High Temperature Constitutive Study Of Titanium Alloy For High Performance Turbine Blades

As a metallic material with good mechanical properties,titanium alloy is widely used in aerospace,medicine,chemical industry and other fields.In the steam turbine industry,the material of the last stage blade has changed from stainless steel to titanium alloy;In particular,the large steam turbines of the last stage blade are gradually dominated by Ti-6Al-4V alloy.Due to the limitations of Ti-6Al-4V alloy,the performance and working life of the last stage blade are limited.Therefore,developing a new titanium alloy to replace Ti-6Al-4V alloy in the application of the last stage blade has become one of the today’s hot topics。The flow behavior of Ti-10V-2Cr-3Al alloy at high temperature was quantitatively analyzed.It was found that the flow stress decreased with the decrease of strain rate and the increase of deformation temperature.The discontinuous yield phenomenon was more obvious at higher temperature but weaker with the decrease of strain rate.The constitutive model of Ti-10V-2Cr-3Al alloy was established and modified by Arrhenius equation.The softening mechanism during thermal deformation was analyzed by the constitutive model.By studying the microstructure of the samples under the same strain rate and different deformation temperatures,secondary α phase distributed in punctate of β matrix,β phase elongated,when it’s below the β-phase transition temperature;secondary a phase distributed in needle shape or strip shape,when it is above the β-phase transition temperature;and secondary α phase volume fraction of the deformed object decreases with the increase of the temperature.The processing map of Ti-10V-2Cr-3Al alloy is established.The alloy was found that it was prone to flow instability near the phase transformation point,and the flow instability was more likely to occur with the increase of strain rate.With the increase of strain,the flow instability in the low temperature region was gradually stable,but in the phase transition point region,the flow instability region gradually extended to the low strain rate.The constitutive equation and user subroutine was embedded into ABAQUS simulation software.We could obtain the stress distribution and strain distribution under different deformation conditions.In the high temperature environment,temperature stress was existed.As the temperature was greater than the phase transition point,the temperature stress was gradually distributed from the bottom to all parts of the model.With the downward displacement applied to the upper end face of the model,the strain of the upper and lower end face didn’t change with the change of strain rate,and decreased with the increase of deformation temperature.The change of stress was consistent with the change of experimental stress.The volume fraction of large deformation region could increase with the increase of strain rate and deformation temperature.