DSC and microstructure analysis of high temperature Ni-Ti-Hf, low hysteresis Ni-Ti-Cu and conventional super-elastic and shape memory Ni-Ti alloy ingots and wires

Publication date: Available online 5 October 2019Source: Materials Today CommunicationsAuthor(s): J.N. Lemke, A. CodaAbstractThe progression of martensitic transformations in calorimetric experiments on NiTi-based shape memory alloys (SMA) depends significantly on the material composition, processing history and the thermo-mechanical treatment which is performed to prepare the material for use in application. The phase transformations in Ni-Ti alloys are first order transitions, i.e. the microstructure symmetry changes occur spontaneously and superheating and supercooling effects emerge. Thus, the thermal scanning rate in differential scanning calorimetry (DSC) affects the observation of important material parameters for the characterization of shape memory alloys like onset temperatures, hysteresis width and change in enthalpy of phase transformations. This work depicts how the transformation characteristics as observed by DSC measurements vary significantly by altering the alloy composition and processing conditions of the material. An in-depth calorimetric study on a wide range of NiTi-based alloys which were prepared as heat treated ingot and processed wire was performed. In order to evaluate also the rate effect on the transformation of distinct alloys, DSC rates from 1 – 30°C/min were tested, highlighting the interplay between thermal scanning velocity and material parameters. Manifold results are presented on how chemistry, microstructure, DSC sample geometry and pr...
Source: Materials Today Communications - Category: Materials Science Source Type: research