Microstructure and Wear Properties of Laser Treated Ni3Al Coatings on Low Alloy Medium Carbon Steel

Abstract

Laser modification of nickel-aluminide (Ni3Al) coatings on low alloy medium carbon steel substrate was carried out with the help of industrial CO2 laser. The depth of the laser melted zone (modified surface) was controlled as a function of input energy by varying the laser beam travel speed. The laser treated specimens were characterized for microstructure, chemical composition, and micro-hardness profile with respect to the laser penetration depth. Microstructural examination revealed that the laser treated surface was composed of ultrafine grain structure which evolved as a result of laser re-melting and solidification (cooling) rate used in this experiment. Microhardness results showed that as the depth of the laser melted zone increases the hardness of the modified surface decreases and vice versa. Further, the wear behavior of the laser treated surface was also studied with the help of ball-on-disc tribometer and by selecting 2000 m sliding distance. Wear test showed that as the depth of laser melted zone increases the wear of the surface increases as well and vice versa. The possible reason behind this phenomenon was the migration of iron (Fe) atoms from substrate into the surface layer which resulted the dissolution of Ni3Al coating particles in the surface layer and this was confirmed by the EDX analysis.