Microhardness and deformation storage energy density of NiTi thin films

Abstract

The NiTi thin films were deposited onto copper substrates by magnetron sputtering. X-ray diffraction profile Fourier analysis method has been used to study the mechanical properties of deformation NiTi thin films. Tensile tests were carried out on CSS-44100 electron universal test-machine. From the dislocation data it has been found that the dislocation density and the deformation storage energy density increased with elongation increased. The calculated results showed the microhardness values were not in a good agreement with the measured values. The oxide layer on the surface of NiTi thin film affects the measured values of microhardness. The average dislocation density and the average elastic stored energy density values gradually increase as strain increases in the strain range of 0 to 6.78% and rapidly increase in the strain range of 6.78% to 8.21%. The peak coefficient of friction corresponds with the oxide layer of the films. There is a rapid increase in the average coefficient of friction after strain range of 4.80%. This raise could be attributed to the increase of average elastic stored energy density values with elongation.