Revealing the evolution mechanisms of microstructure, texture and mechanical behavior in Zr702 alloy plates fabricated by accumulative roll bonding

Abstract

In the present work, the influence of number of cycles on microstructure, texture and mechanical behavior of Zr702 plates has been systematically studied using the accumulative roll bonding (ARB) method. Electron back-scatter diffraction and transmission electron microscopy have been used to study the development of microstructure and texture. Results show that the {0001} bimodal texture is obvious in all the samples. At the same time, the <112‾0> fiber is weakened and the <101‾0> fiber is strengthened gradually with the increase of ARB cycle number from 1 to 3. In addition, some unbroken coarse grains with c-axis close to normal direction can be observed in ARB samples. The reason for this phenomenon is that the prismatic <a> slips are not easily activated due to unfavorable orientation. The tensile test results along the rolling direction show that the strength increases and the elongation decreases with the increase of ARB cycle number. Compared with the as-received plate sample, the yield strength of ARB sample subjected to 3 cycles is increased by about 99%, while still maintain 7.4% of the elongation to fracture. In order to clarify the mechanical mechanisms during deformation, the back stress hardening caused by the heterostructure mixed with coarse and fine grains and substructure have been discussed in detail. In addition, the calculation results of Schmid factor (SF) show that prismatic <a> slip is the dominant slip mechanism in the deformation process of all samples. However, the average SF value of the basal <a> slip systems decreases with the increasing number of ARB cycles, which maybe another significant factor leading to the change of yield strength.