Anisotropy of Young's modulus and tensile properties in cold rolled α′ martensite Ti-V-Sn alloys

Young's modulus and tensile properties of cold rolled Ti-8 mass% V and (Ti-8 mass% V)-4 mass% Sn alloy plates consisting of alpha' martensite were investigated as a function of tensile axis orientation in this work, A single phase of alpha' (hcp) martensite is obtained in Ti-8 mass% V and (Ti-8 mass% V)-4 mass% Sn alloys by quenching after solution treatment. By 86% cold rolling, acicular a' martensite microstructures change into extremely refined dislocation cell-like structure with an average size of 60 nm, accompanied with the development of cold rolling texture in which the basal plane normal is tilted from the plate normal direction (ND) toward transverse direction (TD) at angles of +/- 49 degrees for Ti-8% V alloy and +/- 46 degrees for (Ti-8 mass% V)-4 mass% Sn alloy. No apparent anisotropy of Young's modulus (E) is observed for as-quenched Ti-8% V (E= 76-83 GPa) and (Ti-8% V)-4%Sn (E= 69-79 GPa). In contrast, Young's modulus increases with increasing angle from the rolling direction (RD) to TD for cold rolled Ti-8% V (E= 72-94 GPa) and (Ti-8% V)-4%Sn (E= 63-85 GPa). The observed anisotropy of Young's modulus can be reasonably explained in terms of the cold rolling alpha' texture. 0.2% proof stress and tensile strength are independent of tensile orientation for cold rolled Ti-8% V and (Ti-8% V)-4%Sn alloys. In contrast, larger elongation to fracture is obtained in specimens deviated by 30 degrees, 45 degrees and 60 degrees from RD than by 0 degrees, 75 degrees and 90 degrees. Scanning electron microscopy (SEM) fractographs reveal that quasi-cleavage-like fracture plane appears in 0 degrees specimen of cold rolled Ti-8% V which shows brittle fracture and other specimens of cold rolled Ti-8% V and (Ti-8% V)-4%Sn alloys are fractured accompanied with necking and dimple formation. It is suggested from these results that brittle fracture is related to the activation of limited number of slip system and Sn addition leads to the activation of multiple slip systems. (C) 2008 Published by Elsevier B.V.