Microstructure and tensile behavior of nickel-based single crystal superalloys with different Re contents

Abstract

To expand the selection range of materials for blades in gas turbines, new single crystal superalloys with different Re contents were developed and the microstructures, high temperature tensile properties and fracture behaviors were investigated. The dendrites and γ+γ′ eutectic are observed in the as-cast superalloys. After heat treatment, the γ+γ′ eutectic in the interdendritic regions is completely eliminated and cubic γ′ phase with regular morphology maintains a coherent relationship with γ matrix. The size of γ′ phase decreases with the increasing Re due to its inhibition effect on the growth of γ′ phase. The three alloys have little differences in strength below 850 °C and possess the maximum tensile strength at 760 °C. However, the strength of 3Re and 0Re alloys is obviously higher than that of 1.5Re alloy at 980 °C due to the higher content of refractory elements. In addition, all alloys have a very obvious work hardening peak below 760 °C before fracture. With the increasing temperature, the characteristics of plastic fracture become more obvious due to the changes of dislocation motion. At 650 °C, the alloys show quasi-cleavage fracture. At 980 °C, numerous dimples can be clearly seen while no slip deformation trace is found, showing obvious dimple aggregation fracture. The γ′ phase elongates along the direction of stress loading, and the γ channel perpendicular to the direction of the stress axis widens. The rafting phenomenon of γ′ phase in the all three single crystal superalloys does not appear, indicating the alloys have good microstructure stability.

Keywords

• Single crystal superalloy
• Microstructure
• Tensile properties
• Fracture morphology
• Fracture behaviour