Thermal expansion-adjustable carbon-doped FeCoCrNiMn high-entropy alloys for electronic packaging

Abstract

Application of an electronic packaging material is always limited by its established coefficient of thermal expansivity (CTE) and poor plastic working capacity. Here, we explored that a ductile high-entropy alloy (HEA) could achieve adjustable CTE values via decomposing at 500 °C. The carbon-doped equiatomic FeCoCrNiMn HEAs (0.8, 1.0, and 1.3 at% C) decomposed into B2, L10, M23C6 and σ phases during annealing. The adjustable CTE of the carbon-doped HEAs can be ascribed to the relatively low CTE values of the formed B2, L10, M23C6, and σ phases. The CTE value of a single face-centered cubic (FCC)-structured FeCoCrNiMn-1.3 at% C HEA is 16.7 × 10–6 °C−1, yet it can be continuously adjusted to 11.3 × 10–6 °C−1 when the FCC matrix is gradually decomposed into the B2, L10, M23C6, and σ phases. Furthermore, the decomposition rate and fractions of the B2, L10, M23C6, and σ phases can be controlled via changing carbon concentration and rolling reduction. More importantly, the CTE range of the 1.3C HEAs meets the requirements of electronic packaging. This work provides a way to design HEAs with desirable CTE for electronic industry via annealing at intermediate temperature.