Abstract
Internal friction (IF) in the martensite phase of a Ti-base shape memory alloy, Ti-24mol%Nb-3mol%Al, with a strong texture was investigated by a dynamic mechanical analyser (DMA) in a tensile mode. The IF in the martensite (C-orthorhombic) phase, tanδ=0.01〜0.05, was much higher than that of the parent phase in all the test conditions. In addition to high IF-background, IF peak of tanδ-0.1 appeared in the martensite phase at around 153K. The IF-peak height clearly depended on the stress amplitude and the IF peak In addition, a threshold stress for the appearance of the IF peak existed in the DMA test and it was in good agreement with the yield stress (0.2% proof stress) in a tensile test at 153K. These results mean that a long-range motion of twin-boundaries is necessary for the appearance of the IF peak.
