Deformation Mechanism And Microstructure Evolution Of β-γ TiAl Alloy During Hot Rolling

In order to implement the policy of high temperature structure materials which is“stronger,lighter,more heat-resistant”and to meet the needs of aero-engine development,TiAl alloys are attracting more attention because of their low density,high specific strength and excellent high-temperature oxidation resistant.The novel beta-gamma TiAl alloy can overcome the shortcomings of traditional TiAl which is with low room temperature plasticity and poor process ability.However,many studies about TiAl alloys focus on the forging process and ignore the rolling process of TiAl alloy.As we know,the formation of sheet and foil is mainly done by rolling.Therefore,the research on the rolling of TiAl alloy is indispensable.In this paper,plane strain compression experiment was carried out to simulate the hot rolling of TI-43Al-9V-0.2Y alloy,and microstructural evolution and dynamic recrystallization mechanism was also studied.Based on the result of the plane strain compression experiment,Ti-43Al-9V-0.2Y alloy was hot rolled without canning,the formation mechanism of hot rolling structure was researched.The plane strain compression experiment was used to study the high temperature softening mechanism and microstructure evolution of the Ti-43Al-9V-0.2Y alloy during hot rolling.It is revealed by the true strain and true stress curves that the deformation resistance of the alloy is low and work-hardening exponent is 6000.That is to say,Ti-43Al-9V-0.2Y alloy has a better high temperature deformability.In addition,by calculating the dynamic recrystallization critical strain,dynamic recrystallization becomes more and more difficult with the deformation reduction increases.Furthermore,the microstructure is remarkably refined and the degree of recrystallization is high when the deformation reduction is above 40%.When the reduction pass is 6 and the stain rate is 0.05s^-1,the phase transformation ofγ→α₂ andβ/B2→α₂ occurred.By judging the orientation relationship,theα₂ andγphases are satisfied with Blackburn relationship.The degree of recrystallization increases with the increase of deformation reduction and the decreases of strain rate.The deformation mechanism ofγphase is discontinuous dynamic recrystallization.Besides,the deformation ability of the alloy decreases with the decrease of strain rate and the increase of deformation reduction.In addition to this,the content of pseudo twins gradually decreases with the increase of strain rate.And the influence of deformation reduction on pseudo twins is negligible.The Ti-43Al-9V-0.2Y alloy was subjected to uncanned hot rolling with a rolling process of 1200℃/0.05s^-1/60%and 1250℃/0.05s^-1/60%.It was found that the microsturcture consists of grains and acicularγgrains when rolling inβsingle-phase（1250℃）.while the microstructure consis ofα/γlamellar colony andβ/γlamellar after rooling withinα+β+γphase field region（1200℃）.The analysis of two rolling processes shows that the deformation abilities of the three phases are completely different.Theβphase has more slipping systems.In contrast,theαslip system is less and deformation ability is poor.The deformation mechanism ofαis dynamic recovery.Besides,The texture strengthrolling at 1200℃is high,while the texture rolling at 1250℃ is low.