Effect of Cr content on thermally activated deformation in single-crystal micropillars of Fe-Cr binary alloys

This study identifies the role of solute Cr in the thermal activation process in the plastic deformation of alpha-(Fe, Cr) ferrite (BCC solid solutions) using micropillar compression tests for micron-sized single-crystals fabricated on various Fe-Cr binary alloys that were solution-treated at 1573 K. Fe-18%Cr single-crystal micropillars with a mean diameter d of similar to 2 mu m exhibited a relatively higher strain rate sensitivity (m) of 0.12 for the stress required for slip initiation. Larger Fe-18%Cr micropillars (d = 5 mu m) exhibited a lower m value of 0.04. The corresponding activation volume of 50 b(3) was equivalent to the millimeter-sized pure Fe and Fe-18%Cr alloy specimens (60-70 b(3)), indicating the prevalence of a general mechanism involving dislocation motion (kink-pair nucleation of screw dislocations). This mechanism controls the thermal activation process of plastic deformation in the Fe-18%Cr alloy, which has sufficient sources for dislocation multiplication. In the Fe-25%Cr and Fe-40%Cr single crystal micropillars, a less pronounced size-dependent m value (0.01-0.03) was determined, almost independent of specimen size. The corresponding activation volumes of large micropillars (74-77 b(3)) were similar to those of millimeter-sized specimens, which indicates a mild effect of solute Cr atoms on the thermal activation process of dislocation motion in Fe-Cr binary alloys at ambient temperature. Initial dislocations, rather than Cr content in Fe-Cr binary alloys, led to the low changes in size-dependent activation volume of Fe-Cr alloys with higher Cr content. Planar faults (Cr-enriched regions) were observed in Fe-40%Cr alloys, which may become sufficient sources for dislocation nucleation. However, the influence of Cr-enriched regions on dislocation motion remains unclear.