Premelting in dissolution of cemented carbides

The dissolution behavior of tungsten carbide (WC) particles in liquid cobalt is investigated using 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.