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, hightemperature 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 M 3 B 2 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 hightemperature 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.

Wide-Gap Brazing of K417G Alloy Assisted by In Situ Precipitation of M3B2 Boride Particles

“…As a result, relatively large cracks or worn areas (>1.5 mm) are discovered in aerospace components, where the narrow gap TLP bonding technique would be inadequate [ 13 ]. For wide-gap brazing, the selection and design of the filler metal composition is the key factor to improve the brazing performance [ 14 , 15 , 16 , 17 , 18 , 19 ]. Considerable effort has been devoted to adding a second gap-filler powder, (hereafter termed additive powder) of similar composition to that of the base metal (BM), to the joint gap, for use with braze powder during the high-temperature brazing process [ 14 , 20 , 21 ].…”

“…Considerable effort has been devoted to adding a second gap-filler powder, (hereafter termed additive powder) of similar composition to that of the base metal (BM), to the joint gap, for use with braze powder during the high-temperature brazing process [ 14 , 20 , 21 ]. During the entire wide-gap brazing process, additive powder with a high melting point remains largely unmelted, thereby providing the necessary capillary force to retain the molten braze powder that would otherwise be too fluid to bridge the faying gap surfaces [ 16 , 17 ]. However, the formation of hard and brittle eutectic structures with uneven distribution cannot be avoided due to their sensitivity to the chemical composition of the filler metal, brazing temperature, and brazing time [ 22 , 23 , 24 , 25 ].…”