A study on the mechanical behavior and microstructure of NiTiHf shape memory alloy under hot deformation

作者：Belbasi Majid^*; Salehi Mohammad T; Mousavi Seyed Ali Asghar Akbari; Ebrahimi Seyed Mohammad

来源：Materials Science and Engineering A-Structural Materials Properties Microstructure and Processing, 2013, 560: 96-102.

DOI：10.1016/j.msea.2012.09.039

• Hot deformation
• Ni49Ti36Hf15
• Dynamic recrystallization
• Flow localization

In the present work, the hot deformation behavior of Ni49Ti36Hf15 alloy was investigated. Compression tests were carried out at temperatures ranging from 800 to 1100 degrees C and at the strain rates of 0.001-1 s(-1). The peak stress decreased with the increase in the deformation temperature and decrease in strain rate, which could be represented by the Zener-Hollomon parameter. It was realized that dynamic recrystallization (DRX) was responsible for flow softening. Most of the samples exhibited single peak stress followed by a gradual fall-down stress in stress strain curves. Microstructure evolution showed that new recrystallized grains were formed in the vicinity of grain boundaries at 1100 degrees C. No new recrystallized grain was observed at 800 degrees C. However, DRX occurred at 900 and 1000 degrees C only at higher strain rates. The hyperbolic-sine-type constitutive model of Ni49Ti36Hf15 alloy was obtained to provide basic data for determining reasonable hot forming process. The high value of activation energy (410 KJ/mol) obtained for Ni49Ti36Hf15 can be attributed to the strengthening effect of (Ti,Hf)(2)Ni second phase. The study shows that Ni49Ti36Hf15 alloy was not suitable for hot working due to occurrence of flow localization at all temperatures and strain rates.

• 出版日期2013-1-10