It was recalled that blocking of dislocations by multiple types of obstacle occurred in many engineering alloys. Theories had rationalized two different scaling laws for the total strength, tα = 1α + 2α, with α = 1 or 2, where 1 and 2 were the strengths of the two individual obstacle types. Simulations had clearly demonstrated α = 2, while so-called friction-strengthening had to correspond to α = 1. Here, line-tension simulations of dislocation glide through two types of point obstacle were performed to examine the friction limit. One obstacle type was weak (critical angle approaching 180°) but with very high density, approximately corresponding to solute strengthening; and the second obstacle type was stronger (smaller critical angle) but with lower density, approximately corresponding to forest or precipitate strengthening. Additive strengthening α = 1 was obtained when the densities of the two obstacle types differ by more than a factor of ~67, while a transition to α = 2 occurred with increasing density of the second obstacle. These simulations confirmed the long-held metallurgical wisdom regarding additivity of solute or friction strengthening with other strengthening mechanisms and also demonstrated that apparent intermediate scaling laws with 1 < α < 2 could arise for a range of relative obstacle densities. Investigation of several literature experimental studies showed some agreement with the model here but quantitative comparisons remained difficult.

Scaling of Dislocation Strengthening by Multiple Obstacle Types. Y.Dong, T.Nogaret, W.A.Curtin: Metallurgical and Materials Transactions A, 2010, 41[8], 1954-60