| Abstrakt: |
Single crystals of iron and its alloys with 0·5, 0·9, 1·8 and 3 wt% Si oriented for single slip have been cyclically deformed in tension-compression at plastic strains between 10-4 and 10-2. The effects of cyclic hardening, changes of specimen cross-section, slip traces and dislocation arrangements have been studied at 295 and 524 K and a strain rate of 1·6 x 10-3 s-1.The cyclic deformation of b.c.c. Fe-Si alloy crystals at both temperatures and of f.c.c. metal crystals shows similarly shaped cyclic hardening and cyclic stress-strain curves, and similar strain localization in the persistent slip bands (PSBs) and development of the dislocation arrangement.Unlike in f.c.c. metals, in Fe-Si crystals there is appreciable secondary slip at the beginning of the saturation stage, leading to a cell structure in PSBs. The dislocation cell structure is typical of PSBs throughout their whole existence. The surface relief of emerging PSBs also differs from that in f.c.c. metals.Changes in specimen cross-section take place during cyclic deformation. The changes are more marked in iron crystals than in Fe-Si crystals.In iron crystals at 524 K the plastic strain is localized in PSBs, which are similar to those in Fe-Si crystals. At 295 K the cyclic deformation of iron is significantly different to that in Fe-Si crystals and f.c.c. metals. The cyclic stress-strain curve exhibits two plateaux, and PSBs do not form.The similar cyclic deformation of Fe-Si crystals at 295 K and f.c.c. metals indicates the absence of the low-temperature regime of plastic deformation in Fe-Si crystals below their critical temperature. An explanation is given in terms of the dislocation mobilities, which are modified by the strong solution hardening in Fe-Si crystals with respect to iron. |
