Surface Modifications of Zirconium Alloys by Laser Glazing
Surface modification of Zr-2.5Nb and Zircaloy-2 materials by laser glazing has been studied. The effects of laser glazing parameters and conditions on the surface contamination and surface finish, the microstructure, the microhardness and the tensile properties have been characterized using light microscopy, scanning Auger microscopy, transmission and scanning electron microscopy, and microhardness and tensile tests. A smooth surface finish, free of contamination, could be produced if the laser glazing was performed at high scan rates (i.e., 1.92 m/s traverse speed) in a protective atmosphere of argon, with helium as a cover gas. The resulting microstructure was found to consist of a uniform, fine, α′ HCP martensite in both Zr-2.5Nb and Zircaloy-2 alloys, although very fine intermetallic particles could be observed in the Zircaloy-2. Post-glaze ageing resulted in precipitation of very fine ellipsoidal particles of Nb-rich β-phase particles in the Zr-2.5Nb and in finer and additional intermetallic particles in the Zircaloy-2. Based on these results, the potential of laser glazing to improve the corrosion resistance of Zr-2.5Nb and Zircaloy-2 pressure tube materials is discussed. Laser glazing is expected to improve the corrosion resistance of Zircaloy-2 material, while Zr-2.5Nb will require post-glaze ageing before optimum corrosion resistance is achieved.
KeywordsTraverse Speed Intermetallic Particle Transmission Electron Microscopy Examination Improve Corrosion Resistance Scan Auger Microscopy
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