Surface Gas Nitriding of Titanium (Ti–6Al–4V) Alloy

The effects of gas nitriding were studied for Ti–6Al–4V alloy at different time and temperatures. Gas nitriding was performed from 600 to 1200 °C for the duration of 4–8 h using Dilatometer. The surface roughness was also compared to get insight into the tribology behaviour. Specimen color appearance after nitriding was different from the base metal, and the changes of color demonstrated the variation, with time and temperature. After nitriding, the basic metallic silver color was converted into blue, golden and gray. At lower temperatures, blue and golden colors were common, and as temperature increased, the color changed to grayish. Initially, at lower temperatures (i.e., 600 and 700 °C), titanium alloy’s silver metallic color turned into blue/golden, and the intensity of this color was increased with the increase in temperature and time of nitriding. Moreover, above β-transus temperature at 1000, 1100 and 1200 °C, the material appeared to be gray. The hardness after nitriding was increased with increase in nitriding layer thickness. The maximum hardness value HV0.5 was reported to be 1735. Surface micrographs were taken by scanning electron microscopy (SEM), and these micrographs revealed that the formation of nitrides was started from the grain boundaries.