Slip Versus Twinning Competition at {113}/<110> Crack Tip in BCC Iron: An Atomistic Simulation Study

The present study investigated the effect of temperature and Cr addition on the slip-twinning competition in BCC-Fe through molecular dynamics simulations. A sharp crack {113}/ $$\langle 110\rangle$$ with a crack plane {113} and crack tip $$\langle 110\rangle$$ was created. A tensile load with a strain rate of 108 s-1 was applied along the crack plane direction. Plastic deformation through twinning was noticed at two locations in the pure BCC-Fe system at T = 10 K, one at the crack tip and the other at the hard grip and the surface intersection region (surface region). A twinning to slip transition was noticed at T = 600 K at the crack tip due to the coupling of local stresses with thermal energy. However, the same transition was observed at a much higher temperature, 1000 K, in the surface region. A strong coupling between local stress concentration and thermal energy changed the deformation mode in BCC-Fe. Further, the effect of Cr on the deformation mode in BCC-Fe was studied at a fixed temperature of 10 K. Slip-stabilized twinning (slip followed by twin) was noticed at the crack tip and the surface region at 18 at.% Cr and 50 at.% Cr additions in BCC-Fe, respectively. Twinning to slip transition was noticed at the crack tip at 70 at.% Cr addition indicated the strong coupling between local and internal stresses. Further, twinning to slip transition in the entire Fe−70 at.% Cr binary alloy system was observed at 1300 K. Strong thermal energy, internal, and local stress coupling were noticed in the present study. The slip occurred through 1/2 $$\langle 111\rangle$$ type edge dislocation nucleation.