| Since the concept of smart material system has been proposed in the late1980s, peoplepay close attention to smart material. After more than20years′development, the study ofsmart material has made tremendous progress, which has formed a multi-disciplinary and verypromising area of research. As one of the most important components in smart materialsystems, shape memory alloys (SMAS) have aroused the interest of researchers. It has a dualfunction both as sensor and actuator in intelligent materials system. It can not only be used assensors to sense stress，temperature and magnetic field in specific environments, but also as areinforcement in composites to improve the performance of materials (such as polymer,metal).The research of SMAs reinforced metal matrix composites starts relatively late, as themost excellent alloy in shape memory alloys, NiTi alloy is the most commonly usedreinforcement. At present, the domestic and foreign scholars pay more attention to NiTi shapememory alloy reinforced aluminum matrix composites, but few researches on theenhancement of magnesium alloy. Compared to aluminum matrix composites, magnesiummatrix composites with lower density, higher strength and stiffness as well as goodelectromagnetic shielding and damping properties are becoming very promising materials inaerospace. In NiTi SMA fiber reinforced Mg-Li alloy composites, the shape memory effect ofSMAs is used to achieve and enhance the strength of magnesium alloy matrix as well as toimprove its high-temperature behavior. Therefore, the study of NiTi SMA fiber reinforcedMg-Li alloy composites has important practical significance.In this thesis, we mainly study the preparation technology of NiTi fiber reinforced Mg-Lialloy composites, and finish the following work:1．We have explored the vacuum hot pressing process of NiTi SMA fiber/Mg-9Licomposite and NiTi SMA fiber/Mg-11Li composite and used optical microscopy, SEM, EDS,XRD to analyze the microstructure of composites prepared by different preparation process.Then combine with DSC test of the NiTi fiber, we determine a suitable compositespreparation process. The preparation for NiTi SMA fiber/Mg-9Li composite is at thetemperature of803-833K for a total processing time of1800-3600s under a pressure of8MPa,while NiTi SMA fiber/Mg-11Li composite is at the temperature of783K for a holding timeof1800-3600s. 2．We study tensile properties of the composites at room temperature, the results showthat NiTi shape memory alloy fiber enhanced magnesium-lithium alloy, and with theincreasing volume fraction of NiTi fiber, a significant increase in the tensile strength of thecomposite. In addition, we also find that the reaction temperature have a great influence onthe tensile strength composite. The higher temperature, the greater tensile strength. However,reaction time has no significant effect on the performance of composite materials.3．We calculate the strength of the composites using the mixing rule formula. The resultsshow that tensile strength of the composites is lower than the theoretical value. The tensilestrength is more close to the theoretical value when the reaction temperature increases.4．in order to overcome the shortcomings of traditional vacuum hot pressing in preparingcomposites such as high cost, low efficiency, the author use a high pressure hydraulic machinewhich can provide a pressure of300t and two stainless steels which are heated to873K as aheat source to prepare NiTi SMA fiber/Mg-9Li and NiTi SMA fiber/Mg-11Li composites.Then we use SEM, EDS, XRD to analyze microstructure of the composites. The results showthat the combination of TiNi fiber and magnesium-lithium alloy is good and atomic diffusionoccurred in the interface layer. The DSC measurement carried out on the NiTi fiber indicatesthat the NiTi fiber has no organization transformation. The room temperature tensile testsshow that the NiTi fiber has played an enhanced role on the two different Mg-Li alloys,achieving the same objectives of the composites prepared by vacuum hot pressing. |
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