Effect Of ECAP On Structures And Properties Of Pure Titanium

Equal Channel Angular Pressing(ECAP)technology is one of the most effective and rapid methods to prepare ultrafine materials.It is to refine grains and improve mechanical properties of materials through severe plastic deformation.In this paper,pure titanium is successfully processed by ECAP up to 6 passes with a die of 120° at room temperature,and the ultrafine samples with different reduction are obtained by combining room temperature rolling(RTR)and cryogenic temperature rolling(CTR).In addition,a die of 90° is used to obtain 4 secondary ECAP deformation samples with different back pressures at 350℃.OM,SEM,TEM,XRD,EBSD,microhardness tester and tensile tester are used to systematically study the microstructure and mechanical properties of pure titanium processed by ECAP,ECAP and cold rolling(CR),and ECAP with back pressure(BP-ECAP)deformation samples.The main findings are as follows:(1)When multi-pass ECAP deformation occurs at room temperature,the grain size of pure titanium samples decreases with the increase of ECAP passes,and the grain refinement effect is best after the 6-pass ECAP deformation,with an average grain size of about 161nm.In addition,the texture of the samples gradually changes from Y texture to inclined texture due to cylinder slip with the increase of ECAP passes.The strength and hardness of the samples both increase with the increase of ECAP passes,with the most obvious increase of 1 pass,and the strength and hardness reach 599MPa and 216.8HV respectively after 6 passes.(2)In the deformation of ECAP and cold rolling,the grain refining effect becomes more obvious with the increase of the reduction.Compared with RTR,the average grain size of the samples processed by CTR is smaller,about 125nm and 94nm respectively.In addition,the texture in the tissue is typical of titanium rolling texture,and the cold rolling condition and the reduction have little effect on it.The strength,hardness and elongation of the samples all increase with the increase of the reduction,and the samples processed by CTR have higher strength and hardness,and keep good plasticity.The CTR deformation with 71%reduction can obtain better comprehensive mechanical properties.(3)In the deformation of ECAP with back pressure,the grain size decreases slightly with the increase of back pressure,from 2.29μm to 1.71μm.At the same time,the texture of the tissue is B fiber texture,back pressure having little effect on the texture.The strength and hardness of the samples also decreases slightly with the increase of the back pressure,but the elongation increases greatly,and the ECAP with the back pressure of 200MPa could obtain better comprehensive mechanical properties.