Study On Preparation Of The Novel Co-Al-W Superalloys And Cladding Layer

Conventional Co-based superalloys lack effective precipitation strengthening by intermetallic compounds with the L12 structure as the case in the Ni-based superalloys, and depend on solid-solution elements and precipitation of low volume fraction of carbides for their high-temperature strength. The novel Co-Al-W superalloys are strengthened by a ternary compound with the L12 structure,γ′-Co3(Al,W), which precipitates in the disordered y face-centered cubic cobalt matrix with high coherency and with high melting points. And the novel alloys showing a high-temperature strength greater than those of conventional nickel-base superalloys, will become the candidates for next-generation high-temperature materials.Optimizing the alloy composition design on the basis of existing research.The novel Co-Al-W superalloy were prepared by vacuum arc melting (VAM). Laser cladding technology and Tungsten Inert Gas (TIG) welding was used to deposit Co-Al-W alloy on 304 austenite stainless steel substrate and cladding layer shape, dilution, Vickers hardness, microstructure and distribution of alloying elements were investigated. The main results as follows:(1) The microstructure of Co-Al-W alloy annealed at 900℃for 72 hours after solution treatment at 1300℃for 2 hours prepared by vacuum arc melting is composed of richγ-Co matrix,γ′Co3(Al,W) phase and few carbides.The novel Co-Al-W alloy is strengthened by a ternary compoundγ′-Co3(Al,W) phase with precipitation strengthening, which is 50 to 100℃higher than those of Ni-base superalloys. Tungsten stabilizeγ' phase with effect ofγ'precipitation strengthening, the melting temperatures gradually increasing with the increasing of tungsten concentration. The solvus temperatures of theγ'phase increased because of the addition of Nb.This result showed that Nb stabilized theγ'phase.(2) Laser power and scanning speed affect the performance of coating shaping significantly,while overlapping has less influence on shaping. Under the experimental conditions and when Co:Al:W proportion is 78:12:10(atom rate),the optimized parameters are as follows:laser power is 3kW,scanning speed is 3mm/s,overlapping-is 10%.(3) The phases in the cladding layer were composed ofγface-centered cubic cobalt matrix and intermetallics CoxAl and carbide (Cr23C6, Co6W6C and CoCx). (4) Laser cladding layer with lower dilution rate, about 17%; and TIG cladding layer with higher dilution rate, approximately 32%. We obtained high hardness cladding layer through the laser and TIG cladding. The maximum hardness up to 1050 (HV0.1).