Effect Of Rolling Annealing On Microsturcture And Mechanical Properties Of TC21 Titanium Alloy

Titanium and its alloys are widely used in aerospace and other high-tech field,due to their excellent mechanical properties.The mechanical properties of titanium alloys are closely related to the microstructure.Thus,controlling the microstructure is an important method to control the mechanical properties of titanium alloys.The effect of heat treatment on microstructure and mechanical properties of titanium alloys is significant.In this paper,we took TC21 titanium alloy as a raw material.The equiaxed microstructure with different initial phase content was obtained by heat treatment and annealed after hot rolling deformation.The microstructure parameters including grain morphology,phase content and crystallographic orientation during annealing were characterized in detail,and the effects of initial microstructure and annealing parameters on the microstructure and mechanical properties of TC21 titanium alloy were studied by combination of experimental characterization methods including metallographic microscope(OM),scanning electron microscopy(SEM),electron back-scattered diffraction(EBSD),transmission electron microscopy(TEM).The main conclusions are summarized below:(1)Static recrystallization(SRX)occurs more easily and sufficiently in β phase than α phase.And the recrystallization mechanisms of the two phases are different,resulting in different grain morphology evolution.Most elongated α grains generated during rolling remain in the early annealing stage,and get a coarsening with increasing annealing time due to the enhanced static recrystallization and boundary splitting.The β grain shows a fully equiaxed morphology during annealing,and the equiaxed β grain size increases gradually with increasing annealing time.(2)The evolution of texture between α phase and β phase is different.The α phase exhibits the(0001)basal texture first,and then forms the TD-split texture originated from the combining effect of oriented nucleation and oriented growth.The β phase exhibits a {001}<110> texture originated from the oriented growth at every annealing time.(3)When the initial α phase content increases,the deformation storage energy in the α phase is higher after rolling,which promotes the SRX of α phase.The initial microstructure has little effect on the texture evolution of α phase.While the content of α phase increasing,the size of β grain decreases and the number of grain boundaries increases,which promotes the SRX of β phase.The effect of initial microstructure on the microstructure evolution of β phase is remarkable.The grain size of β phase increases obviously and the texture is dispersed gradually with increasing annealing time.(4)Annealing temperature has great effect on mechanical properties,but annealing time and anisotropy have little effect on mechanical properties.Increasing annealing temperature,the yield strength and ultimate tensile strength increases and the elongation decreases.Increasing annealing time,the yield strength and ultimate tensile strength decreases and the elongation increases.The yield strength and ultimate tensile strength is lower and the elongation is higher in the rolled direction(RD)than in the transverse direction(TD).