Reinforcing potential of MWCNTs on mechanical and machining performance of hot-pressed ZTA-MgO ceramic cutting inserts

Abstract

A new generation cutting insert was manufactured by multi-walled carbon nanotube (MWCNT) reinforcement (0–0.25 weight percentage (wt%)) into zirconia toughened alumina (ZTA)- magnesium oxide (MgO) ceramic matrix using a powder metallurgy route. The hot-press sintering technique was used to compact the uniformly mixed ZTA-MgO-MWCNT powders, sintered at 1500 °C followed by morphological, mechanical and functional characterizations. The relative densities of the samples were between 98 % and 99 %. The mechanical properties of the matrix were improved up to 0.15 wt% MWCNTs. The highest microhardness was ~2366 HV0.5 for 0.15 wt% due to grain refinement by synergistic pinning between spinel (MgAl2O4) and MWCNTs. Similarly, the highest indentation fracture toughness was ~7.33 MPa.m1/2 for 0.15 wt% MWCNT content due to micromechanical interlocking mechanism from a combined effect of MWCNT size variation and inter-particle distance between MWCNTs featuring proper crack bridging and crack deflection. To function as a cutting insert, the sintered samples up to 0.15 wt% was selected and shaped according to SNGN120408 cutting tool geometry. For minimum cutting force with high surface roughness, the optimized parameters were observed as a cutting speed of 300 m/min, feed rate of 0.12 mm/rev and 0.2 mm depth of cut using the design of experiment technique while machining AISI 4340 steels. Furthermore, regression models were developed to correlate the machinability with machining conditions. The comparative study suggested that the significant improvement of cutting force (~26.4 %), surface roughness (~55.3 %) and tool life (~29.4 %) was achieved for ZTA-MgO-0.15 wt% MWCNT ceramic tool with respect to ZTA-MgO inserts depending upon self-lubrication phenomenon alongside with the retention of proper tool geometry for a longer tool life ~44 min. The morphological and Raman spectra analysis of the worn region justifies the self-lubricating phenomenon at the interface by breaking and rolling of MWCNTs.