The Effect of Alloy Composition on the Metastable Pitting Behavior of Ni-Cr-Mo Alloys in Hot Dilute Chloride Solution

The plane-front solidified eutectic alloys consisting of aligned tantalum monocarbide fibers in a nickel alloy matrix are currently under consideration for future aircraft and gas turbine blades. The MC fibers provide exceptional strength at high temperatures. In these alloys, the Ni matrix is strengthened by the precipitation of the coherent γ' phase (ordered L12 structure, nominally Ni3Al). The mechanical strength of these materials can be sensitively affected by overall alloy composition, and these strength variations can be due to several factors, including changes in solid solution strength of the γ matrix, changes in they γ' size or morphology, changes in the γ-γ' lattice mismatch or interfacial energy, or changes in the MC morphology, volume fraction, thermal stability, and stoichiometry. In order to differentiate between these various mechanisms, it is necessary to determine the partitioning of elemental additions between the γ,γ', and MC phases. This paper describes the results of such a study using energy dispersive X-ray spectroscopy in the analytical electron microscope.

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Influence of Heat Treatments on Microstructures in an Fe-Co-V Alloy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100052572 ◽

1974 ◽

Vol 32 ◽

pp. 512-513

Author(s):

S. Mahajan ◽

M. R. Pinnel ◽

J. E. Bennett

Keyword(s):

Single Phase ◽

Alloy Composition ◽

Supersaturated Solid Solution ◽

Cell Formation ◽

Heat Treatments ◽

Air Cooling ◽

Iced Brine ◽

Transmission Electron ◽

The Matrix ◽

Bcc Structure

The microstructural changes in an Fe-Co-V alloy (composition by wt.%: 2.97 V, 48.70 Co, 47.34 Fe and balance impurities, such as C, P and Ni) resulting from different heat treatments have been evaluated by optical metallography and transmission electron microscopy. Results indicate that, on air cooling or quenching into iced-brine from the high temperature single phase ϒ (fcc) field, vanadium can be retained in a supersaturated solid solution (α2) which has bcc structure. For the range of cooling rates employed, a portion of the material appears to undergo the γ-α2 transformation massively and the remainder martensitically. Figure 1 shows dislocation topology in a region that may have transformed martensitically. Dislocations are homogeneously distributed throughout the matrix, and there is no evidence for cell formation. The majority of the dislocations project along the projections of <111> vectors onto the (111) plane, implying that they are predominantly of screw character.

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NiAl precipitation in Fe-12w/o Cr-5w/o Ni-4w/o Al

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010007480x ◽

1983 ◽

Vol 41 ◽

pp. 202-203

Author(s):

L.E. Murr ◽

J.S. Dunning ◽

S. Shankar

Keyword(s):

Solid Solution ◽

Stainless Steel ◽

Stainless Steels ◽

Alloy Composition ◽

Chromium Content ◽

Scale Up ◽

Optical Metallography ◽

Property Evaluation ◽

310 Stainless Steel ◽

Microstructural Studies

Aluminum additions to conventional 18Cr-8Ni austenitic stainless steel compositions impart excellent resistance to high sulfur environments. However, problems are typically encountered with aluminum additions above about 1% due to embrittlement caused by aluminum in solid solution and the precipitation of NiAl. Consequently, little use has been made of aluminum alloy additions to stainless steels for use in sulfur or H2S environments in the chemical industry, energy conversion or generation, and mineral processing, for example.A research program at the Albany Research Center has concentrated on the development of a wrought alloy composition with as low a chromium content as possible, with the idea of developing a low-chromium substitute for 310 stainless steel (25Cr-20Ni) which is often used in high-sulfur environments. On the basis of workability and microstructural studies involving optical metallography on 100g button ingots soaked at 700°C and air-cooled, a low-alloy composition Fe-12Cr-5Ni-4Al (in wt %) was selected for scale up and property evaluation.

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AEM analysis of solidification catalysts in atomized Fe-Ni

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100144395 ◽

1986 ◽

Vol 44 ◽

pp. 584-585

Author(s):

Matthew R. Libera

Keyword(s):

Powder Particle ◽

Alloy Composition ◽

Particle Diameter ◽

Metastable Phases ◽

Liquid Droplets ◽

Nucleation Kinetics ◽

Ni Alloys ◽

Nonequilibrium Solidification

The liquid droplets produced by atomization processes are believed to undergo substantial supercooling during solidification, because the catalytic heterogeneities, for statistical reasons, tend to be isolated in the larger droplets. This supercooling can lead to the nucleation of metastable phases. As part of a study on the effect of liquid supercooling on nonequilibrium solidification, three binary Fe-Ni alloys have been produced by conventional argon atomization (Fe-20Ni, Fe-30Ni, and Fe-40Ni). The primary variables in these experiments are: i) the alloy composition; and ii) the powder particle diameter (inversely proportional to supercooling). Of particular interest in this system is the competitive nucleation kinetics between the stable fee and metastable bec phases. Bcc is expected to nucleate preferentially with decreasing %Ni and decreasing particle diameter.

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