Friction and wear of nanocomposite Al2O3 + G processed by spark plasma sintering

Abstract

The effect of allotropic carbon modification content, graphene (G), in the range of 0.5 – 2.0 wt.% on tribological, strength and structural characteristics of Al2O3/G nanocomposite processed by 10-min plasma spark sintering (pressure 50 MPa, temperature 1550 °C) of nanopowder mixture previously subjected to ultrasonic dispersion in organic solvent is studied. The results of tests for friction and wear without lubricant on a tribometer under a load of 20 N at room temperature and roundabout motion of a ruby ball penetrator on a disk are presented along with data on kinetic indentation with determination of the nanohardness and elastic module and observations of the fracture surface structure and friction track using a scanning microscope. Methods of the transmission electron microscopy of thin foils in dark and bright fields and Raman spectroscopy, respectively, were used to determine the microstructure in the bulk of a nanocomposite and prove the graphene thermal stability during plasma spark sintering. It is shown that introduction of graphene contributes to the increase of micro- and nanohardness, elastic modulus, wear resistance by two or three orders of magnitude and a slight decrease in the coefficient of friction. Increase in graphene content to 2 wt.% changes the wear mechanism from brittle breakage to viscous shear due to strengthening in coupling of matrix grains and presnrce of agglomerates. Lack of degradation and retention of graphene thermal stability are proved. The morphology of graphene particles indicates to their preferential arrangement inside the corundum grains and more rarely — on the grain boundaries.