Enhancing microstructure, nanomechanical and tribological properties of TiAl alloy processed by spark plasma sintering with Si3N4 ceramic particulates addition
Azeez Lawan Rominiyi, Peter Madindwa Mashinini, Moipone Linda Teffo
Abstract
TiAl matrix composites reinforced with varying weight fractions of Si 3 N 4 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 Ti 2 AlN, unreacted Si 3 N 4 ceramic particles and dominant Ti 5 Si 3 intermetallic phases within the TiAl matrix at Si 3 N 4 content above 1.5 wt%. The in-situ precipitated phases enhanced the nanomechanical and tribological properties of the composites. The 7Si 3 N 4 /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. 7Si 3 N 4 /TiAl composite exhibited the lowest specific wear rate of 0.38 ± 0.55 10 -4 mm 3 /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 Ti 2 AlN, Ti 5 Si 3 and unreacted Si 3 N 4 particles in the TiAl matrix. The composites displayed a transition from adhesive wear to predominantly abrasive wear where the hard Si 3 N 4 particles prevented direct metal-to-metal contact and facilitated the formation of a protective tribolayer, resulting in enhanced wear resistance. Hence, the developed Si 3 N 4 /TiAl composites are suitable for various structural and tribological applications. • Fully densified Si 3 N 4 /TiAl composites with network structure were fabricated by spark plasma sintering technique. • Incorporation of Si 3 N 4 particles significantly enhanced nanohardness and elastic modulus of the TiAl alloy matrix. • Wear resistance of Si 3 N 4 /TiAl composites improved compared to the unreinforced TiAl alloy. • Strong interfacial bonding between the in-situ formed phases and the TiAl matrix facilitated effective load transfer. • Improved nanomechanical and wear properties make Si 3 N 4 /TiAl composites suitable for structural and tribological applications.