Effect of heat treatments on a Ni-Ti alloy sintered by Electro-Sinter-Forging

This paper is focused on the thermal treatments (annealing and ageing) of Ni-Ti samples produced by an unconventional powder metallurgy process called Electro-Sinter-Forging (ESF). Powder metallurgy has gained considerable interest for fabrication of Ni-Ti alloys and ESF allows to overcome some issues related to sintering. Annealing is usually performed on Ni-Ti alloys to remove or reduce strain hardening while ageing treatments control type, size ad amount of the precipitates in the alloy: these steps are fundamental to control the transformation temperatures and phases involved in thermal cycling in shape memory materials. The aim of this work is to verify the structural (by x-ray and electron backscattered diffraction - XRD and EBSD), microstructural (through optical and scanning electron microscope observations), chemical (by energy dispersive x-ray spectrometry - EDS), thermal (using differential scanning calorimetry - DSC) and mechanical (by Vickers micro-hardness indentations) effects of annealing and ageing treatments on an ESF sintered Ni-Ti alloy.