Unraveling the mechanism for thermal stability of a high-strength Cu alloy produced by a novel cryogenic ECAP route

Abstract

This investigation aimed to design a thermally stable microstructure of an ITER-grade Cu-0.7Cr-0.07Zr alloy. The chosen approach involved employing a novel Equal Channel Angular Pressing (ECAP) at cryogenic temperatures (CT), in which the temperature was strictly controlled, followed by subsequent ageing. Post-ECAP ageing at 400 °C for 15 min resulted in a substantial enhancement in yield strength in CT-processed specimens, with a remarkable increase of 22% in comparison to their pre-aged counterparts. Additionally, ageing under these conditions yielded a more stable microstructure at elevated temperatures, with average grain size variation below to 1 μm. The observed stability was attributed to the formation of fine Cr-rich precipitates during ageing that hinder grain boundary motion, thereby preventing grain growth and potential softening of the CuCrZr alloy. These findings elucidate a promising thermomechanical processing avenue for strengthening microstructures processed by cryogenic severe plastic deformation and/or exposure to elevated temperatures. Finally, the adopted processing route in this study not only facilitated but distinctly culminated in attaining the paramount strength/ductility relationship for CuCrZr alloys with a stable microstructure at medium-to-high temperature range.