Microstructural evolution and dimensional stability of 45vol% SiC/Al composites under long-term aging

Abstract

Long-term aging will inevitably affect the dimensional stability of the material, which causes reliability decrease of the precision instruments. Currently, the dimensional stability mechanism of SiC/Al composites under long-term aging is unclear. Specifically, how the alloying elements, precipitates, dislocations and internal stress together cause the dimensional change of SiC/2024Al composites and how to regulate the microstructure to improve dimensional stability. In this paper, 45 vol% SiC/Al composites were successfully prepared by pressure infiltration method. The dimensional stability mechanism of SiC/2024Al composites under long-term aging was revealed through in-situ heating XRD, spherical aberration correction transmission electron microscopy and high-precision thermal dilatometer. The results showed that the precipitates and alloying elements coupled with other factors to affect the dimensional change. There were mainly two sources of the dimensional change in the SiC/2024Al composites. One was the combined effect of precipitates-dislocations, which led to dimensional decrease. The other was the combined effect of precipitates-alloying elements-internal stress, which led to dimensional increase. The former was similar to the dimensional stability mechanism in 2024Al alloys, while the latter was a unique mechanism which only existed in SiC/Al composites. And the dimensional change of SiC/2024Al composites caused by the two sources could be regulated from + 10-4 to + 10-5 by changing aging temperature.