High Temperature Deformation Behavior And Microstructure Evolution Of Hydrogenated ZrTiAlV Alloy

Most zirconium alloy and titanium alloys are widely used in aerospace materials,ships and chemical industry because of their advantages of good heat and corrosion resistance,high strength and hardness.However,generally speaking,the plasticity of zirconium alloy and titanium alloy is poor at room temperature,and it is easy to produce cracking during the deformation process.It needs to be processed and formed at a high deformation temperature and a low strain rate.The thermal deformation range is narrow,and the deformation resistance is too great,so its application in all aspects is greatly limited.Hydrogen treatment is to improve the phase composition and microstructure by using hydrogen as temporary alloying element,so as to effectively reduce the high-temperature flow resistance,promote dislocation movement and dynamic recrystallization,significantly improve the high-temperature deformation capacity,improve the thermal processing performance and reduce the manufacturing cost.The 47Zr-45Ti-5Al-3V alloy without hydrogen and with hydrogen content of3.46×10^-2wt.%was obtained by controlling the hydrogen partial pressure of the hydrogen melting equipment.The thermal compression simulation experiment was carried out by Gleeble-1500D dynamic thermal simulation machine.The influence of hydrogen treatment on the thermal deformation behavior and microstructure of47Zr-45Ti-5Al-3V alloy was studied by Metallographic Microscope(OM),X-ray Diffractometer(XRD),Backscattering Electron Microscope(EBSD).These include:(1)By using dynamic thermal simulation test machine,the as-cast ZrTiAlV alloy with and without hydrogen was subjected to thermal compression under different deformation conditions.The influence of hydrogen treatment on the deformation behavior and microstructure evolution of the alloy under different deformation temperature and strain rate was studied systematically.As the strain rate decreases and the deformation temperature increases,the flow stress decreases gradually.Adding hydrogen can significantly reduce the flow stress and deformation activation energy of ZrTiAlV alloy.After hydrogenation,the activation energy is from 339.7 k J/mol reduce to 286.5 k J/mol.Through the comparison of thermal processing map,the window of thermal processing map of hydrogenated alloy is significantly expanded and the deformation instability zone is significantly reduced.For the alloy without hydrogen ZrTiAlV alloy,the optimal plastic deformation interval is the 775-900?,0.01-0.1 s^-1.The optimal plastic deformation interval of hydrogenated ZrTiAlV alloy was extended to 650-900?,0.01-1 s^-1.(2)For as-cast ZrTiAlV alloys,the effect of hydrogen on microstructure,transition point and phase composition is revealed by optical microscope and X ray diffractometer.The results show that hydrogen,as a?phase stability element,lowers the transition point and expand the phase area,increases the better plastic?phase content and refines microstructure,which is beneficial to improve the plasticity of as-cast alloys.(3)Through studying the influence of hydrogen on the microstructure evolution of ZrTiAlV alloy under different deformation conditions,it is found that when the strain rate is constant and the deformation temperature is low(600-700?),the hydrogen significantly increases the angle between the adiabatic shear band and the compression axis direction,and reduces the deformation resistance of the alloy.As the deformation temperature rises(800–900?),hydrogen promotes dislocation movement and nucleation and growth of dynamic recrystallized grains,significantly increasing the number of dynamic recrystallized grains.When the deformation temperature is constant and the strain rate is low,dynamic recrystallization occurs and the dynamic recrystallization mechanism is continuous continued dynamic recrystallization(CDRX).As the strain rate increases gradually,the softening mechanism of the alloy is dynamic recovery,accompanied by partial dynamic recrystallization,and the dynamic recrystallization mechanism is mainly discontinuous dynamic recrystallization(DDRX).The dynamic recrystallization fraction of hydrogenated alloy is obviously improved,the microstructure is refined and the dislocation density is reduced,but the dynamic recrystallization mechanism remains unchanged.(4)By studing the effects of hydrogen on microstructure evolution of ZrTiAlV alloys under different deformation conditions at(?+?)phases.On the one hand,hydrogen can promote the movement of alloy atoms and dislocations,thus increase the diffusion coefficient of grain boundary,promote the nucleation rate of dynamic recrystallization and the growth rate of dynamic recrystallization grains.On the other hand,hydrogen can increase the content of?phase with better plasticity through hydrogen induced transformation,thus reducing the flow resistance of the alloy in the dual phase region and improving the thermal processing properties of the alloy.