Hot Compression Shear Deformation Behavior And Microstructure Evolution Of Equiaxed Titanium Matrix Composites

Light-weight,high-strength,high-temperature resistant titanium matrix composites（TMCs）have always been ideal materials for aerospace engines and important structural parts of aircraft.Among them,the TMCs with reinforced phases distributed in a quasi-continuous network have received more and more attention due to their higher strength,hardness and the applicable temperature.It is a very effective way to achieve the purpose of improving the strength and toughness of TMCs through thermal processing and heat treatment.Based on the theory that regulating material organization can optimal mechanical properties,this paper prepared a quasi-continuous network TMCs using the“low-energy ball milling+hot press sintering"powder metallurgy process.Then adjusted its microstructure through solid solution aging treatment to obtain equiaxed TMCs,and analyzed the hot compression shear deformation process in the actual process to explore the microstructure evolution and dynamic recrystallization behavior of the composites.In this paper,the solution temperature was 950-1100℃and the solution time was 1 h,the aging temperature was 400-600℃,and the aging time is 6 h.The percentage content of phases after heat treatment are calculated,and the solution temperature was 930-1010℃and aging temperature of 400-600℃,the percentage content of each phase had a linear relationship with the heat treatment temperature,and the functional relationship is quantified.The functional relationship can be used to predict the content of each phase of the material after heat treatment under certain conditions.After extending the aging time from 6 h to 12 h,the microstructure of the composites was equiaxed.The room temperature mechanical properties of the two kinds of composites were tested and found that the strength,hardness and plasticity of the composites with exquiaxed microstructure had been improved.The high temperature tensile results revealed the fact that the tensile strength of the composites with exquiaxed microstructure can still reach nearly 200MPa at 700℃.Through the analysis of the high temperature fracture mechanism,it was found that the fracture mode is a typical intergranular fracture of micropores aggregation.The temperature selected for hot shear-compression deformation was 850-950℃,and the strain rate was 10^-3S^-1-10^-1S^-1.The engineering stress-strain curves were converted into equivalent stress-strain curves by an empirical formula based on Arrhenious formula,and the constitutive equations were established using Deform software to simulate the hot compression shear deformatio n process.The equivalent stress-strain curves obtained by experiment and numerical simulatio n were simular,and there were no obvious plastic deformation between the upper and lower ends of the sample.The deformation is mainly concentrated in the narrow gap.The area with the smallest strain rate and strain was the transition zone between the narrow slit and the two ends,and the effect variables such as the narrow slit have close linear relationship with time.At the beginning of the deformation,the axi al compression deformation and the shear deformation along the narrow slit direction existed at the same time and the compression deformation was slightly higher.As the deformation continues,the shear deformation began to dominate.Observation and analysis of the microstructure after hot shear-compression deformation using optical microscope and scanning electron microscope and revealed that there was a clear dividing line between the deformed area and the non-deformed area,and this dividing line was consistent with the 45°deformation zone of the samples.These results indicate that the microstructure of the deformation area was mainly deformed along the shear direction during the deformation,which was also consistent with the conclusion that the shear deformation was dominant.Through the analysis of the dynamic recrystallization mechanism of the deformation area microstructure,it was concluded that not only c DRX,but also d DRX has taken place during the dynamic recrystallization process of the matrix in the deformation zone.While c DRX was the main mechanism.And the recrystallization process was not complete becaues not all of the grains was equiaxed.As the strain rate decreased,the recrystallization type did not change,but the recrystallized grains grew significantly after prolonging the deformation time.