Comparison of nozzle gas shielding techniques for laser cladding of zirconium

The use of zirconium is widespread in nuclear, chemical and biomedical industries considering its low thermal neutron cross-section, high corrosion resistance and good biocompatibility [1-3]. The present work studies the application of laser cladding using a powder spray laser deposition system. Commercially pure zirconium is deposited on a zirconium alloy substrate without the use of an enclosed atmosphere to limit oxygen and nitrogen contamination. The use of different powder nozzle designs and argon shielding gas flow rates are examined as the only mechanism for protecting the molten zirconium from the atmospheric contamination, in order to evaluate the feasibility of in-situ cladding and more convenient cladding systems. The powder nozzle geometry and gas flow rates are compared in terms of the cladding chemistry, microstructures, and microhardness. It is shown that the use of a powder delivery nozzle which only utilizes one stream of argon within the powder carrier gas is not sufficient to prevent atmospheric contamination. The addition of an auxiliary argon stream provides far greater protection to both the clad and substrate, which suggests it is possible to achieve acceptable zirconium claddings without the use of an enclosed shielded environment.