A study on in-situ synthesis of TiCN metal matrix composite coating on Ti–6Al–4V by laser surface alloying process

Abstract

Laser surface alloying of Ti6Al4V substrate with in-situ synthesized TiCN was carried out by melting preplaced titanium and graphite powders in 3:1 ratio (wt%) in nitrogen atmosphere at different scan speeds in 400–1400 mm/min range, maintaining the laser power and the beam diameter constant at 1200 W and 3 mm respectively. Molten pool thermal history during the alloying process was recorded using an IR pyrometer. With the decrease in scan speed, the cooling rate was found to decrease, while the molten pool lifetime increased which caused densification of TiCN dendritic structure. Though it enhanced the hardness, coatings were found to fail exhibiting brittle fracture during the scratch test, while coatings processed at higher scan speeds (800 mm/min −1400 mm/min) were found to be intact. Further, coatings processed at higher scan speeds also exhibited better wear resistance. Linear polarization electro-chemical corrosion test was performed on the coatings and it was observed that even corrosion properties were better in case of coatings processed at higher scan speeds.