Lattice misfits in four binary Ni-base {gamma}/{gamma}{prime} alloys at ambient and elevated temperatures
- International Rectifier, El Segundo, CA (United States)
- Univ. of California, Los Angeles, CA (United States). Dept. of Materials Science and Engineering
High-temperature X-ray diffractometry was used to determine the in situ lattice parameters, a{sub {gamma}} and a{sub {gamma}{prime}}, and lattice misfits, {delta} = (a{sub {gamma}{prime}} {minus} a{sub {gamma}})/a{sub {gamma}}, of the matrix ({gamma}) and dispersed {gamma}{prime}-type (Ni{sub 32}X) phases in polycrystalline binary Ni-Al, Ni-Ga, Ni-Ge, and Ni-Si alloys as functions of temperature, up to about 680 C. Concentrated alloys containing large volume fractions of the {gamma}{prime} phase ({approximately}0.40 to 0.50) were aged at 700 C to produce large, elastically unconstrained precipitates. The room-temperature misfits are 0.00474 (Ni-Al), 0.01005 (Ni-Ga), 0.00626 (Ni-Ge), and {minus}0.009226 (Ni-Si), with an estimated error of {+-}4 pct. The absolute values of the lattice constants of the {gamma} and {gamma}{prime} phases, at compositions corresponding to thermodynamic equilibrium at about 700 C, are in excellent agreement with data from the literature, with the exception of Ni{sub 3}Ga, the lattice constant of which is much larger than expected. In Ni-Ge alloys, {delta} decreases to 0.00612 at 679 C, and in Ni-Ga alloys, the decrease is to 0.0097. In Ni-Si and Ni-Al alloys, {delta} exhibits a stronger temperature dependence, changing to {minus}0.00285 at 683 C (Ni-Si) and to 0.00424 at 680 C (Ni-Al). Since the times required to complete the high-temperature X-ray diffraction (XRD) scans were relatively short (2.5 hours at most), the authors believe that the changes in {delta} observed are attributable to differences between the thermal expansion coefficients of the {gamma} and {gamma}{prime} phases, because the compositions of the phases in question reflect the equilibrium compositions at 700 C. Empirical equations are presented that accurately describe the temperature dependences of a{sub {gamma}}, a{sub {gamma}{prime}}, and {delta} over the range of temperatures of this investigation.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 417849
- Journal Information:
- Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science, Vol. 27, Issue 10; Other Information: PBD: Oct 1996
- Country of Publication:
- United States
- Language:
- English
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