Creep and directional coarsening in single crystals of new γ-γ′ cobalt-base alloys

Single crystal tensile creep tests have been performed on L12-containing cobalt-based alloys loaded along the [0 0 1] orientation. Co-Al-W alloys with additions of Ni, Ta, Cr and Mo were crept at 900 °C. Four of five alloys investigated exhibited directional coarsening parallel to the applied stress, indicating a positive misfit between the γ and γ′ phases. Alloys containing a high volume fraction of γ′ exhibited superior creep properties compared to alloys with low volume fraction of precipitates.