THE EFFECT OF LASER SURFACE TREATMENTS ON THE TRIBOLOGICAL BEHAVIOR OF TI-6AL-4V

Laser surface treatments were tried with the objective of improving the tribological performance of Ti-6Al-4V. The surface treatments used were laser surface melting, laser nitriding and laser nickel alloying, which were performed using a 1.4 kW CO2 laser. The process parameters for laser surface treatments were optimized. The microstructures produced and the compounds formed were analyzed using standard metallographic and X-ray diffraction techniques. The abrasive, erosive and sliding wear behaviors of the laser-treated surfaces were studied. It was found that, whereas laser nitriding and nickel alloying reduced abrasive wear, laser surface melting did not. The reduction in the abrasive wear rate of laser-nitrided and nickel-alloyed specimens is attributed to the formation of TiN and Ti2Ni respectively in the molten and resolidified region. All three laser surface treatments resulted in improving the dry sliding wear resistance. This is attributed to the increased hardness as well as the formation of wear-resistant compounds in nitriding and nickel alloying. The mechanism of wear in the untreated titanium alloy was primarily ploughing but in the laser-treated cases material was removed by the formation and rupture of adhesive bonds. The increased hardness is believed to change the mechanism of sliding wear from ploughing to adhesion. It was found that the laser treatments did not have any effect on the erosion resistance of Ti-6Al-4V when impacted by coarse particles at a high velocity. The above results are supported by electron microscopy of the worn surfaces.