Abstract
In this study, Al-Ti-Zr and Cr-Ti-Zr metallic coatings with thichness of 250-280 μm were fabricated successfully on Zr alloy using pulsed laser cladding. By jointly employing multiple characterization techniques, microstructural characteristics of the coatings were probed with their formation reasons explored. The Al-Ti-Zr coating consists of a single BCC solid-solution phase (average size 8.6 ± 6.3 μm) with hardness of 405.5 ± 16.6 HV that is more than twice that of the substrate (198.7 ± 2.0 HV). Such marked hardening is mainly related to the contribution from the solid-solution strengthening produced by Al and Ti. The Cr-Ti-Zr coating consists of cellular BCC phase (average size 0.9 ± 0.4 μm) and C14-type Cr2(Ti,Zr) Laves phase with nanoscale lamellar structures. Its average hardness is 584.8 ± 33.6 HV, about three times of that of the substrate, which can be ascribed to synergistic effects of solid-solution, grain refinement and second phase strengthening. The formation of the single BCC solid-solution phase in the Al-Ti-Zr coating is mainly due to the relatively small differences in atomic size and electronegativity between Al, Ti and Zr. For the Cr-Ti-Zr coating, however, due to large atomic size and electronegativity differences between Cr and Zr (as well as Cr and Ti), Cr2(Ti,Zr) Laves phase was formed in addition to the BCC phase.
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