Phase Evolution and Thermal Expansion Behavior of a γ′ Precipitated Ni-Based Superalloy by Synchrotron X-Ray Diffraction

Abstract

The phase evolution and thermal expansion behavior in superalloy during heating play an essential role in controlling the size and distribution of precipitates as well as 2 optimizing thermomechanical properties. Synchrotron X-ray diffraction is able to go through the interior of sample and can be carried out with in-situ environment, thus it can obtain more statistics information in real time comparing with traditional methods, such as electron and optical microscopies, etc. In this study, in-situ heating synchrotron X-ray diffraction was carried out to study the phase evolution in a typical γ′ phase precipitation strengthened Ni-based superalloy, Waspaloy, from 29 °C to 1050 °C. The γ′, γ, M23C6 and MC phases, including their lattice parameters, misfits, dissolution behavior and thermal expansion coefficients were mainly investigated. The γ′ phase and M23C6 carbides appeared obvious dissolution during heating and re-precipitated when the temperature dropped to room temperature. Combining with the microscopy results, we can indicate that the dissolution of M23C6 leads to the growth of grain and γ′ phase cannot be completely dissolved for the short holding time above the solution temperature. Besides, the coefficients of thermal expansions of all the phases are calculated and fitted as polynomials.

Double Diffraction or ω-Fe Diffraction in Body-Centered Cubic {112}<111>-Type Twinned Martensite

“…Unlike a completely disordered crystal structure, some crystals can have an ordered structure, such as the atomic layers in ABABAB-type stacking structure (hexagonal close-packing (hcp) structure), or diamond-like structure, as shown in Figure a. This kind of ordering structure tends to produce extra (double diffraction) or superlattice peaks in X-ray powder diffraction patterns and electron diffraction patterns. − In Figure b, the double diffraction in electron diffraction patterns can also come from dual-phase or multiphase structure, such as the one from the matrix phase and the other from fine precipitates embedded in the matrix. A twin is commonly regarded as a dual-component system.…”