Effect of trace boron on microstructural evolution and high temperature creep performance in Re-contianing single crystal superalloys

The effect of trace B on the microstructure and creep properties under 1100 °C/130 MPa in three single crystal superalloys with various levels of B (0, 0.01 and 0.02 wt %) additions was investigated. Compared with the boron-free alloy, the creep rupture life decreased slightly for the alloy with 0.01 wt % B, but dropped obviously for the 0.02 wt% B contained alloy. The low B addition had a slight effect on the main element compositions of γ/γ′ by the high precision atom probe tomography (APT) analysis and no significant change of γ/γ′ misfit was observed. However, the contents of Re, Mo, Cr in γ phase were decreased with the high B addition, resulting in the decrease of γ/γ′ misfit and increase of the spacing of γ/γ′ interfacial dislocation networks. Meanwhile, the residual (γ+γ′) eutectics and borides with a large volume fraction obviously decreased the creep rupture properties in the high B addition alloy. This study is helpful for understanding the boron's role of strengthening mechanism in high temperature creep of Ni-base single crystal superalloys. [Display omitted] •B addition promoted the formation of borides and decrased the incipient melting temperature.•High B addition decreased the elemental partitioning ratios of Re, Mo and Cr.•Script-like borides were considered to be responsible for the significant decrease of creep properties in high B alloy.