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 alloy have been prepared by quenching the melt in sealed quartz ampoules in standing water at room temperature. The diameter of the sample, as well as the thickness of the ampoule wall, plays an important role in 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 diameter retain a primarily amorphous phase, characterized by two broad halos 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 intermediate (I) phase, of composition close to a metastable cubic phase NiZr2 supersaturated by Zr, along with hcp-Zr and tetragonal (T) Ni11Zr9 phase. On thermal annealing at 1050 K, the I-phase precipitates the excess Zr and results in a refined nanocrystalline microstructure of T-phase and hcp-Zr.