Tantalum is bcc crystal structure with high melting point (2996 ℃) and density (16.6 g/cm3). In addition, Ta also has excellent extensibility and high corrosion resistance. Based on the above unique physical and chemical properties, tantalum and its alloys have been widely used in various industrial fields, such as electronics industry, superalloy industry, chemical industry, aerospace and defense industry. High purity tantalum ingots prepared by electron beam melting (EBM) have coarse columnar crystals, the size of which can be up to centimeters, and can not be used directly. Therefore, in the process of production, forging, rolling, drawing and other deformation methods are often combined with intermediate heat treatment to refine the grain in order to obtain the microstructure to meet the requirements. However, after the above thermal mechanical processing of Ta products, such as the traditional way of rolling tantalum plate, due to the uneven deformation, texture along the thickness of the plate uneven distribution, mainly manifested as the plate surface to texture or α fiber texture, with the depth of the plate surface increase, gradually to the plate in the middle of the γ fiber texture transformation. This seriously affects the mechanical properties of Ta products or the sputtering properties of tantalum targets. For example, in the industrial production of Ta target, in order to ensure the quality of the sputtering film, the average grain size of Ta target is required to be below 100 μm, the grain is equiaaxial and the texture is randomly distributed, which requires the processing process using cyclic deformation and combined with multiple intermediate annealing. tantalum recrystallization annealing is generally carried out in vacuum high temperature environment. Multiple intermediate annealing will greatly consume energy and increase production cost. Therefore, it is particularly important for tantalum product manufacturers to shorten the processing flow and optimize the processing technology.
The strain path is different when the material is deformed under different processing methods, such as compression, extrusion, torsion, forging, rolling, etc. The change of strain path has significant effects on grain size, texture, dislocation arrangement and recrystallization kinetics, and thus changes the properties of the material. Because traditional rolling (such as one-way rolling) is easy to cause texture gradient along the thickness direction, many new rolling techniques have been used to improve the uniformity of texture and microstructure, such as cross rolling, asynchronous rolling and cross rolling. It was found that strong γ fiber texture was formed in Mo plate prepared by cross rolling, which was beneficial to improve its forming property. The experiment of asynchronous rolling on non-gap atomic steel shows that it is beneficial to produce uniform annealing structure and enhance its isotropy. The forming property of magnesium alloy sheet was improved by cross rolling rolling. The above methods have also been applied in tantalum. The γ fiber texture in Ta plate is enhanced by cross rolling, which is beneficial to improve the tensile property. The grain size of Ta plate was refined by asynchronous rolling and the random texture distribution was obtained. The whole shear strain of Ta plate is introduced by equal diameter Angle extrusion to obtain the fine crystal structure of the block. However, this technology is limited by the sample size, so it is not mature in industry and has a narrow application.
