室温ECAP变形纯钛孪生行为研究  

Twinning Behavior of Pure Titanium Processed by ECAP at Room Temperature

作　　者：刘晓燕[1] 强萌 杨西荣[1] 罗雷[1] Liu Xiaoyan;Qiang Meng;Yang Xirong;Luo Lei(School of Metallurgical Engineering,Xi'an University of Architecture and Technology,Xi'an 710055,China)

机构地区：[1]西安建筑科技大学冶金工程学院,陕西西安710055

出　　处：《稀有金属》2023年第10期1352-1358,共7页Chinese Journal of Rare Metals

基　　金：国家自然科学基金项目(51474170);陕西省教育厅重点实验室项目(20JS075);陕西省自然科学基金面上项目(2020JM-493)资助。

摘　　要：室温下对纯钛进行多道次等径弯曲通道变形(ECAP),分别采用光学显微镜(OM)、透射电镜(TEM)、电子背散射衍射仪(EBSD)、室温拉伸和显微硬度观察,测试纯钛变形过程组织演变和力学性能变化规律,探讨纯钛室温变形机制和孪生行为。结果表明,纯钛ECAP变形过程中出现■拉伸孪晶和■压缩孪晶,随着挤压道次的增大,孪晶数量先增大后减小。孪晶的出现有效改变晶格取向,激发进一步位错滑移,辅助塑性变形过程,使纯钛显微组织有效细化,经过4道次ECAP变形,平均晶粒尺寸由约63.79μm细化至约2.81μm。1道次变形后晶粒细化效果最显著,平均晶粒尺寸比变形前减小约94%;随着变形道次的增加,晶粒细化效果减弱,4道次变形后平均晶粒尺寸累积减小约95.6%。同时,大量位错、孪晶和亚晶的形成,使得位错、孪晶以及亚晶之间的相互作用加强,显著提高了纯钛的屈服强度和显微硬度,4道次变形后,屈服强度从215 MPa增加到600 MPa,增幅为179%;显微硬度从HV 129增加到HV 200。由于1道次变形后晶粒细化效果最显著,并且出现大量孪晶和位错,屈服强度与硬度的增幅也最大。Equal channel angular pressing(ECAP)is a kind of severe plastic deformation method which can refine grain size of metallic materials effectively and obtain bulk ultrafine grained materials by approximate pure shear deformation.Pure titanium with a composition of O 0.18,H 0.015,N 0.03,C 0.08 and Fe 0.2(%,mass fraction),and the rest was titanium,was processed by multi-passes of ECAP at room temperature.ECAP was performed at the ram speed of 2.5 mm·s~(-1),Route C,which required the sample rotation of180°around its longitudinal axis between adjacent passes.The internal channel angle and outer arc curvature angle of the die were135°and 20°correspondingly,which gave an equivalent strain of about 0.46 for each pass,and the cumulative equivalent strain of about 1.84 after 4 passes of ECAP.The microstructures including average grain size,dislocation density and deformation twinning of the longitudinal section of pure titanium during ECAP process were observed using optical microscope(OM),transmission electron microscope(TEM)and scanning electron microscope(SEM)equipped with an electron backscattering diffraction(EBSD),respectively.The mechanical properties were evaluated by tensile tests and Vickers micro-hardness tests at room temperature.It was evident from the high dislocation density in TEM images and lots of deformation twins in twinning statistics that the deformation mechanisms of pure titanium during ECAP process included dislocation slips and deformation twinning,and there were■tensile twins and■compression twins appeared during ECAP process of pure titanium.The twin type of pure titanium during ECAP process was affected by deformation temperature,strain rate,die angle,ECAP pass,grain size,impurity elements and so on.With the increase of ECAP passes,the area fraction of twins first increased and then decreased.Twinning would also affect the microstructure and mechanical properties of pure titanium during ECAP process,correspondingly.There were a few annealing twins in the original pure titanium,about 0.53

关 键 词：纯钛 等径弯曲通道变形(ECAP) 孪晶 孪生机制 

分 类 号：TG146[一般工业技术—材料科学与工程]