EFFECT OF COOLING RATES ON THE MICROSTRUCTURE AND CRYSTALLOGRAPHIC PROPERTIES OF Ni-Ni3B EUTECTIC

Abstract

The crystallographic and microstructural properties of the binary lamellar Ni – Ni₃B eutectic prepared under various cooling rates had been investigated using differential thermal analysis (DTA), scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). It was observed that for low cooling rates, the theoretical law “λ²V = constant” was valid. However, for high solidification rates (meltspinning), the interlamellar spacing (λ) seemed independent of the cooling rate. Crystallographic orientation relationships between the two phases of the eutectic under three cooling conditions were proposed. In the DTA mode (slow cooling), the relationship between the two phases was stable. However as the cooling rates increased ( quenching and meltspun modes), the relationship tended towards metastability.


KEY WORDS: alloy, solidification, microstructure, eutectic, volume fraction.


Global Jnl Pure & Applied Sciences Vol.10(1) 2004: 101-110