Influence of microstructural features on the impact toughness of infiltrated Al2O3|P-steel composites

Application of Al2O3|P-steel MMCs as wear resistant components is often restricted due to their lack of toughness under impact stress. Therefore, the influence of the microstructural features on the impact toughness was studied for Al2O3|P-steel MMCs fabricated by Ti-activated melt infiltration. Composites differing in ceramic reinforcement fraction and size as well as in the steel matrix were evaluated by means of Charpy impact testing, tensile testing and microscopic analysis.Although, MMCs exhibit brittle fracture behaviour, local plastic behaviour was identified. Based on the results the effect of Al2O3-reinforement phase is not the primary factor to improve impact behaviour of MMCs. Ti-enrichment was identified as having the most crucial effect on the composite impact toughness. Enrichment of Ti-activator within the matrix steel as well as brittle Ti-rich precipitations combined with hardening of the steel due to melt processing decrease the MMC toughness drastically. Hence, a matrix steel insusceptible to precipitation hardening and Ti-enrichment or a reduction of Ti-activator amount are therefore key requirements to produce high-volume fraction MMCs with adequate impact toughness.