[SY-N2] Symposium N-2

[SY-N2] Using free energy calculations and statistical mechanics to probe the brittle to ductile transition of bcc metals

Invited

^○Thomas Swinburne¹ (1.CINaM, CNRS/Aix-Marseille Univ., France)

The fracture response of bcc metals is known to be controlled by dislocation mobility, which in turn is dependent on the slow, thermally activated nucleation of kink pairs on <111> screw dislocations. We present a general, efficient scheme to calculate free energy barriers in large crystalline systems[1] which we apply to the kink nucleation process, finding significant anharmonic contributions at low homologous temperatures. A statistical mechanical approach is then used to study kink-limited dislocation motion through a field of obstacles[2]. We identify a crossover obstacle density below which the activation energy for plastic flow is half the free energy barrier for kink pair nucleation. Our results show striking agreement with fracture experiments across a wide range of bcc metals and are applied to interpret experimental data on irradiation induced embrittlement.
[1] TD Swinburne and M-C Marinica, Physical Review Letters 120 (13), 135503
[2] TD Swinburne and SL Dudarev, Physical Review Materials 2 (7), 073608