Mechanisms of microstructural evolution in high-volume TiC reinforced steel composites: Insights into particle coarsening, morphology, and thermochemical reactions

Titanium carbides reinforced steel matrix (TiC-steel) composites exhibit a range of excellent properties, including increased strength-to-weight ratio, high-temperature strength, and outstanding wear resistance. Prior research has demonstrated that the mechanical properties of TiC-steel composites are significantly affected by particle coarsening and the associated core-rim structure. Nevertheless, the fundamental mechanisms of thermochemical reactions that govern the formation of the final microstructure in these composites, including the core-rim structure, remain incompletely explored. This study elucidates the microstructure evolution mechanism of high-volume TiC-steel composites, particularly particle coarsening, through thermodynamic calculations and chemical analysis. The investigation unveils the coarsening process, shedding light on the formation of more stable phases and associated compositional changes, including the incorporation of substitutional elements and carbon depletion (resulting in low stoichiometry, x<1) within the newly developed (Ti,M)Cx. Additionally, the increased carbon content contributes to pearlite emergence within the steel matrix. Notably, key factors influencing the distinct morphologies observed in growing TiC particles are identified, attributed to variations in Mo, V, and W concentrations, as elucidated by rigorous thermodynamic and first-principles calculations. This study represents significant progress in understanding the intricate microstructure development of high-volume TiC-steel composites.