The microstructures and mechanical properties of K465 superalloy joints, brazed with different clearances

Abstract

K465 superalloy was brazed with brazing clearance of 0.1 and 0.5 mm, respectively. The microstructures of the brazed joints were observed, and compositions of typical microzones were analyzed by means of scanning electron microscope (SEM), energy-dispersive spectroscopy (EDS), and electron probe microanalysis (EPMA). In addition, high-temperature tensile tests for the brazed joints were also conducted. The results showed that for the brazed joints with 0.1 mm clearance, the low-melting phases such as the white blocky shaped (W, Cr)B boride phases and gray skeletal phases M₃B₂ boride phases were mainly precipitated in the central region of the brazed seam. However, the microstructure of the brazed joints with 0.5 mm clearance, which was pre-filled fully with one type of Ni-based alloy powder prior to brazing, was remarkably improved. Compared to the brazed joints with 0.1 mm clearance, the pre-filling of the alloy powder changed the distribution and morphology of low-melting phases, which was favorable to the improvement in high-temperature tensile properties of the brazed joints with 0.5 mm clearance. At 900 °C, the average tensile strength of the brazed joints with 0.1 mm clearance was only 488 MPa, while the average tensile strength of the brazed joints with 0.5 mm clearance increased to 615 MPa, which is 75 % of the K465 base metal tensile strength.