In-situ Study On The Deformation Coordination Mechanism Of Duplex Titanium Alloys

TC21 duplex titanium alloy,as a damage tolerance titanium alloy independently developed in China,is widely used in various fields because of its excellent performance.However,in the process of titanium alloy processing,the microstructure evolution and plastic deformation mechanism are relatively complex,and there is a lack of systematic research,which limits the processing,manufacturing and engineering application of titanium alloy related products to a certain extent.In this paper,TC21 titanium alloy with bimorphic structure was used as the original material,the sheet structure and equiaxial structure were obtained through different heat treatment systems,and the in-situ tensile experiment at room temperature was carried out,and the slip trace,crystal orientation,grain boundary orientation difference,local stress distribution and other information in the tensile deformation of each tissue specimen were obtained by combining electronic scanning and electron backscattering diffraction technology,and the microstructure evolution law,slip system start law and influencing factors in the deformation process of duplex titanium alloy at room temperature were analyzed.The correlation between mechanical properties,microstructure state and deformation mechanism of duplex titanium alloys was discussed.The tensile deformation process of duplex TC21 titanium alloy was studied,and a large number of small-angle grain boundaries were generated after yielding,in particular,the proportion of small-angle grain boundaries under 9% stretching amount reached 71.6%;The crystal orientation changes faster with the increase of the amount of stretching,and the tendency of the orientation of the α phase is weakened by stretching.The local plastic deformation of the two phases is different,and the stress concentration of the grain in the later stage of stretching is intensified.The starting of the slip system is affected by the critical slitting stress,Schmitt factor,surrounding grains,etc.,and the combined action of these factors determines the coordinated deformation behavior of different grains.The rotation angle and path of the grain are closely related to its original orientation,and the interaction between the grains has a non-negligible influence on the rotation path and angle of the grain.The yield stress of the bimorphic tissue was slightly greater than the yield stress of the sheet tissue of 870 MPa,while the fracture strain of 0.15 was much greater than that of the lamellar tissue at 0.09.In bimorphic tissues,the primary α phase boundary,the primary αand β phase boundary,the primary α and the cluster interface and the cluster and cluster interface can effectively prevent dislocation slip,and the small primary α grain and bundle size can obtain higher yield strength,and the slight strengthening of the phase interface can also increase the yield stress.Bimorphic structures exhibit the greatest fracture strain,not only because of their small grain size,but also because the intergranular β phase also affects the deformation of their adjacent α grains.