Effect Of Rolling And Annealing On The Microstructural Evolution Of ?-ZrTiAlV Alloy

Steels and titanium alloys have been traditionally used in aerospace vehicle's moving parts.With the advancement of the aerospace industry,they have failed to meet the development requirements.Compared with these traditional materials,zirconium and zirconium alloys have advantages such as resistance to radiation damage,erosion of antigen and oxygen,and small expansion coefficient,which have the development potential as spacecraft moving component materials.Alloying is one of the effective ways to improve mechanical properties of metal materials.At present,researchers have developed new zirconium alloys with different compositions,such as ZrAl,ZrTi,ZrTiAl,ZrCr,ZrB,ZrTiAlV and ZrBe.Compared with pure zirconium,the tensile strength of ZrTiAlV alloys is significantly higher,which is even more than 1600 MPa.The microstructural characterization of the new zirconium alloys will promote the development and utilization of them in our country and provide sufficient experimental data and theoretical support for the optimization of the processing technology.In this paper,the new?-51.1Zr40.2Ti4.5Al4.2V alloy was chosen.The deformation and annealed microstructures were characterized by optical microscopy(OM),X-ray diffraction(XRD)and backscattered electron diffraction(EBSD)techniques.Firstly,the?-ZrTiAlV alloy was obtained as starting material by solution treatment and then cooling quenching.Subsequently,the?-ZrTiAlV alloy was rolled at room temperature and liquid nitrogen temperature.The deformation microstructure was observed and analyzed by OM,XRD and EBSD.The result showed that the?-ZrTiAlV was metastable,when it was rolled at room temperature or liquid nitrogen temperature,it would partially transformed into hexagonal close-packed?'phase due to strain-induced phase transformation,with the Burgers relationship:(0001)_?'?{011}_?,<11-20>_?'?<111>_?.At room temperature,when the rolling reduction is less than 50%,the volume fraction of?'martensite increased with the increasing rolling reduction,and when the rolling reduction is greater than 50%,the martensite transformation stopped.Under the condition of liquid nitrogen temperature,the deformation capacity for this alloy is reduced due to the suppression of dynamic recovery.The strain-induced martensite morphology changed during rolling deformation.When the specimen was subjected to the rolling reduction of 5%,plate-like deformation-induced martensite appeared in the equiaxed parent?grains.However,when the rolling reduction increased to 10%,the deformation-induced martensite would be generated fully within some?grains.There are no 12 theoretical?'variants in the phase transition process.In the process of strain-induced martensite transformation,strain-induced(101?2)<1?011>twinning was also produced in plate-like?'martensite.The number of twin was affected by rolling reduction and temperature.Increasing rolling reduction and rolling at liquid nitrogen temperature would promote the formation of twinning.Afterwards,the deformed structure was annealed at 700°C-800°C,and the annealed structure was observed by EBSD.It found that in terms of deformed microstructure,the deformation-induced?'-phase martensite transformed to?-phase again.When the annealing temperature was 700°C,the specimens with the rolling reduction of 20%were in the recrystallization nucleation stage,the grain boundaries of the distorted original?grains can be clearly observed,and only a small number of recrystallized nuclei appeared at the original?grain boundaries.As the rolling reduction increased,the recrystallization fraction increased,and the grain boundaries of the original deformed?grains disappeared;when the annealing temperature is further increased,the recrystallized grains completely replaced the deformed matrix,and the recrystallization process is completed.In terms of grain size,when the annealing temperature is less than or equal to 750°C,the average size of recrystallized grain gradually decreased with the increase of the rolling reduction at the same annealing temperature and annealing time;When the annealing temperature exceeded 750°C,twice recrystallization,which is a phenomenon of abnormal grain growth,occurred,causing extremely inhomogeneous grain size,and the average grain size of the annealed specimens after annealing at 850°C for 60 minutes with the rolling reduction of 70%was maximized.In terms of texture,the samples with rolling reduction of 20%have uniform orientation distribution and no obvious recrystallization texture.For the samples with the rolling reduction of 50%and 70%,when the annealing temperature?750°C,the grains with{111}orientation were localized to form orientation band and have{111}texture.When the annealing temperature?750°C,the{111}orientation grains dominated in the annealed structure and formed{111}texture,but the orientation band with{111}orientation disappeared.