Helmholtz Free Energy and the Activation Volume of Steady-State Creep in FGH96 Superalloy

The creep properties of FGH96 superalloy were studied in the temperature range of 650 °C to 750 °C and stress range of 690MPa to 897MPa. The results show that the creep life of the alloy decreased significantly with the increase of stress and temperature. However, the temperature produced more effects than that of stress. The most suitable service temperature and stress were also obtained based on the creep results. A physical model base on crystal-plasticity theory was established, but the simplification of the Helmholtz free energy and the activation volume might reduce the accuracy of strain rate prediction. Based on the results of creep at different stresses and temperatures, the Helmholtz free energy and the activation volume of steady-state creep were obtained, which would play a key role in creep life prediction.

Numerical Analysis of Welded Branch Tube Operating in Creep Range

Pressure components used in energy and resources industries may be subjected to various damages including plasticity and creep. Life prediction of such components is an important consideration for engineers who design, build, or operate them. This paper aims to present a comprehensive study to investigate the problem of creep life assessment of a complex welded component containing multiple zones with different material properties unlike almost all of the previously developed methods that have been based on the secondary creep condition alone that cannot be considered as a true representative for the creep behaviour of materials. Thus, the necessary information to estimate the life of a branch tube based on the primary, secondary, and tertiary creep conditions are presented. Results confirm the experimental data from the literature producing the most conservative life.

Review on Mechanical Thermal Properties of Superalloys and Thermal Barrier Coating Used in Gas Turbines

This paper describes the manufacturing method and properties of a superalloy as a gas turbine blade material and a thermal barrier coating to protect it. The development process of superalloy and characteristics of each casting method were introduced. In particular, the single crystal superalloys were analyzed for creep and tensile properties with temperature according to chemical composition. In addition, the theories of creep life prediction models were summarized and comparative analysis was performed. Finally, the manufacturing processes of thermal barrier coatings were introduced, and the characteristics and effects of mechanical, thermal, and durability characteristics of each manufacturing process are described. We believe that this comprehensive review will help not only the gas turbine industry/community, but also material scientists, measurement physicists/engineers, and theorists interested in superalloys and high-temperature ceramics.