In-situ interfacial reactions in boron nitride-reinforced zinc implants for achieving strength and toughness

Boron nitride (BN), as a nano-reinforcement, offers notable benefits for zinc (Zn)-based implants due to its distinct asymmetric hexagonal structure and high fracture strength. However, the limited interface adhesion between BN and Zn limits its potential for strengthening and toughening. In this study, copper (Cu) was in situ grown on acidified BN through chemical synthesis and subsequently incorporated into laser additive manufacturing of Zn to enhance interface bonding. During this process, the Cu on BN experienced a displacement reaction with Zn due to thermal reduction induced by the high-energy laser, leading to the replacement of Cu by Zn and the formation of a robust covalent bond between BN and the Zn matrix, thereby improving load transfer. Additionally, the reduced Cu further interacted with Zn to produce the CuZn₅ phase, which was evenly dispersed in the Zn matrix under Marangoni vortices, resulting in both dispersion and Orowan strengthening. Consequently, the ultimate tensile strength of the composites achieved (251 ± 7) MPa. The fracture toughness also showed a notable increase from 12.10 to 24.03 MPa·m^1/2, as the unique structure of BN effectively redistributed stress at the crack tip and absorbed considerable fracture energy. Furthermore, the Cu@BN/Zn implants demonstrated excellent antibacterial properties.