Enhancing microstructure, nanomechanical and tribological properties of TiAl alloy processed by spark plasma sintering with Si3N4 ceramic particulates addition

Abstract

TiAl matrix composites reinforced with varying weight fractions of Si₃N₄ ceramic particles were successfully fabricated by the spark plasma sintering method. The microstructure, nanomechanical and tribological properties of the sintered composites were investigated. The microstructural characterization revealed the evolution of a quasi-continuous and continuous network structure consisting of minor fractions of in-situ formed Ti₂AlN, unreacted Si₃N₄ ceramic particles and dominant Ti₅Si₃ intermetallic phases within the TiAl matrix at Si₃N₄ content above 1.5 wt%. The in-situ precipitated phases enhanced the nanomechanical and tribological properties of the composites. The 7Si₃N₄/TiAl composite displayed the best nanomechanical properties, including nanohardness, elastic modulus, and H/E_r ratio among the sintered samples. The specific wear rate of the composites decreases with increasing reinforcement content. 7Si₃N₄/TiAl composite exhibited the lowest specific wear rate of 0.38 ± 0.55 $\times$ 10⁻⁴ mm³/Nm, representing a 95.6 % improvement in wear resistance compared to the unreinforced pure TiAl alloy. The improved wear performance of the composites was attributed to their load-bearing capacity and wear resistance of the hard, in-situ Ti₂AlN, Ti₅Si₃ and unreacted Si₃N₄ particles in the TiAl matrix. The composites displayed a transition from adhesive wear to predominantly abrasive wear where the hard Si₃N₄ particles prevented direct metal-to-metal contact and facilitated the formation of a protective tribolayer, resulting in enhanced wear resistance. Hence, the developed Si₃N₄/TiAl composites are suitable for various structural and tribological applications.