Influence of pre-compression on microstructure and creep characteristic of a single crystal nickel-base superalloy

The P-type γ′ rafted structure of a nickel-base single crystal superalloy with [0 0 1] orientation is formed by means of the pre-compressive stress treatment. An investigation has been made to detect the microstructure evolution and creep features of a single crystal nickel-base superalloy by means of the measurement of creep curves and SEM observation. Results show that creep resistance of alloy with the P-type structure exhibits a marked sensitivity of the applied stress and temperature. When the temperature is lower than 1000 °C under the applied stress of 200 MPa, compared with the alloy with the cuboidal γ′ phase, the P-type rafted structure alloy possesses both a lower minimum creep rate and longer rupture lifetime. When the applied temperature is higher and the applied stress is larger, the properties of the alloys are worsened. This indicates that the P-type rafted structure is beneficial to improving creep resistance of the alloy under the conditions of lower temperature and stress. Compared with the cuboidal γ′ phase alloy, the microstructure evolution of the P-type structure alloy occurs in the steady state of tensile creep. The P-type γ′ rafted structure in the alloy is gradually broken up, and twisted along the 〈1 1 0〉 orientation as creep goes on. After crept up to fracture, the twisted γ′ phase is coarsened, and transformed into the microstructure that the rafted γ′ phase is rearranged along the direction roughly perpendicular to the applied stress axis.