Local atomic structure of Ni60Pd20P20 and Ni60Pd20P17B3 bulk metallic glasses and the origin of glass forming ability

Ni60Pd20P17B3 alloy has high glass forming ability (GFA) and forms bulk metallic glass (BMG) which exhibits good mechanical properties of a high strength and a large plasticity. Furthermore the plastic strain of the Ni60Pd20P17B3 BMG increases with lowering temperature by 3.4 times from 295 K to 77 K. In order to know the origin of such mechanical properties and reasons of high glass formability of this alloy from an atomic scale point of view, XAFS and X-ray diffraction measurements for Ni60Pd20P20 and Ni60Pd20P17B3 metallic glasses have been done using the large scale synchrotron radiation. XAFS results of the Ni and Pd K-edge for the Ni60Pd20P20 metallic glass can be well represented by the Pd4Se-type structure model. A result of interatomic distances agrees with those of the ab initio calculations. Temperature dependence of the Debye–Waller factor reflects strong Ni–P and Pd–P bondings and a large thermal fluctuation of metal–metal bondings. A high GFA of the Ni60Pd20P17B3 alloy compared with Ni60Pd20P20 is discussed based on the XAFS and total pair distribution results.