Microstructural evolution of rhenium Part II: Tension

Abstract

The microstructural evolution of Re under tension was investigated using EBSD, in-situ and ex-situ TEM. The samples had a texture that suppressed possible {112̅1}〈112̅6〉 twinning, while favoring <a> type 〈112̅0〉 basal dislocations during tensile straining. In-situ tensile straining was performed on rhenium both at room temperature and at 920 °C to investigate the low strain region of deformation, where it was found that <a> type b⃗=[112̅0] screw dislocations operated on the basal planes in loosely aligned slip bands. Through Schmidt factor analysis, EBSD had shown that pyramidal slip activated appreciably only at strain values above half of the failure strain. At failure stresses, <a> type b⃗=[112̅0] basal screw dislocations observed in dislocation slip bands and <c+a> type b⃗=[112̅3] pyramidal screw dislocations formed dislocation nets interfering with <a> type glide. HAADF STEM imaging was used to view the morphology of tension-induced {112̅1}〈112̅6〉 twins at higher strain values. Twin transmission with {112̅1}〈112̅6〉 twins changing twin planes between parent and matrix orientations was observed. The twin structure observed in tension were representative of classical twin structures, contrary to the {112̅1}〈112̅6〉 type twins seen in compression which consisted of twin aggregates. Our results suggest that the compression-tension asymmetry in Re is likely due to the twin favorability of the microstructure forcing the creation of many more twins during compression as compared to tension. The exceptionally-high work hardening rate in Re was found to be mainly due to large scale twin formation coupled with basal slip activity during initial straining.