Plastic deformation of FeNi invar alloys

Abstract

We report on the deformation behaviour of FeNi single crystals oriented for single slip in the temperature region between 77 and 610 K. Below the Curie temperature the critical shear stress of the Invar alloys increases much more rapidly than that of any f.c.c. substitutional alloy investigated till now. Simultaneously the activation volume decreases down to 10–20 b 3. Below the Curie temperature the stress-strain curves of the Invar crystals differ from those of other f.c.c. alloys. All results taken together indicate a dependence of the dislocation mobility on the magnetic properties of FeNi Invar. It is shown that the experiments cannot be understood with a simple magnetic friction stress arising from the interaction between the hydrostatic stress field of the edge dislocations and the stress dependence of the magnetization [3]. However, they can be described with an empirical friction law which had been introduced originally [18,19] for the case of strongly localized thermal activation, e.g. kink motion.