A Novel Two-Stage Strengthening and Toughening Behavior of Sic Fiber Reinforced Porous Ti-Nb Based Smas Composites

Abstract

Low strength is the main obstacle of high porosity Ti-based shape memory alloys (SMAs) for biomedical application. In this study, SiC fibers with BN coating was used to reinforce the porous Ti-based SMAs for the first time. The SiC f /Ti-12Nb-18Zr composites with fiber contents of 1 ~4 vol.% and a porosity of 50% were successfully fabricated by low temperature (1000 °C) sintering using hydride powders (TiH 2 , ZrH 2 ) and Nb powders. The interfacial microstructure shows that the interfacial reaction between SiC fibers and the TiNbZr matrix is effectively alleviated by the low temperature sintering and the BN coating . In comparison with the unreinforced sample, t he composite with 3 vol.% SiC fibers increases the compressive strength and fracture strain by about 3 times and 0.5 time, respectively. In addition, its compressive strength and compressive fracture strain are more than twice that of the reported porous Ti-Nb based SMAs with similar porosity. Due to the non-oriented distribution of SiC fibers in the matrix and in the pores, the composite presents a novel two-stage strengthening and toughening behavior. Firstly , t he SiC fibers in the matrix and pores bear the external force and increase the strength of the composite (first reinforcement). After the yield stage, the fibers bearing the external force relieve the stress concentration at the defects on the pore walls of the matrix, and effectively inhibit the generation of cracks, so that the composite is strengthened further and enters the pore densification stage, and the strength increases again greatly as the result of fiber strengthening and pores densification (second reinforcement). Meanwhile, during the first stage strengthening the composite exhibits a plastic deformation similar to that of the porous matrix (first plastic deformation). During the densification stage of porous matrix, the plastic deformation capacity of the matrix is enhanced, therefore the plasticity of the composite is greatly increased (second plasticity increase).

Keywords: Porous Ti-based SMAs, SiC fibers, Sintering, Reinforcement, Toughening