Dynamic phase transformation driven microstructure and texture development during deformation of Zr-2.5wt.%Nb in α plus β phase field

This work demonstrates and explains how, during the hot deformation of a Zr alloy in the two-phase field, the texture developed in the alpha phase is influenced by that developed in the beta phase. For this Zr-2.5wt.%Nb alloy was hot compressed in the alpha+beta phase field (700, 750 and 800 degrees C) at 0.1 s_ 1 to a true strain of 1.1. The microstructure and texture were characterized using scanning electron microscopy and electron backscatter diffraction. The flow curves showed a sharp drop in flow stress at epsilon approximate to 0.01 due to plastic deformation induced alpha ->beta phase transformation. At 700 degrees C, alpha-Zr developed (2113) parallel to compression axis (||CA) (as is commonly observed in alpha-Zr system), whereas at 750 and 800 degrees C (2110)||CA formed. At all studied temperatures, beta-Zr developed {001}(110) and {111}(110) texture components that were shown to be dependent on the elongated morphology of the alpha-Zr grains and not on the alpha-Zr texture. From experimental observations and thermodynamic calculations of the free energy changes in absence and presence of stress, it was shown that the formation of (2110)alpha_Zr||CA occurred by migration of beta-Zr into (2113)alpha_Zr followed by the reverse beta ->alpha transformation (through Burgers orientation relationship) driven by low flow stress in (2110)alpha_Zr and low Nb content in the transforming beta-Zr. It was concluded that the presence of beta-Zr with (001)||CA and (111)||CA is a necessary condition for the formation of (2110)||CA in alpha-Zr. In addition, temperature promotes the development of (2110)alpha_Zr through enhanced boundary mobility of beta-Zr into harder alpha-Zr.

Automated summary

This study demonstrates and explains the influence of beta phase texture on the alpha phase texture during the hot deformation of a Zr alloy in the two-phase field. The presence of beta-Zr and temperature both promote the development of the (2110) texture in alpha-Zr.