Overview of the Development of L12 γ′-Strengthened Cobalt-Base Superalloys

Abstract

AbstractHigh-temperature technology is of major importance in many industrial applications, such as aircraft engines and land-based power generation gas turbines. Demands for high fuel and engine efficiency require the increasing service temperature of superalloys. The further development of widely used Ni-base superalloys hits a bottleneck due to the limitation of the melting point of Ni. In 2006, the discovery of γ/γ′ Co–Al–W alloys began a new era in the development history of high-temperature materials. Compared with Ni-base superalloys, the higher melting temperature by 50~150 °C, the greater creep resistance, and the comparative mechanical properties spotlight the research of novel γ/γ′ Co–Al–W-based alloys as one of the candidates for high-temperature materials for future generations of advanced propulsion systems. Despite the extraordinary improvement achieved in the various aspects of novel γ/γ′ Co–Al–W-based superalloys, several drawbacks still restrict the wide applications, such as metastable nature of γ′ precipitates, narrow γ/γ′ composition range, overhigh mass density, inferior medium–low-temperature strength. In this chapter, we review the current exploration of γ′-strengthened Co-base superalloys in view of these drawbacks, including phase stability of γ′ precipitates, γ′-solvus temperature, development of low-density γ/γ′ Co-base superalloys and CoNi-base superalloys, and high-temperature mechanical capability of γ/γ′ Co-base superalloys. Finally, the challenges and future research needs in the development of novel Co-base superalloys are prospected.KeywordsCo-based superalloysPhase stabilitySolvus temperatureLow-densityMechanical properties