Strengthening by {110} and {112} edge dislocations in BCC high entropy alloys

Mechanical tests and microscopy studies on body-centered cubic (BCC) high entropy alloys reveal transitions from screw to edge dislocation slip and from {110} to {112} slip plane activity. Here, a strengthening theory for BCC edge dislocation slip on {112} planes is thus developed that parallels a recent theory for {110} slip. Using the atomistic dislocation pressure fields for four BCC elements (Nb, Ta, Mo, W) as proxies to span the range of likely alloy cores, theory predicts that the zero temperature yield strength for {112} slip is slightly lower (0%-20%) than that for {110} slip but that the associated energy barrier is slightly (0%-20%) higher. This leads to cancelling effects, and hence very similar strengths, at finite temperatures and strain rates. Full atomistic results on selected dilute binary alloys show some shifts in these trends, but with similar magnitudes and cancelling effects. The close strengths of {110} and {112} slip modes indicate that subtle aspects beyond the scope of the theory will determine which slip system controls the observed strengthening. This closeness in strength cements the use of the {110} edge theory for guiding alloy design independent of actual slip system.