Mechanical behavior of TiNi shape memory alloy under axial dynamic compression

Abstract

Intermetallic compound TiNi alloys are known as shape memory alloys (SMAs) because of the thermoelastic martensitic transformation (MT) and reverse martensitic transformation. Apart from the shape memory effect (SME) [1], TiNi alloys also possess excellent pseudoelasticity (PE) [1], wear-resistance [2], corrosion-resistance [3], high damping capacity [4], good bio-compatibility [5] and outstanding mechanical properties [6]. Therefore, TiNi shape memory alloys have attracted considerable attention in recent years as functional materials in a variety of industrial and medical applications. They are called important smart materials due to their ability to perform both sensing and actuating functions [7]. A great number of investigations have been conducted on SME and PE associated with the thermoelastic martensitic transformation. Nevertheless, the transformation behavior and mechanical properties of TiNi alloys are susceptive to thermomechanical treatments such as cold working [8], thermal cycling [9], stress cycling [10], annealing temperature [11], aging of Ni-rich alloys [12] and addition of a third element [13]. Quite a few investigations on pseudoealsticity of TiNi alloys have been carried out by means of the tension test while the mechanical behavior under compression has not been studied. Since the materials are subjected to compression, impact as well as combinations of normal and tangent stresses in many engineering applications, it is needed to investigate, in a detailed way, the factors affecting properties of TiNi alloys under relevant conditions to extend their practical engineering applications. In this article, for the sake of simplicity, the Ni-rich Ti-50.9at% Ni alloy was selected for studying the influence of the strain rate on the mechanical behavior of TiNi alloys under axial dynamic compression and some significant results were obtained. The Ti-50.9at%Ni alloy was melted by the vacuum induction method in a graphite crucible with an argon atmosphere. The alloy ingot was homogenized at 1000 ◦C for 4 hr, then quenched in water. After removing the surface layer, the ingot was forged and rolled into bars of 6 mm in diameter. Before being cut into