Characterization of brazed joints of C-C composite to Cu-clad-Molybdenum
Abstract Carbon–carbon composites with either CVI matrix or resin-derived matrix were joined to copper-clad-molybdenum using two active braze alloys, Cusil-ABA (1.75% Ti) and Ticusil (4.5% Ti). The brazed joints revealed good interfacial bonding, preferential precipitation of Ti at the composite/braze interface, and a tendency toward de-lamination in resin-derived C C composite due to its low inter-laminar shear strength. Extensive braze penetration of the inter-fiber channels in the CVI C C composites was observed. The relatively low brazing temperatures ( C/Cu-clad-Mo joints with relatively low thermal resistance may be promising for thermal management applications.
Strain energy distribution in ceramic-to-metal joints
Abstract This work introduces a framework for evaluating the strength characteristics of ceramic-to-metal joints with multiple interlayers. Strain energy in the ceramic is used as a strength metric instead of maximum tensile stress. Based on the FEM analysis and order of magnitude scaling (OMS), simple analytical formulations between the strain energy and material properties are developed, which provide a guideline in designing multiple interlayers. Our analysis reveals the important role of multiple interlayers, which reduce the strain energy in the ceramic, increasing the strength of the joint. Based on the proposed design rule, Si 3 N 4 to Inconel 718 joints have been brazed with single, double and triple interlayers and the joint strength was evaluated using a shear test. The experimental results support the design rules and confirm that strain energy is a good strength metric.
Finite element analysis of thermal residual stresses at graded ceramic‐metal interfaces. Part I. Model description and geometrical effects
An elastic‐plastic finite element method numerical model has been formulated to study residual stresses developed at graded ceramic‐metal interfaces during cooling. The results were compared with those obtained for sharp (nongraded) interfaces to assess the potential for achieving residual stress reductions. Analyses were conducted for various axisymmetric cylindrical specimen geometries relevant to structural joining, coating, and thick film applications. The graded microstructure was treated as a series of perfectly bonded layers, each having slightly different properties. Constitutive relations for the interlayers were estimated using a modified rule‐of‐mixtures approximation, and strain and stress distributions were calculated for simulated cooling from an assumed fabrication temperature. The results demonstrate the importance of accounting for plasticity when comparing graded and nongraded interfaces. Significant geometrical effects on peak stresses were observed in the graded materials. It is shown ...