EFFECT OF LASER SURFACE MELTED ZIRCONIUM ALLOYS ON MICROSTRUCTURE AND CORROSION-RESISTANCE

Zirconium alloys were laser surface melted (LSM) using a continuous wave CO2 laser at energy densities of 4,7 and 10 kJ cm-2. LSM samples examined using SEM and optical microscopy exhibited resolidified regions with several different microstructures, including ultrafine martensite. Corrosion performance was obtained by steam autoclave tests and immersion tests in 10% FeCl3 at room temperature. Coarser microstructures performed better than fine microstructures in autoclave tests, while fine microstructures performed better than coarse microstructures in 10% FeCl3 immersion tests. Accelerated corrosion in the autoclave and immersion tests was observed to occur near the laser beam overlap region. The surface chemistry was examined for alloy segregation using secondary iron mass spectroscopy. Tin and iron alloy elements segregated near the periphery of each melt pool. Segregated regions containing increased iron concentrations associated with each laser pass were responsible for accelerated corrosion.