Influence of Chemical Composition and Melting Process on Hot Rolling of NiTiHf Shape Memory Alloy

Tuesday, May 21, 2013
OREA Pryamida Hotel
Mr. Majid Belbasi , Iran University of Science & Technology, Tehran, Iran
Dr. Mohammad Taghi Salehi , Iran University of Science & Technology, Tehran, Iran
In NiTi shape memory alloys an important aim is to elevate the martensitic transformation temperature in order to satisfy the high temperature applications and addition of Pt, Au, Zr or Hf to NiTi can increase the transformation temperatures above 100°C. Among these high temperature shape memory alloys, NiTiHf alloys seem to be more practical for engineering applications, because of their high transformation temperatures, good thermal stability and lower price. But their recovery strain in comparison with binary NiTi alloys is less. One of methods for improvement of recovery strain is thermomechanical treatment. In this research, the as-cast ingot of Ni50Ti40Hf10 shape memory alloy was prepared by vacuum arc melting and then specimens hot rolled for a 10-30% thickness reduction. Result obtained by bending test showed that with increasing applied strain, the amount of recovery strain increased. In all hot rolled samples until 3% strain, recovery is complete but in above 3% strain due to occurrence of slip deformation, full recovery not happened. In hot rolled specimens, due to increasing of strength and also critical stress for slip, recovery strain increased.