Cobalt-free Hard-facing for Reactor Systems

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Cobalt-based (Co) alloys are extensively used in nuclear reactors, particularly in regions prone to wear and galling such as valves and pumps. This is because they provide outstanding wear resistance, and so improve component life and reduce maintenance requirements. However, these alloys are responsible for a large portion of the radiation exposure of workers at nuclear utilities, due to the formation of Cobalt-60, a gamma-emitting radioactive isotope. For this reason, replacing Co-based hardfacing alloys in future nuclear reactors is highly desirable. For the current Indian prototype fast breeder reactor (PFBR) Nickel-based (Ni) alloys have been used as an alternative, however these alloys are expensive and very susceptible to cracking. A new class of Iron (Fe) based, silicide strengthened systems have shown great potential for hardfacing application. In response to the scale of components that require hardfacing in the PFBR, plasma transfer arc (PTA) deposition is proposed, a highly flexible manufacturing technique, as an alternative to HIPbonding. To date, however, PTA manufacturing of Fe silicide strengthened alloys is yet to be explored. Indeed, the residual stress resulting from PTA processing nickel (Ni)-based alloys, a key driver in the formation of unacceptable cracks and defects, is still to be understood. Successful characterisation, optimisation and simulation of the PTA process and application to Fe based alloy systems is a key step in eliminating Co from nuclear plant.