Young’s modulus of titanium alloy VT6S and its structural sensitivity

Abstract

According to literature data, values of Young’s modulus, E, measured in a two-phase titanium alloy VT6 (Ti-6Al-4V) can vary from 90 to 145 GPa. Elasticity modulus is an important material parameter, which enters the basic equations describing the structural strength of materials. Due to such a wide scatter of E values, there is a problem of a correct choice of this parameter for the strength analyses of responsible aircraft structures. This also makes doubtful the accuracy of computational models assuming a constancy and structural insensivity of Young’s modulus of an alloy used. An absence of systematic data in this field requires carrying out experiments, which would allow one to estimate the stability of elastic and strength properties of VT6‑type two-phase titanium alloys subjected to long term processing at superplastic deformation temperatures, i.e. about 900°C. Experiments carried out in the present paper have shown that long-term vacuum annealing of sheet titanium alloy VT6S with an initial average grain size of 1 μm at 900°C for 50 hours leads to a considerable, about 14 %, reduction in Young’s modulus. The average grain size increases up to 6 μm during 50 hours annealing. Along with the reduction of elastic properties, a considerable, about 14 % too, decrease in the room temperature tensile strength has been found. Vacuum annealing at 900°C preserves the existing anisotropy of mechanical properties, which is inherited due to a weak change of the original crystallographic texture. The revealed change of mechanical properties in sheet of titanium alloy VT6S after vacuum annealing correlates with structural changes including changes in phase composition and crystallographic texture.