Wide gap brazing using Ni-B-Si and Ni-B-Si-Cr-Fe filler metals: microstructure and high-temperature mechanical properties

Microstructure, shear strength and stress rupture time at 850 degrees C of Inconel 738LC joined by wide gap brazing were studied. As low-melting alloys (LMAs), Ni-3.2B-4.5Si (B1 samples) and Ni-3.2B-4.5Si-7Cr-3Fe (B2 samples) were used. The effects of LMA amounts at levels of 40, 50 and 60% were examined for both LMAs. The B1 samples showed higher porosity than the B2 samples. g/Ni3B was the main eutectic phase in the B1 samples and accounted for about 62% in the sample containing 60% LMA along with less than 12% CrxB and (Cr,Mo)yB. Whereas in the B2 samples, g/Ni3B is below 38%, and Cr-rich borides are formed more than in the B1 samples. Hardness analysis shows that the hardness of Cr-rich borides is more than 1500 HV and Ni3B is about 900 HV, which is higher than g solid solution matrix. The B1 samples showed higher shear strength than the B2 samples. The maximum shear strength of 395 MPa was obtained using 50% LMA. The B1 samples also showed a longer lifetime of 5.8 h at 850 degrees C under 250 MPa. These differences in mechanical properties are due to the lower amount of CrxB and (Cr,Mo)yB in the B1 samples. Hence, the B1 samples showed higher shear strength and stress rupture time, and a key factor in microstructure of WGBed joints is Cr-rich borides.(c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).