Low Pressure Wire Arc and Vacuum Plasma Spraying of NiTi Shape Memory Alloys

Abstract

Abstract Thermal spray technology offers the advantage of producing thin-walled parts. Especially thermal spraying of NiTi shape memory foils demands highest control of atmospheric conditions due to their affinity to e.g. oxygen, hydrogen and nitrogen at high temperatures. This article describes two inert thermal spray techniques in order to produce free-standing shape memory foils, namely low pressure wire arc (LPWAS) and vacuum plasma spraying (VPS). The advantage of low pressure wire arc spraying is the ability to use NiTi wire from commercial suppliers without the detour of powder production, which may result in additional undesired reactions and phases. The benefit of vacuum plasma spraying is the higher kinetic energy of the particles due to higher plasma gas amount and speed. Within the scope of this paper, coatings produced with both methods (LPWAS and VPS) are discussed with regard to their coating microstructure and physical / chemical properties, transformation temperatures (DSC), porosity (%) and their shape memory effect.