deposit is higher than that of the substrate. As the result, the spray deposit restricts thermal shrinkage of the substrate. The validity of estimated residual stress was shown.