Applied stress anisotropy effect on melting of tungsten: molecular dynamics study

Atomic-level insight into pre- and post- melting phenomena under complex stresses spanning compression, tension, and shearing in refractory metals is critical. The exploration of high temperature and melting behavior in tungsten under magnitude- and orientation-dependent uniaxial and biaxial compression and tension, approaching pure shear stresses was thoroughly investigated by molecular dynamics using extended Finnis-Sinclair potential. Using equilibrium solid-liquid coexistence simulations, we demonstrated the enhancement (reduction) of the melting point temperature T_m taking place with the increase of applied compression (tension) stress magnitudes, reaching a minimum under pure shear stress. Explored heating and melting behaviors under various stress types, magnitudes, and orientations were well supported by the corresponding trends in radial distribution function g(r) and Lindemann index δ. The highest resistance to melting was found under uniaxial compression likely due to bonds stiffening. On the other hand, the highest compliance to melting was revealed under pure shear stress, triggered by the accelerated vibrational instability and destruction of the bcc crystalline order driven by simultaneous shear deformation and formation of fcc and hcp phases.