Quality of surface treatment and plastic deformation of titanium alloys at 2.5 to 293 K

Abstract

The influence of the quality of surface (after grinding, chemical or electrolytic polishing) of smooth samples of various sections (circle, rectangle, ellipse) upon the mechanical properties of commercial titanium and TiAlV alloys is investigated under quasistatic tension at plastic deformation rate ⋗3 ranging within 1.5 × 10 −6 to 3 × 10 −2 s −1 and temperatures 2.5–293 K. The effect is the most pronounced quantitatively below 20 K at ⋗3 = 1.5 × 10 −3 s −1 . Polished circular samples, as compared to ground ones, display a 10–15% increase in the yield strength, no athermic region in the dependence σ o·2 ( T) obtained for Ti and its low alloys and a change in the character of the fracture, etc. Below 20 K the relative elongation of the Ti6Al4V alloy increases from 2–3% to 8–10% on removal of edges. The results obtained are analysed on the basis of the concept of an increasing importance of surface dislocation sources to the development of plastic deformation and fracture genesis at low temperatures.