Development of a Co-free, Ni-based alloy layer (Ni-SD) for sealing surfaces of nuclearpower valves cladding by hollow laser beam

To avoid the activated radiation of elemental cobalt and meet the requirements of critical working conditions in which operate the sealing surface of nuclear-power valves, a new cobalt-free Nibased alloy (Ni-SD) was developed. The powder was deposited on a stainless-steel substrate by a novel hollow laser beam cladding technique. The experimental results reveal that the microhardness of Ni-SD can approach 700 HV0•3, which is much higher than that of the common Cobased alloy Stellite6 (500 HV0•3) that is currently used in nuclear-power valves. Analytical results indicate that γ-Ni is the primary phase in the Ni-SD coating and that it proportionally dissolves metallic and non-metallic elements. In addition, the Ni-SD coating contains some hard phases, such as carbides and borides. High-temperature measurements indicate that the Ni-SD alloy offers excellent advantages such as high wear resistance and high-temperature operation.