Young's modulus and damping of Ti6Al4V alloy as a function of heat treatment and oxygen concentration

Abstract

Young's modulus and damping of texture-free Ti6Al4V alloy were evaluated at room temperature by longitudinal resonance vibration tests on cylindrical bars of measured length and density. Damping was determined from the half-width Δf of the resonance peaks. The alloy's properties were evaluated as a function of solution heat treatments between 600 and 1200 °C with subsequent quenching, aging treatments between 200 and 550 °C, and plastic deformation of solution-treated and quenched alloy. The effects of oxygen concentration were determined on identically produced Ti6Al4V alloys but with systematic variation of oxygen concentration between 0.17 and 0.30 wt.% (0.50–0.88 at.%). Heat treatment alone accounts for variations in Young's modulus E O by as much as 10% of the nominal value and in damping by more than an order of magnitude. Interstitial oxygen increases Young's modulus in addition to and independent of heat treatment, according to E alloy ( GPa) = E 0 + 13.5 (weight per cent of oxygen) Oxygen was found to have little effect on the damping capacity at room temperature. Low Young's modulus values are obtained when the second phase contains a vanadium enrichment of about 10 wt.% V. In the quenched state the second phase is actually a metastable (β + α″) phase mixture with a very low specific modulus values of about 74 GPa and a high specific damping capacity of 1 × 10 −2. The largest damping capacity (Q −1 > 10 −3) of the alloy is obtained after solution treatment and quenching (STQ) from 800 °C. High damping is also obtained after STQ from just below 1000 °C. The high damping is believed to arise from anelastic deformation of the second phase when it is present as metastable (β−α″) or (α″−α′) mixtures respectively. The damping capacity of STQ-treated alloys decreases rapidly on aging, even at low aging temperatures of 200°C, to Q −1 values of less than 1 × 10 −4.