Nucleation and motion of kink pairs on partial dislocations were examined by elasticity theory for materials with a high Peierls stress. Two approaches were used: one considers the change in average stacking-fault energy due to alloying elements and the other considers the change in local stacking-fault energy due to a nearby solute atom. Both approaches highlighted the role played by the stacking-fault energy in kink nucleation, propagation and annihilation and both furnished the strain rate as a function of stress, temperature and stacking-fault energy. Model predictions were compared with yield stress data for 2 systems: firstly, an intermetallic, MoSi2, which softens for alloying elements (V, Nb, Cr, Al) that decreased the stacking-fault energy and hardened for Re additions that increased the stacking-fault energy; secondly, a ceramic oxide, MgO-Al2O3 spinel, which softens with increasing addition of excess alumina and at the same time exhibited a decrease in stacking-fault energy. The average stacking-fault energy approach agreed qualitatively with the data while quantitative agreement was obtained with the local stacking-fault energy approach. The possibility was considered that the model applied to other materials, such as TiAl, HfV2 and Fe3Al, which exhibited softening with certain alloying additions. One requirement was that the dislocations were dissociated by more than a few atomic distances; otherwise kink nucleation occurred on the perfect dislocation (or simultaneously on both partials). Hence the model did not apply to materials such as body-centered cubic metals which only had a core dissociation. Normal hardening effects of solutes from size and modulus misfits were additive with any softening effects from a decrease in stacking-fault energy and so might mask the latter, as occurred for W additions to MoSi2.

Nucleation of Kink Pairs on Partial Dislocations - a New Model for Solution Hardening and Softening. T.E.Mitchell, P.M.Anderson, M.I.Baskes, S.P.Chen, R.G.Hoagland, A.Misra: Philosophical Magazine, 2003, 83[11], 1329-46