Damping Capacity of Ti-Nb-Al Shape Memory β-Titanium Alloy with {001}_β⟨110⟩_β Texture

抄録

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 (M_s) 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 (σ_o) and φ. The peak height of tanδ during the martensitic transformation, Δtanδ, was proportional to σ_o for each φ and also proportional to the maximum transformation strain along the loading direction (ε_MAX) which is determined by the crystallography of the transformation. A proportional relationship between Δtanδ and σ_oε_MAX 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.