Plastic deformation of single crystals of Pt3Al with the L12 structure having a far Al-rich off-stoichiometric composition of Pt-29at.%Al

The plastic deformation behaviour of single crystals of Pt3Al with the L1(2) structure having an off-stoichiometric composition of Pt-29at.%Al has been investigated in compression from 77 to 1273 K. The L1(2) phase is stable at least down to 70 K at a composition of Pt-29at.%Al, in contrast to Pt-27at.%Al, in which transformation into a tetragonal phase occurs at around 220 K. Slip occurs along < 1 1 0 > both on (0 0 1) and on (1 1 1) with slip on (0 0 1) being the primary slip system that operates at considerably smaller critical resolved shear stress (CRSS) values in most crystal orientations, except for a narrow orientation region close to [0 0 1]. The CRSSs for both slip on (0 0 1) and (1 1 1) decrease rapidly with increasing temperature at low temperatures, and they are both higher for Pt-29at.%Al than for Pt-27at.%Al due to solid-solution hardening effects. Dislocations with b (Burgers vector) = dissociate into two collinear superpartials with b = 1/2 separated by an APB (anti-phase boundary) on the corresponding slip plane for both slip on (0 0 1) and (1 1 1). The large negative temperature dependence of CRSS for slip on (1 1 1) at low temperatures is not due to the motion of superlattice intrinsic stacking fault (SISF)-coupled superpartials with b = 1/3 < 1 1 2 > but is due to the Peierls mechanism acting on APB-coupled superpartials with a non-planar core structure. The core of APB-coupled superpartials gliding on (0 0 1) is considered to be planar, and hence, the large negative temperature dependence of CRSS for slip on (0 0 1) is due to solid-solution effects arising from the off-stoichiometric composition.