Residual stresses in metal/ceramic brazes: Effect of creep on finite element analysis results
Creep-induced stress relaxation of a braze alloy can be an important factor in successful processing of certain metal/ceramic braze joint geometries where there is a mismatch in thermal expansion. The inclusion of a creep constitutive law in finite element analysis (FEA) codes makes it possible to calculate the effect of a particular cooling rate from the braze temperature on residual stresses in the ceramic. Valid calculations require a constitutive law for creep of the brazement which accurately predicts the minimum strain rate over a wide range of temperatures. Using data from previous investigations on the creep of recrystallized Cu, we have developed minimum strain rate creep correlations at both high and intermediate temperatures for pure Cu. At the higher temperatures, a power law is used, with the activation energy obtained by regression analysis quite close to the value of lattice self diffusion in Cu. At intermediate temperatures (350-600{degree}C), we have found that the Garofalo sinh equation obtains the best fit to the data, with an activation energy approximately equal to 2/3 of the activation energy for lattice diffusion, attributable to dislocation core diffusion. Results for FEA calculations of the residual stresses obtained in Cu brazing of a metallic feedthrough pin to a metallized alumina ceramic are presented using both time-independent and creep constitutive laws for pure Cu. At higher temperatures, the creep law predicts lower residual stresses in the alumina compared to the elastic/plastic constitutive law. However, at lower temperatures, the results obtained with the elastic/plastic constitutive law indicate lower stress levels in the ceramic compared to the predictions obtained with the various creep constitutive relations. The lower temperature results are discussed in the context of primary creep behavior. 23 refs., 14 figs.
- Research Organization:
- Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
- Sponsoring Organization:
- USDOE; USDOE, Washington, DC (USA)
- DOE Contract Number:
- AC04-76DP00789
- OSTI ID:
- 5882141
- Report Number(s):
- SAND-90-0973C; CONF-901008-11; ON: DE91011233
- Resource Relation:
- Conference: Fall meeting of the Minerals, Metals and Materials Society (TMS) on physical metallurgy and materials in conjunction with materials week and the material applications and services exposition, Detroit, MI (USA), 7-11 Oct 1990
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ALUMINIUM OXIDES
BRAZED JOINTS
RESIDUAL STRESSES
CERAMICS
ACTIVATION ENERGY
COPPER
CREEP
CRYSTAL LATTICES
FINITE ELEMENT METHOD
GEOMETRY
HIGH TEMPERATURE
MANGANESE
MEDIUM TEMPERATURE
MOLYBDENUM
RECRYSTALLIZATION
REGRESSION ANALYSIS
SEALS
STRESS RELAXATION
THERMAL EXPANSION
ALUMINIUM COMPOUNDS
CHALCOGENIDES
CRYSTAL STRUCTURE
ELEMENTS
ENERGY
EXPANSION
JOINTS
MATHEMATICS
MECHANICAL PROPERTIES
METALS
NUMERICAL SOLUTION
OXIDES
OXYGEN COMPOUNDS
RELAXATION
STATISTICS
STRESSES
TRANSITION ELEMENTS
WELDED JOINTS
360103* - Metals & Alloys- Mechanical Properties
360203 - Ceramics
Cermets
& Refractories- Mechanical Properties