Superelastic shape memory alloy for seal applications produced by low pressure thermal spray technology

摘要

The objective of this development program was to demonstrate the feasibility of producing superelastic NiTi shape-memory alloy (SMA) foil material by the low pressure plasma spraying (LPPS) process for the development of robust, corrosion resistant and long life sealing technology. A conventional LPPS facility was retooled for the use of electric wire arc spraying and the process parameters were reconfigured. Foil specimens sprayed up to 1 .5mm thickness showed good ductility after consolidation heat treatment at 950°C for 1 hour. Subsequent rolling of the foil specimens to a thickness of 0.5mm exhibited superelastic behavior. The amount of superelasticity will have to be determined. In addition, thin (0.2 mm) and thick (0.76mm) wall tubes have been produced in the 12.5mm diameter range. These samples were heat treated and subjected to Hot Isostatic Pressing (HIP). Metallographic examination revealed dense, solid microstructures after heat treatment and rolling, and hot isostatic pressing respectively. It was concluded, that this development established the feasibility to produce near net shape superelastic NiTi foil with a retooled Low Pressure Wire Arc Spraying (LPWAS) process, modified to permit substitution of NiTi-wire for NiTi-powder as feed stock.