Anisotropic Creep Behavior of DD15 Single Crystal Superalloy

Abstract:

DD15 single crystal superalloy with [001], [011] and [111] orientations was cast by seed method in the directional solidified furnace. The creep properties of the alloy with different orientations were investigated at 980 °C/300 MPa. In order to obtain the microstructure evolution after different creep time, the creep after 50 and 100 h and the creep fracture of three kinds of tests were investigated. The alloy microstructure with different orientations were investigated by SEM and TEM. The results show that the alloy with different orientations has obviously various microstructure characteristics on the section perpendicular to the crystal growth direction. The γ′ phase with [001] orientation is regular square, that with [011] orientation is rectangular, and that with [111] orientation is polygon. The creep properties of the alloy exhibit obvious anisotropy at 980 °C/300 MPa. The creep life of the alloy decreases in the sequence of [111], [001] and [011] orientation. The creep strain of the alloy under different conditions decreases in the sequence of [001], [011] and [111] orientation. The common feature of the creep curves is a very short primary creep stage. Compared with creep curves of the [001] and [111] orientation, the creep curve of [011] orientation has a shorter third creep stage. The degree of γ′ coarsening is obviously different for alloy with different orientations after creep. The rafting speed of [001] oriented sample is larger than that of [011] and [111] oriented sample. After creep fracture, the dislocation network of [001] or [111] oriented alloy is denser and better than that of [011] oriented alloy.

Key words:single crystal superalloy;DD15;creep behavior;anisotropy