Brazing of Silicon Nitride and Steel with Cu-Based Filler Metals: Mechanism and Residual Stress in its Joints

Abstract

This paper addresses the mechanism of active metal brazing of silicon nitride and metal with Cu-based filler metals Cu-Sn-Ti, Cu-In-Ti and Cu-Cr, and analyzes the residual stress in/around the brazed silicon nitride/steel joints using Ag-Cu-Ti filler metal and Cu, W, Mo and kovar interlayers by a finite element method. The distribution of various elements in the joints are analyzed by scanning electron microscopy (SEM), electron probe microanalysis (EPMA) and X-ray diffraction analysis (XDA). The mechanism of ceramic/metal joining using the active filler metal is that the active elements diffuse from filler metals to ceramic, react with it, and accomplish the joining. The tested results suggest that these Cu-based filler metals are applicable in ceramic/metal brazing and the shear strengths of joints using Cu-Sn-Ti or Cu-In-Ti filler metals are similar to that of the joints using Ag-Cu-Ti filler metal. The finite element method and tensile test are further applied to analyze the residual stress caused by thermal expansion mismatch between the ceramic and metal in the joints. High residual stresses with a complex distribution have been observed in the Si{sub 3}N{sub 4}/steel joint. The predicted maximum residual stress locations agree with the real fracture surface initiation. The effects of the properties and thickness of the filler metal and interlayer in reducing the residual stress are also analyzed by finite element method. (orig.)