Revealing the mechanism of internal stress on dimensional stability in SiC/Al composites under long-term thermal exposure

Long-term thermal exposure causes irreversible dimensional changes of materials, which in turn affects the reliability of precision instruments. Yet, the dimensional stability mechanism of Al matrix composites (AMCs) under long-term thermal exposure is still unclear. In this paper, the mechanism of internal stress on dimensional stability in SiC/Al composites was revealed using high-precision thermal dilatometer, in-situ heating XRD and TEM method. The dimensional change of the quenched composites significantly increased in the early stage of thermal exposure while the annealed composites remained dimensional stable. The results showed that the difference of dimensional change in quenched and annealed composites originated from the internal stress accumulated in the matrix at the beginning of thermal exposure. And the entangled dislocation morphology, higher dislocation density and severer lattice distortion in quenched composites would accumulate higher internal stress and thus causing significant dimensional change during thermal exposure. In addition, the non monotonic dimensional change of SiC/Al composites with thermal exposure temperature is related to the type and level of internal stress accumulated at different temperatures.