Crystallographic analysis of nucleation for random orientations in high-purity tantalum
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Shifeng Liua) College of Materials Science and Engineering, Chongqing University, Chongqing 400044, China; and Electron Microscopy Center of Chongqing University, Chongqing University, Chongqing 400044, China
Haiyang Fan Department of Mechanical Engineering, KU Leuven, Heverlee B-3001, Leuven, Belgium
Chao Deng and Lingfei Cao College of Materials Science and Engineering, Chongqing University, Chongqing 400044, China; and Electron Microscopy Center of Chongqing University, Chongqing University, Chongqing 400044, China
Xiaodong Wu and Qing Liu College of Materials Science and Engineering, Chongqing University, Chongqing 400044, China (Received 17 March 2018; accepted 9 May 2018)
Strain path changes during clock rolling cause more serious interaction between adjacent grains, resulting in the occurrence of interactive regions (IRs) with random orientations. Furthermore, plenty of new grains with relatively random orientations are introduced by the subsequent annealing of these IRs. The morphology of the IR and the origin of random orientations were therefore investigated in this study, and the electron backscatter diffraction technique was used to characterize crystallographic orientations of nuclei and deformed matrices. A short-time annealing was imposed on a specimen to catch the transient nucleation behaviors. The results indicate that the orientations of nuclei are similar to their surrounding deformed matrices, especially the points with larger local-misorientation. Additionally, the shape of new grains depends on where it forms, and it is suggested that this fact mainly results from the great difference in stored energies between deformed matrices with {111} and {100} orientations.
I. INTRODUCTION
The booming integrated circuit industry puts forward new demands on the quality of tantalum (Ta) sputtering targets. The sputtering rate depends highly on the crystallographic orientation of each grain due to the different density of clustering atoms at different crystal planes, and not the texture concentration but the randomization has favorable effects on the uniformity of films.1–4 Therefore, randomizing the recrystallization texture of Ta is necessary to improve the sputtering performance of targets. Recrystallization grains originate from the deformation microstructure, and the size, shapes, and orientations of recrystallization grains are related to the morphology and textures of deformed matrices.5–7 Thus the investigations on deformation microstructure, especially the methods to homogenize the microstructure and randomize the orientations of deformed matrices, are of significant importance. Our recent work reported that clock rolling can not only homogenize the deformation microstructure but also a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2018.164
randomize the recrystallization texture when compared with the unidirectional rolling.8–10 It is of great interest when the clock rolling, in which the specimen is rotated by 135° around the normal direction (ND)
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