Concentrated solar energy for in-situ elaboration of wear-resistant composite layers. Part I: TiC and chromium carbide surface enrichment of common steels

Abstract

Having already demonstrated the feasibility of using Concentrated Solar Energy (CSE) as a high temperature heat source for the in-situ elaboration of composite surface layers onto steel base metal, the present study focuses on the comparative evaluation of such “solar” titanium and chromium carbide hardfacings with respect to their microstructure characteristics and tribological performance. TiC and Cr3C2 powders were pre-deposited onto common steel base metal and the effects of solar irradiation time and repetition of solar exposure on the obtained microstructure of the surface layer were used as criteria for determining an adequate solar processing path for each specific carbide type. In the case of TiC powder, a single-step solar processing was sufficient to induce homogeneous dispersion of the carbide particles and, hence, surface reinforcement. For the Cr3C2 powder, single-step solar processing above a certain threshold solar processing time period was found to be necessary for the complete incorporation of the chromium carbide within the liquid metal pool, resulting in, however, carbides dissolution and surface alloying rather than carbides dispersion within the ferrous matrix. Thus, a second step of solar exposure of the previously obtained surface alloy above temperatures sufficient to cause re-melting, is necessary to obtain primary chromium carbide precipitates that provide the high wear resistance required. This was, indeed, demonstrated via dry sliding friction tests performed against an Al2O3 ball during which both “solar” surface layers exhibited relatively low specific wear rates. Microscopic observations on the worn surfaces indicated the synergy of distinct wear micro-mechanisms, different for each carbide particle type dispersed in the metallic matrix. These results in combination with the respective ones for WC-based hardfacing layers obtained via the same route and reported in the second part of this study, assist to identify the crucial metallurgical reactions that govern the successful implementation of the proposed “solar” technology.