Redetermination of the Eutectic Composition of the Ni-P Binary Alloy

A series of Ni-P alloys (Ni-rich) have been synthesized and solidified. It is found that the solidification microstructure of the Ni-19.0 at.%P alloy that has long been regarded as the eutectic composition contains many primary phase dendrites besides rod eutectics. In contrast, only rod eutectic microstructure appears in the samples of Ni-19.6 at.%P, and this alloy shows the lowest end temperature of melting among all the compositions investigated. The results indicate that the actual eutectic composition at the Ni-rich part of the Ni-P system is Ni-19.6 at.%P. The eutectic temperature is determined to be about 1163 K by the differential scanning calorimetry analysis.