Plastic deformation of single crystals of Pt_3Al with the L1_2 structure

Abstract

The plastic deformation behaviour of single crystals of Pt3Al with the L12 structure having an off-stoichiometric composition of Pt–27 at% Al has been investigated in compression from 77 to 1073 K. The L12 structure is not stable below around 220 K, transforming into either a D0c or D0c′ structure. Slip occurs along 1 1 0 both on (001) and on (111) with slip on (001) being the primary slip system, which operates for most crystal orientations except for near [0 01], accompanied by a considerably lower CRSS (critical resolved shear stress). The CRSS tends to decrease gradually with increasing temperature for both slip in the temperature range where the L12 phase is stable, except for a moderate increase in CRSS observed above 673 K for slip on (001). Dislocations with b = [1‾01] dissociate into two collinear superpartials with b = 1/2[1‾01] separated by an APB on the corresponding slip plane for both slip on (001) and (111). For slip on (111), dislocations tend to align along their screw orientation at room temperature, suggesting the high Peierls stress for their motion. The possibility of showing the normal (large negative) temperature dependence of CRSS at low temperatures as well as the reason for the absence of the anomalous (positive) temperature dependence of CRSS for slip on (111) at high temperatures is discussed.