Mechanical behaviour of NiTi parts prepared by powder metallurgical methods

Abstract

Abstract Powder metallurgical (PM) production processes feature some potential advantages for NiTi compared to the common melt processes. Segregation and grain growth can be avoided and with methods of net shape manufacturing the difficult and expensive machining of the parts do not apply. An established method for semifinished parts with theoretical density is hot isostatic pressing (HIP). An advanced near net shape method is metal injection moulding (MIM), which is commonly used to produce small complex shaped parts. Among other characteristics, such as phase transformation temperatures and impurity level, the mechanical behaviour of PM parts is a criterion for the validation of the processes in comparison to the conventionally used melting processes. Therefore, for the present investigation tensile test samples were prepared from prealloyed, NiTi powders. Samples from a Ni(50.85 at.%)Ti powder capable to precipitate were produced by MIM and HIP and from Ni(49.55 at.%)Ti powder not capable to precipitate only by MIM. From HIPed cylinders, samples were cut using spark erosion. For MIM, optimised parameter sets for injection, debindering and sintering were used. Specimens from powders able to precipitate were heat treated to get an defined microstructure. Tensile tests were conducted at temperatures above austenite finish and at room temperature.