Structural Stiffness of X-750 Alloy Bump Foil Strips for Compliant Foil Bearings With Different Heat Treatments

This paper focuses on the structural stiffness of bump foils which are used for compliant foil bearings with different heat treatments. After heat treatments in vacuum environments, the mechanical properties of the foil strips were tested, and the structural stiffness was estimated from the static load versus displacement curves obtained from the experiments. High cycle dynamic load tests were also applied to the bump foil under different cycle loads, and the shape of the foil was scanned after the tests to measure the height variation of the bumps. The results show that the modulus of elasticity and strength of Inconel X-750 strip with thickness of 0.1 mm after different treatments are lower than that with the thickness of 0.18 mm at room temperature. Moreover, the sample foil strips which have been treated with a lower solution anneal temperature at 980 °C (2 hrs) and precipitation heat treatment at 732 °C (16 hrs) have the largest modulus of elasticity and strength at room temperature. Therefore, heat treatments have a great influence on the structure stiffness of the bump foil. At last, the results of the high cycle dynamic load tests show that the bump foil with suitable heat treatment will have a good load capacity and stress-relaxation property.