Spark plasma sintered Al-0.5 wt% MWCNT nanocomposite: Effect of sintering pressure on the densification behavior and multi-scale mechanical properties

The current study aims to understand the effect of sintering pressure on densification behaviour and mechanical properties of multi walled carbon nanotube (MWCNT) reinforced aluminum (Al) based nanocomposite synthesized via spark plasma sintering (SPS). Physio-chemical functionalization, a novel dispersion technique, was followed which led to homogenous dispersion of MWCNTs in Al matrix. The crystallite size and density of the synthesized Al-0.5 wt% MWCNT nanocomposites increased with increase in sintering pressure. The relative density increased from 90.4% to 95.1% upon increasing the sintering pressure from 30 MPa to 80 MPa. To understand the densification behaviour, the movement of graphite punch within the die filled with Al-MWCNT powder mixture during sintering was monitored. Higher sintering pressure led to early onset of sintering and the total punch displacement during sintering increased from 0.38 mm to 1.48 mm upon increasing the applied pressure from 30 MPa to 50 MPa. The impact of high sintering pressure, leading to enhanced densification, was also translated in the improvement in mechanical properties. Compressive strength and microhardness increased by similar to 30% and similar to 13%, respectively as sintering pressure was increased from 30 MPa to 80 MPa. Higher sintering pressure leading to significantly enhanced mechanical properties at micro and macro scale was also replicated at nano-scale as confirmed by the results of nanoindentation and nanoscratch tests.