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

摘要

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 nanocrystailine thin film filler metal Ni - 8Si - 5Nb wt.% was proposed to solve the brittle boron nitride problem. The melting interval 1103-1120 °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 °C. The metallographic studies of the brazed joint were carried out. To determine the joint strength characteristics, the microhard-ness 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 °C for 30 min. As a result of this work, the possibility of using boron-free nanocrystailine thin film filler metal for brazing heat-resistant nitrogen-containing steels has been demonstrated. High-strength joints were obtained.