A review on application of nickel base hardfacing alloys in sodium-cooled fast reactor

Abstract

An overview on processing, performance, and applications of Nickel base hardfacing alloys in Sodium-cooled Fast Reactors (SFR) is presented in this review article. For many components in SFR, the need for superior wear-resistant material with reliable tribological properties is a prerequisite for ensuring the safety of the reactor. Hardfacing of the base material is a common practice followed in nuclear industries for improving the wear resistance of structural components. Recently, Ni base hardfacing alloys have drawn significant attention as a potential replacement of Co base hardfacing alloys for nuclear reactor components. This is because cobalt base alloys are known for causing occupational radiation exposure in nuclear reactors. Nickel base hardfacing alloys are deposited on the base alloy by various methods. Among them, laser cladding, Plasma Transfer Arc Welding (PTAW) and Gas Tungsten Arc Welding (GTAW) have generated interest owing to their high process efficiency and ability to produce superior hardfacing overlays on the substrate material. However, the potential application of these processes is achieved only via proper control of process parameters and with minimum dilution from the base material. The wear performance of Ni base hardfacing alloy mainly depends on its microstructural constituents. It has been reported that boride and carbide precipitates in Ni alloys impart excellent hardness and superior wear resistance at a wide range of temperatures. In this review article, the sliding wear behaviour of these alloys is reported at service temperature ranging from room temperature to 700 °C. The analysis of worn track and worn debris from the wear test of Ni alloys showed that abrasive and adhesive wear were dominant mechanisms at ambient temperature; whereas, at a higher temperature, adhesive wear was the dominant mechanism which was accompanied by the formation of oxide tribo-layer. The formation of oxide tribo-layer is known to play a major role in decreasing the coefficient of friction.