Effect of Pd Substitution on Phase Formation and Stability in Ti-Zr-Ni Quasicrystalline Alloys

Pd can be used as an adding element to improve hydrogenation properties of Ti-Zr-Ni quasicrystalline alloys. However, the action mechanism of Pd addition is unclear yet. The effects of Pd substituting Ti and Zr in Ti45Zr38Ni17 and Ti40Zr40Ni20 alloys were studied by means of XRD, TEM and DSC examination. The results show that icosahedral quasicrystal can be formed purely through 4%∼6% Pd substitution for Ti or 4% for Zr in the Ti45Zr38Ni17 alloy, as well as 3%∼4% for Ti or possibly below 3% for Zr in the Ti40Zr40Ni20 alloy. This indicates a higher substitution limit for Ti in order for the heritance of the quasicrystal phase. Two derived quasicrystals Ti39Zr38Ni17Pd6 and Ti36Zr40Ni20Pd4 can be transformed into crystalline phases after annealing at 400 °C, demonstrating their lower thermo-stabilities in comparison to such Ti-Zr-Ni alloys being stable at about 700 °C. Both the replacement tendency and the decrease of the thermostability of quasicrystal phase might be ascribed to appropriate atomic size of Pd.