Effects of chromium on crack growth and oxidation in nickel aluminide

Transmission electron microscope investigation has been performed concerning the effect of Cr-precipitation on the mechanical properties of B2-ordered NiAl containing 4 mol.% to 8 mol.% of Cr. By aging at temperatures around 973 K after solution annealing, fine spherical precipitates appeared homogeneously in the NiAl matrix and the alloys hardened appreciably. The selected area electron diffraction patterns have not revealed any additional extra-spots during aging, because the Cr-particles have a cube-cube orientation relationship and keep perfect coherency with the ordered matrix lattice. Dislocations bypass the particles during deformation. Although the dispersion of Cr-particles increases the yield strength of NiAl at intermediate temperature, the strength decreases appreciably at higher temperatures. Atom location by channeling enhanced microanalysis technique has been used to determine the site occupancy of Cr in NiAl.

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“…The addition of chromium is also thought to be effective to prevent hot embrittlement caused by oxygen enrichment at the grain boundaries [3].…”

Section: Introductionmentioning

confidence: 99%

RETRACTED ARTICLE: The behavior of α-Cr precipitation on the high temperature deformation of B2-ordered NiAl

2009

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“…This in turn enhances the possibility of [111] slip in NiAl, which is required to satisfy the Von Mises criterion for ductility of polycrystalline materials. The addition of chromium is also thought to be an effective means of preventing hot embrittlement caused by oxygen enrichment *Corresponding author: hancs@hoseo.edu ©KIM and Springer at the grain boundaries [14]. A number of studies have been done on the pseudo-binary NiAl-Cr section [15].…”

Section: Introductionmentioning

confidence: 99%

RETRACTED ARTICLE: A study on the microstructure of precipitation strengthened B2-ordered NiAl

Han

2011

Met. Mater. Int.

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Microstructural control to produce a multiphase structure and there by improve the high temperature strength as well as low temperature ductility of intermetallics has received much attention. A transmission electron microscopy investigation has been performed in the present work on the precipitation of supersaturated B2-ordered (Ni,Co)Al and α-Cr in B2-ordered β-NiAl with different stoichiometry. Precipitation behavior and hardening were investigated by measuring the hardness variation. The hardness of (Ni,Co)Al and β-NiAl increases appreciably by the fine precipitation of (Ni,Co)2Al and α-Cr, and overage softening occurs after prolonged aging. In the case of B2-ordered (Ni,Co)Al, the (Ni,Co)2Al phase has a hexagonal structure and takes a rod-like shape with the long axis of the rod parallel to the <111> directions of the B2 matrix. By aging at temperatures below 873 K, a long period superlattice structure appears in the hexagonal (Ni,Co)2Al phase. The orientation relationship between the (Ni,Co)2Al precipitates and the B2-(Ni,Co)Al matrix is found to be (0001)p//(111)B2 and [1210]p//[110]B2, where the suffixes p and B2 denote the (Ni,Co)2Al precipitate and the B2-(Ni,Co)Al matrix, respectively. (Ni,Co)Al hardens appreciably by fine precipitation of the (Ni,Co)2Al phase. On the other hand, in the case of B2-NiAl, perfect lattice coherency is retained at the interfaces between the α-Cr particles and the matrix during the initial stage of aging. After prolonged aging, a loss of coherency occurs by the attraction of matrix dislocations to the particle/matrix interface followed by climbing around the particles.

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“…Such ªoverdopingº caused by reactive elements has been observed in other alumina-forming materials, too; e.g. in FeCr-5Al alloys caused by yttrium and titanium/zirconium [13], in Fe 3 Al and Ni 3 Al caused by cerium [17,18,27,28], in FeCr-5Al alloys caused by mischmetal [18] and in ODS alloys caused by yttrium [14]. The upper limit of reactive elements to avoid overdoping depends on the total concentration of reactive elements and on the aluminium concentration.…”

Section: Discussionmentioning

confidence: 99%

Factors affecting the oxidation behaviour of thin Fe-Cr-Al foils. Part II: The effect of alloying elements: Overdoping

Klöwer¹

2000

Materials and Corrosion

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Effects of chromium on crack growth and oxidation in nickel aluminide

Cited by 28 publications

References 11 publications

RETRACTED ARTICLE: The behavior of α-Cr precipitation on the high temperature deformation of B2-ordered NiAl

RETRACTED ARTICLE: The behavior of α-Cr precipitation on the high temperature deformation of B2-ordered NiAl

RETRACTED ARTICLE: A study on the microstructure of precipitation strengthened B2-ordered NiAl

Factors affecting the oxidation behaviour of thin Fe-Cr-Al foils. Part II: The effect of alloying elements: Overdoping

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