Study On The Mechanical Behavior And Adiabatic Shearing Sensitivity Of TC21 Titanium Alloy Under Different Heat Treatments

TC21 is independent research and development of two-phase titanium alloy with high strength and high damage-tolerant in China,which has better comprehensive mechanical properties,and it will be regarded as a important structural material on the application of advanced aircraft in the future.In order to more accurately grasp the deformation behavior of the material in practical application,and broaden its range of application,it is important to research the mechanical behavior of the TC21 titanium alloy under the quasi-static and high strain rate loading.In this paper,the microstructure evolution of TC21 titanium alloy under the double and triplex heat treatment by the different cooling ways in the ?+?,near ? and? region are researched by optical microscope.The three kinds of typical microstructure,such as equiaxed,binary and basket-wave microstructure,and the samples of the heat treatment with water quenching,air cooling and furnace cooling in the ?+? area are obtained.These samples had been tested respectively by the universal material testing machine and split Hopkinson pressure bar,and the effects of typical microstructure and type of cooling on mechanical properties and the adiabatic shear behaviors of TC21 titanium alloy are studied by analyzing the stress-strain curves,stress-time curves,and observation of the fracture and adiabatic shear zone.The results are as follows:The influence of heat treatment on microstructure of TC21 titanium alloy is obvious.With the increasing of solution temperature,the content of the equiaxed ?phase is decreased,and gradually formed a typical binary microstructure.In the near? region,however,the equiaxed ? phase is few and fine.When it is treated in the ?region,the equiaxed ? phase has disappeared completely.With continuous elevated temperature,there will be a formation of clear ? grain.Under the double heat treatment,with the loss of the cooling rate,the precipitation of secondary phase increases gradually,resulting in coarse grains of furnace cooling sample microstructure,and fine microstructure of the water-cooled sample.And under the triple heat treatment,as a result of the action of the second high temperature,theorganizations of alloy become more uniform and larger grains,in which unstable phase retained is decomposed fully.The effect of typical microstructure on the mechanical behaviors and adiabatic shearing sensitivities of TC21 titanium alloy is prominent.The equiaxed microstructure has the best plasticity,but lower intensity;Binary microstructure has higher strength and poor ductility;Basket-wave microstructure has higher strength and better plasticity under the condition of quasi-static.Under high strain rates,dynamic mechanical properties of three kinds of microstructure of TC21 titanium alloy are similar to that of quasi-static mechanical properties.Three kinds of microstructure of TC21 titanium alloy are very sensitive to strain rate.The strain rate sensitivity subsequence of three kinds of microstructure of TC21 titanium alloy is binary microstructure,basket-weave microstructure,equiaxed microstructure in turn according to in sort descending.In the adiabatic shearing testing,the adiabatic shear bands can be observed in three kinds of samples,and its adiabatic shearing sensitivities have been studied by combining the loading time with the microstructure analysis of adiabatic shear bands,which show that the adiabatic shearing sensitivity of three kinds of samples orderly decline with binary microstructure,basket-wave microstructure,equiaxed microstructure.The effect of cooling ways on the mechanical behaviors and adiabatic shearing sensitivities of TC21 titanium alloy is larger.The furnace cooling sample has the best plasticity,but the intensity is lower;Water quenching sample has higher strength,but bad ductility;Air cooling sample has higher strength and better plasticity at the same time under the condition of quasi-static.Under high strain rates,its dynamic mechanical properties are similar to the quasi-static mechanical properties.Three kinds of microstructure obtained by different cooling way are very sensitive to strain rate.The strain rate sensitivity from high to low is water quenching sample,air cooling sample and furnace cooling sample.However,the subsequence of the adiabatic shearing sensitivity is air cooling sample,furnace cooling sample and water quenching sample in turn according to sort in increasing.