Atom Probe Field-Ion Microscopy Characterization of Nickel and Titanium Aluminides

AbstractThe near atomic spatial resolution of the atom probe field ion microscope permits the elemental characterization of internal interfaces, grain boundaries and surfaces to be performed in a wide variety of materials. Information such as the orientation relationship between grains, topology of the interface, and the coherency of small precipitates with the surrounding matrix may be obtained from field ion microscopy. Details of the solute segregation may be obtained at the plane of the interface and as a function of distance from the interface for all elements simultaneously from atom probe compositional analysis. The capabilities and limitations of the atom probe technique in the characterization of internal interfaces is illustrated with examples of grain boundaries and interphase interfaces in a wide range of materials including intermetallics, model alloys, and commercial steels.

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Atom Probe Field Ion Microscopy of Titanium Aluminides

Microscopy and Microanalysis ◽

10.1017/s1431927600020626 ◽

1998 ◽

Vol 4 (S2) ◽

pp. 100-101

Author(s):

D. J. Larson ◽

M. K. Miller

Keyword(s):

Mechanical Properties ◽

Titanium Aluminides ◽

Atom Probe ◽

Probe Field ◽

Field Ion Microscopy ◽

Ambient Temperatures ◽

Preferential Evaporation ◽

Ion Microscopy ◽

Analytical Tools

Titanium aluminides have a number of potential high temperature applications due to their good elevated-temperature mechanical properties, low density, and good creep and oxidation resistance. However, fabrication of commercial components of these materials has been impeded by their poor mechanical properties at ambient temperatures. Significant efforts with various degrees of success have been made to improve the mechanical properties of these TiAl alloys by doping them with a variety of different elements including B, C, Cr, Er, Fe, Mn, Mo, Ni, Nb, P, Si, Ta, V and W. One of the optimum analytical tools for investigating the effects of these additions on the microstructure is the atom probe field ion microscope. However, relatively few studies of titanium aluminides, compared to some other intermetallic compounds, have performed by atom probe field ion microscopy. This lack of attention can be attributed to the brittle nature of the material, in-situ transformations that occur during the field ion microscopy and preferential evaporation problems that were encountered in some of the early studies.

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Characterization of Phosphorus Segregation in Neutron-Irradiated Pressure Vessel Steels by Atom Probe Field Ion Microscopy

MRS Proceedings ◽

10.1557/proc-373-113 ◽

1994 ◽

Vol 373 ◽

Cited By ~ 3

Author(s):

M. K. Miller ◽

R. Jayaram ◽

K.F. Russell

Keyword(s):

Pressure Vessel ◽

Boundary Segregation ◽

Atom Probe ◽

Probe Field ◽

Phosphorus Segregation ◽

Field Ion Microscopy ◽

Narrow Region ◽

Pressure Vessel Steels ◽

Ion Microscopy

AbstractAn atom probe field ion microscopy characterization of A533B and Russian VVER 440 and 1000 pressure vessel steels has been performed to determine the phosphorus coverage of grain and lath boundaries. Field ion micrographs of grain and lath boundaries have revealed that they are decorated with a semi-continuous film of discrete brightly-imaging precipitates that were identified as molybdenum carbonitride precipitates. In addition, extremely high phosphorus levels were measured at the boundaries. The phosphorus segregation was found to be confined to an extremely narrow region indicative of monolayer-type segregation. The phosphorus coverages determined from the atom probe results of the unirradiated materials were in excellent agreement with predictions based on McLean's equilibrium model of grain boundary segregation. The boundary phosphorus coverage of a neutron-irradiated weld material was significantly higher than that observed in the unirradiated material.

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