Estabilidade microestrutural da liga Cu-0,8Cr-0,07Zr após extrusão em canal angular em temperatura criogênica

Abstract

Severe Plastic Deformation (SPD) are well established routes with regard to the intense microstructural refining of metals and alloys up to the submicrometer (< 1 μm) and/or nanometer (< 100 nm) scales. Lowering the processing temperature is also a way to increase the severity of the imposed strain, favoring strengthening and grain refinement. Therefore, it is expected that the combination of SPD and temperatures on the cryogenic scale allow obtaining materials with higher strength. However, severely deformed microstructures at cryogenic temperatures have limited use due to their microstructural instability, a consequence of the high internal energy stored as crystalline defects (vacancies and dislocations). In order to study the mechanical behavior at low temperature and design severely deformed microstructures that are stable in the long term, the present work investigated the Cu-0.8Cr-0.07Zr alloy after Equal Channel Angular Pressing (ECAP) processing at -80 °C, in terms of microstructural stability, comparing it to pure copper processed under the same conditions. Regarding the mechanical behavior of the studied alloy, it was defined that there is the occurrence of both dislocation slipping and mechanical twinning, depending on the level of deformation and temperature. Post-ECAP results indicated that for the Cu-0.8Cr0.07Zr alloy it was possible not only to overcome the obstacle of microstructural instability by post-processing cryogenic ECAP processing, but also to provide an additional increase in the yield stress (+ 22%). Both effects were possible due to the formation of chromium-rich precipitates on a severely deformed microstructure, which hindered the movement of dislocations and grain boundaries. Thus, this set of results allowed us to understand about the strengthening mechanisms, microstructure evolution and thermal stability of the Cu-0.8Cr-0.07Zr alloy, useful for practical applications of materials processed by cryogenic DPS.