Abstract
The effect of adiabatic heating on microstructure evolution during high strain rate subtransus forging of a Ti-6Al-4V alloy having equiaxed initial microstructure was studied through experiments and modelling. Ø45 × 67.5 mm cylindrical billets with embedded thermocouples were forged at four different α+β temperatures on a Schuler 2100t screw press to evaluate the extent of adiabatic heating in different parts of the billet. In the centre of the billet, the highest temperature increase due to adiabatic heating exceeded the β transus (~1000 °C) during forging. The microstructure of the forged billets was examined for any changes in β phase volume fraction due to adiabatic heating. The forging process was then simulated in Deform 2D/3D software. High strain rate compression testing in the α+β and β temperature fields was carried out using a Phoenix forge simulator to generate input mechanical properties for the model. The effect of the billet size on the α-β phase transformation during forging and post-forge cooling is also discussed.
Highlights
Most of the mechanical energy is dissipated in the form of heat during plastic deformation of metals; only a small fraction is stored in the material. α-β titanium alloys have a relatively high flow stress for all α-β working temperatures and, a large amount of heat is generated during hot deformation
The temperature increase might lead to changes in microstructure of the material and affect the resultant mechanical properties of the forged part
The temperature increase due to forging decreases with distance from the centre of the billet presumably due to the lower strain that the material experiences during forging at the periphery compared to the billet centre
Summary
Most of the mechanical energy is dissipated in the form of heat during plastic deformation of metals; only a small fraction is stored in the material. α-β titanium alloys have a relatively high flow stress for all α-β working temperatures and, a large amount of heat is generated during hot deformation. Most of the mechanical energy is dissipated in the form of heat during plastic deformation of metals; only a small fraction is stored in the material. Α-β titanium alloys have a relatively high flow stress for all α-β working temperatures and, a large amount of heat is generated during hot deformation. The relatively low thermal conductivity of titanium alloys prevents this heat from being effectively dissipated. High strain rates limit the time available for the heat dissipation. The combination of these factors results in adiabatic heating during forging. The effect of adiabatic heating on the α-to-β phase transformation in a Ti-6Al-4V alloy during high strain rate forging was examined
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