Effect of humidity level on the creep properties of alloy 903 at 650°C

Alloy 903 (FeNiCo+Nb) is currently used for certain components in industrial gas turbines for low coefficient of thermal expansion applications. A variance in creep behavior for material quality control evaluations suggested a possible effect of moisture level on stress rupture properties. To investigate the role of water vapor on the creep properties of alloy 903, controlled laboratory experiments were conducted at 650°C with 0 to 100% relative humidity. The water content was controlled by flowing dry air through a water bath at a constant temperature. A significant decrease of lifetime was observed in the presence of water vapor, which is likely related to grain boundary embrittlement by the inward diffusion of hydrogen. The increase of the microstructure grain aspect ratio by different forging processes generally improved the rupture lifetime and elongation in air. However, all specimens had reduced lifetime in the presence of water vapor despite the microstructure grain aspect ratios.