Dry sliding wear behavior of in situ Ti6Al4V/TiN composites 3D manufactured by Laser-Directed Energy deposition

In this work, the wear behavior of Ti6Al4V/TiN composites additively manufactured by laser-directed energy deposition has been studied. The substitution of argon for nitrogen created a reactive atmosphere during the fabrication process, triggering a direct reaction between the molten Ti6Al4V and the nitrogen molecules, creating in situ TiN ceramic reinforcement within the Ti6Al4V metal matrix. The effect of fabrication parameters, such as laser power and scanning speed, on the wear resistance of the different samples was evaluated and compared with the unreinforced base material, which was manufactured under argon. Samples were classified according to heat input: 37.5, 75, 95, and 190 J/mm. Wear tests were performed using a pin-on-disc configuration, employing 316L stainless steel as the counterbody material. The observed wear mechanisms were subsequently identified based on the test results. The influence of microstructure and microhardness on the coefficient of friction, mass loss of pins and counterbodies, and wear rate of each material was also evaluated. The percentage and distribution of the reinforcement generated during fabrication depended on the percentage of nitrogen diffusing into the titanium, which was intrinsically linked to the fabrication parameters. The nitrogen uptake increased with higher heat input, thereby affecting the wear rates and wear mechanisms. The measured Ti6Al4V/TiN Vickers microhardness was double that of the unreinforced samples, although this trend decreased at higher laser power. The Ti6Al4V/TiN sample manufactured with a heat input of 75 J/mm exhibited the highest microhardness (1300 HV2). The formation of TiN reinforcement led to reduced pin mass losses and wear rates, as well as increased coefficients of friction. The Ti6Al4V/TiN samples fabricated at 37.5 and 95 J/mm exhibited the lowest wear rates (2,5 x 10 –13 m 3 /Nm). An abrasive wear mechanism was observed in all Ti6Al4V/TiN samples, predominating when the laser scanning speed was lower (75 and 190 J/mm), due to greater nitride phase formation, which enhanced hardness. This mechanism combined with an oxidative component at a heat input of 190 J/mm, where a mechanically mixed layer was formed, while combining with an adhesive wear mechanism at higher scanning speeds (37.5 and 95 J/mm).