Investigation of crystallinity, mechanical properties, fracture toughness and cell proliferation in plasma sprayed graphene nano platelets reinforced hydroxyapatite coating

Graphene nanoplatelets (GNPs) (0, 1 wt% and 2 wt%) reinforced hydroxyapatite (HA), denoted by HA, HA-1G and HA-2G respectively, coatings were fabricated on titanium substrate (Ti-6Al-4V) through atmospheric plasma spraying. The major parameters such as porosity, crystallinity, mechanical properties, toughness and cell proliferation were manipulated by varying plasma power from 15 kW to 35 kW and content of GNPs. For the coating synthesized at all plasma power, GNPs were found to be retained by Raman spectroscopy. GNPs reinforcement has led to an improvement in the crystallinity of the composite coatings as compared to HA coatings. On the contrary to it, increase in plasma power from 15 kW to 35 kW resulted in decrease in crystallinity for all three individual coating. Further, Increment in plasma power from 15 kW to 35 kW delivered a significant enhancement in hardness, elastic modulus and fracture toughness up to 81%, 149% and 282% respectively for HA-1 wt% GNPs coating, while it improved to 20%, 50% and 173% respectively on the addition of 2 wt% GNPs in HA coating fabricated at 35 kW. Enhancement in hardness, elastic modulus and fracture toughness was due to three simultaneous reasons: (1) Reduction in porosity (2) Uniform dispersion of GNPs and (3) Toughening mechanism offered by GNPs. Further, the addition of GNPs showed a remarkable improvement in the rate of cell proliferation in the HA coating. A detailed discussion over the reasons behind every results have been made profoundly