Line Phenomenon Of Electron Concentration Of The Ternary Quasicrystal Alloy System

Formation rule of quasicrystals is a fundamental problem. Following previous work in our group, the present work investigated Ti-Zr-Fe and Ti-Zr-Co alloys to search for the relationship between quasicrystals and their approximants, with the aim of verifying our empirical composition rule for quasicrystals. Samples were prepared by suction-casting method and analyzed by XRD, SEM and TEM. The suction-casting cooling process was simulated to study in-depth distribution of cooling rate. The results are summarized in the following.1. Icosahedral quasicrystal Ti₆0Zr₁5Fe₂5 are obtained. It has four approximants, namely the Ti₂Ni-type fcc phase, the p-type bcc phase, the a-1/1 approximant, and MgZn₂-type hep phase. The valence electron concentrations (e/a) of the quasicrystal and all its four approximants are close to 1.125, which is consistent with the e/a-constant theory for ternary quasicrystals.2. In Ti-Zr-Co alloy system, only approximants (the hep Laves phase, the a phase and the Ti₂Ni fcc phase) were observed.3. The cooling rate in the outmost layer of the sample is calculated to be about10⁷ K/s through computer simulation. The average cooling rate is about 10³ K/s and 10 K/s at 50pm from surface layer and at the center, respectively.4. The computer simulation also reveals that water cooling is not important role when the thickness of the copper mould exceeds 22mm. Therefore, in order to fabricate samples containing more quasicrystals, thinner copper mould is needed for the water cooling system to be effective.5. After a literature survey, we show that the e/a-constant line is a common phenomenon in ternary quasicrystal alloy systems. This rule can be applied in finding quasicrystals and their approximates.