Microstructures of graphite spherulites grown in carbon-saturated liquid nickel matrix under high pressure
- Korea Inst. of Science and Technology, Seoul (Korea, Republic of)
In steel processing, the nodular or ductile cast irons containing spherical particles of carbon have been studied extensively. The spherical particles are known as graphite spherulites (GS). The GSs are obtained by direct solidification of the melt of a ductile cast iron with addition of an inoculant. Besides the GSs in the nodular cast irons, GSs were formed in a liquid Ni-C alloy at atmospheric pressure by adding lanthanum or simply by rapid cooling from a liquid state. Impurities have been assumed to play an important role on the morphological changes of graphite from flakes to spherulites. Interestingly, the GSs were also formed in a liquid nickel at high pressures and temperatures. The formation of GSs was ascribed to an abrupt dissociation of nickel carbide (Ni{sub x}C) during cooling since the Ni{sub x}C could exist only at high pressures and became unstable at atmospheric pressure above 900 C. The formation and growth mechanisms of GSs in the Ni-C alloy have not yet been studied. The objective of the present study is to determine the internal microstructure of GSs formed in a liquid nickel in contact with graphite at diamond-stable conditions and to propose a growth mechanism of GSs.
- OSTI ID:
- 509209
- Journal Information:
- Scripta Materialia, Vol. 36, Issue 12; Other Information: PBD: 15 Jun 1997
- Country of Publication:
- United States
- Language:
- English
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