In the present study, the effects of graphene content (0.1, 0.3, 0.5 wt-%) on the mechanical and tribological properties of aluminium matrix composites were reported. The experimental results reveal that the best apparent density (2.58 ± 0.02 g cm⁻³), highest Vickers hardness (57 ± 2.5 HV), lowest mass loss (1.6 and 9.7 mg for 10 N and 40 N), and lowest wear rate (12 × 10⁻⁵ and 18 × 10⁻⁵ mm³/Nm for 10 N and 40 N) were obtained at aluminium–0.1% graphene composite when compared with pure aluminium. The ultimate compressive strength of composites increases from 106 ± 4 to 138 ± 4 MPa with increasing graphene nanoplatelet contents. All results showed that graphene has been a very effective reinforcement and solid-lubricant material for Al matrix composites.

In this study, the effect of the sintering time, temperature and graphene amount on titanium properties was examined for the first time in detail. From the results, the highly dense (4.39 g/cm³), most hard (from 390 HV to 566 HV) and improved microstructure for 0.15 wt% graphene addition were performed at 1100℃ for 120 min. The titanium composite properties have been reduced with increasing graphene due to damaged graphene and titanium carbide formation above 0.30 wt% graphene. To summarise, when pure titanium is compared with graphene reinforced titanium composites, the properties enhanced due to dislocation and fine grain strengthening mechanisms.

In this study, pure aluminum was reinforced with pure silicon nitride (varying from 1 to 12 wt%), pure graphene nanoplatelets (changing from 0.1 to 0.5 wt%), and their hybrid form (silicon nitride/graphene nanoplatelets) by using powder metallurgy method. The results show that Vickers hardness increased to 57.5 ± 3 HV (Al-9Si₃N₄) and 57 ± 2.5 HV (Al-0.1GNPs) from 28 ± 2 HV (pure aluminum). Similarly, ultimate compressive strength of the pure silicon nitride and pure graphene nanoplatelet-reinforced aluminum composite was improved to 268 ± 6 MPa (Al-9Si₃N₄) and 138 ± 4 MPa (Al-0.5GNPs) from 106 ± 4 MPa (pure aluminum), respectively. Interestingly, the highest Vickers hardness, ultimate compressive strength, and ultimate tensile strength of aluminum-silicon nitride-graphene nanoplatelet hybrid composites were determined as 82 ± 3 HV (Al-9Si₃N₄-0.5GNPs), 334 ± 9 MPa (Al-9Si₃N₄-0.1GNPs), and 132 MPa (Al-9Si₃N₄-0.1GNPs), respectively. The Vickers hardness (for Al-9Si₃N₄-0.5GNPs), ultimate compressive strength (for Al-9Si₃N₄-0.1GNPs), and ultimate tensile strength (for Al-9Si₃N₄-0.1GNPs) improved ∼193%, ∼215%, and ∼47% when compared to pure Al, respectively. Above 9 wt% silicon nitride and 0.1 wt% graphene nanoplatelets content, an adverse effect was observed due to the agglomeration of silicon nitride and graphene nanoplatelets in aluminum matrix composites. Also, energy-dispersive X-ray and scanning electron microphotographs confirmed the presence of both silicon nitride and graphene nanoplatelets and uniformly distributed in the aluminum matrix.