Temperature and Uniaxial Stress Dependence of the Martensitic Transformation Temperature in Ni₆₃ Al₃₇

Physics Department, John Carroll University, Cleveland, OH 44118, U.S.A.

Abstract

A study of the martensitic transformation in Ni₆₃Al₃₇ single crystals was made using optical, ultrasonic and atomic force microscope techniques. The transformation was studied as a function of temperature and uniaxial stress applied on (110) and (001) surfaces. Surface relief was observed optically several degrees above the bulk transformation determined ultrasonically. Atomic force measurements of the surface relief show clear evidence of the surface transformation at slightly higher temperatures, and the height of the thermally induced surface relief band increased from 20 nanometers to 3 microns when the band is fully developed. The stress induced bands are smaller and have different orientations. These measurements clearly show that the transformation emanates at the surface near regions of high local strain. Uniaxial stress applied along the [001] direction has a profound effect on the martensitic phase transformation temperature and the ultrasonic studies yield a value of dM_s/dT = 0.4 K/MPa. These results will be compared with recent neutron diffraction of the uniaxial stress dependence of the phonon behavior in Ni_62.5Al_32.5 and thermal expansion studies.