Synergetic Strengthening of Grain Refinement and Texture in Gradient Zircaloy-4 by Surface Mechanical Rolling Treatment
- PDF / 3,603,811 Bytes
- 11 Pages / 593.972 x 792 pts Page_size
- 79 Downloads / 216 Views
JMEPEG https://doi.org/10.1007/s11665-019-04358-8
Synergetic Strengthening of Grain Refinement and Texture in Gradient Zircaloy-4 by Surface Mechanical Rolling Treatment Chao Xin, Qiaoyan Sun, Lin Xiao, and Jun Sun (Submitted January 28, 2019; in revised form August 10, 2019) A Zircaloy-4 rod was subjected to surface mechanical rolling treatment (SMRT) to form a gradient structure, and the evolution of the resulting sub-grain-boundary property and texture across the gradient structure was characterized using electron backscattered diffraction. Dual-gradient structures in grain size and orientation were formed; the grain size was refined from several microns at the center to approximately 400 nm at the topmost surface. Texture analysis revealed that the c-axis gradually tilted from a random orientation toward the parallel-to-radial direction on the radial–tangential plane. The SMRT-induced formation of the dual-gradient microstructure is attributed to the formation of gradient distributions of stress and strain, which resulted in various deformation mechanisms (twinning and dislocation) being active at different depths. During the SMRT process, twinning and dislocations were activated to refine the grains. When the dual-gradient microstructure formed, twinning was mainly activated at the subsurface near the matrix, whereas dislocations were activated across the entire gradient. The geometrically necessary dislocation density increased with decreasing depth and then slightly decreased near the surface. The synergetic strengthening of the dual-gradient microstructure resulted in a gradient distribution of the microhardness near the surface. Thus, the Zircaloy-4 rod exhibited a good combination of strength and ductility. Keywords
microhardness, microstructure gradient, nanomaterials, rolling, texture gradient, Zircaloy-4
1. Introduction Materials with a gradient microstructure have attracted considerable attention because of their remarkable ability to possess a superior combination of ductility and strength (Ref 18). Gradient structures can be defined as microstructures with macroscopic gradients of one or a combination of microstructural features including, but not limited to, grain size (Ref 1-8), texture (Ref 9), dislocation density (Ref 10), twin density (Ref 10), and precipitates. The most common and well-studied gradient structure is the grain-size gradient structure (Ref 1-8). Wu et al. (Ref 11) reported that under uniaxial tension, a grainsize gradient induces the formation of a macroscopic strain gradient and converts the applied uniaxial stress into multiaxial stresses because of the evolution of incompatible deformation along the gradient depth. The accumulation and interaction of dislocations are thus promoted, resulting in additional strain hardening and a clear increase in the strain-hardening rate. Such extraordinary strain hardening is inherent to gradient structures and does not exist in homogeneous materials. Li et al. (Ref 12) used a dislocation density-based theoretical model to quanti-
Chao Xin, Q
Data Loading...
