Effect of Alloying Additions on the Properties Affecting Shape Memory Properties of Cu–12.5Al–5Mn Alloy

Abstract

The paper discusses the attempt made to understand the role of different alloying additions (Fe, Ni, Cr and Ti) to a Cu–12.5Al–5Mn alloy known to exhibit shape memory behaviour on its microstructure, phase precipitation and effect on transition temperatures after optimising the heat treatment cycles to precipitate the required martensite phase. The effect of the additions has been studied on the optimising conditions, phases precipitated through microstructural analysis‚ X-ray diffraction and transformation temperatures through Differential Scanning Calorimetric studies. In this study, the samples were prepared through liquid metallurgy route by melting pure metals. The cast alloys were subject to homogenisation treatment at 200 °C for 2 h in a muffle furnace and furnace cooled. In an attempt to precipitate the maximum amount of the desired microstructure of martensite in the quenched samples, the quenching cycle was optimised for each alloy by holding them for different duration of time from 30 to 120 min at 920 °C followed by ice quenching. X-ray diffraction studies carried out on the quenched samples indicate martensitic phase precipitation; however, in some cases, the precipitation is incomplete. Differential Scanning Calorimetric (DSC) studies carried out on quenched samples indicate clear transformation peaks in all the samples which are significantly higher than conventionally reported. The range of phase retention was used to determine the enthalpy and entropy changes. The findings confirm the possibility of changing the shape memory properties such as martensite formation, transitions temperatures, retention times, thermal properties as in entropy and enthalpy change with changing alloying constituents. Attempts have been made to study the shape memory properties of selected alloys that have exhibited promising improvement over the base alloy. The study can help pinpoint compositions with the desired properties in such alloy systems.