Investigation Of Microstructure And Texture Of TA19 Titanium Alloy

TA19 is classified as near a titanium alloy,which is similar to the Ti6242S titanium alloy in American and its nominal composition is Ti-6AL-2Sn-4Zr-2Mo-0.1 Si.TA19 was usually used as the aircraft skin and blade of engine in temperature range of 500?550 ?.Generally speaking,the mechanical properties of titanium alloys depend on the microstructure and texture of it.Thus,to investigate the evolution of microstructure and texture during hot working can be of quietly great importance.In this work,the variation of microstructure,texture and tensile mechanical properties in a big TA19 forging billet was firstly researched.Then,by isothermal compression experiment,at two phase field temperature(970?),a study was made about the variation regular of microstructure and texture of this alloy.The investigation indicated that,for the TA19 forging billet with scale of ?260*130mm,in edge,the less plane stress and fast cooling rate after forging in ?+? phase temperature lead to the finest grains.Furthermore,the unlimited metal flow cause the random texture was formed in the position.Fine grains and random texture determined the optimal tensile mechanical properties in edge.In R/2 position,microstructure are mainly made up of equiaxed grains and the(11-20)[1-100]and(11-20)[0001]texture with moderate density were developed,so excellent match between strength and plasticity was obtained.As regards the position of center,equiaxed ?p grains and as colonies with relatively big size are the main characterization of microstructure.In addition,the symmetrical cubic texture with very high density was formed.Therefore,the strength,no matter tensile strength or yield strength dropped quickly.By the analysis of EBSD technology,the spheroidizition of ?p laths formed in ? forging stage was completed by stress-induced in edge but the spheroidizing mechanism was grain boundary migration in both R/2 and center.The evolution of microstructure and texture during plastic deformation was dominant by prism<a>slip system.As regards to the isothermal compression deformation behavior of TA19 titanium alloy at 970?,the dislocation density grow rapidly and the flow stress increased quickly at initial stage.After peak stress,the dynamic softening caused by dynamic recrystallization eliminated the working hardening and the flow stress decrease subsequently.When the strain surpassed 50%,due to the function of fiction during tests,the flow stress stop decreasing and instead of increasing.For the condition of multiple deformation to 70%,the dislocation produced during each pass made climbing and sliding motion and further developed into subgrains,thus the density of dislocation within TA19 decreased quickly,the alloy elements made a sufficient diffusion in holding time stage.During the subsequent hot compressional deformation,a majority of mobile dislocation was produced at both a and ? grain boundaries,which lead to the occurrence of yield drop phenomenon.During the process of isothermal compression,when the deformation strain arrive at 30%,most of ?p grains were aligned along the metal flow direction,only the hard-oriented grains were kinked or bend.When the strain surpass 50%,almost all of ?p grains made dynamic recovery or recrystallization and was fined further with increase of strain.Fibre texture type of {11-20}//YO and {20-23}//YO was developed at various deformation strain.But the texture density is different.This is relative to the dynamic recovery and recrystallization during hot compression.By EBSD technology,the misorientation between adjacent grains was getted,by analyzing,it can be certain that variants selection occurred during ???,which lead to the strong fibre texture of {20-23}//YO within the TA19 titanium alloy.