Borophene reinforcing copper matrix composites: Preparation and mechanical properties

The excellent mechanical properties that combine strength, flexibility and toughness make borophene a highlighted material system for innovative applications of nanoelectronic devices and promising for reinforcing metal matrix composites. However, the experiments have not been reported so far due to the difficulty of macroscale preparation of borophene sheets. Recently, large-scale, free-standing, ultrastable hydrogenated borophene sheets have been synthesized in our group using an in-situ multi-step thermal decomposition method of sodium borohydride. Here, borophene reinforcing copper matrix composites were prepared by in-situ thermal decomposition of sodium borohydride powder in hydrogen rich environment. The corresponding bulk three-dimensional borophene sheets network/copper composites were prepared by spark plasma sintering. The structure of borophene in the samples before and after sintering is well consistent with that of triangular borophene. The mechanical properties of the composites are significantly improved by the introduction of borophene. The yield strength and ultimate tensile strength of the composites are close to the reported highest values of graphene in copper matrix and far beyond those of boron nitride in copper matrix. The change of fracture mode from ductile fracture to brittle fracture is ascribed to the stronger interfacial affinity between borophene and copper compared with that between graphene and copper. This study paves the way for the practical application of borophene in high-performance metal matrix composites.