Z. Hu, J. W. Brooks, H. S. Ubhi, I. C. Wallis, QinetiQ Ltd., Farnborough, United Kingdom; A. Wisbey, Serco Technical Services, Warrington, United Kingdom
Increasing temperature requirements in various applications are determining the need to include some ceramic based materials into structures. A major difficulty with these components can be interfacing them with conventional metallic parts. In the work presented here the brazing of Al2O3 and SiC monolithic ceramics to a nickel base alloy (Nimonic 90) has been investigated. As part of these investigations the bonds have been modelled to identify potential routes to minimise residual stresses and so optimise the brazing cycle. A Ag-Cu-Ti braze alloy has been found to be particularly successful in producing metallurgical joints between the ceramic and metal components. As part of the process modelling the high temperature deformation behaviour of this braze alloy has been determined to allow time dependent plastic deformation effects to be included in the calculation of bond stresses. A variety of bond geometries have been considered, from simple butt joints, to more complex tube – flange geometries. This work has indicated the importance of careful joint design on the minimisation of the residual stresses, including the potential application of soft compliant layers. Preliminary validation work on the predicted strains at the bond interfaces, carried out using electron-back scattered electron diffraction analysis, is presented.
Summary: Increasing temperature requirements in various applications are determining the need to include some ceramic based materials into structures. A major difficulty with these components can be interfacing them with conventional metallic parts. In the work presented here the brazing of Al2O3 and SiC monolithic ceramics to a nickel base alloy (Nimonic 90) has been investigated. As part of these investigations the bonds have been modelled to identify potential routes to minimise residual stresses and so optimise the brazing cycle. A Ag-Cu-Ti braze alloy has been found to be particularly successful in producing metallurgical joints between the ceramic and metal components. As part of the process modelling the high temperature deformation behaviour of this braze alloy has been determined to allow time dependent plastic deformation effects to be included in the calculation of bond stresses. A variety of bond geometries have been considered, from simple butt joints, to more complex tube – flange geometries. This work has indicated the importance of careful joint design on the minimisation of the residual stresses, including the potential application of soft compliant layers. Preliminary validation work on the predicted strains at the bond interfaces, carried out using electron-back scattered electron diffraction analysis, is presented.
