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The effect of pre-deformation induced by the tensile fracture at room temperature on the microstructure evolution of Ni Al model single crystal superalloy during thermal exposure at 1000 °C, was investigated by scanning electron microscope and transmission electron microscopy. Recrystallization occurs near the fracture surface where the most severe plastic deformation was suffered. The average size of recrystallization grains in front of the recrystallization area is much larger than that of at the fracture surface. Far from the fracture surface, the average size of coarsened γ′ precipitates in the slip bands is larger than that of out of the slip bands. [ABSTRACT FROM AUTHOR]

In-situ tensile experiments of Ni-Al, Ni-Al-Re and Ni-Al-Re-Ru model single-crystal superalloys were performed in scanning electron microscope (SEM) at room temperature. The plastic deformation mechanisms of all the three model superalloys were double-oriented slipping of dislocations. Micro-cracks were often formed at the intersection of two sets of slip lines. The fracture surfaces of Ni-Al and Ni-Al-Re-Ru alloys were nearly parallel to (010) planes and that of the Ni-Al-Re alloys was nearly parallel to (1−11) plane. The dislocation configuration was analyzed by transmission electron microscopy (TEM). The a/2<110> dislocation pairs coupled with antiphase boundary (APB) cut into γʹ phase in the Ni-Al and Ni-Al-Re-Ru model superalloys. In addition to these dislocations, stacking faults also cut into γʹ phase in Ni-Al-Re model superalloys. The different fracture surfaces of different model single-crystal superalloys were attributed to the influence of elements Re and Ru on the dislocation configuration. [ABSTRACT FROM AUTHOR]

In this paper, long-term thermal treatment of a binary Ni–Al model nickel-based superalloy was performed at 1000 °C for 50 h, 100 h and 200 h. The evolution of the γ/γ′ interface was studied. As the treatment time increased, the γ′ precipitates coarsened and grew. Regular interface instability was observed that the shape of the γ/γ′ interface changed from flat to wavy. This interfacial instability was caused by the dynamic balance of strain energy and surface energy at the interface between the two phases. In addition, secondary γ′ precipitates were observed after long-term treatment and some of the larger ones took on pillow-like shapes. The pillow-shaped distortion was because that the growth rate of the cube vertices was faster than that of other locations due to the different strain states at different locations. [ABSTRACT FROM AUTHOR]

Ex-situ and quasi in-situ thermal exposure experiments have been conducted to explore the coarsening behavior of γ′ phases in the Ni-Al binary model single crystal superalloy at 1000 °C. It is obtained in ex-situ experiments that the number density and volume fraction of γ′ phases decrease with the exposure time increasing, while the average size increases. The coarsening of γ′ phases in the width direction obeys the cubic law described by the LSW theory, while the average size change in length is much greater than that in width. In quasi in-situ experiments, it is observed that small γ′ phases shrink or dissolute, the large ones tend to grow up. The coalescence of γ′ phases is also observed, which induces a sharp increase in the length direction. • Ex-situ and quasi in-situ thermal exposure experiments are carried out at 1000 °C. • Shrinkage or dissolution, growth and coalescence of γ′ phases are observed. • The smaller the size is, the faster the γ′ phases decrease. • The coarsening of γ′ phases in the width direction follows the LSW theory. • The coalescence of γ′ phases leads to a deviation from the LSW theory. [ABSTRACT FROM AUTHOR]