Papers by Author: N. Saunders

Abstract: The strength of nickel-based superalloys usually consists of solid solution strengthening from the gamma matrix and precipitation hardening due to the gamma' and/or gamma" precipitates. In the present work, a model was developed to calculate the high temperature strength of nickel-based superalloys, where the temperature dependence of each strengthening contribution was accounted for separately. The high temperature strength of these alloys is not only a function of microstructural changes in the material, but the result of a competition between two deformation modes, i.e. the normal low to mid temperature tensile deformation and deformation via a creep mode. Extensive validation had been carried out during the model development. Good agreement between calculated and experimental results has been achieved for a wide range of nickel-based superalloys, including solid solution alloys and precipitation-hardened alloys with different type/amount of precipitates. This model has been applied to two newly developed superalloys and is proved to be able to make predictions to within useful accuracy.

Abstract: Many Aluminium alloys use the precipitation of metastable phases to generate optimum properties. The effect of including additional structures such as θ’ and GP zones is described in the context of a hierarchy of metastable structures. Extending a Thermodynamic data base that has been designed solely to deal with equilibrium conditions is a vital prerequisite to handling the heattreatment of aluminium alloys. It is then possible to generate TTT and CCT diagrams, using the Johnson-Mehl-Avrami treatment previously applied in to other materials providing provision is made for the presence of supersaturated quenched-in vacancies. Calculations using JMatPro are given for the expected behavior of commercial aluminium alloys of increasing complexity, including AA319, AA6061 and AA7075.