Laser radiation enhancement of the corrosion resistance of an amorphous ribbon alloy

Abstract

The effects of pulsed laser radiation on the corrosion resistance, surface morphology, and composition of liquid-quenched amorphous Fe32Ni36Cr14P12B6 (Allied Corporation Metglas¯ 2826A) are reported. Scanning electron microscopy, Auger depth profiling, and x-ray diffraction were used to characterize the surface, while the corrosion resistance was determined by anodic polarization in H2SO4. The surface of the as-received melt-spun ribbons exhibited many defects, including cracks, compositional irregularities, and microcrystals of Ni5P4. These microcrystals differ from those found upon bulk crystallization. Melting and rapid solidification by radiation with a Q-switched Nd–YAG laser [30 ns full width at half maximum (FWHM)] modified the surface morphology (leaving composition constant), removing the microcrystals and cracks and reducing the carbon and oxygen contamination. The reduction of these surface defects resulted in improved corrosion resistance of the Metglas¯ 2826A ribbon. For example, spontaneous passivation is observed for the laser-treated samples, as opposed to critical current densities of 10μA/cm2 and 1000μA/cm2 for the as-received amorphous and crystallized Metglas¯ alloy, respectively.