Formation mechanism of nano-sized η and ω structures in β phase in ECP treated Cu-40Zn alloy

Two nano-scaled hexagonal distortions in high temperature BCC phase during cooling is commonly observed in many alloys systems. Although efforts have been made on studying the lattice softening of the BCC structure during cooling, the distortion mechanisms are less addressed. Thus, the formation of two hexagonal structures in the beta precipitates in a Cu-40Zn alloy treated by ECP was thoroughly investigated. Results show that the beta precipitates contain two kinds of nano-sized and diffuse atomic clusters one with a eta structure obeying the Burgers OR and the other a omega structure obeying the Blackburn OR. They were each formed through a two-stepped atomic displacement. For the eta structure, the first step is the atomic shuffle of each second {110}(beta) plane in the <1<(1)over bar>0> (beta) direction and the second is a structure change mainly by a {1 (1 ) over bar2} < <(1)over bar>11> (beta) shear. For the omega structure, the first is an atomic shuffle on each second and third {11 (2) over bar}(beta) plane in the +/- [1 1 1 ](beta) directions and then normal strains in three mutually perpendicular directions. The concomitant formation of the two structures minimizes the lattice distortion of single formation. The present results provide new information on the formation mechanism of the two hexagonal structures in a BCC matrix. (C) 2022 The Authors. Published by Elsevier Ltd.

Automated summary

This study thoroughly investigated the formation of two hexagonal structures in Cu-40Zn alloy treated by ECP. The results show that these structures are formed through two-step atomic displacements, and their concomitant formation minimizes lattice distortion.