Premartensitic microstructures as seen in the high-resolution electron microscope: A study of a Ni-Al alloy

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The present study indicates that the B2 ..beta..-phase in quenched Ni/sub 62.5/Al/sub 37.5/ is distorted by displacement waves involving a planar shufflin of atoms resembling the final 7R martensite structure and with wavelenghts of the order of 1.3 nm. The appearance of a <110><110> type modulation with the indicated periodicity corresponds well with recent inelastic neutron scattering results which reveal nonlinear behavior in the TA<110> phonon dispersion curve around the same wavelengths indicating a partial lattice softening for such waves. In bulk material all six equivalent wave-vectors are equally present. These distortional modulations are configured in some form of three-dimensional ... continued below

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Pages: 5

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Schryvers, D.; Tanner, L. & Van Tendeloo, G. February 12, 1988.

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The present study indicates that the B2 ..beta..-phase in quenched Ni/sub 62.5/Al/sub 37.5/ is distorted by displacement waves involving a planar shufflin of atoms resembling the final 7R martensite structure and with wavelenghts of the order of 1.3 nm. The appearance of a <110><110> type modulation with the indicated periodicity corresponds well with recent inelastic neutron scattering results which reveal nonlinear behavior in the TA<110> phonon dispersion curve around the same wavelengths indicating a partial lattice softening for such waves. In bulk material all six equivalent wave-vectors are equally present. These distortional modulations are configured in some form of three-dimensional assembly. Following the interpretation given above, it can be concluded that a one-dimensional domain structure along one of six <110> directions may exist. However, the beating of six displacement waves with apparently uncorrelated phase and wavelengths rules out the existence of a ''conventional'' three-dimensional domain structure. For this reason it is uncertain whether much more information can be gained from such image simulations. There are now numerous indications that the underlying structure to the tweed contrast in this alloy is a precursor effect of the martensitic transformation. However, a detailed description of the effective correlation between the distorted parent phase and the martensitic product phase has yet to be developed. Recent HREM results reveal the existence of a sequence of different structures in the transition region between the modulated ..beta..-phase and the martensitic phase, depending on parameters such as the local composition and stress. Such transition structures include modulated k..beta..-phase in which only one (110) modulation is preferred or in which the periodicity differs from the above described 1.3 nm and the FCT L1/sub o/ martensite with single shear defects. 1 fig., 26 refs.

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Pages: 5

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NTIS, PC A02/MF A01; 1.

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  • NATO advanced study institute on alloy phase stability, Crete, Greece, 14 Jun 1987

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  • Other: TI88008042
  • Report No.: UCRL-98231
  • Report No.: CONF-8706103-9
  • Grant Number: W-7405-ENG-48
  • Office of Scientific & Technical Information Report Number: 5030273
  • Archival Resource Key: ark:/67531/metadc1052614

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  • February 12, 1988

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  • Jan. 22, 2018, 7:23 a.m.

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  • Jan. 26, 2018, 3:36 p.m.

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Schryvers, D.; Tanner, L. & Van Tendeloo, G. Premartensitic microstructures as seen in the high-resolution electron microscope: A study of a Ni-Al alloy, article, February 12, 1988; United States. (digital.library.unt.edu/ark:/67531/metadc1052614/: accessed December 17, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.