Browsing by Author "Jyothi Menon"

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An electron microscopic study of a rapidly solidified Al-5 wt. % Co alloy
(1987) Jyothi Menon; C. Suryanarayana
An Al-5 wt. % Co alloy has been rapidly solidified from the liquid state, resulting in the formation of a slightly supersaturated aluminum solid solution and the monoclinic Al9CO2 phase. High-resolution electron microscopy and electron diffraction have been extensively employed to characterize the as-solidified as well as the annealed foils. The high-resolution micrographs of the as-solidified solid solution showed the presence of clustering and D la- type ordering on an extremely small microscopic scale. Annealing at temperatures above 623 K resulted in the precipitation of Al9CO2 in the form of platelets arranged in a Widmanstatten pattern. Orientation relationships between the Al9CO2 platelets and the matrix have been established. Guinier-Preston zonelike platelets on close-packed {111} planes, however, have also been observed upon electron irradiation in the annealed alloys, presumably due to the enhanced diffusivity of cobalt atoms. © 1987, Materials Research Society. All rights reserved.
An electron microscopic study of the decagonal phase in a melt-spun Al-26 wt.% Co alloy
(1987) C. Suryanarayana; Jyothi Menon
[No abstract available]
Dislocation loops in a decagonal Al‒Co alloy
(1988) Jyothi Menon; C. Suryanarayana
[No abstract available]
In situ transformation behavior of icosahedral and decagona quasicrystalline phases
(1988) C. Suryanarayana; Subash Chandra; Jyothi Menon
Results of in situ hot-stage electron microscopic investigations on the transformation behavior of icosahedral Mg32(Al,Zn)49 and decagonal Al-Co quasicrystalline phases are presented. It is shown that in both the cases the transformation begins with the formation of fine holes. This has been interpreted on the basis of the lower density of the quasicrystalline phase. Differences in the transformation behavior between the icosahedral and decagonal phases are highlighted. © 1988, Center for the Study of Law and Religion at Emory University. All rights reserved.
Metallography of a melt-quenched aluminum-cobalt alloy
(1988) Jyothi Menon; C. Suryanarayana
Rapid quenching from the melt of an Al-5 wt.% Co alloy has resulted in the formation of a supersaturated solid solution at very high cooling rates as obtained in the gun technique. With decreasing cooling rate (and increasing thickness of the specimen), e.g., in melt-spun condition, a variety of microstructures has been produced consisting of fine dendritic patterns, cellular-dendritic structures, and precipitation of coarse intermetallic particles. Two metastable phases have also been detected-one with a bcc structure and a = 0.286 nm corresponding to β-AlCo, and the other having an fcc structure with a lattice parameter a = 0.52 nm. Electron microscopy, electron diffraction, and x-ray microanalysis have been extensively employed to fully characterize the phases present in the melt-quenched alloy. © 1988.
On the nature of the quasicrystalline phase in rapidly solidified Al-Co-Si alloys
(1989) Jyothi Menon; C. Suryanarayana
An Al-20 at.% Co-5 at.% Si alloy was rapidly solidified from the liquid state and its structure in the as-quenched as well as transformed states was characterized through transmission electron microscopy techniques. Contrary to the expectation that an icosahedral phase will be produced, this rapidly solidified alloy contained only a decagonal quasicrystalline phase, probably due to the insufficient amount of silicon present to reduce the effective atomic size of the aluminum atoms. Diffraction patterns from this ternary alloy have been found to be more complex than those from the binary Al–Co alloy. The phenomenon of polytypism continues to be observed in the ternary alloy also. Formation of holes during transformation of the quasicrystalline phase has been interpreted on the basis of the lower density of the quasicrystalline phase in comparison to the equilibrium crystalline phases. © 1989, The Japan Institute of Metals. All rights reserved.
STRUCTURE OF VAPOUR-DEPOSITED METGLAS 2826 MB FILMS.
(1985) Jyothi Menon; Challapalli Suryanarayana
Detailed electron microscopic and diffraction investigations have been carried out on vapor-deposited METGLAS 2826 MB (Fe//4//0Ni//3//8Mo//4B//1//8) alloy. In the as-deposited condition, a supersaturated fcc solid solution with a equals 0. 422 nm was found to form. Subsequent annealing resulted in the formation of two phases, one with an fcc structure and a equals 0. 442 nm and the other with a simple cubic structure and a equals 0. 57 nm. Differences in the annealing effects on melt-quenched and vapor-deposited alloy are discussed in detail.