Tribo-mechanical performance and wear parameter optimization of stir-cast hypoeutectic LM25 hybrid composites reinforced with TiB 2 and Si 3 N 4

The objective of this study is to investigate the effect of dual ceramic reinforcement (TiB₂ and Si₃N₄) on the microstructural evolution, mechanical properties, and tribological performance of LM25 aluminum alloy-based hybrid metal matrix composites fabricated by stir casting. In this study, five compositions were prepared by varying the Si₃N₄ content from 0 to 5 wt.% while maintaining TiB₂ at 3 wt.%. Microstructural analysis using an optical microscope revealed a uniform distribution of reinforcements up to 3 wt.% Si₃N₄, with significant grain refinement and improved interfacial bonding. Beyond 3 wt.%, particle agglomeration and porosity were observed. Mechanical characterisation showed that the LM25/3% TiB₂/3% Si₃N₄ composite achieved the highest hardness (70 BHN), tensile strength (146 MPa), elongation (6.7%), and compression strength (420 MPa), indicating optimal reinforcement synergy. Tribological performance, evaluated through wear rate and friction coefficient (CoF), demonstrated enhanced wear resistance and reduced friction for LM25/3% TiB₂/3% Si₃N₄ composite. The application of Grey Relational Analysis (GRA) based on Box – Behnken design identified the optimal tribological parameters: 0.5 km sliding distance, 10 N normal load, and 1 m/s sliding velocity, achieving a wear rate of 0.007 g/km and a CoF of 0.26.HighlightsLM25 aluminum alloy-based hybrid composites reinforced with TiB₂ and Si₃N₄ were successfully fabricated using stir casting.Uniform reinforcement distribution, grain refinement, and strong interfacial bonding were achieved up to 3 wt.% Si₃N₄ addition.The LM25/3% TiB₂/3% Si₃N₄ composite exhibited superior mechanical properties, including maximum hardness, tensile strength, elongation, and compression strength.Tribological performance showed significantly reduced wear rate and coefficient of friction for the optimised hybrid composite.Grey Relational Analysis coupled with Box – Behnken design identified optimal wear conditions at low load, sliding distance, and velocity.