The potential of active brazing filler metal modification by ceramic particle addition, with the aim of to reduce the cooling induced stresses and enhance the strength of ceramic metal joints, is studied. The addition of ceramic particles allows tailoring the mechanical properties of the filler metal and improving its mechanical behaviour at higher temperature, however simple reinforcing of the interlayer has a detrimental effect at lower temperature because, due to the filler strengthening, residual stress relief via plasticity is limited. Thus a layered joint structure is proposed: reinforced and not reinforced layers of different thicknesses and compositions are combined in an optimal manner to minimize residual stress.
Reinforced active filler alloys are produced by adding SiC particles to Ag-Cu-In-Ti alloy Incusil-ABA up to 30% vol. and used in combination with the pure filler alloy for joining Si3N4-TiN ceramics to 14NiCr14 steel. The joints produced are tested in 4-point bending. Bending strengths of joints with different layouts (thickness and composition of layers) are compared with experimental data obtained for the same material systems brazed with single unreinforced filler metals.
The evaluation of residual stresses and the optimization of the joint layout are carried out by FE modelling; temperature dependent mechanical properties are assumed for all the constituents, the elasto-plastic properties of the reinforced filler metals are obtained by homogenization.
Both experimental and numerical results indicate as an optimal solution a “sandwich” layout with a central reinforced layer between two unreinforced layers in contact with the base materials; experimental data show that the average bending strength of such joints is 20% higher than that of joints brazed with a single layer of unreinforced filler metal.

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