Tungsten carbide (WC) bonded by cobalt (Co) is a material of significant industrial and technological importance which has a unique combination of hardness and toughness inherited from the hard WC and ductile Co constituents. It is extensively used for various cutting, milling, drilling, and turning tools and, therefore, is important for today's industrialized society [1,2]. We employ classical molecular dynamics calculations, using reactive interatomic potentials based on an analytical bond-ordered scheme developed using experimental data and first principles calculations [3], to study the structure and dynamics at the WC(solid)–Co(liquid) interfaces upon manufacturing of cemented carbide. The molecular dynamics (MD) simulations are carried out using the Large-scale Atomic Molecular Massively Parallel Simulator (LAMMPS) package [4] to perform time integration of Nose-Hoover style non-Hamiltonian equations of motion which are designed to generate positions and velocities sampled from the canonical (NVT) ensemble.
First, we compute some thermodynamic properties of WC and Co substances through MD simulations to verify the performance of the analytical bond-ordered interatomic potential [2]. Supercells of WC and Co 70×70×70 containing ~82000 atoms are created and thermalized for 1ns to the desired temperatures in the range 1800–3000 K, with an increment of 100 K, using a time step of 1fs and an isothermal-isobaric ensemble (NPT). Subsequently we thermo equilibrate the system using a Langevin type thermostat for an additional 1 ns.
After the initial thermalizing of the system, a two-phase WC(solid)-Cu(liquid) system is created by cutting a piece of solid WC and embedding it into a corresponding hole cut in the supercell of liquid Co. The system is quickly equilibrated at each temperature in the considered range; subsequently an additional MD run is carried out for 2 ns to study the inter-diffusion processes at the WC(solid)–Co(liquid) interface. The inter-diffusion is analyzed using the Open Computer Vision Library OpenCV [5] and the Canny edge detection algorithm [6] to observe the interface properties and velocity during the liquid-solid interface MD simulations.
Dissolution of WC into the liquid Co is observed in our simulations, in agreement with previous studies. As a result, we also obtain the interdiffusion characteristics such as penetration depths and concentration profiles across the studied interfaces for temperatures of 1800–3000 K. Other interesting properties and behavior at the studied liquid–solid interfaces are to be discussed.

Keywords: diffusion, solid-liquid interface, atomistic simulation, molecular dynamics.

References:
    1. H. E. Exner, Physical and chemical nature of cemented carbides. Int Mater Rev 24,149-73 (1979).
    2. Y. V. Milman, S. Luyckx, I. Northrop, Influence of temperature, grain size and cobalt content on the hardness of WC–Co alloys, Int. J. Refract. Met. Hard Mater. 17(1999). H. E. Exner, Physical and chemical nature of cemented carbides. Int Mater Rev 24,149-73 (1979).
    3. N. Juslin, P. Erhart, P. Träskelin, J. Nord, K. O. E. Henriksson, K. Nordlund, et al. Analytical interatomic potential for modeling nonequilibrium processes in the W–C–H system. J Appl Phys 98, 123520 (2005).
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    6. https://docs.opencv.org/3.4/da/d22/tutorial_py_canny.html