Research On The Deformation Behavior And Modification Mechanism Of Hydrogenated Ti-46Al-2V-1Cr-0.3Ni Alloy At High Temperature

Due to the low density and good high temperature mechanical properties,TiAl based alloys show a remarkable development prospect in the aerospace industry.However,the intrinsic brittleness,poor hot working ability,narrow hot working temperature range,etc.severely increase the processing cost and restrict the engineering application.Thermo hydrogen processing where hydrogen is used as a temporary alloying element improves the hot working properties,which does not increase the density.Such technology is a new approach for enlarging the engineering application of TiAl based alloys.However,the mechanism of hydrogen influencing the hot working properties has not been systematically investigated.The research material is a cast Ti-46Al-2V-1Cr-0.3Ni?at.%?alloy.After hydrogenation,the maximum hydrogen content of the alloy is 0.8 at.%.Hydrogenation has no significant effect on room temperature microstructural morphology,grain size and phase composition and content.By use of isothermal compression test,the effect of hydrogen on the mechanical properties at high temperature of the cast alloy.Compared with the unhydrogenated alloy,the flow stress of the hydrogenated alloy is obviously decreased.The mean decrease of the peak stress due to hydrogen addition is about 25%.Moreover,hydrogen can decrease the flow stress of the cast alloy deformed at high temperature,i.e.the hydrogen-softened effect.Moreover,hydrogen-softened alloy is more obvious at high temperature and low strain rate.Hydrogen can activate the slip system and promote dislocation movement,and hence many lamellae experience bending in the colonies.On one hand,this decreases the rotation and slip of lamellar colonies,and on the other hand,this decreases the stress concentration at boundaries of lamellar colonies,which prevents cracks.The precipitation of fine ? lamellae in the ?₂ lamellae is attributed to hydrogen-promoted the movement of Shockley incomplete dislocation 1/6<10???0>,which leads to more fine ? lamellae in the hydrogenated alloy.Hydrogen can effectively promote element diffusion,which promotes the decomposition of lamellae.Hydrogen-induced the precipitation of B2 phase in the ?/?₂ interfaces promotes the decomposition of ?₂ lamellae.Hydrogen-promoted ? twinning and hydrogen-promoted ?₂ dislocation movement leads to bamboo-like ?₂ lamellae which more easily experience decomposition.That hydrogen promotes lamellar decomposition,twinning and decreases stacking fault energy leads to more dynamic recrystallization.Hydrogen obviously promotes the discontinuous dynamic recrystallization that consumes a lot of dislocation,which restricts continuous dynamic recrystallization to some extent.All in all,hydrogen enhances the high temperature deformation ability of the cast Ti-46Al-2V-1Cr-0.3Ni alloy.The canned forging process is investigated and the size and structure of the can is determined: the optimum deformation temperature is 1220?,the strain rate is 0.01s^-1,two-step forging contains a strain of 50%,and the total strain is 75%.Hydrogen has positive effect on the forging process and increases the plasticity of the cast alloy,and thus the hydrogenated alloy shows better deformability.Hydrogen obviously promotes the lamellar decomposition and dynamic recrystallization,which leads to finer and more uniform microstructure.Hydrogen softens the alloy and makes the flow softening appears earlier.Hydrogen decreases the stacking fault energy to decrease the critical resolved shear stress for twinning,and so 180°<111> true-twin boundaries are more in the hydrogenated alloy.The phase transformation leads to 120°<111> rotation-relationship boundaries and mechanical twinning leads to 180°<111> true-twin boundaries.The interaction between 180°<111> true-twin and 120°<111> rotation-relationship boundaries leads to 60°<111> pseudo-twin boundaries.Only from the texture intensity point of view,cubic components are weakened and R component is enhanced with increasing temperature and total strain.Under the higher temperature and larger strain,? DRX more easily occurs,which partly contribute to the stronger recrystallization texture component.Furthermore,cubic textures seem to be readily weakened because of the ???₂ and ?₂?? lamellae transformations,while R texture is not significantly influenced.