Abstract: Because of the large coefficient of thermal expansion (CTE) (23 ppm K^-1), aluminum faces challenges in meeting the demands of high dimensional stability in precision instruments, microelectronics, and aerospace. Filling negative thermal expansion (NTE) particles into aluminum can create composites with either zero or low CTEs. However, the resulting composites usually have poor thermal conductivity due to their monolithic configuration, i.e., the NTE particles are filled randomly. Thus, heat sinks should be equipped to assist their usage (e.g., in thermal management). This in turn causes strong thermal stress in the packaging system owing to the high contrast in the CTEs between those monolithic composites and heat sinks typically made of copper or aluminum. Here, we propose a gradient configuration for low-CTE aluminum composite, inspired by the bamboo structure. The gradient distribution of NTE particles (Zn_0.5Sn_0.3Mn_0.2NMn₃, ZSM) was obtained by laying up several layers of ZSM/Al with the ZSM fraction ranging from 0 to 28 vol.%. In the gradient composite, the CTE near room temperature varies from 3.4 pm K^-1 on one side to 21 ppm K^-1 on the other side. Such a gradient CTE distribution would facilitate the low-thermal-stress designs and thus help stabilize the dimension of a precision system. Furthermore, this composite has a high thermal conductivity of 130 W m^-1 K^-1 and strong toughness when the flexural loading is applied on the 28 vol.% ZSM/Al side. Our research provides a novel approach to designing metallic matrix composites with unprecedented performance.

Key words: Biomimetic materials, Gradient materials, Low thermal expansion, High thermal conductivity, Toughness