Crack-Tip Deformation Mechanisms in α-Fe and Binary Fe Alloys: An Atomistic Study on Single Crystals

Abstract

Molecular statics simulations are employed using semiempirical interatomic interaction potentials to examine the near crack-tip deformation mechanisms in iron and iron alloy single crystals under pure mode-I loading. The deformation mechanisms are found to be strong functions of the crack orientation. For pure Fe systems, the sensitivity of the overall response is explored by comparing the behavior of a number of recently developed potentials. The competition between ductile and brittle responses is interpreted between the well-known Griffith and Rice criteria, but is found to be lacking in predicting a priori the qualitative failure mechanism near the crack tip. The influence of Ni and Cr additions as ordered substitutional solutes is probed at concentrations up to 9.375 at. pct, and several qualitative differences in crack-tip behavior are observed.

Three-dimensional crack initiation mechanisms in bcc-Fe under loading modes I, II and III

“…(4)-(6), we use the surface energies computed by Gordon et al [2] and Müller et al [22] for the empirical potential employed here. These authors found values of 1.65 J/m 2 for f011g surfaces, 1.79 J/m 2 for f001g surfaces and 1.91 J/m 2 for f112g surfaces.…”

“…Gordon et al [2] also calculated the unstable stacking fault energies for all slip systems in bcc Fe. Their results are given in Table 2.…”

“…(see e.g. [1][2][3][4][5][6]). These works reveal the nucleation of dislocations at or near the crack tip that act as carriers of matter away from it.…”

Origin of hydrogen embrittlement in vanadium-based hydrogen separation membranes

“…In the case of single crystals, simulation specimens with four different crack orientations were prepared as indicated in Table 1 [32]. The number of total atoms in pure vanadium specimen is around 200,000 and given amounts (5, 20 at%) of hydrogen atoms are randomly distributed into the tetrahedral interstitial sites to generate hydrogen charged specimens.…”

“…Through the mode-I crack propagation and mode-II dislocation emission simulations, it can be concluded that the most promising mechanism of hydrogen embrittlement in Table 1 e Summary of crack orientations considered for mode-I fracture simulations [32]. q is the angle between the direction of crack propagation and the slip direction.…”