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

Abstract

This study identifies the role of solute Cr in the thermal activation process in the plastic deformation of α-(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 ∼2 μm 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 μm) exhibited a lower m value of 0.04. The corresponding activation volume of 50 b3 was equivalent to the millimeter-sized pure Fe and Fe–18%Cr alloy specimens (60–70 b3), 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 b3) 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.