Interfacial characteristics and normal mechanical strength of a NiTi shape memory alloy fiber reinforced Mg3AlZn (SMAFR-AZ31) composite sheet

Abstract

In this paper, a novel NiTi shape memory alloy fiber reinforced Mg3AlZn (SMAFR-AZ31) composite sheet was successfully fabricated by laminate structure design combined with hot pressing method using Mg3AlZn (AZ31) foils and continuous NiTi shape memory alloy fibers. The interfacial microstructure of the SMAFR-AZ31 composite sheet was systematically characterized by a high resolution transmission electron microscopy (FEI-TEM Talos F100) combined with an FEI Helios 600i focused ion beam/scanning electron microscopy (FIB/SEM) system. The normal tensile strength of the SMAFR-AZ31 composite sheet was tested using a novel direct tensile sample configuration with the tensile direction perpendicular to prior AZ31 foils. Results showed that a well-densified AZ31 matrix and uniformly distributed NiTi fiber reinforcements were obtained in the SMAFR-AZ31 composite sheet after hot pressing. A continuous interfacial reaction layer consisting of nanocrystalline-amorphous mixture and a few intermetallic phases were formed around the NiTif/AZ31 interface. The nanocrystalline was identified as dual phase coexistence grains of MgO and TiO2, and the amorphous phase was a mixture of Mg–Ti–O and Mg–O. A newly Ti2Ni intermetallic phase that obeys a specific orientation relationship with NiTi fiber ([4‾21‾] NiTi// [1‾12] Ti2Ni, (132) NiTi// (11‾1) Ti2Ni with an angle difference of 6.27°) precipitated adjacent to the interface reaction layer. A Ni-rich intermetallic phase identified as AlNi formed at the NiTif/AZ31 interface. Furthermore, it is found that large plastic deformation occurred near the interface reaction region in the AZ31 matrix, which is responsible for the successful embedding of NiTi fibers. Compared with the AZ31 laminate sheet without NiTi fibers, the SMAFR-AZ31 composite sheet possessed a superior normal tensile strength, which is attributed to the formation of the amorphous phase at the NiTif/AZ31 interface.