Effect of cyclic heat treatment on abnormal grain growth in Fe-Mn-Al-based shape memory alloys with different Ni contents

Cyclic heat treatment that can continuously promote abnormal grain growth is widely used for the preparation of single‐crystal Fe‐Mn‐Al‐based shape memory alloys. However, it takes a long time to prepare large‐size Fe‐Mn‐Al‐based alloy single crystals via the reported cyclic heat treatments. Meanwhile, the long‐time cyclic heat treatment at high temperatures leads to the development of defects including oxidation and a decrease in Mn, which would deteriorate superelasticity in the Fe‐Mn‐Al‐based shape memory alloys. To shorten the fabrication time of single crystals, the effect of the cyclic heat treatment process on the abnormal grain growth in the Fe‐Mn‐Al‐based alloys with different Ni contents was systematically investigated. It is found that the abnormal grain growth of Fe‐Mn‐Al‐based alloys was not significantly affected by the Ni contents (within 2.1 at.%–6.2 at.%). In addition, the abnormal grain growth could be promoted by 1–2 °C min–1 cooling rate, high solution temperature, and multiple cycles, while it was insensitive to other processes including heating rate, dual‐phase time as well as long‐time solution treatment. These findings can guide optimizing the fabrication process of single crystals by cyclic heat treatment. Finally, the Fe41.9Mn37.8Al14.1Ni6.2 single crystal prepared by the optimized cyclic heat treatment showed a recoverable strain of about 4%.