Characterization of segregation in nickel and titanium aluminides
- Oak Ridge National Lab., TN (United States). Metals and Ceramics Div.
Atom probe field ion microscopy has been used to characterize the distributions of microalloying additions in the microstructure of a variety of nickel and titanium aluminides. In Ni{sub 3}Al, boron additions were found to segregate to dislocations, low angle boundaries, stacking faults, antiphase boundaries, and grain boundaries. The boron and aluminum levels at grain boundaries were found to vary both from boundary to boundary and also along an individual boundary segment. In some cases, a boron-enriched film up to {approximately}3 nm thick was observed. In aluminum-enriched Ni{sub 3}Al, ultrafine clusters containing up to approximately 10 boron atoms were detected in the matrix. In contrast, the majority of the boron additions in NiAl was determined to be in the form of ultrafine MB{sub 2}-type precipitates. These precipitates offset the benefits of the boron segregation to the high angle grain boundaries. In molybdenum-doped NiAl, atom probe analyses indicated extremely low solubilities of the molybdenum and other trace impurities in the matrix and significant enrichments of molybdenum, nitrogen and silicon, boron, and iron at the grain boundaries. In boron-doped two phase {alpha}{sub 2} + {gamma} TiAl containing chromium, niobium, and tungsten, the boron level was found to be significantly depleted from the bulk level in both the {alpha}{sub 2} and {gamma} phases and a variety of coarse borides including TiB, TiB{sub 2} and a finer chromium-enriched (Ti, Cr){sub 2}B precipitate was observed. The tungsten and chromium were determined to partition preferentially to the {alpha}{sub 2} phase and also to segregated to the {alpha}{sub 2}-{gamma} and {gamma}-{gamma} interfaces. These results indicate that a significant proportion of the microalloying elements are consumed by the boride precipitates.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE Office of Energy Research, Washington, DC (United States)
- DOE Contract Number:
- AC05-96OR22464
- OSTI ID:
- 459428
- Report Number(s):
- CONF-970486-1; ON: DE97004128; TRN: AHC29708%%93
- Resource Relation:
- Conference: International symposium on structural intermetallics, Champion, PA (United States), 27 Apr - 1 May 1997; Other Information: PBD: [1997]
- Country of Publication:
- United States
- Language:
- English
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