Effect of Sc addition and aging on microstructure and transformation behaviour of NiTiHfSc high temperature shape memory alloys

Tuesday, May 14, 2019: 3:45 PM
Saal 8 (Hall 8) (Bodenseeforum Konstanz)
Prof. Yunxiang Tong , Harbin Engineering University, Harbin, China
Ms. Xiaomin Fan , Harbin Engineering University, Harbin, China
Dr. Feng Chen , Harbin Engineering University, Harbin, China
Dr. Bing Tian , Harbin Engineering University, Harbin, China
Prof. Li Li , Harbin Engineering University, Harbin, China
In past decades, NiTiHf-based high temperature shape memory alloys(HTSMAs) have been regarded the most promising candidates for practical applications working in the range of 373-573K because of their desired properties. Quaternary alloying and precipitation strengthening are effective in tailoring microstructure and functional properties of SMAs. Previous results show that for NiTi and NiTiPd alloys, the addition of Sc may reduce the transformation temperature and enhance shape recovery properties. However, it remains unknown how the addition of Sc and the aging influence microstructure, transformation and functional behaviors of NiTiHf HTSMAs.

In present work, a Ni-rich NiTiHf HTSMA was selected as the starting material. Sc was added into the alloys at expense of Ti. Microstructure, martensitic transformation and superelasticity of NiTiHfSc alloys were investigated by TEM, DSC and compression tests. The addition of Sc does not change the microstructure obviously, which is different from that in Ni-lean NiTiHf alloy. H-phase precipitates present as a product of aging. With increasing Sc content, the transformation temperatures first increase and then decrease due to the change of matrix composition. After aging at 823K for 3h, the transformation temperatures are elevated. The addition of Sc and aging can significantly improve the thermal cycling stability of martensitic transformation, resulting from the strengthening effect. The present alloys show well-defined superelasticity at a temperature above 473K. The results indicate that the proper addition of Sc and aging can be used to optimize the functional properties of NiTiHf-based HTSMAs.

See more of: Alloy Development and Future Alloys III
See more of: Technical Program