Nacre-like hybrid aluminum-matrix composite with simultaneously enhanced strength and toughness

Abstract

Architecture design, especially nacre-like structure, allows multi-mechanism co-ordination of strengthening and toughening to improve the comprehensive mechanical properties of metal-matrix composites (MMCs). Here a bio-inspired 20 vol% (TiB2p-TiBw)/2024Al composites with nacre-like structure were prepared via freeze casting combined with squeeze casting, where the TiB whiskers (TiBw) were introduced into the composites by in-situ reaction between Ti and TiB2 (Ti + TiB2 → 2TiBw), significantly reducing the sintering temperature of the (TiB2p-TiBw) preforms. We found that the introduction of the ceramic layers inhibited the dissolution of the Cu-rich phase and accelerated the ageing behavior of the Al matrix reducing the duration of peak aging. Both the optimum solution and the aging condition were determined to be 510 °C for 2 h and 160 °C for 16 h respectively, resulting in a superior compressive strength of 886.5 MPa, flexural strength of 709.8 MPa, and crack propagation toughness of 36.1 MPa.m1/2. The exceptional compressive and flexural properties are due to the nacre-like structure, which increases matrix deformation resistance, improving the deformation coordination between the Al matrix and ceramic layers. The high damage resistance was attributed to the multiple extrinsic toughening mechanisms such as interfacial delamination, crack deflection, multi-crack extension, crack blunting and TiBw pull-out.