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Abstract:
In this paper, the effects of heating parameters, including temperature ranging from 900 ℃ to 1000 ℃, heating rates ranging from 2 ℃∙s-1 to 100 ℃∙s-1, and 120 s soaking on the non-equilibrium microstructure evolution of Ti-6Al-4V alloy were studied. Microstructures after heating were characterized to reveal the mechanism of non-equilibrium phase transformation. Uniaxial tensile tests at room temperature were carried out to evaluate the effects of non-equilibrium microstructure on the mechanical properties. Results show that higher heating rate and lower temperature lead to lower β phase volume fraction and finer β grains. A transition region with element gradient forms in the αp grain near the αp/β phase boundary and transfers into β phase gradually during the heating. Rapid heating could confine the movement of the transition region, and therefore reduce the α→β transition and growth of the β phase. When the Ti-6Al-4V alloy was heated to 1000 ℃ at a rate of 50 ℃/s and then quenched immediately, the tensile strength was improved by 19.5% and reached up to 1263.0 MPa with the elongation only decreasing from 13.6% to 9.6% compared with the initial material. The main strengthening mechanism is that the rapid heating in the single-phase region avoids the rapid growth of the β phase, which leads to fully fine martensite formation after water quenching.

Keywords:
Rapid heating,Non-equilibrium microstructure,Mechanical properties,Strengthening mechanisms