| NiTi shape memory alloy (SMA) has attracted much interest for their potential use as functional materials in many engineering applications such as active, adaptive or smart structure, as well as certain biomedical applications. Recently, considerable attention has been attracted on porous NiTi alloy. The porous NiTi SMA could be used as hard tissue implants because of its porous structure, good mechanical properties, biocompatibility and shape memory effect (SME).This dissertation has investigated the fabrication of NiTi shape memory alloy by metal injection molding. An injection pressure of 400bar, a feedstock temperature of 353K and a mould temperature of 328K are testified to be the adequate parameters providing homogeneous properties of the molded compacts. A two-step debinding process is necessary for the selected binder system: solvent debinding and thermal debinding. The results show that the weight loss of the binder could reach 98.8%. The debinding rate could be divided into three portions with time. Pores with different sizes are formed in the molded compact after solvent debinding and thermal debinding.In this dissertation, the porous NiTi shape memory alloy (SMA) sintered by self-propagating high-temperature synthesis (SHS) has been investigated experimentally and numerically. The experimental results show that the microstructure of the pore structure of the porous NiTi alloy is observed by SEM, the porosity is 75 vol.%. There are numerous pores with various sizes and shapes. The average pores size is about 1000μm. The pores are almost three-dimensionally interconnected and form an open porous structure. Both the porosity and the pores size for the molded compact are much higher than those for the pressed compact. It can be found that the SHS process results in the formation of several intermetallic compounds, such as NiTi, and NiTi2. The B2 and B19′phases are predominantly present. The SHS reaction process could be divided into three steps: preheating, ignition and sintering. The ignition time would increase with the decrease of the coil temperature and the preheating temperature. The temperature keeps increasing with the propagation of combustion wave along the axis due to the heat release by the reaction, when the local temperature reaches 1573K, the temperature would keep unchanged. For a certain preheating temperature, the temperatures for different locations are almost independent on the combustion time, this means that the mode of the combustion has transferred from self-propagating high-temperature synthesis to thermal explosion. The transient degree of the conversion, molten fraction and mean velocity of the combustion wave are also investigated systematically. The results of experiment and numerical simulation were shown in good consistence. In this dissertation transient thermal response of porous shape memory alloy actuator by thermal enhancement has been investigated numerically and experimentally. The results show that the temperature of the SMA actuator would fluctuate at the same frequency of heating-cooling regularly after several minutes. The maximum temperature not only for experiment but for simulation is much higher than the austenitic finish temperature of NiTi shape memory alloy. The minimum temperature is lower than the martensitic finish temperature of NiTi shape memory alloy. This means that the actuator can be driven completely. The numerical model was divided into two sections: flow in pipe and flow in the porous membrane. For the flow in pipe, the model was adopted the standard k-εturbulence model and energy conservation equation; for the flow in the porous membrane, the flow was adopted the laminar model. They show consistence between the experimental data and the numerical results.The restoring force of the shape memory alloy actuator is investigated numerically in two dimensions. The transient restoring force in a period is obtained by using the method of finite element. The result shows that the maximum restoring force could reach 402MPa. Based on these results, the shape memory alloy actuator is designed based on the PLC. It is found that the actuated frequency may reach 2.27 Hz in the experimental condition.
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