A TEM in situ study of alloying effects in iron. I-Solid solution softening caused by low concentrations of Ni, Si and Cr

In situ straining experiments were carried out in various FeNi, FeSi and FeCr alloys, between 95 and 300 K, in order to determine the origin of the softening effect of a low concentration of substitutional solute atoms in iron. Dislocations multiply and annihilate by glide in {1 1 0} planes and cross-slip, as in pure Fe. Curved non-screw parts are highly mobile, though they are subjected to a frictional stress which has been estimated. Straight screw segments have a slow and steady motion at all temperatures, corresponding to a classical kink-pair mechanism. In particular, they do not exhibit the transition to jerky motion that has previously been observed in pure Fe at low temperatures, and which has been correlated with the hump in the stress-temperature curve. Under such conditions, the softening effect is interpreted as being due to the shift of the transition and corresponding hump to lower temperatures, as in FeC.