A computational study of thin cubic carbide films in WC/Co interfaces

First-principles study of an interfacial phase diagram in the V-doped WC-Co system

“…53). The absolute value of a carbide/Co interface energy can change substantially (∼0.4 J/m 2 ) when treating Co as either ferromagnetic or nonmagnetic, 27,53 although the relative differences between various carbide/Co interfaces do not. 27 The influence of the magnetic state of Co will be further discussed in Sec.…”

“…As a function of the number of V layers in the segregation structure, the total interface energy converges to a sum of WC/VC and VC/Co interface energies within just two V layers. 3,27 For conditions where the bulk (V,W)C phase itself is thermodynamically unstable, this means that the maximal thickness of an equilibrium segregation structure should be limited to two metal atom layers and, therefore, we may restrict our modeling to include only such ultrathin structures.…”

“…(14) within the methodology presented in earlier papers. 3,[25][26][27] In the following, we will by γ k 0 refer to the thermodynamic ground state of the interface at T = 0, i.e., the lowest-energy configuration for given n W , n V , etc.…”

“…Several experimental studies of WC/Co and, in particular, WC(0001)/Co interfaces exist, [16][17][18][34][35][36][37][38][39][40][41][42][43][44] allowing for comparison between model and experiment. In our previous DFT modeling, we found the interface energy between pure VC and Co to be lower than that between WC and Co. 3,27 This energetic difference together with a good parametric fit between VC and WC is the underlying reason for the V segregation to WC/Co interfaces. 3,27 The current extended modeling allows us to calculate the WC(0001)/Co interface diagram, the segregated amount of V, and its effect on WC(0001)/Co interface energy as function of temperature and chemical potential of V.…”

“…For modeling of interfaces with complex bonding, DFT has proved its usefulness, 23,24 and the WC/Co interface has been previously studied by us with same method. 3,[25][26][27] In this paper, our previous modeling is extended by also including configuration free energies into an interface model which we explicitly couple with thermodynamic modeling of the W-C-Co-M system. Configuration free energies at finite temperatures are obtained from Monte Carlo (MC) simulations with interactions based on the cluster expansion (CE) method.…”