M3B2-type borides effect on the wide gap brazing of K417G alloy with mixed powder

Abstract

Aerospace components are often exposed to high temperature and high pressure, which may cause relatively large wear zones. The effective repair of wide gaps is an important requirement of industrial production. In this study, a gap (width of 20 mm) was bonded by wide gap braze (WGB) technology. The Ni-based K417G alloy was used as the base metal, and a mixture of low-melting boron-containing nickel-based alloy powder and high-melting nickel-based alloy powder (similar to the base metal composition) was used as the filler material for the repair. Desired mechanical properties of the repaired joint were obtained by controlling the microstructure and the content of M3B2-type borides in the bonding layer, and by altering the size, morphology, and distribution of these boride particles. The K417G alloy repaired by sintering at 1200 °C exhibited a tensile strength of 971 MPa, completely exceeding the strength of the base metal (935 MPa). The microstructures of the joints were examined and found to include 97.56% equiaxed/spherical γ + γ′ matrix with 2.44% dispersed M3B2-type boride precipitates (∼1.4 μm). The results indicate that M3B2 boride particles mainly nucleate at the interface of γ and γ′ phases, and γ acts as the nucleation point of the high-energy grain boundary. The fine particles of M3B2-type borides are coherently precipitated in-situ in the γ phase and uniformly dispersed, facilitating excellent repair.