Atom probe and field ion microscope investigation of the negative creep mechanism in nickel-base superalloy
Introduction
Negative creep is caused by contraction of the material during the creep test. The phenomenology of negative creep is the changes of the microstructure of nickel-base superalloy during the creep test 1, 2. Using the field ion microscope and the atom probe (AP–FIM) the atomic arrangement of the metal surface can be observed directly and the specimen analyzed chemically, over small regions (a few atoms) with atomic resolution. AP–FIM is therefore well suited for studies of the microstructure of an alloy that has undergone the creep test. The microstructure of the nickel-base superalloy consists essentially of an f.c.c solid solution (r) and finely-dispersed ordered precipitate (r′). In general, the mechanisms of phase transformations and short-range ordering have been proposed for explanation of the negative creep phenomenon 3, 4in the nickel-base superalloy, but experimental evidence is still lacking. The purpose of the present work is to study the coarseness and the microstructure of precipitates in the nickel base superalloy by AP–FIM during the creep test. The changes in the concentration of Ni, Al and Cr were determined by following the sample AP depth profile. The AP experiment established for the first time that reciprocal diffusion of Al and Cr atoms is created in the r–r′ phase boundary when the sample has suffered creep. The replacement of Al atoms by Cr atoms in the crystal lattice of Ni3Al induces the lattice constant to decrease. It is shown that the negative creep effect in this material results mostly from reciprocal diffusion of Al and Cr between the r–r′ phase boundary.
Section snippets
The experimental procedure and results
The experiments were carried out in an AP–FIM, the detailed description of the equipment being available elsewhere [5]. The field ion microscope is capable of imaging the surface of a tip and each distinct point on the image is an individual atom, provided that the specimen is cooled by liquid nitrogen. The mass spectrometer is used to analyze the sample chemically, with single atom sensitivity for all elements. The instrument has a straight flight tube (mass spectrometer of time-flight) and is
Discussion
The microstructure of the nickel-base superalloy consists of essentially a f.c.c. solid solution (r) and dispersed ordered precipitated (r′), which r′ phase occupied about 45 wt.%, but the lattice parameter is decreased by about 4×10−3 A [6]. The AP mass spectrum of the nickel-base superalloy by AP selective area analysis is shown in Fig. 3, where (a) displays the result of AP analysis of the r′ phase and (b) of the r phase. The mass spectrum shows the difference of the concentrations atoms of
Acknowledgements
This project was supported by NSFC and NAMCC under grant number 59291000. The author would like to thank Mr Zhang Yu for providing the samples for the tests.
References (7)
Z. Metallkd.
(1994)- M. Heilmater, B. Reppich, Creep Fracture Eng. Mater. Structure (1993)...
- et al.
Trans. Am. Soc. Met.
(1959)
Cited by (6)
Effect of creep deformation on the microstructure evolution of Inconel 625 nickel-based superalloy additively manufactured by laser powder bed fusion
2023, Materials Science and Engineering: APhase transformation and segregation to lattice defects in Ni-base superalloys
2007, Microscopy and MicroanalysisDifferent roles of stacking fault energy and diffusivity in the creep performance of nickel-based single-crystal superalloys
2021, Materials Research ExpressNextGenPower - Demonstration and component fabrication of nickel alloys and protective coatings for steam temperatures of 750°C
2014, Advances in Materials Technology for Fossil Power Plants - Proceedings from the 7th International ConferenceEvaluation of susceptibility of Alloy IN740 to HAZ stress-relaxation cracking
2013, Welding JournalAP-FIM study on the microstructures of TiAl intermetallic compounds fabricated by ingot metallurgy and centrifugal spray deposition
2000, Acta Metallurgica Sinica (English Letters)