Formation of Ni 80 P 20 solid solution phase under high pressure
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Formation of NisoP2O solid solution phase under high pressure Z. L. Mao Amorphous Research Laboratory, Beijing University of Aeronautics and Astronautics, Beijing, 100083, China H. Chen Institute of Physics, Academia Sinica, Beijing, 100080, China Ai-Lien Jung Amorphous Research Laboratory, Beijing University of Aeronautics and Astronautics, Beijing, 100083, China (Received 24 June 1993; accepted 19 April 1994)
A N i - P solid-solution phase was obtained by quenching from the melt under a pressure of 4.5 GPa. It was considered as a metastable high-pressure phase. Metastable phases with the same composition as the melt, such as supersaturated solid solutions and amorphous phases, are easily prepared using a high pressure quenching method.
At present, high pressure solid solution phases are obtained mainly by the crystallization of amorphous alloys under pressure1; for example, Pd4oNi4oP2o metallic glass can be transformed into a P d - N i - P solid-solution phase under pressure.2 In the process of crystallization of amorphous alloys, generally the resolution of phases occurs and is completed through the diffusion of atoms. But the process of diffusion of atoms is depressed under pressure and can even be arrested. As a result, an amorphous phase tends to be transformed into a metastable supersaturated solid-solution phase without phase separation. In our experiment, we do not choose the method of crystallization of metallic glass under pressure, but the high-pressure quenching method to prepare metastable phases. Using this method, a Ni8oP2o metastable solid-solution phase is obtained successfully. Whether nucleation or crystal growth, all require atomic diffusion. For the case in which the composition of the crystal phase is the same as the melting phase, a short-range diffusion of atoms across the solid-liquid interface plays a dominant role. Otherwise, nucleation or crystal growth depends on the long-distance diffusion of atoms. The high pressure quenching means that the metallic melt cools down under high pressure so that the long-distance diffusion of atoms in the melt is suppressed. Because solidification with a change of composition from the melt phase is hindered, the melt is easily transformed into metastable phases that have the same composition. Hence, it is possible to obtain a solid solution phase under pressure. J. Mater. Res., Vol. 9, No. 8, Aug 1994
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The Ni8OP2o ingots were prepared from pure Ni (99.99%) and P (99.8%). The ingot was crushed and a fragment of Ni8OP2o was put into a BN sample chamber which was filled with BN powder. Pyrophyllite was used as pressure-transmitting media. The sample chamber was put into a Belt container and a nominal pressure was applied. With a graphite heater, the sample was heated to 1300 K for 1-2 h in order to enable complete melting. Then the electric power was turned off and the sample cooled down. A NiCr-NiAl thermocouple was used to measure the temperature. The cooling rate of the sample was estimated to be
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