2007 Volume 48 Issue 3 Pages 395-399
Damping capacity (tanδ) of Ti-24 mol%Nb-3 mol%Al (Ti-Nb-Al) shape memory alloy (SMA) with {001}β⟨110⟩β texture was examined upon cooling from 423 K to 123 K by dynamic mechanical analysis (DMA) in a tensile mode. The {001}β⟨110⟩β texture was well developed by a cold-rolling with reduction in thickness of 99% followed by a heat treatment at 873 K for 3.6 ks. The apparent phase of the material at room temperature was the β-phase (bcc) containing small amount of α-phase (hcp) and the martensite start temperature (Ms) of the β-α″(C-orthorhombic) thermoelastic martensitic transformation was about 250 K. The β-phase was equiaxed and averaged grain size was 2 μm. The angle between the longitudinal direction of the DMA specimens and the rolling direction (RD) was defined as φ and was 0, 30, 45, 60 and 90 degrees on the normal plane. Damping capacity, tanδ, depended on the stress-amplitude (σo) and φ. The peak height of tanδ during the martensitic transformation, Δtanδ, was proportional to σo for each φ and also proportional to the maximum transformation strain along the loading direction (εMAX) which is determined by the crystallography of the transformation. A proportional relationship between Δtanδ and σoεMAX was found and indicated that the interaction between the transformation and the applied stress plays an important role in the damping of the textured SMA.
