Preferred orientation and anisotropy in titanium

Variations of some physical and mechanical properties of polycrystalline titanium rod and sheet with direction of testing have been studied, and results have been correlated with preferred orientation. Structure-insensitive properties measured were Young's modulus and coefficient of thermal expansion, while several types of tests were used to investigate plastic anisotropy, including tensile and compression tests, cupping, bending and hardness measurements. Young's modulus for an aggregate of randomly oriented crystals of α-titanium is 17.3 · 106 lb./sq.in., compared with a value of 15.4 · 106 lb./sq. in. in the basal plane. Values usually quoted for polycrystalline titanium are close to the latter figure. The coefficient of expansion in the a-direction is very slightly greater than the coefficient in the c-direction, the respective values being 10.0 and 9.95 · 10−6/°C in the range 20–600°C. In commercial purity titanium sheet, values of tensile strength are almost independent of testing direction, but a greater degree of anisotropy with respect to tensile strength occurs in titanium bar and in a titanium alloy in sheet form. An aggregate having basal planes parallel to the tension axis has lower strength than a random aggregate; for commercial purity titanium differences in 0.1% proof stress and maximum tensile strength of 20% and 3.5% respectively are found.