Effects of orientation and temperature on deformation behavior of Fe0.19Ti0.39Mn single crystals

Abstract

The orientation dependence of the critical resolved shear stress (CRSS) of Fe0.19Ti0.39Mn single crystals was investigated at temperatures between 77 and 373 K (−321 and 212 °F). Three orientations were chosen so that slip could be examined on {110} planes (orientation D) and {112} planes in the twinning (orientation A) and antitwinning (orientation B) directions. The shear stress-shear strain behavior of these crystals was compared with previous results for Fe0.16Ti and ZrH 2-purified iron crystals of similar orientations. The effect of the addition of manganese to the FeTi crystals was to produce solid solution hardening at 295 and 373 K (72 and 212 °F) and solid solution softening at 195 K (−108 °F). At temperatures below 295 K the FeTiMn crystals showed significantly greater uniform shear strains than the FeTi crystals for all orientations and at 143 and 195 K the FeTiMn crystals of orientations D and B exhibited greater uniform shear strain than the iron crystals of these orientations. At these temperatures the FeTiMn and iron crystals of orientation A had similar uniform shear strains. At 77 and 143 K there was no appreciable orientation dependence of the CRSS in the FeTiMn or the FeTi crystals, in sharp contrast with the pronounced orientation dependence of the CRSS in the iron crystals. This lack of an orientation dependence of the CRSS in the FeTiMn and FeTi crystals is in qualitative agreement with extended core impurity models of the low temperature deformation behavior in b.c.c. metals because of the expected slightly lower mobile interstitial content in the titanium-gettered FeTiMn and FeTi crystals than in the ZrH 2-purified iron crystal. However, the expected difference in mobile interstitial contents is only a few parts per million and there are no quantitative models that can account for such small mobile interstitial contents which give rise to large differences in the orientation dependence of the CRSS.