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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]