INVESTIGATION ON MECHANICAL AND DRY SLIDING WEAR BEHAVIOUR OF ALUMINUM HYBRID COMPOSITES REINFORCED

摘要

Aluminium matrix composites have been reinforced with Boron carbide (B4C) and Graphite (Gr) for increasing mechanical properties, wear resistance and ultimate tensile strength and reducing the density. Addition of Boron carbide (B4C) improve both strength and wear resistance of composite, but, addition of B4C alone in higher amounts makes the composite brittle and machining difficult. Thus, B4C can be advantageously used as a reinforcement to overcome the problem of strength reduction in Gr reinforced composites, resulting in hybrid composites. Aluminium matrix composites reinforced with up to 12 wt B4C and 3 wt Gr particulates are investigated in the present study. Addition of boron carbide and graphite particles reduces the density of hybrid composites thus resulted in a light weight hybrid composites suitable for automobile applications. Hardness and tensile strength of the hybrid composites increased with an increase in weight fraction of boron carbide. Composite with !2wt.%B4C/3wt% graphite reinforcement showed a significant increase in hardness and correlate well with strength and wear resistance. % Elongation decreased in a linear fashion with increasing reinforcement and AI/9B4C/3Gr hybrid composite showed a reduction in ductility when the B4C content was increased from 0 to 12 wt%. Dry sliding wear and friction behavior of unreinforced alloy and hybrid composites showed that the wear rate increased with increasing load and the highest wear was observed at 30 N for all the three sliding speeds (1 to 3 m/s). Maximum wear rate was observed in unreinforced Al alloy (Al) and the lowest in AI/9%B4C/3%Gr composites which can be attributed to the significant improvement in resistance due to presence of B4C and graphite particles. Increasing percent B4C reinforcement promotes stronger material transfer from the counter face. Oxidation due to high interfacial temperature resulted in the formation of a protective Mechanically Mixed Layer (MML). Wear resistance increased with increasing B4C reinforcement upto 9 per cent in the composites and mixing B4C beyond 9% decreases the wear resistance. Among the hybrid composites, AI/9B4C/3Gr hybrid composite exhibited the highest wear resistance and lowest COF for all applied loads. SEM fractograph showed mixed morphology involving brittle fracture and debonding of boron carbide particles, growth and coalescence of voids in the matrix and brittle transgranular fracture. SEM micrograph showed that reinforcement of hard B4C resulted the decreased groove width as well as debris formation due to the improvement in load carrying capacity of composite, thus enhanced the abrasion resistance of composites and thus the decreased wear rate.