Experimental investigation of stresses in a ceramic-to-metal brazed joint

There is increasing use of joined ceramic and metallic material combinations exposed to a widening range of temperature. However, difficulties arise from the interaction of the different thermal expansion and ductility properties of component materials when a brazed joint is cooled from brazing to room temperature. Reliability demands on equipment employing ceramicto-metal bonds in structural and sealing applications justify the efforts made for a more complete understanding of the mechanics invelved. For this investigation, specimens were made by copper brazing the ID of a thin-wall metal ring to the OD of a ceramic disk. Residual stresses were induced as the bond metal solidified at the interface of the ring and disk. Electrical-resistance strain gages were fastened to the OD of the metal ring to determine change in stress as the braze material was removed. An apparatus and technique were developed for chemical removal of the braze material while protecting the specimen materials and instrumentation from corrosion. Stress-strain curves of the metals involved were obtained up to 1500°F. This data was used to predict the magnitude of the stresses. The calculated and measured stresses were in reasonable agreement.