Rolling technology is a kind of material forming common technology, widely used in the production of sheet or strip. During rolling, strain rate, strain per pass, total strain, and strain direction are important control parameters. In general, the sheets of multi-pass one-way rolling will form strong texture and produce anisotropy of mechanical properties. This is beneficial in some cases. For example, in the production of deep drawing low carbon steel, strong {111} {UVW} texture will be formed by one-way rolling, which is beneficial to improve the deep drawing property. However, in some cases, such as in the production of sputtering targets, there is a tendency to obtain random textures with no preferred orientation, i.e. isotropic materials. This is difficult to obtain through traditional thermal mechanical processing. In order to reduce or eliminate the anisotropy caused by unidirectional rolling, many new rolling methods have been developed, including strain reversal rolling, cross rolling, asymmetric rolling, etc. The results show that by changing the strain path, the deformation microstructure and dislocation morphology can be changed, the texture can be weakened, and then the subsequent annealing and recrystallization process can be affected. It is an effective means to control the microstructure and texture of the material.
The demand of high purity
tantalum (
Ta) as a sputtering target for integrated circuits is increasing. Traditional one-way rolling method produces typical {111} {uvw} fiber texture in
Ta plate, while cross rolling method can produce strong {100} {uvw} texture. However, after annealing, the recrystallized Ta plate produced by the above method tends to have texture gradient or texture band along the thickness direction. This is extremely harmful to the sputtering performance of the target material. In order to improve the uniformity of microstructure and eliminate the influence of orientation on rolled products, Ta plates were prepared by multi-direction forging and cross rolling. And adopt the method of continuous change rolling direction (after a time before a time compared to the rolling direction of the rolling direction clockwise rotate 135 ° Angle, referred to as circumferential rolling) preparation of Ta, by controlling the processing time or quantity each time and get the two sets of rolling deformation zone shape parameters, studied the deformation zone shape parameters on the Ta plate rolling texture and the influence of annealing on microstructure uniformity. The texture of the surface layer and intermediate layer of 8 and 16 passes rolled
tantalum plates were characterized by XRD, and the annealed microstructure was observed by EBSD technique.
Two groups of deformation zone shape parameters were obtained by controlling the rolling reduction of each pass. The sample with 70% deformation was obtained by circumferential rolling of the high purity tantalum plate, and the sample was subjected to vacuum annealing (1050/1 h).X-ray diffraction (XRD) technique was used to measure the macrotexture of the surface layer and the intermediate layer of the rolled samples. The microstructure and microtexture of the rolled samples along the thickness direction were characterized by backscattered electron diffraction (EBSD) technique. The microstructure and texture of the annealed samples were also characterized by backscattered electron diffraction (EBSD).The results show that the large deformation zone shape parameters (2.01~3.29) introduce obvious shear strain on the surface of the rolled plate, and serious texture gradient is easily generated along the thickness direction of tantalum plate. The surface layer of tantalum plate forms {HKL} {110} texture and {100} {uvw} texture, and the middle layer forms strong {111} {uvw} texture. Smaller shape parameters (1.67~-2.28) are beneficial to produce uniform deformation, which can effectively weaken the {100} {uvw} texture and strengthen the {100} {uvw} texture in the middle layer. The enhanced {100} {UVW} texture in the rolled microstructure can inhibit the abnormal growth of {111} {UVW} orientation recrystallized grains, which is beneficial to the refinement of microstructure.
