A synergetic effect of ternary refractory nitride reinforcements on densification, mechanical, tribological and thermal stability characteristics of spark plasma sintering-developed Ti6Al4V matrix composites

Abstract

This paper reports the possibility of developing advanced Ti6Al4V matrix composites (TMCs) with enhanced mechanical properties and highly improved resistance to wear and thermal degradation for structural and high-temperature aerospace applications. The synergetic effect of different weight compositions (1, 1.5 and 2 wt. %) of ternary reinforcements consisting of h-BN, TiN and AlN nanoparticles on the characteristics of the microstructure, phase constitution, densification, mechanical, tribological and thermal stability of Ti6Al4V matrix composites developed by spark plasma sintering (SPS) is investigated. The unreinforced Ti6Al4V exhibited a two-phase microstructure made up of α/β phases, however the simultaneous reinforcements resulted in notable microstructural changes and emergence of nitride-rich secondary phases. The relative densities of the composites decrease with increasing reinforcement addition, whereas the nanohardness and elastic modulus values of the composites continue to improve with increasing reinforcement from 1 wt. % (28.319 ± 0.525 GPa and 219.43 ± 6.77 GPa) to 2 wt. % (55.642 ± 0.693 GPa and 314.59 ± 7.58 GPa) compared to the unreinforced Ti6Al4V (5.838 ± 0.323 GPa and 115.07 ± 3.63 GPa). The unreinforced alloy yields higher average COF values, while the composites at equivalent applied normal loads yield lower average COF values. Thus, in comparison to the unreinforced alloy, the produced composites exhibit considerably lower specific wear rates (with increasing applied normal load). Based on thermogravimetric analysis, the oxidized composite reinforced with 1 wt. % of ternary reinforcements exhibits the highest thermal stability in the high-temperature oxidizing environment, as evidenced by its greatest resistance to oxidation and its smallest weight gain of 1.55%.