Study On Microstructure Evolution And Mechanical Properties Of TC10 Titanium Alloy During Heat Treatment And Cladding Rolling Process

TC10 titanium alloy is a typicalα+βtwo-phase titanium alloy.Its nominal composition is Ti-6Al-6V-2Sn.It has good hardenability and high strength,which makes the application of this alloy very extensive.Heat treatment process is one of the important means of titanium alloy strengthening,and it is also a hot research topic at home and abroad.There has been a lot of basic work in this field,but with the continuous expansion of the application field of TC10 titanium alloy,there is still a lack of systematic research on its heat treatment process,especially the application of new heat treatment process on TC10 titanium alloy.Due to the high strength of TC10 titanium alloy,the plastic deformation process of TC10 titanium alloy is mainly forging at home and abroad,and there are few reports on the application of other plastic deformation processes to this alloy.With the rapid development of military industry and aerospace field,the demand for titanium alloy plates is increasing.Therefore,it is necessary to study the microstructure evolution,texture evolution and mechanical properties of TC10 titanium alloy during rolling process.In this paper,TC10 titanium alloy is taken as the research object,and the effects of three different heat treatment processes of solid solution aging,annealing and BASCA（βannealing+slow cooling+aging）on the phase transformation and microstructure of TC10 titanium alloy are studied respectively.The precipitation behavior of each phase in the microstructure and the influence of microstructure on the mechanical properties of the alloy are analyzed,and the crack propagation mechanism of different types of microstructure is studied.The effects of different rolling deformations on the microstructure and texture evolution of TC10titanium alloy sheet in the cladding rolling process were studied.The tensile properties and anisotropy of the sheet were analyzed.This paper mainly draws the following conclusions:In the solution aging process,the alloy only precipitatesα’phase andα"phase after solution treatment.In the annealing process,there is noα’phase andα"phase in the microstructure of the alloy after single annealing,onlyαphase andβphase exist.In the BASCA process,the structure treated by the BASC（βannealing+slow cooling）process also only hasαphase andβphase,and there is no other phase.At the same time,it is found that the content and size ofα_s phase in the microstructure are mainly affected by aging temperature and secondary annealing temperature.In terms of mechanical properties,the tensile properties of the alloy are affected by the precipitation degree ofα_p phase,α’phase,α"phase andα_s phase.Theα’phase andα_s phase play a strengthening role,and theα"phase andα_p phase play a role in increasing plasticity.In addition,theα"phase and theα_p phase will increase the plastic zone at the notch tip of the impact specimen and make the crack propagation path more gentle as a whole,while theα’phase and theα_s phase show the opposite effect.Among the three heat treatment processes,it is found that the alloy treated by BASCA process can obtain very excellent comprehensive mechanical properties.The tensile strength is 1090 MPa,the elongation after fracture is 16%,and the fracture toughness is 82.4MPa·m^1/2.The comprehensive performance is much higher than that of the same type ofα+βtype alloy,and is close to the high strength and high toughness nearβtype titanium alloy.The fracture propagation mechanism of four different types of microstructures,such as equiaxed microstructure,bimodal microstructure,fine lamellar microstructure and coarse lamellar microstructure is studied.It is found that the essential behavior of crack propagation process is the result of competition between microporous polymerization fracture and cleavage fracture mechanism.The transformation process of crack propagation mechanism of different types of microstructure will affect the fracture morphology.The macroscopic fracture morphology of the fracture toughness specimens with equiaxed structure and bimodal structure is relatively flat and smooth,the fluctuation of the crack propagation path on the side of the specimen is small,and the fracture morphology is mainly composed of a large number of equiaxed dimples.The surface of the macroscopic fracture morphology of the fine lamellar structure and the coarse lamellar structure has very obvious concave and convex undulations.The overall fluctuation of the crack propagation path on the side of the sample is large and the serrated morphology is obvious.The fracture morphology of the two is mainly rock-like morphology,the crystal shape is obvious,and the tearing edge appears.In the cladding rolling process,it is found that theαphase in the microstructure gradually became equiaxed and the grain orientation changed during the rolling reduction rate increased from 94%to 99.6%.It is found that when the rolling reduction rate is 94%,there is anisotropy between the strength of the TD direction and the RD direction of the sheet,which is caused by the difference between the microstructure morphology and the Schmid factor.At the same time,it is found that when the rolling reduction rate is 99.6%,the anisotropy between the strength of the TD and RD directions of the plate disappears,and there is a clear T-shaped texture in the microstructure.After analysis,the existence of intragranular substructure is the main reason for the lack of obvious anisotropy of the plate with T-shaped texture.The tensile fracture morphology of the plate is dominated by a large number of equiaxed dimples.When the rolling reduction rate is small（94%）,the tensile fracture morphology also contains voids,tearing edges and fine microcracks.