Interfacial resistivity of precipitate-decorated grain boundaries: A case study of additively manufactured Al-Si alloys

Interface resistivity of grain boundaries (GBs) is a crucial property determining the electrical properties of conductive materials. GB resistivity is determined by the material type, the boundary character, and segregation-induced chemistry. This work focuses on the interfacial resistivities of precipitate-decorated GBs in Al-Si alloys, additively manufactured using directed energy deposition. Resistivities across individual low-angle and high-angle GBs (LAGB and HAGB, respectively) decorated with precipitates are resolved for as-printed and annealed alloys. The boundary's contribution to resistivity is evaluated using a four-point probe method performed inside a scanning electron microscope. Moreover, the interfacial GB resistivity is measured by a scanning four-point probe technique applied on an individual GB isolated using focused ion beam nanopatterning. We find that the resistivities of LAGB and HAGBs are 2.7 and 10 × 10⁻¹⁴ Ω m², respectively, about two orders of magnitude larger than the resistivity of GBs in pure Al. In addition, we find that heat treatments lead to a larger decrease of resistivity for HAGBs compared to LAGBs. Also, we show that Fe impurities, the most common impurity in Al alloys, segregate to the GBs, consequently decreasing their resistivity. Eventually, the reported GB resistivities are discussed with respect to interfaces in different materials systems.