Concentrated solar energy for in-situ elaboration of wear-resistant composite layers. Part II: Tungsten carbide surface enrichment of common steels

Abstract

The present work constitutes the second part of a study concerning the application of Concentrated Solar Energy (CSE) for the in-situ elaboration of carbide-reinforced surface layers onto common steels, employing WC as a model system. As in the first part that involved titanium and chromium carbides as reinforcing compounds, “solar hardfacing” experiments were carried out in the solar furnace SF40, at the installations of Plataforma Solar de Almería (Spain). Parametric studies performed were targeted to clarify the effects of solar irradiation time and inert or reactive processing atmosphere on the structural integrity, microstructure, carbide dispersion and hardness of the surface layers obtained. The results were used, on the one hand to identify conditions for the elaboration of wear resistant surface layers and on the other hand to elucidate the fundamental mechanisms governing the dispersion of WC particles in a liquid ferrous matrix that is, subsequently, re-solidified. In contrast to the TiC particles, WC ones are subjected to liquid metal attack transforming progressively to mixed FeW carbides, as determined by scanning electron microscopy and X-ray diffraction. Under inert atmosphere, solar processing beyond a threshold time period decreases the in-depth homogeneity of the carbides dispersion and increases the extent of the attack, deteriorating hence the composite character of the layer obtained. Reactive nitrogen atmosphere mitigates the negative effects of prolonged exposure, allowing the elaboration of thick hardfacing layers. Finally, dry sliding friction tests allowed defining the friction coefficient and specific wear rate, as well as the synergy of the wear micro-mechanisms involved. These results complemented with the respective ones for titanium and chromium carbide-based hardfacing layers, provide a first framework for the rational and optimized elaboration of wear resistant carbide-based surface layers using concentrated solar energy.