Development of nickel-based filler metal for producing high-strength joints in critical products from heat-resistant materials

Manufacturers of nozzles for liquid rocket engines from heat-resistant austenitic and austenitic-ferritic steels faced the problem of brittle boron nitride formation in the joints. Joints are obtained using high-temperature diffusion brazing in vacuum by filler metal based on Ni - Cr - Fe - Si - B system. This technology is based on the isothermal solidification of the filler metal melt, occurring due to the diffusion of boron into the base material. The developed boron-free nanocrystalline thin film filler metal Ni - 8Si - 5Nb wt.% was proposed to solve the brittle boron nitride problem. The melting interval 1103-1120 degrees C of the filler metal is determined by the method of differential thermal analysis. It's structural and phase state was revealed by X-ray methods. Technological modes of high-temperature diffusion brazing of austenitic and austenitic-ferritic steels have been developed in the temperature range of 1150-1200 degrees C. The metallographic studies of the brazed joint were carried out. To determine the joint strength characteristics, the microhardness was investigated in the brazed zone and mechanical uniaxial tension tests were carried out according to GOST (Russian State Standard) 28830-90. The best result on the tensile strength 450 +/- 30 MPa was achieved on samples obtained at an isothermal holding temperature of 1150 degrees C for 30 min. As a result of this work, the possibility of using boron-free nanocrystalline thin film filler metal for brazing heat-resistant nitrogen-containing steels has been demonstrated. High-strength joints were obtained.