Roles of B and Zr addition on the microstructure and strength in a novel as-cast Ni superalloy

Despite their extremely low concentrations in nickel-based superalloys, trace elements have a considerable impact on the microstructure and mechanical properties of these materials. According to the properties of the trace elements, the elements B and Zr are chosen to be introduced into the K4XX superalloy matrix. This paper focuses on the effect of trace alloying elements B and Zr on the transformation of metal carbides morphology, microstructure evolution and mechanical properties during the solidification process. With the addition of 0.004 wt% B and 0.006 wt% Zr in the superalloy matrix, the ultimate tensile strength (UTS) of BK4XX and BZrK4XX is about 1069 MPa and 1078 MPa, which is a 4.2 % and 5.1 % improvement compared to K4XX(1026 MPa). Similarly, the elongation of BK4XX and BZrK4XX is about 10.0 % and 10.6 %, which is also 34.1 % and 41.3 % improvement compared to K4XX(7.5 %). And the morphology of precipitated phase metal carbides also appears to be transformed with the addition of trace elements. The participation of B and Zr elements in the second phase precipitation provides a strengthening effect. This work provides experimental support for the effective control of trace element content in the as-cast nickel-based superalloys, which is helpful to improve the metallurgical quality of the as-cast nickel-based superalloys.