Executive Summary : | Cladding by cobalt-basis Tribaloy alloys has been deemed very attractive for the protection of metallic components operating in harsh environments involving high-temperature wear, corrosion, and oxidation. Components, where they have already excelled, include sink and stabilizer rolls in the galvanizing industry, gas turbine combustor components, valves and valves seats, bearings, bushings, fluidized bed heat exchanger elements, etc. The very high hardness and wear resistance of these alloys is due to the presence of hard, intermetallic hcp Laves phase having composition Co?Mo?Si and/or CoMoSi. Among the Tribaloy alloys, Tribaloy T800 contains the highest amount of Laves phases and correspondingly, it shows the best wear and corrosion resistance properties. However, due to the brittle nature of the Laves phases, they reduce the fracture toughness of the alloy and make it susceptible to cracking and brittle fracture. While Tribaloy alloys with a lower Laves phase content have a reduced propensity to cracking, there is a concomitant reduction in hardness and correspondingly wear resistance, the primary application of the alloy. Hence, developing a Tribaloy-based material with increased resistance to cracking while maintaining its wear and corrosion resistance properties has tremendous potential. Among the techniques employed to apply Tribaloy T800 clads, laser processing has the advantages of strong metallurgical bonding with the substrate and pore-free clads, yielding excellent properties. However, due to the rapid cooling rate in laser processing, the clads with a large amount of brittle Laves phase content undergo severe cracking. While several studies on cast Tribaloy T800 have shown that the presence of some amount of Fe in the alloy has a significant influence on the amount of Laves phase and correspondingly mechanical properties, this has never been studied systematically in clads deposited via laser processing. Within the scope of this work, mixed powders of Tribaloy T800 and various Fe- and Ni-containing alloy powders (such as Ni/Fe/SS316/SS430 powder, etc.) will be deposited on SS316 substrate via laser direct energy deposition (DED) process. After establishing the optimum DED parameters and substrate surface roughness, the content of the alloying powders in the powder mixture will be systematically varied to obtain an optimum combination of wear and corrosion resistance without cracking. The performance of the clads will be compared with unmixed laser deposited Tribaloy T800. The ultimate aim of the proposed project is to develop a novel crack-free multi-layered Tribaloy T800 component with high wear resistance at the surface and a tough core underneath. |