Of Ti-zr-ni System Block Of Pure Quasi-crystal Performance

This thesis consists of two parts:In the first part, the state-of-the-art of quasicrystals (QCs) are introduced briefly. Then the composition optimization criteria of quasicrystals as derived from ternary phase diagrams are explained.QCs and its approximants are Hume-Rothery phases, which are all located near a straight line with a constant e/a ratio (e/a-constant line phenomenon) in a given ternary phase diagram. We further noticed that a ternary QC, its related binary QC, and the third element lie along a straight line (e/a-variant line phenomenon). The ideal composition of a ternary QC is located at the intersection point of the e/a-constant and the e/a-variant lines.The above phase diagram features of quasicrystal systems constitute the empirical formation criteria to optimize and to search for new QCs compositions.In the second part of the thesis, we prepare almost pure-phase quasicrystal Ti-Zr-Ni using the optimized composition. Then we carry out a series of experiments to measure its mechanical, corrosion, wear performances.The ambient mechanical properties of the Ti40Zr40Ni20 bulk quasicrystal are examined by using an HX-1000 microhardness tester and an une-axial compression machine. The microhardness value is about 5.5GPa, the fracture strength 430 MPa, and the elastic strain 1.49%. These data are remarkably higher than those of the conventional Al-based quasicrystals and are comparable to those of the Zr-based and Ti-based bulk metallic glasses. The fracture of Ti40Zr40Ni20 quasicrystal is of cleavage type,typical for a brittle transgranular fracture. However, the quasicrystal tolerates a certain plastic deformation under the complicated stress state in the hardness tests.The quasicrystal samples manifest the best corrosion resistance against alkali and the worst against salt in comparison with crystallized samples after annealing. All the samples have better corrosion resistances than stainless steels.The friction and wear characteristics of the Ti40Zr40Ni20 bulk quasicrystalline under dry sliding against the GCr15 steel is investigated. The crystalline phases precipitated after the annealing process are also evaluated under the same testing conditions as a comparison. Results indicated that the Ti40Zr40Ni20 bulk quasicrystal has a friction coefficients 0.13 which is lower than 0.14 of the crystal phases. The microhardness value of the Ti40Zr40Ni20 bulk quasicrystal is about 5.6GPa under a pressure of 400mN, while that of the crystalline phase is 2.0GPa. Both of them are characterized by abrasive wear, but the Ti40Zr40Ni20 bulk quasicrystal manifests abetter friction resistance.The thermal expansion coefficient of the Ti40Zr40Ni20 quasicrystal is similar to platinum, and increases with increasing temperature. The Ti40Zr40Ni20 quasicrystal has a very high resistivity, about 3230u.Cm, which is comparable to those of the Al-based quasicrytals.