Effect of trace solute titanium on plastic deformation of α-(Fe, Cr) single-crystal micropillars fabricated from 18Cr ferritic stainless steel

Abstract

Abstract The effect of a trace amount (~0.1 at.%) of solute Ti on the compression response of cylindrical single-crystal micropillars fabricated from a 18Cr ferritic stainless steel was investigated. The micropillars of the solution-treated steel samples were fabricated on a special grain with different diameter ranges (d = 2–3 μm or 5–6 μm). By this process, the flow stress required for slip initiation (corresponding to the yield stress) and its strain rate dependence could be determined. The compression tests on the micropillars revealed that Ti addition (solute Ti in the α-(Fe, Cr) ferrite matrix) has a slight effect on the activated slip system and stress level required for the slip initiation of 18Cr steel specimens with two different sizes. In addition, the strain rate sensitivity (m) of the yield stress at an offset strain of 0.2% (0.2% proof stress) in the small micropillars (d = 2–3 μm) of the micron-sized 18Cr steel specimens decreased slightly (from 0.12 to 0.08), owing to the Ti addition. However, the m value (0.04) of the large micropillars (d = 5–6 μm) of the 18Cr steel is unaffected by Ti addition and is equivalent to the m value measured for millimeter-sized specimens (conventional bulk specimens). The low activation volume (v*) values (18–19 b3) were obtained for the small micropillars of both the 18Cr and Ti-added steels. For the large specimens, the v* value of the 18Cr steel decreased slightly from 50 b3 to 46 b3 owing to the Ti addition and is close to the value obtained from the millimeter-sized specimens. These results indicate that the trace amount of solute Ti has a slight effect on the thermal activation process for controlling the dislocation motion in the 18Cr ferritic stainless steels. The intriguing low activation volume in the small micropillars is discussed in comparison with the results of micron-scale specimens of various bcc metals and alloys.