Laser Nitrided and TiN Coated Ti-6Al-4V Alloy surfaces

摘要

Titanium alloys are widely used in aerospace industry due to their low density and high toughness to mass ratios. However, the wear resistance of the titanium alloys is poor and requires surface treatment for the effective usage. One of the methods to improve the surface properties is to nitride the surface forming the nitride rich compounds in the surface region. Titanium nitrides provide the hard surfaces and improve the tribological properties of the surface. The gas assisted laser nitriding of the titanium alloy surface is desirable, since it involves with fast processing, precision of operation, and low cost. TiN PVD coating of the surface of the nitrided layer reduces the surface roughness and further improves the surface properties through forming a hard envelope at the surface. Consequently, laser gas assisted nitriding of Ti-6Al-4V alloy is carried out. The nitrided surfaces are TiN PVD coated in the coating unit. The melt depth layer is predicted using the analytical formulation. The maximum coating thickness achieved is in the order of 2 µm and maximum nitrided depth layer is 80 µm. It is found that the laser gas assisted nitriding provides a uniform thickness of the treated layer below the surface. The nitrided layer is free from the cracks and other defects such as porous and cavities. The TiN coating at the surface modifies the surface roughness and the elastic modulus of the nitrided layer. In this case, surface roughness reduces slightly and elastic modulus of the treated layer increases. The predictions of the melt layer depth agree with the experimental data.