Thermal oxidation and indentation studies of ceramic-reinforced Ti6Al4V matrix composites fabricated by spark plasma sintering

Abstract The dual-phase titanium alloy (Ti6Al4V), widely utilized for weight reduction in aerospace production, has not fully realized its potential in high-temperature structural applications due to insufficient resistance to thermal oxidation and indentation. In this study, Ti6Al4V matrix composites were fabricated using spark plasma sintering, incorporating titanium nitride (TiN) and aluminium nitride (AlN) nanoparticles at 1, 3, and 5 wt. %. The fabricated composites' microstructure, phase constitution, thermal oxidation, and indentation characteristics were analyzed. The microstructure and phase analyses indicate that the sintered composites exhibit no significant porosities or cracks, and show no evidence of damaging intermetallic phases. Composites reinforced with 5 wt. % TiN exhibited the highest resistance to thermal oxidation, resulting in a weight gain of 2.06%, while those reinforced with 5 wt. % AlN showed the lowest resistance, with a weight gain of 3.6%. Compared to the unreinforced alloy, TiN- and AlN-reinforced composites showed a consistent increase in microhardness: 427.18 ± 11.26 HV to 491.06 ± 17.16 HV and 441.25 ± 12.78 HV to 504.68 ± 22.56 HV. Similarly, TiN-reinforced composites increased nanohardness and elastic modulus, from 7163 ± 380 MPa and 128.09 ± 3.11 GPa to 10,062 ± 270 MPa and 171.64 ± 8.08 GPa. Meanwhile, AlN-reinforced grades exhibited values ranging from 9519 ± 258 MPa and 162.2 ± 4.14 GPa to 11,832 ± 519 MPa and 179.05 ± 2.67 GPa. The strong particle–matrix bonding and load transmission from the Ti6Al4V alloy matrix to the harder reinforcement particles stiffen and dispersion strengthen, inhibiting dislocation motion. The unreinforced Ti6Al4V alloy has the highest plasticity index and the highest nanoindentation plastic deformation. The incorporation of ceramic reinforcements to the Ti6Al4V alloy matrix increased the elastic recovery index, elastic strain at failure resistance, and yield pressure, improving the composites' impact resistance and anti-wear performance.