Laser alloyed Al-Ni-Fe coatings

The aim of this work was to produce crack-free thin surface layers consisting of binary (Al-Ni, Al-Fe) and ternary (Al-Ni-Fe) intermetallic phases by means of a high power laser beam. The laser surface alloying was carried out by melting Fe and Ni based powders on an aluminium substrate. The mixture of the Fe and Ni powders was varied in order to create Fe-rich and Ni-rich intermetallic phases. A Rofin 4.4 kW Nd: YAG laser was used for melting the powders and the substrate. The thin layers were analysed by means of X-ray diffraction (XRD), optical and scanning electron microscopy (SEM). It was found that when alloying with Fe-rich mixtures, the thin surface layers contained a number of cracks in the heat affected zones (HAZ). Alloying with Ni-rich mixtures produced crack-free surface layers on the substrate. The average thickness of the layer was ∼1.5mm. The XRD analyses of the alloyed layer showed a variety of intermetallic phases including Ni₃Al, NiAl, FeAl, Fe₃Al and Al₅FeNi. The hardness of the surface layers was 3∼4 times higher than that of the Al 1200 substrate.