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Non-equilibrium Microstructure and Thermal Stability of Plasma-sprayed Al–Si Coatings

Published online by Cambridge University Press:  01 August 2005

K.H. Baik ,
H.K. Seok ,
H.S. Kim  and
P.S. Grant
K.H. Baik*
Affiliation:
Department of Metallurgical Engineering, Chungnam National University, Yuseong, Daejeon 305-764, Korea
H.K. Seok
Affiliation:
Division of Materials Science and Technology, Korea Institute of Science and Technology, Seoul 136-791, Korea
H.S. Kim
Affiliation:
Department of Metallurgical Engineering, Chungnam National University, Yuseong, Daejeon 305-764, Korea
P.S. Grant
Affiliation:
Department of Materials, University of Oxford, Oxford OX1 3PH, United Kingdom
*
a) Address all correspondence to this author. e-mail: [email protected]
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Abstract

A splat-quenched, thick Al–Si deposit was manufactured by low-pressure plasma spraying (LPPS) and investigated in terms of microstructural inhomogeneity, Si solid solubility in α–Al, formation of metastable phases, and thermal stability. The LPPS Al–Si deposit had an inhomogeneous, layered microstructure consisting of splat-quenched lamellae and the incorporation of unmelted or partially melted particles. The splat-quenched Al–Si lamellae were formed by deposition of a fully liquid droplet and had an almost featureless microstructure at relatively low magnifications. There was a significant reduction in the α–Al lattice parameter in the LPPS Al–Si deposit because of extended Si solubility in the α–Al matrix. Transmission electron microscopy investigations showed that the splat quenching of liquid Al–Si droplet led to (i) columnar grain growth of α–Al(Si), (ii) formation of nano-sized Si precipitates in the Al matrix which was supersaturated with Si; and (iii) formation of amorphous Si phase embedded in the crystalline Al matrix. On reheating, the amorphous Si transformed into fine crystalline Si by interdiffusion of Al and Si atoms. Simultaneously, Si precipitation occurred in the supersaturated α–Al matrix. The overall activation energy for the Si crystallization/precipitation was estimated as ∼81 kJ/mol from a modified Kissinger analysis.

Keywords

Rapid solidificationSpray depositionTransmission electron microscopy (TEM)
Type
Articles
Information
Journal of Materials Research , Volume 20 , Issue 8 , August 2005 , pp. 2038 - 2045
Copyright
Copyright © Materials Research Society 2005

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