Effect of B2O3/TiO2 Mole Ratios in Al-TiO2-B2O3 Reaction System on the Wear Resistance of in-situ Exothermic-Dispersion Reaction Synthetic Al-Based Composites

A series of Al-based composites were fabricated from the Al-TiO_2-B_2O_3 reaction systems of different B_2O_3/TiO_2 mole ratios, using exothermic dispersion in-situ synthesis. A pin-on-disc test rig was performed to evaluate the wear resistance of the resulting Al-based composites sliding against AISI52100 steel unlubricated condition at ambient temperature. An optical microscope and a scanning electron microscope were used to observe the microstructure of the Al-based composites and the morphologies of the worn surfaces and worn cross-sections. The results indicated that the wear mass loss of the Al-based composites increased almost linearly with increasing sliding distance. It increased with increasing sliding velocity until coming to the maximum at a velocity of 0.9 m/s, then it slightly decreased with further increase of the sliding velocity. The incorporation of B_2O_3 in the reaction system helped to improve the wear resistance of the Al-based composites, thus the wear resistance of the composites increased with increasing B_2O_3/TiO_2 mole ratio in the reaction system. The reinforcements were composed of Al_2O_3 particulates and rod-like Al_3Ti in the absence of B_2O_3 in the reaction system, in this case the corresponding composite had poor wear resistance, because of the severe ploughing action of the wear debris detached from the Al_3Ti rods. With increasing B_2O_3/TiO_2 mole ratios in the reaction system, the amount of Al_3Ti rods decreased, which was beneficial to decrease the grain size of the matrix grains finer, therefore the strength and plasticity of the composites were greatly increased. Moreover, the Al-based composites made from the Al-TiO_2-B_2O_3 reaction systems of different B_2O_3/TiO_2 mole ratios had differences in terms of the wear mechanisms as well. Namely, the Al-based composite made in the absence of B_2O_3 was dominated by abrasive wear and slight adhesion wear, while that made at a B_2O_3/TiO_2 mole ratio of 1.0 was dominated by adhesion wear and slight abrasive wear.