Exchange effects in Invar hardening: Fe0.65Ni0.35 as a test case - art. no. 184421

Art increase of the critical resolved shear stress of Invar alloys (Invar h ardening) with a lowering temperature is explained. The effect is caused by a growth of the exchange interaction between dangling d-electron states of dislocation cores and paramagnetic obstacles (e.g., Ni atoms in FeNi alloy s) that occurs below the Curie temperature. The spins of the two electrons align along the magnetization due to the exchange interaction with the surr ounding atoms of the ferromagnetic. The exchange interaction between the di slocations and obstacles is enhanced in Invars due to a strong growth of th e magnetic moments of atoms under the action of elastic strains near the di slocation cores. Parameters characterizing the exchange interaction are det ermined for the case of the Fe0.65Ni0.35 Invar. The influence of the intern al magnetic held on the dislocation detachment from the obstacles is taken into account. The obtained temperature dependence of the critical resolved shear stress in the Fe0.65Ni0.35 Invar agrees well with the available exper imental data. Experiments facilitating a further check of the theoretical m odel are suggested.