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.
(Received June 6, 1989)
Keywords: decagonal quasicrystal, aluminum-cobalt-silicon, rapid solidification, transmission electron microscopy, selected area diffraction, polytypism
*Department of Metallurgical Engineering, Banaras Hindu University, Varanasi-221 005, India.
**Present address: Wright Research and Development Center, WRDC/MLLS, Wright-Patterson Air Force Base, OH 45433-6533, USA.