Ceramic-to-metal brazing is being simulated using finite element analysis (FEA) codes to investigate the effects of braze alloy, braze process, and geometry variations on stress levels generated during brazing.  The accuracy of these simulations is critically dependent on how realistically braze material behavior is understood and modeled.  A viscoplastic model for braze alloys was developed. This model uses a hyperbolic sine function of effective stress in its kinetic equation for the inelastic strain rate.  Evolution equations for the internal state variables describe competing mechanisms of power-law hardening and thermal recovery.  Material parameters for the Ag-2Zr and Ag-1Cu-2Zr active braze alloys were obtained from a combination of experiments including uniaxial compression and creep compression. The 1 wt.% Cu addition to the Ag-2Zr alloy was developed to help avoid excessive runout on Kovar alloy flanges.  The 1% Cu addition produces an alloy with a solidus/liquidus gap of approximately 20°C. 
 
This paper includes a brief description of the viscoplastic model, a description of the parameter selection process, a table with material parameters. FEA stress analysis results for a typical ceramic-to-metal braze joint using Ag-2Zr are compared to results obtained with the Ag-1Cu-2Zr  braze alloy.  It will also include a discussion of the merits of these two active braze alloys for metal/ ceramic braze joints relative to other commercial active braze alloys.
 
* Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin  Company, for the United States Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.