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M. Schöbel, H.P. Degischer, W. Altendorfer, T. Buslaps, M. di Michiel:
"Thermal fatigue in particle reinforced composites for heat sink applications";
Talk: 2nd Fatigue Symposium Leoben, Leoben; 04-23-2008 - 04-24-2008.

Particle reinforced metal matrix composites are developed for heat sink materials because of their good thermal conductivity combined with a low coefficient of thermal expansion, for example for power electronic devices like IGBT (Insulated Gate Bipolar Transistors). A baseplate material with a low CTE is necessary to avoid debonding between the baseplate and the ceramic insulator. Highly conducting matrices with high volume fraction of ceramic particles like SiC or diamond combine their properties for this application. Residual stresses are built up between the matrix and the reinforcements during temperature changes owing to a mismatch in thermal expansion. These stresses can cause debonding between the matrix and the reinforcements and/or damage in the matrix. The interface bonding quality is critical for the long term stability of the MMC during thermal cycles.

AlSiC MMCs are commonly used as baseplate material for this application. Diamond with the best known thermal conductivity is a promising reinforcement to increase the thermal conductivity of MMCs for this purpose. Comparable studies on AlSiC and AlCD MMCs investigate the interface bonding quality and long term stability of these MMCs under thermal load. Insitu residual stress analysis and micro tomography with synchotron radiation sources reveal the changing void volume fractions related to the internal stresses created during thermal cycles. While the voids in AlSiC close during heating, those in AlCD open up. Residual stresses and the void kinetics are quantified by the of synchotron tomography and diffraction.

MMC, heat sink, synchrotron, diffraction, tomography