Study On The Temperature Effect And Twinning Behavior Of Pure Titanium Deformation

With the progress of industrialization and science and technology,the exploration of the deformation mechanism and mechanical properties of pure titanium has more and more practical significance.Among them,exploring the twin behavior of pure titanium and its influence mechanism on the mechanical properties of pure titanium has important academic value.Including the study of the deformation mechanism and tensile behavior of pure titanium at room temperature and low temperature,and the study of high-temperature thermal stability of high-density twinned pure titanium.This article takes TA2 industrial pure titanium as the research object,and adopts the cold rolling + annealing process to prepare homogeneous structure pure titanium with different grain sizes.This paper mainly uses optical microscope,scanning electron microscope,electron backscatter diffraction technology and transmission electron microscope to study the evolution of the microstructure of pure titanium under different deformation conditions,and uses hardness and uniaxial tensile experiments to test the mechanical properties of pure titanium at room temperature and liquid nitrogen temperature.The main conclusions are as follows:(1)The temperature effect and twinning behavior of pure titanium during tensile deformation was explored.The strength and plasticity of equiaxed pure titanium with the same grain size prepared by cold rolling + annealing at liquid nitrogen temperature are greater than that at room temperature;at the same time,with different grain sizes of equiaxed pure titanium,its strength and plasticity at liquid nitrogen temperature increase with the increase of the original grain size.This is because when the crystal grain size increases,the inside of the crystal grain can allow more twins to nucleate and grow at liquid nitrogen temperature,which leads to an increase in plasticity.As the density of twin boundaries increases,dislocation slipping across the interface is more hindered,and they are packed at the grain boundaries,thereby increasing the strength.Secondly,the EBSD also shows that under the same grain size condition,more twins were produced in the grains at liquid nitrogen temperature compared to room temperature;at liquid nitrogen temperature,the larger the grain size,the more twin nuclei,and the more serious the grain refinement.The number and size of fracture dimples also showed that with the increase of the original grain size,the more the number and the smaller the diameter of the liquid nitrogen temperature tensile dimples,the stronger the ductility.(2)EBSD technology was used to investigate the twinning behavior of pure titanium when compressed along the direction perpendicular to the c-axis at room temperature and liquid nitrogen temperature.For equiaxed pure titanium with the same grain size,the number of twin nuclei produced by liquid nitrogen temperature compression is more than that of normal temperature compression,but the thickness of the former twin layer is smaller than that of the latter.Secondly,the primary and secondary twin conversion laws were studied systematically in compressed titanium.Finally,the Schmid factor of twins was calculated in pure titanium compressed at liquid nitrogen temperature,and it was found that the selection of variants in the twins was mainly controlled by the Schmid factor,and the variants with high Schmid factor were easy to nucleate,and variants with lower Schmid factors were difficult to nucleate.(3)The detwinning behavior of pure titanium with high-density twinned structure at high temperature was explored.Pure titanium with more than 50% of the volume of twins is prepared by rolling at liquid nitrogen temperature,and the pure titanium with a high-density twin structure is annealed at different temperatures and times.The results show that the internal twin structure evolution of pure titanium is the most intense when annealed at 600℃.The EBSD characterization of the samples annealed at different times at this temperature shows that{11(?)2}CT has the strongest thermal stability,and the reasons need to be further studied.