Comprehensive microstructural and mechanical characterization of transient liquid phase bonded austenitic stainless steel by Ni–Cr–Si–B amorphous interlayer

Abstract

In this research, along with the joining of the gas turbine fuel nozzle part from austenitic stainless steel 316L alloy with BNi-2 interlayer by the transient liquid phase bonding process, microstructure test, shear strength and tensile strength tests have been placed. Bonding at a temperature of 1080 °C and a holding time of 45 min has led to the completion of isothermal solidification in the bonding zone. Microstructural and phase investigations showed that austenitic stainless steel 316L undergoes phase transformation after exposure to temperature conditions and the δ ferrite phase is formed as separate areas due to the diffusion of the solid state of ferrite-forming elements, and the grains of the base metal are 32 μm have reached 43 μm, which has caused a decrease in the shear strength of the base metal from 362 MPa to 347 MPa. Despite the completion of isothermal solidification in the joint centerline due to the boron diffusion of the solid state into the base metal and achieving the maximum shear strength of the joint (402 MPa), two generations of boride deposits have been formed. The first-generation borides based on nickel-iron-chromium-molybdenum are formed during heating up to the bonding temperature, and the second-generation boride deposits are based on iron-chromium-molybdenum, which were deposited in situ during the isothermal solidification stage. The microhardness test confirms the uniform distribution of hardness in each of the bonding zones, which feedback was determined in the tensile strength test. The tensile strength of the bonded sample was 485 MPa, which is approximately 82 % of stainless steel 316L. In both shear and tensile tests, the presence of small dimples indicates the ductile failure of the joint samples in base metal.