Electron beam additive manufacturing of Ni-Ti alloy

Abstract

Shape memory alloys (such as Ni-Ti) are a unique class of active materials, which can recover to their original shape after applying stimuli, such as deformation due to stress, heat or magnetic field. These alloys possess attractive characteristics such as ability to provide large recoverable strain during mechanical loading (pseudoelasticity), shape recovery upon heating (shape memory effect), and potent biocompatibility, which make alloys one of the suitable actuators for biomedical applications. In the present paper the results of microstructure, martensitic transformation behaviour and superelastic properties of Ni-Ti alloys fabricated using a EBAM technique, which applies wire as the additive material were presented. It was revealed that the microstructure of the deposit exhibited typical solidification features of columnar grains of austenite, due to epitaxial growth mechanism. Moreover, EBSD investigations revealed that the preferential grain orientation in [001] is a result of the adopted material layer deposition. TEM studies have shown presence of martensitic needles partially twinned within austenitic matrix, and a low dislocation density within austenite confirming ability of the EBAM manufactured sample to pseudoelastic deformation at room temperature.