OBSERVATION OF A METASTABLE INTERMEDIATE PHASE IN WATER QUENCHED ZR65.0AL7.5NI10.0CU17.5 CYLINDERS

The cylinders of 4, 6 and 10 mm diameters of Zr65.0Al7.5Ni10.0Cu1.75 a lloy have been prepared by quenching the melt in sealed quartz ampoule s in standing water at room temperature. The diameter of the sample, a s well as the thickness of the ampoule wall, plays an important role i n designing the final microstructure of the sample at moderate cooling rate of the order of 10(2) K/s. Thus the samples quenched in 4 mm dia meter retain a primarily amorphous phase, characterized by two broad h alos of scattering vector k = 25.6 and 6.6 +/- 0.1 nm(-1) in the X-ray diffractogram. Samples of larger diameters have precipitates of an in termediate (I) phase, of composition close to a metastable cubic phase NiZr2 supersaturated by Zr, along with hcp-Zr and tetragonal (T) Ni11 Zr9 phase. On thermal annealing at 1050 K, the I-phase precipitates th e excess Zr and results in a refined nanocrystalline microstructure of T-phase and hcp-Zr.