Characterization of γ′ Precipitates in Cast Ni-Based Superalloy and Their Behaviour at High-Homologous Temperatures Studied by TEM and in Situ XRD

Abstract

In situ X-ray diffraction and transmission electron microscopy has been used to investigate René 108 Ni-based superalloy after short-term annealing at high-homologous temperatures. Current work is focused on characterisation of γ′ precipitates, their volume fraction, evolution of the lattice parameter of γ and γ′ phases and misfit parameter of γ′ in the matrix. Material in the initial condition is characterised by a high-volume fraction (over 63%) of γ′ precipitates. Irregular distribution of alloying elements was observed. Matrix channels were strongly enriched in Cr, Co, W and Mo, whereas precipitates contain large amount of Al, Ti, Ta and Hf. Exposure to high-homologous temperatures in the range 1100–1250 °C led to the dissolution of the precipitates, which influenced the change of lattice parameter of both γ and γ′ phases. The lattice parameter of the matrix continuously grew during holding at high temperatures, which had a dominant influence on the more negative misfit coefficient.

The Influence of the Cooling Bores on Crystal Orientation and Lattice Parameter in Single-Crystalline Cored Turbine Blades

“…As a result, the interfacial boundary in hypothetically-perfect superalloys is considered coherent [ 1 , 10 ]. Local changes in the lattice parameter can cause changes in the structure of the γ/γ′ boundary and, in consequence, of changes in its stability during the high-temperature creep of the blade [ 11 , 12 ].…”

Characterization of the microstructure, microsegregation, and phase composition of ex-situ Fe–Ni–Cr–Al–Mo–TiCp composites fabricated by three-dimensional plasma metal deposition on 10CrMo9–10 steel

“…In accord with this principal reaction, the intermetallic γ' phase (Ni 3 Al) forms, and can coast the M 23 C 6 carbides. The γ' (L1 2 structure) usually is characterized by a lattice parameter close to that of the γ-matrix, which can impede their distinguishment on HRTEM images, whereas its diffraction pattern is characterized the additional superlattice reflections [42]. Aluminum is one of the alloying elements in the composites and its slight enrichment near M 23 C 6 occurred, but despite intensive observation, the presence of γ′ precipitates was not confirmed.…”

Correlation between the Dendritic Structure and Lattice Parameter of γ′-Phase in Single-Crystalline Turbine Blades Made of Superalloys

“…It is known that changes in the crystal lattice parameters may be related to changes in a lattice misfit and thus also related to changes in strength parameters. It is widely accepted that the large γ/γ lattice misfits influence the yield strength, creep life, and rupture life [28][29][30]. The lattice misfit stresses during thermal exposure may influence the dislocation structure [26] and hence-the creation of lowangle boundaries.…”