Quantified Relation Between Grain Boundary Angle and Interfacial Stability of PWA1484 Superalloy During Thermal Exposure

Nowadays, the tolerance of grain boundaries (GBs) is a crucial subject of single crystal (SX) superalloys. Quantitatively deciphering the effect of GBs on the interfacial stability may provide theoretical guidance for the technological design and engineering application of SX superalloys. In this article, [001] tilt artificial GBs with grain boundary angles (GBAs) of 5, 15, 25, 35, and 45 deg, respectively, have been prepared by directional solidification for PAW1484 SX superalloy. The microstructural evolution at GBs under thermal exposure at 1070 °C up to 1000 hours was quantitatively investigated. It has been revealed that low-angle grain boundaries (LAGBs) (< 15 deg) maintained a straight and narrow interface and have no precipitates (mainly carbides) around GBs. For GBAs higher than 25 deg, however, the γ′ layer was widened and coherent MC carbides with orientation relationships [001]MC//[001]matrix and 〈001〉MC//〈001〉matrix, together with blocky and closely spaced M6C carbides, were precipitated. By carefully scaling, the width of the γ′ layer and the ratio of carbides to the γ′ layer were quantitatively determined as a function of GBAs and thermal exposure time. Furthermore, it has been confirmed that the topological-closed-packed (TCP) phase precipitated along the 45 deg GB with the increase of thermal exposure time.