Study On Grain Orientation Distribution And Deformation Mechanism Of Pure Titanium During Combined Deformation

Visco plastic self consistent model(VPSC)can predict the evolution of hardening and texture related to plastic forming.In this paper,the VPSC self consistent model is used to simulate the pure titanium combined deformation process.At the same time,XRD is used to test the pure titanium combined deformation process,and the mtex tool in MATLAB is used to process the results.The grain orientation distribution and property change of the two are compared and analyzed.The test of tensile and hardness were carried out on the pure titanium samples in different stages of the two passes equal channel angular pressing(ECAP)+rolling+rotary swaging.The main research results are as follows:When two passes of ECAP+rolling+rotary swaging combined deformation occur in pure titanium samples,the grains gradually refine with the increase of ECAP deformation passes,the average grain size decrease from 24 ?m to 12 ?m,while the proportion of small angle grain boundaries increase to 7.2%.As the combined deformation continues,the small angle grain boundary decreases and the large angle grain boundary gradually increases.The large angle grain boundary is the largest after the rotary swaging deformation,reaching 95.9%.The texture changes from typical P1 basal texture to coexistence of P texture and C2 texture after one pass of ECAP deformation,while two passes of ECAP deformation make only C2 texture exist;when two passes of ECAP+rolling combined deformation occur,P1 texture and Y texture coexist;finally,P1 texture changes to coexistence of P1 texture after rotary swaging.After 4 passes of ECAP+rolling+rotary swaging,the texture of pure titanium changes from the original P1 basal texture to the P texture after rotary swaging.It can be seen that the number of passes of EC AP affects the final texture type of combined deformationThe VPSC self-consistent model is used to simulate the ECAP+rolling+rotary swaging combined deformation.The texture types obtained by VPSC is consistent with the results obtained by XRD.And the calculation of the Schmid factor in various states shows that the original pure titanium samples are mainly base texture,which is prone to cylinder slip,and the compression twin {1122}<1123>is in a state of easy activation;after one pass of ECAP deformation,the base texture disappears,which is mainly cone texture,and the cylinder slip system is easier to start,and the compression twin{1122}<1123>is in the state of easy activation;after two passes of ECAP deformation,the specimen is mainly cylinder texture,which is prone to base slip,and the tensile twin{1121}<1126>is easy to be activated;the pure titanium specimen after rolling and swaging deformation is prone to cylinder slip,and the compression twin {1122}<1123>is easy to be activated.The main deformation mechanism of pure titanium specimen in the process of ECAP+rolling+rotary swaging is as follows:the base slip and cylinder slip are the main deformation mechanisms when the pure titanium specimen is subjected to 1 or 2 passes of ECAP deformation;when it is rolled,it is the result of the combined action of the slip system and the twin system;when pure titanium is subjected to rotary swaging,cylindrical slip and base slip are the main deformation mechanismsThe hardness and strength of pure titanium samples increase gradually with two passes of ECAP+rolling+rotary swaging combined deformation,and the elongation decreases gradually.After rotary swaging deformation,the microhardness of pure titanium reaches the maximum,2369.25MPa in ED direction and 2236.85MPa in ND direction;the strength reaches the maximum,in which the yield strength is 774MPa,the tensile strength is 910mpa,and the elongation reaches the minimum of 12.90%According to the VPSC simulation results,the hardness and strength of 4 passes ECAP+rolling+rotary swaging combined deformation are higher than that of 2 passes ECAP+rolling+rotary swaging combined deformation.