Microstructure of WC reinforced nodular cast iron composites and its effects on tribological behavior

WC particles reinforced nodular cast iron composites (WC/NCI) with WC and spheroidal graphite distributing homogenously in the matrix were fabricated by casting, and their microstructure and tribological behavior were investigated. The results indicated that the addition of WC significantly affected the microstructure of nodular cast iron. The graphite nodule count increased but their size decreased with increasing WC. The matrix of WC/NCI composites was consisted of upper bainite, retained austenite, a small amount of ferrite surrounding spheroidal graphite, and a limited quantity of eutectic carbides (Fe₄W₂C or Fe₃W₃C). The upper bainite increased but ferrite and eutectic carbides decreased with increasing WC. Consequently, the hardness and compressive yield strength of composites was greatly improved with the increasing WC. The composite containing 30 vol.% WC exhibited the best wear resistance, which was closely related to its low friction coefficient resulting from the presence of graphite on the tribo-surface and high hardness. The abrasive wear and surface fatigue failure were detected for the composites containing 10 vol.% and 20 vol.% WC. However, the abrasive wear was effectively suppressed and surface fatigue was alleviated for the composite containing 30 vol.% WC due to the increasing WC in the matrix. Therefore, only slight spalling was observed for the composite containing 30 vol.% WC.