Exploring Microstructural Characteristics, Mechanical Behavior, Hydrogen Embrittlement, and Long-Term Stability of Polycrystalline CoNiCr-Based Superalloys

Polycrystalline γ/γ′ CoNiCr-based superalloysSuperalloys have a promising combination of properties for aerospace and stationary gas turbine applications. In this study, four alloys, CoWAlloy1, 2, 3, and 6, were selected for further investigation. MicrostructuresMicrostructure of fully heat-treated materials were characterized by scanning and transmission electron microscopyTransmission electron microscopy, and long-term stabilityLong-term stability at 750 °C was examined for various durations up to 1000 h. Tensile tests were performed between 25 °C and 700 °C, revealing dynamic strain agingDynamic strain aging in CoWAlloy2, 3, and 6 at intermediate temperatures of 400–650 °C. Hydrogen charging induced a decrease in tensile ductility at 25 °C in the µ phase containing CoWAlloy3. CreepCreep experiments were performed on CoWAlloy1, an alloy with increased Ti and Ta content, at 750 °C and 800 MPa, with variations of the secondary γ′ precipitatePrecipitates size and grain sizeGrain size to identify optimal microstructural parameters. It was found that smaller grain sizesGrain size lead to a significantly higher creep resistanceCreep resistance at these testing conditions.