J. Mater. Sci. Technol. ›› 2024, Vol. 172: 196-201.DOI: 10.1016/j.jmst.2023.06.049

• Letter • Previous Articles     Next Articles

Abnormal grain growth induced by δ → γ phase transformation in Fe-based shape memory alloys

Huabei Penga,*, Liqiu Yonga, Gaixia Wanga,b,*, Jiazhen Yana, Bing Xua, Yuhua Wena   

  1. aSchool of Mechanical Engineering, Sichuan University, Chengdu 610065, China;
    bScience and Technology on Reactor Fuel and Materials Laboratory, Nuclear Power Institute of China, Chengdu 610041, China
  • Received:2023-04-04 Revised:2023-05-20 Accepted:2023-06-24 Published:2024-02-10 Online:2023-08-12
  • Contact: *E-mail addresses: penghuabei@scu.edu.cn (H. Peng), gaixia.wang@foxmail.com (G. Wang)

Abstract: We investigated the effect of cooling rate on the grain growth of δ-ferrite and γ-austenite in an Fe-18.80Mn-6.15Si-8.89Cr-4.81Ni shape memory alloy underwent δ→γ phase transformation. The anomalous grain growth of δ-ferrite occurred prior to the δ→γ phase transformation. Additionally, the δ→γ phase transformation introduced abundant sub-grains within γ-austenite. The abnormal grain growth of γ-austenite occurred after the δ→γ phase transformation because theses sub-grains provided the driving force of grain boundary migration. Furthermore, a slower cooling rate before and after the δ→γ phase transformation resulted in achieving bigger grains for both δ-ferrite and γ-austenite. By utilizing the δ→γ phase transformation, the austenitic grains of above ∼600 μm, even at a millimeter-level, were obtained. Finally, we achieved a recovery strain of above ∼ 6%, breaking through the recovery strain ceiling of 6% in processed Fe-Mn-Si-based shape memory alloys.

Key words: Shape memory alloys, Martensitic phase transformation, Abnormal grain growth, Interface migration, Sub-grains