Analysis of second phase particles in a powder metallurgy HIP nickel-base superalloy

Abstract

The nature of the second phase particles associated with LC Astroloy prepared using powder metallurgy techniques has been examined. The individual particles have been identified using energy dispersive X-ray analysis and convergent beam electron diffraction. Four distinct types of particles have been observed: a cubic MC carbide in which M is either titanium or titanium plus molybdenum, a monoclinic phase ZrO₂, a trigonalα-Al₂O₃ and a tetragonal M₃B₂ phase in which M is molybdenum or molybdenum and chromium. The observations indicate that, although some MC carbides are associated with the ZrO₂ phase, the majority of the prior particle boundary precipitates are separate entities. Hot isostatic pressing or subsequent heat treatments above or below the γ′ solvus were observed to have little effect on the incidence or distribution of the precipitation associated with the prior particle boundaries. In contrast, heat treatments above the γ′ solvus resulted in the dissolution of the M₂B₃ phase and its preferential precipitation on the grain boundaries.