Effect of Ta Addition on Properties and Microstructures of Fe-28Ni-11.5Al Shape Memory Alloys

Abstract

The effects of Ta additions (x=0, 0.5, 1.0, 1.5) in Fe60.5-xNi28Al11.5Tax(at.%) shape memory alloys on microstructure, thermal expansion, and pseudoelasticity of the aged alloys were investigated by metallurgical microscope, X-ray diffraction, SEM, EDS, high-temperature dilatometer spectrometer and pressure test machine. The results showed that with the increment of Ta additions, the γ' phase content increased which strengthened the austenitic matrix, meanwhile the compressive strength, the recoverable strain and the maximum strain of the aging state alloys decreased first and then increased, and the alloy’s residual strain firstly decreased and then increased. When the Ta content was 1.0 at.%, the alloy’s compressive strength, recoverable strain and plastic deformation strain reached its maximum value, 2.5Gpa, 14.4%, and 16.0% respectively. Thus, the alloy had the best pseudo-elastic at this time. The mean thermal expansion coefficient of the alloys decreased with Ta additions, when the Ta content was 1.0 at.%, the mean thermal expansion coefficient was at its minimum.