Abstract. The strength of nickel-based superalloys usually consists of solid solution strengthening from the gamma matrix and precipitation hard-ening 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 temper-ature strength of these alloys is not only a function of microstructural changes in the material, but the result of a competition between two deforma-tion 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 nickelba-sed 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.

1. Introduction

    Nickel-based superalloys have been widely used in aircraft engines and land-based gas turbines where high strength at elevated temperatures is required. It has always been an important task to develop alloys with better high temperature properties. Improved properties may be achieved by modifying alloy chemistry and processing route. Traditionally, alloy design follows a trial-and-error approach which is both costly and time cons-uming. It is now highly desirable to develop advanced computer models to facilitate the design of alloy composition and processing route.The str-ength of nickel-based superalloys arises from solid solution strengthening in the γ matrix and precipitation hardening due to the ordered γ' preci-pitates which are coherently embedded in the matrix. When temperature increases, both strength contributions will be affected, resulting in a chan-ge in the alloy’s strength. In the present work, a computer model has been developed such that the strength of nickel-based superalloys can be calculated as a function of alloy composition, heat treatment and temperature. The model is based on general theories on phase transformations (including thermodynamics and kinetics) and strengthening, and is therefore able to perform calculations in a predictive manner to within useful accuracy. Recently a similar attempt was made by Nembach and co-workers.[1] However, their model only dealt with two alloys and many impor-tant material parameters, set as constants, were obtained by fitting calculation with experimental results for each alloy. Since in reality the values of these parameters differ from alloy to alloy, such model has little predictive capacity.

    In the first part of the paper, the procedures for developing the model are described in detail. The second part features validation of the model over a wide range of commercial alloys including solid solution alloys and precipitation-hardened alloys with different type/amount of precipitates. The model was then applied to two newly developed nickel-based superalloys. The model for high temperature strength calculation forms part of the development of a computer software, JMatPro, which allows the present calculations to be carried out readily via a user-friendly graphical inter-face.

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