| For many years, Ni-based super alloys have been one of the leading materials used in high temperature due to their excellent high temperature performance. Al, Si, Cr, Ta and Zr are all important alloying elements which can improve the fatigue, creep, room temperature tensile, hot-corrosion and oxidation resistance of the super alloys. To better super-alloys' comprehensive qualities and to meet the demand of the rapid development in modern aeronautics, it is necessary to study the phase equilibrium relation and phase stability in super-alloy system both experimentally and thermodynamically. In this dissertation, an investigation of the Ni-based system was carried out systematically by coupling the diffusion triple methods, alloying methods and EMPA microanalysis with the Calphad technique. Its detailed content includes:1) The experimental study and thermodynamic assessment of theNi-Ta binary systemThe equilibrium composition of the solid phases in Ni-Ta binary system at 1123 K, 1173 K and 1223 K. were determined experimentally. Based the present experimental data and the data from literature, the Ni-Ta binary was then re-evaluated. A set of self-consistent parameters describing the Gibbs energy of each phase was obtained. The calculated quantities were compared with the experimental information and they are in good agreement.2) The determination of the isothermal section of Ni-Ta-Zr ternarysystem at 1223 KBy diffusion triple methods and EMPA microanalysis technique, the isothermal section of Ni-Ta-Zr ternary system at 1223 K was investigated for the first time. Two ternary compounds were found exist stably in a certain homogeneity range at this temperature. The solubility limit of element Ta in binary compound NiZr2 wasdetermined as 13.5 at% at the present experimental temperature.3) The investigation of the phase equilibrium relation arid the thermodynamic extrapolation of Ni-Cr-Zr ternary system at 1173 KThe isothermal section of Ni-Cr-Zr ternary system at 1173 K was determined and the phase equilibrium relation and their stability were analyzed and discussed. Meanwhile, the thermodynamic property of the ternary was extrapolated and predicated successfully using the thermodynamic description of its sub-binary from literature. By comparison it was found that the predicated quantities and the experimental result are in a good agreement.4) The comprehensive study of the Al-Ni-Si ternary systemThe isothermal section of Al-Ni-Si ternary system at 1023 K and 1123 K were investigated by diffusion triple and alloying methods respectively and two ternary intermetallics were found in this system. Based on the present experimental results and the data from literatures, the thermodynamic property of the ternary was systematically assessed for the fust time. The experimental information from various authors were compared, analyzed and discussed. A set of self-consistent thermodynamic description was obtained and a number of isothermal sections and isopleths were calculated from the current description. In most case, the calculated results reproduced the experimental information satisfactorily.5) The thermodynamic optimization the Ni-Si binary systemBefore the assessment of Al-Ni-Si ternary system, the thermodynamic description of the Ni-Si binary system was re-evaluated to make it compatible with the description of the Al-Ni binary system. A new set of thermodynamic parameters to describe the molar Gibbs energy of the phase Ni3Si were produced and it can be used to extrapolate and calculate the thermodynamic property of the Al-Ni-Si ternary system successfully.To study the phase equilibrium relation and their stability of super-alloy systemcomprehensively, and to construct, develop their thcrmodynamic and the dynamic database have been our ambition and leading subject for many years. Under the basis of assessing Ni-Mo-Ta, Ni-Re-Ta, Ni-Al-Zr, Ni-Al-Ha systems by other members in our group, this work make a great contribution to the above-mentioned database, playing a sound foundat...
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