Anomalous Deformation and Recrystallization Phenomenon in {111} Grains in Clock-Rolling Tantalum Sheets
- PDF / 1,931,239 Bytes
- 5 Pages / 593.972 x 792 pts Page_size
- 1 Downloads / 164 Views
Computations with the Taylor model indicate that shear strain occurred on a few slip systems in {111} grains in a 70 pct clock-rolling sample, which may explain the formation of a heterogeneous deformation microstructure, i.e., well-developed microbands and microshear bands, whereas more slip systems were required to accommodate the strain in {111} grains in the 87 pct clock-rolling sample. The higher stored energy and grain subdivision in the 70 pct sample result in faster recrystallization kinetics upon annealing. The microstructure homogeneity of tantalum (Ta) plate is critical for high-quality sputtering targets used in integrated circuit fabrication. Rolling combined with annealing is a fundamental large-scale and high-efficiency technology to process Ta plates in industry. Severe through-thickness texture gradients, texture clusters, and residual deformation bands often exist in Ta sheets by conventional rolling (i.e., unidirectional rolling) and annealing,[1–3] which is unfavorable for a sputtering target.[4] Recently, Liu et al.[3,5,6] demonstrated that 135 deg clock rolling (sequentially changing the rolling direction by 135 deg around ND) was effective to alleviate the microstructure inhomogeneity introduced by conventional rolling. Interestingly, an anomalous phenomenon was observed when the 135 deg clock-rolling samples with different deformation strains
JIALIN ZHU, SHIFENG LIU, YAHUI LIU, SHUAI YANG, XUANTONG QUAN, ADRIEN CHAPUIS, and LIU QING are with the College of Materials Science and Engineering, Chongqing University, Chongqing 400044, P. R. China. Contact e-mails: [email protected], [email protected] Manuscript submitted July 31, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
were annealed. That is, the {111} grains in the 70 pct sample demonstrated a considerably faster recrystallization rate than that in the 87 pct sample. Dislocation slip is the primary deformation mechanism in Ta characterized by ultrahigh SFE (220 mJ/m2).[7,8] During conventional rolling, {111} deformed grains {h111i//normal direction (ND)} usually contain microbands (MBs) owing to inhomogeneous deformation caused by a limited number of activated slip systems.[6,9] Microshear bands (MSBs), more severe strain localization into narrow bands, will further operate to share surplus high-density dislocations since MBs cannot accommodate the strain effectively owing to increasing strain.[10] Chen and Colleagues[11] demonstrated that well-developed MBs were formed in the {111} grains in Ta-2.5W alloy when the reduction reached 20 pct, and MSBs appeared when deformation increased to 40 pct. The appearance of MSBs and MBs within the {111} grains due to the continuous trapping of mobile dislocations significantly increases the stored energy, which depends on the configuration of dislocations and their density. More MSBs and MBs appear in the {111} grains to further allow plastic flow due to increasing deformation. Upon annealing, recrystallized nuclei preferentially appeared in the {111} grains, particularly in the region with MSBs as
Data Loading...
