Comparison of Tribological Characteristics of LM13/B4C and LM13/Ilmenite Composites at High-Temperature Conditions

Abstract

In this work, high-temperature tribological characteristics of ilmenite-reinforced LM13 aluminum alloy–based matrix composites (AMCs) and boron carbide–reinforced AMCs are compared. Stir-cast composites were processed using boron carbide (covalently bonded discontinuous particles (CDP)) and ilmenite (natural discontinuous particles (NDP)) particles separately as reinforcements. The particle size range was 106–125 µm, and reinforcement levels were 5, 10, and 15 wt% for both types of composites. Both composites exhibited a uniform distribution of reinforced particles and grain refinement. Compared to the LM13 base alloy, NDP composite containing 15 wt% reinforcement showed significant improvement in hardness (57%), coefficient of friction (57%), mild-to-severe wear transition temperature, average steady-state wear-rate (49%), and coefficient of thermal expansion (55%). CDP-15 composite showed slightly better properties than NDP-15 composite. Microstructure refinement, increased dimensional stability, formation of the oxide layer, and formation of tribolayer due to reinforcement of the ceramic fillers were the main reasons for the improvement in properties of processed AMCs. Scanning electron microscope (SEM)-energy dispersive spectroscopy (EDS) of wear tracks-debris showed abrasive/delamination wear as the main mechanism for materials loss. The research showed that the low-cost ilmenite particles can substitute for the very costly boron carbide particles as reinforcements in AMCs used for dry sliding wear applications under high operating temperatures–applied load conditions of the order of 300 °C–49 N.