Creep behaviour of Ni-base single-crystal superalloys with various γ ′ volume fraction

Abstract

Creep tests at 900 °C, 392 MPa and 1100 °C, 137 MPa were performed on a third generation Ni-base single-crystal superalloy TMS-75 and its γ/γ ′ tie line alloys. These tie line alloys were designed to contain various volume fractions of γ ′, while the compositions of two individual phases were kept the same. The longest rupture life was attained by an alloy with γ ′ content in vicinity of 65% in both creep condition, which is similar trend has been observed in polycrystalline Inconel 713C through an earlier study by one of the authors. However, in comparison with measured amount of γ ′, the creep rupture lives were the longest at about 70% and 55% measured γ ′ volume fraction at 900 and 1100 °C, respectively. In addition, the dependence of the creep rupture life on the amount of γ ′ was more evident in single crystal than in polycrystal. Rafting was observed in the ruptured 80% γ ′ alloy in the direction parallel to the stress axis, unlike the rafting commonly observed in the 40–60% γ ′ alloys, perpendicular to the loading axis. This parallel raft structure can be explained by the interchanges in the relative roles of the matrix and the dispersed phase.