A combinatorial approach is employed to investigate the atomic and electronic structures of a metal vacancy in titanium carbide. It turns out that the usual relaxed geometry of the vacancy is just a metastable state representing a local energy minimum. Using ab initio calculations and by systematically searching through the configurational space of a Ti monovacancy, we identify a multitude of local minima with reconstructed geometry that are lower in energy. Among them, there is a planar configuration with two displaced carbons forming a dimer inside the vacancy. This structure has the optimal number and order of C-C bonds making it the global minimum. Further calculations show that this reconstructed geometry is also the ground state of metal vacancies in other carbides such as ZrC, HfC, and VC. The reconstructed metal vacancies are characterized by localized electron states due to the relatively short C-C bonds. The defect states lie just below the upper and lower valence bands. The existence of reconstructed vacancy configurations is essential for understanding the mechanism of metal self-diffusion in transition-metal carbides.

Vacancy defects in Group 4 and 5 transition metal carbides are studied employing ab initio calculations to obtain the energies of formation of Schottky defects as well as the interaction energies for the pair of vacancies in various spatial arrangements. The present calculations take into account the recently established fact that metal vacancies in these compounds may undergo a reconstruction where the octahedron of carbons surrounding the metal vacancy transforms into a lower-symmetry structure stabilized by formed C–C bonds. This reconstruction significantly lowers the formation energy of Schottky defects in cubic carbides of transition metals and also qualitatively changes the interactions between a metal vacancy and a carbon vacancy, from strong attraction to strong repulsion in the nearest-neighbor shell. The latter result removes the problem of vacancy clustering, that results from the assumption of unreconstructed geometry, and restores the usual view of a Schottky defect as a pair of dissociated vacancies in the studied equiatomic compounds.

Metal self-diffusion in cubic transition-metal carbides exhibits anomalously high activation entropy(∼10–14.5 kB ), unexplained by conventional vacancy or cluster models. Using ab initio molecular dynamics (AIMD), we reveal that the reconstructed ground-state metal vacancy in TiC—a planarC–C dimer (2G structure)—undergoes thermally activated dimer rotation above 1800 K. This dynamic degree of freedom generates significant configurational entropy, contributing up to 8 kB pervacancy. We further compute temperature-dependent Schottky defect formation free energies from 500 to 3000 K, showing a reduction from 7.4 eV at 0 K to ∼3.8 eV at 2500 K due to vibrational and configurational contributions. Supercell size effects are clarified: 2×2×2 cells yield a 1.5 eV overestimate due to artificial vacancy–vacancy repulsion under periodic boundaries, resolved using 3×3×3cells. These findings establish a monovacancy-mediated diffusion mechanism with high entropy, resolving a decades-long discrepancy in TiC and related carbides

Inter-diffusion between the hard ceramic and ductile metallic phases in composite materials such as cemented carbides governs their mechanical properties. Understanding atomic-scale diffusion at these interfaces is key to uncovering the mechanisms that dictate microstructure evolution, establishing a foundation for tailoring the properties of WC Co composites through precise interfacial control. The interface between tungsten carbide (WC) and liquid cobalt (Co) is investigated using molecular dynamics simulations. An integrated approach is presented for computing the solid–liquid interfacial free energy by combining computer vision aided interface detection with the Capillary fluctuation method. Significant inter-diffusion is observed, with atomic displacements primarily localized at the interface for W and C, while Co exhibits homogeneous behavior in the liquid phase. The formation of C C bonded structures at the interface is identified as a critical factor influencing diffusion, introducing localized structural rigidity that reduces atomic mobility. Additionally, premelting phenomena below bulk melting temperatures gives rise to a heterogeneous interfacial zone containing residual solid WC patches and molten W-Co alloy. The inter-diffusion coefficients for W, C, and Co compare well with prior computational and experimental studies, validating the methodology. These findings offer new insights into the atomic-scale mechanisms driving interface evolution and provide a foundation for tailoring the properties of WC Co composites through precise interfacial control.

The dissolution behavior of tungsten carbide (WC) particles in liquid cobalt is investigated using ab initio and classical molecular-dynamics calculations. It turns out that at the atomic level there is a complex interplay between surface properties, bulk diffusion, and dissolution. It is found that carbon-rich shells form around dissolving WC particles, creating a semidissolved state. The dissolution process is decelerated by trapping carbon atoms via the formation of carbon-carbon bonds, both on the surface of dissolving particles and in the surrounding semidissolved shell. Upon reaching a critical particle radius, the dissolution rate sharply increases, driven by changes in the number of carbon-carbon bonds, resulting in a premelting behavior. The existence of a semidissolved shell and premelting behavior advance our understanding of dissolution mechanisms at the atomic scale and can be applicable for controlling dissolution processes that are an important part of coarsening of WC particles, a phenomenon taking place during cemented carbide manufacturing.

Focusing on the reconstruction of metal (W) and carbon (C) vacancies, we systematically analyze their impact on diffusion processes critical to microstructural evolution in WC-Co cemented carbides. We investigate the role of vacancy-mediated diffusion in hexagonal tungsten carbide (WC) using a combination of ab initio molecular dynamics (AIMD) and classical molecular dynamics (MD )simulations. AIMD simulations reveal spontaneous formation of C–C bonds within W vacancies, forming dimers, trimers, and tetramers with bond lengths of 1.4 ˚A to 1.9 ˚A, which stabilize defect structures and hinder carbon diffusion. Classical MD simulations, employing an analytical bond-order potential, demonstrate a nonlinear reduction in carbon diffusion coefficients by up to 40% at moderate W vacancy concentrations (up to 0.06%) and temperatures below 2800 K, following a power-law dependence D ∝ N −αv (α ≈ 0.6). In contrast, C vacancies exhibit minimal C–C bonding and diffusion coefficients close to defect free WC. At higher temperatures (≥ 2800 K) and vacancy counts (≥ 2500), thermal energy disrupts C–C bonds, leading to enhanced, Arrhenius diffusion. These findings shed light on the atomic-scale mechanisms governing diffusion in WC, offering insights into optimizing sintering processes and mechanical properties of cemented carbides.