工业纯钛TA1薄带制备工艺对织构与性能的影响

Texture and Properties of Industrial Pure Titanium Thin Strip with Preparation Technology

TA1常温下具有密排六方结构,滑移系较少,对称性较差,塑性变形机制复杂,加工方法不同会导致其各向异性,造成制耳、起皱等缺陷。为解决该问题,本文选用了厚度为0.5 mm的TA1薄带,通过X射线衍射(XRD)、电子背散射衍射(EBSD)、拉伸成形试验及共聚焦显微镜,研究了由于制备工艺不同而产生的不同织构和组织对其性能的影响规律。研究结果表明:金相分析发现强度和塑性指标与平均晶粒度成反比,形变孪晶的存在使拉伸时孪生与滑移相互作用,促进性能上的各向异性;全纵轧时,棱锥面<c+a>滑移协调c轴运动,产生棱锥型织构(1215)<1212>,(0113)<1120>,使可开动的滑移系分别为易激活的柱面滑移、较难开动的基面滑移或<c+a>滑移,产生各向异性;换向轧制会促进(0001)<1010>,(0001)<1120>基面织构的形成,该织构增加了六方晶粒厚度方向的变形阻力,降低薄带各向异性。改变纵轧规程和换向轧制对细化晶粒和提高基面织构组分比例有利。

Titanium and titanium alloys were widely used in energy,military and aerospace fields due to their low density,high specific strength and good corrosion resistance. After hot rolling and cold rolling annealing,TA1 thin strip was mainly used in power station condenser and plate heat exchanger,and its output accounted for more than half of the processed products. Due to the excellent properties and wide application of titanium alloy strip,the researches on the microstructure and texture of titanium alloy strip were more and more in-depth. Compared with the cubic metal,the symmetry of the metal was poor and the plastic deformation mechanism was complex,so the deformation texture would be formed in the cold rolling process. Different deformation amount would have different effects on the texture. The anisotropy of metal materials due to texture would seriously affect its formability. At present,most of the existing researches focused on the improvement of texture,microstructure and properties of medium thickness titanium plate,while the research on TA1 thin strip with thickness less than 1 mm was still relatively few. In this paper,the cold-rolled annealed TA1 thin strip was selected. By tensile test,forming test,X-ray diffraction(XRD),electron backscatter diffraction(EBSD)and texture analysis,different microstructures and texture types under different preparation processes were obtained. The effects of different metallographic structures and texture types on properties were compared and analyzed,so as to improve the production process and material properties,which provided a theoretical basis for the production and processing of thin strip. After multi pass cold rolling of TA1 industrial pure titanium,when the subsequent annealing temperature was higher or holding time was longer,the total interface energy was reduced,and the grains migrated with large angle grain boundary,resulting in coarse equiaxed grains. At the same time,due to full longitudinal rolling,the grain shape was irregular. The microstructure of the products obtained by reversing rolling was finer and more uniform,and the comprehensive mechanical properties were the best. However,the mechanical properties were anisotropic due to the mechanism of deformation twins coordinating twinning and sliding. As the samples were all cold rolled and annealed,the formation of recrystallization texture was mostly due to the inheritance of cold deformation texture orientation. In full longitudinal rolling,the main slip systems were|1011|<1120> and|1122|<1123>. The pyramid surface produced slip to coordinate the c-axis motion,and its basal texture disappeared,resulting in pyramid texture,which eventually leaded to the generation of plate anisotropy. Due to the insitu recrystallization and genetic mechanism of the deformed grains,the main texture types in annealed samples were pyramid texture (1215)<1212>,(0113)<1101> .(1215)<1010> and (0113)<1120> When tensile test was carried out,the slip systems that can be started were easy to activate cylinder|1010|<1120> slip and difficult to start base slip (002)<1120> or second order pyramid slip. The higher the orientation density of pyramid texture,the greater the anisotropy of its tensile strength. Therefore,the strength index of transverse direction(TD)was larger than that of rolling direction(RD),but the plasticity index showed the opposite trend,that was,the anisotropy of properties. During reversing rolling,a large number of(0001)basal textures were produced. Because the(0001)basal plane was symmetrical hexagonal,and the c-axis was perpendicular to the plate plane,which increased the deformation resistance in the height direction of hexagonal grains,the existence of basal texture reduced the anisotropy of the plate and increased the plastic deformation ratio(R). Therefore,it was beneficial to improve the anisotropy by strengthening the base texture component. In the process of recrystallization annealing,the maximum extreme density of texture increased with the increase of annealing temperature,but the texture strength did not dominate the formability of the test material,and its main influencing factors were the texture type and its distribution. There were many methods to improve the anisotropy in the literature,but they were not widely used in production. How to improve the longitudinal rolling schedule to improve the strip properties was still a big problem. Changing the longitudinal rolling schedule and reversing rolling were beneficial to grain refinement and increase the proportion of basal texture components.