Formation and thermomechanical behaviour of composite surface layer containing shape memory materials during friction-cyclic loading

Abstract

The article contains the results of the study on the formation, thermo-mechanical and deformation behaviour of layered surface composition made of materials with shape memory effect (SME) with different temperatures of phase transformations during friction-cyclic loading. It was demonstrated that the surface layer which is a multilayer composite (Ni–TiNiHf–TiNi), formed by high-velocity oxygen fuel spraying of mechanically activated powders in a protective atmosphere with subsequent thermomechanical processing, enhances the wear resistance and fatigue strength of friction-mechanical loading. The experimental studies have shown that the used technology of high-velocity oxygen fuel spraying of mechanically activated powders provided the formation of a composite surface layer made of shape memory materials with nano-sized structure. It is shown that the main factors that determine the reliability of the products within friction-cyclic loading, are: adhesion, wear, micro-hardness, fatigue strength. We explained the choice of the structure and architecture of the surface composition. We recommended forming a composite coating of materials with shape memory effect in order to improve the reliability and extend the life cycle of products, working in conditions of friction-cyclic loading. Experimental studies of samples with a composite surface layer on fatigue and wear rate, confirmed increase in durability and decrease in wear rate of the surface composition of Ni–TiNiHf–TiNi. It is shown that the temperature rise of the SME layer in the friction area causes the martensite-austenite transformation, and the large pressures generated by the friction cause effect of ductility conversion due to the formation of martensite stress. These processes determine the deformation behaviour of the composite surface layer made of a material with shape memory effect.