Rapidly quenched Ti-Zr-Ni forms an icosahedral quasicrystalline phase that undergoes a series of endothermic phase transformations upon heating. There are numerous scientific and technological reasons for the study of Ti-Zr-Ni-based alloys, including the kinetics of quasicrystal formation, hydrogen storage in quasicrystalline and crystalline alloys, glass formation, and shape memory alloys. The first X-ray powder diffraction studies of in-situ quasicrystal-crystal and crystal-crystal transformations were performed on this alloy system by users from Washington University (St. Louis) using the facilities of the HTML Diffraction User Center. Avoiding oxidation of these alloys was a particular concern, which was met via use of a combination of systems - gettered inlet gas, furnace chamber bake out, active gettering within the chamber, and a preliminary moderate specimen heating.

Combined with differential scanning calorimetry studies, three separate paths were found for the Ti-Zr-Ni quasicrystal-crystal transformation, the path depending on the alloy composition and level of environmental oxygen. The crystalline products included the Ti₂Ni, Laves, alpha-Ti and beta-Ti phases. In the absence of oxygen, the endothermic transformation of the quasicrystal demonstrates that it is the lowest free energy (most stable) phase. Oxygen stabilizes the Ti₂Ni phase, eliminating both the quasicrystal and the Laves phases, at partial pressures as low as a few hundred ppm. The hydrogen storage and recyclability was studied in a second HTML user project.

Publication: R.M. Stroud, K.F. Kelton, and S.T. Misture , ãHigh Temperature X-Ray and Calorimetric Studies of Phase Transformations in Quasicrystalline Ti-Zr-Ni Alloysä, J. Mater. Res. 12 434-438 (1997)