First-principles derived complexion diagrams for phase boundaries in doped cemented carbides

Abstract

This article reviews a method for calculating an equilibrium interfacial phase diagram depicting regions of stability for different interface structures as function of temperature and chemical potentials. Density functional theory (DFT) is used for interfacial energies, Monte Carlo simulations together with cluster expansions based on DFT results for obtaining configurational free energies, and CALPHAD-type modeling for describing the thermodynamic properties of the adjoining bulk phases. An explicit case, vanadium doped cemented carbides, is chosen to illustrate the progress in the research field and the interfacial diagram, a complexion diagram, for the phase boundary WC(0001)/Co is constructed as function of temperature and chemical potentials.

Grain Boundary Complexions and Phase Transformations in Al- and Cu-Based Alloys

“…When the first evidence of the presence of GB phase transformations appeared, these experimental findings are discussed in terms of transitions "pure (or dry) GB → few nanometer thin GBF → thick GB layer of bulk phase". Later, it has been shown that the variety of possible GB states (called complexions) is much richer (see for example References [17,[19][20][21][22][23][24][25][26][27]87,169,170]). One can imagine the transitions from clean GB to single-layer GBF, then to bi-layer, tri-layer etc.…”

“…One can imagine the transitions from clean GB to single-layer GBF, then to bi-layer, tri-layer etc. [17,[19][20][21][22][23][24][25][26][27] Some of these transition lines can finish not only at the lines of bulk transitions but also in critical points in the middle of one-phase area of a bulk phase diagram [17,19,20,23,27,87].…”

“…However, it is not the only unique possible construction to explain the upper point. The Al-Zn system opens many possibilities to construct the lines for GB complexions transitions [17,[19][20][21][22][23][24][25][26][27]87,169,170].…”

“…% Ni polycrystal suddenly increases from 0.3-0.37 at 600-750 • C to 0.6 at 900 • C. Moreover, some microtwins are visible even in UFG samples after HPT (shown by arrows in Figure 1c). Thus, the changes in GB character distribution during grain growth, as well as a certain input of abnormal grain growth, can serve as an indication of GB complexions transitions [17,[19][20][21][22][23][24][25][26][27]87,169,170]. Of course, this phenomenon is only an indirect indication of possible GB complexions transition because the increase of the portion of less mobile low-Σ GBy during grain growth cannot be called unexpected by temperature increase above 0.5 T m .…”

“…Different reviews discuss the experimental works done after the predictions of References [1,2], and various aspects of GB phase transitions have been studied [3][4][5][6][7][8][9][10][11][12][13]. As one of the important results of these works, the new additional lines of GB phase transformations appeared in conventional 3D-phase diagrams [14][15][16][17][18][19][20][21][22][23][24][25][26][27]. It was quite simple to study the GB phase transformations in the two-phase (or multiphase) regions of the bulk phase diagrams.…”