Synthesis, Characterization, and Dry Sliding Wear Characteristics of LM27 Alloy Based AMCs with Ceramic Fillers

Abstract

The present research work deals with the processing of hybrid aluminium matrix composites containing ceramic particle reinforcements. Addition of ceramic particles to aluminium alloys result in reduction of wear rate of the resulting composites due to the high hardness of ceramic particles. The main objective of the present dissertation was to study the effect of addition of sillimanite, rutile, and a blend of both sillimanite and rutile particles on the dry sliding wear characteristics of as-cast LM27 aluminium alloy. In this work, the LM27 alloy was used as matrix whereas sillimanite and rutile were used as the reinforcement. The particle size of these reinforcements was in the range of 1–32 μm. The weight percentage of reinforced particles was varied in the range of 0–15 wt.% in a step of 5 wt.%. Stir casting process was used for processing of composites. The microstructure analysis of formulated composites showed uniform distribution of reinforced particles in the matrix till 15 wt.% of reinforcement level. Beyond this level, the agglomeration of reinforced particles was observed. Further, refinement of silicon phase and change in its morphology (from acicular to non-acicular or globular type) was observed in the formulated composites. Addition of 15 wt.% of sillimanite and rutile (in equal proportion) in LM27 alloy showed maximum value of nanohardness for the matrix phase (i.e. 2.67 GPa). However, at the interface phase and reinforcement region, maximum hardness was shown by sillimanite reinforced composites with 15 wt.% of reinforcement. The high value of hardness at interface indicated good interfacial bonding by sillimanite particles. The wear tests were conducted on pin-on-disc set-up at room temperature. The results revealed that hybrid AMCs containing 15 wt.% of sillimanite and rutile (in equal proportion) exhibited maximum improvement (52.57% improvement over base alloy) in wear behaviour. The wear behaviour of composites showed that wear of material occurs in two main zones i.e. run-in-wear zone and steady-state-wear zone. The run-in-wear zone was further sub-divided into two zones. In the first sub-zone, a sharp increase in wear rate was observed and in the second sub-zone, decrease in wear rate was observed. In the steady-state-wear zone, wear of samples achieved a steady state in which wear rate occurred at a constant rate w.r.t sliding distance. All the composite formulations showed significant reduction in wear loss as compared to base alloy. The hybrid composite containing 15 wt.% of reinforcement level showed highest reduction in the maximum wear rate and also steady state wear rate. Also, for the hybrid composites (referred xi here as dual reinforced composites), the steady-state-wear state was achieved at a lesser sliding distance. Wear track and wear debris were analysed by SEM-EDS to study the wear mechanism involved in the material removal process. Wear tracks obtained showed the presence of grooves along with crater formation whereas wear debris revealed the presence of flake like debris, grooves on flakes and thread like debris. It was observed that at low load (i.e. 1 kg) conditions, abrasive wear was mainly responsible for wear of the pin. However, at high load (i.e. 5 kg) conditions, adhesive wear was responsible for wear of pin.