Microstructure evolution and thermal conductivity of the diamond/Al composite during thermal cycling

The microstructure evolution and performance of Diamond/Al composites during thermal cycling, which is important for their wide application, has been rarely investigated. In the present work, the thermal stability of Diamond/Al composite during thermal cycling up to 200 cycles has been explored: thermal conductivity of the composites was measured, and SEM observation of the marked-out area of the same sample was carried out to achieve quasi-in-situ observation. The interface between (100) plane of diamond and Al matrix was well bonded with zigzag morphology and extensive needle-like Al₄C₃ phases. However, the interfacial bonding between (111) plane of diamond and Al matrix was rather weak, which was debonded during thermal cycling. The debonding length was initially increased rapidly within the initial 100 cycles, which was then increased slowly in the following 100 cycles. The thermal conductivity of the Diamond/Al composite was primarily decreased very abruptly within initial 20 cycles, increased afterward, and then further decreased monotonously with the increase of thermal cycles. The decreased thermal conductivity of the Al matrix and corresponding thermal stress concentration at the interface caused by the thermal mismatch stress is suggested as the main factor especially in the initial period rather than the interfacial debonding.