Measurement of the unconstrained misfit in the nickel-base superalloy CMSX-4 with CBED
- Technische Univ., Berlin (Germany). Inst. fuer Metallforschung
- Friedrich-Schiller-Univ., Jena (Germany). Inst. fuer Materialwissenschaft
The microstructure of nickel base superalloys is built up by the L1{sub 2} {gamma}{prime} phase embedded coherently in a fcc matrix phase. The lattice parameters of the two phase generally differ by a small amount so that an unconstrained misfit {delta}{sub u} = 2 {center_dot} (a{sub {gamma}{prime}} {minus} a{sub {gamma}})/(a{sub {gamma}{prime}} + a{sub {gamma}}) between lattice constants a{sub {gamma}{prime}} of {gamma}{prime} precipitates and a{sub {gamma}} of the matrix phase can be defined. This unconstrained misfit is an important parameter for modeling mechanical behavior of the alloys. Unfortunately, the constrained misfit {delta}{sub c} is measured in X-ray and neutron diffraction experiments. In addition, both experimental set-ups yield integral results so that local lattice parameter differences in the macro- or microstructure can not be detected. In this investigation the authors use Convergent Beam Electron Diffraction, CBED, as a method with high lateral resolution so that misfit variations due to the dendritic structure as well as local differences in the microstructure can be measured. They have developed three different methods for the determination of {delta}{sub u}. The first applies CBED considering the results of FEM calculations by L. Mueller et al., were low strains are postulated in the crossings of matrix channels and in the center of {gamma}{prime} cubes; the second takes advantage of the preferential etching of the {gamma}{prime} phase by distinct etchings and the third one uses the Finite Element Method, FEM.
- Sponsoring Organization:
- Deutsche Forschungsgemeinschaft, Bonn (Germany)
- OSTI ID:
- 616230
- Journal Information:
- Scripta Materialia, Journal Name: Scripta Materialia Journal Issue: 6 Vol. 38; ISSN 1359-6462; ISSN SCMAF7
- Country of Publication:
- United States
- Language:
- English
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