New Co-Base High Temperature Alloys
New structural and functional materials enable a multiplicity of paths to improved efficiency in energy generation, storage, transmission and conversion. While alternative energy technologies are highly desirable, for the foreseeable future fossil fuels will be a primary energy source. This motivates discovery of new structural materials that can increase the operating temperatures within energy generation systems and provide critically needed improvements in the efficiency of power generation.
The discovery of a stable ternary Co3(Al, W) intermetallic compound with an ordered L12 structure has provided a pathway for development of a new class of load-bearing cobalt-base high temperature alloys. The thermodynamic coexistence of the γ -Co solid-solution phase with fcc structure and the γ ' - Co3(Al, W) phase and the similarity of their lattice parameters permit establishment of a two-phase structure with a high degree of coherency. This structure consists of submicron regularly aligned cuboidal γ ' precipitates embedded in a continuous γ matrix phase. This structure is morphologically identical to the microstructure of Ni-base superalloys. Our recent research on ternary and quaternary variants of these two-phase L12-containing systems indicates a potential temperature benefit of up to 150˚C relative to current nickel-base alloys. This translates to a very substantial benefit in energy efficiency for advanced turbine systems. To achieve these benefits, a broader range of composition space must be explored in an efficient manner to optimize properties and concurrently identify compatible environmental and thermal barrier coating systems.