Materials Science Forum Vols. 546-549

Abstract: The structure and magnetic properties of fcc-Fe/Cu (100) superlattices have been investigated by the first-principles total energy calculation based on density functional theory (DFT). Through the optimization of the structure of Fe/Cu superlattices, it has been found that the interlayer spacing of Cu layers is contracted while the interlayer spacing of Fe layers is expanded. There are no obviously changes of Fe/Cu interfaces for Fe3Cu3 and Fe3Cu5 models. The layer spacing for Fe3Cu5 changes larger than that of Fe3Cu3 model, which results to a slightly larger magnetic moment of FeCu5 than that of Fe3Cu3 model. We also analyze the density of state near the Fermi surface and calculate spin asymmetry factor of each layer in Fe/Cu systems. Based on the two-current model, we evaluate the magnetoresistance ratio 21.8% for Fe3Cu3 and 22.8 % for Fe3Cu5 system.

Abstract: The recovery strain in the near-equiatomic, severely cold-deformed NiTi, has been investigated through the study of thermal expansion by employing dilatometer (DL). By designing the shape of the original surface curve, macroscopic domains with different dislocation density were introduced into the NiTi alloys and materials possessing the characteristics of composites were obtained. Results show that in-situ composites of NiTi alloys rendered a distinct recovery strain of shape memory compared to directly cold-deformed NiTi alloys. We presume that the interactions between the dislocation texture and martensite variants are introduced when the NiTi martensite is cold rolled at room temperature might be responsible to the phenomena, which are discussed and compared with the differential scanning calorimeter (DSC) analysis in this paper. All the phenomena above show it is feasible to the method for controlling the thermal properties of a material by a proper design of the dislocation texture.

Abstract: The mechanical behaviors of bare and carburized NiTiCu specimens under dynamic impact loading were investigated using a home-built impact testing system. The contact force was measured with piezoelectric force sensor and digital signal processing system in real time during impact process. Predicted instantaneous velocity and displacement formula were presented. The results show that the maximum deformation depth of carburized specimens was less than that of bare specimens, and the carburization process can increase absorbed energy and cushion effect to impact of specimens during impact process. The decrease of deformation depth and increase of absorbed energy can reduce the contact force and materials damage of specimens during impact process.

Abstract: Four fluorinated polyacrylate dispersions, which based on chlorotrifluoroethylene (CTFE), acrylic acid (AA), vinyl acetate (VAc) and ethenyltriethoxysilane (ETOS) as monomers, are synthesized by free radical polymerization. The influence of xenon lamp and UV-light aging on the film with the fluorine content is discussed. The effect of salt-spray corrosion before and after UV-light aging with F wt% of film is also studied. The results show that low surface energy of high fluorine content film can retard salt-spray corrosion compared with no or low fluorine content films.

Abstract: A strong need exists to develop new kinds of high-temperature shape-memory alloys. In this study, two series of CoNiGa alloys with different compositions have been studied to investigate their potentials as high-temperature shape-memory alloys, with regard to their microstructure, crystal structure, and martensitic transformation behavior. Optical observations and X-ray diffractions confirmed that single martensite phase was present for low cobalt samples, and dual phases containing martensite and γ phase were present for high cobalt samples. It was also found that CoNiGa alloys in this study exhibit austenitic transformation temperatures higher than 340°C, showing their great potentials for developing as high-temperature shape-memory alloys.

Abstract: In this paper the mechanical structure and the operating principle of a fast steering mirror (FSM) are introduced, and a novel FSM based on magnetostrictive actuators is designed. The modal analysis of the FSM is carried out with the help of the finite element method, and relative experiments are also conducted. The experimental results and that of simulation are given and in good qualitative agreement with each other. This paper pays attention to ameliorating the FSM structure for higher mechanical natural frequency and perfect control performance. The experimental results would be helpful for the construction design of the FSM.

Abstract: The rate-dependent hysteresis exhibited by magnetostrictive actuator (MA) presents a challenge in modeling of these actuators. In this paper, a novel rate-dependent hysteresis model was proposed for magnetostrictive actuator. In the model, the modified Prandtl-Ishlinskii operator (PI) is combined with a second order ordinary differential equation in a cascaded structure. The modified PI operator is used to account for the static hysteresis, the connection between ODE and the rate-dependent energy loss was established, including the classical eddy current loss and the mechanical dynamics. Simulation results show a good agreement with the experiment ones.

Abstract: The phase transformation and mechanical behaviors of cold-rolled NiTi shape memory alloys ultra-thin sheet with 100μm in thickness are investigated. The transformation behaviors of the NiTi sheet are found to be remarkably influenced by heat treatment using electric resistance vs. temperature measurements. The martensitic transformation temperature reduced by annealing at 400°C or 600°C, and R-phase transformation appears when annealing at 400°C. The martensitic reorientation occurs when the NiTi sheets annealed at 400°C is deformed at room temperature and the maximum shape memory strain is 3.5% at 100% recovery ratio. For the NiTi sheets annealed at 600°C, a superelastic strain of 5% and a transformation stress about 500MPa are achieved.

Abstract: The effects of NiO on density and mechanic strength of Mn-Zn ferrite used for inertial gyroscope were investigated by measurements of crystal lattice constant, Vickers hardness, bending strength. To investigate this further, powder of Mn-Zn ferrite was characterized by x-ray diffraction (XRD) and the fracture surface of Mn-Zn ferrite was checked by scanning electronic microscope (SEM). The investigation revealed that the substitution of Ni2+ modified crystal lattice constant and crystal grain size so that it caused crystal lattice constant of Mn-Zn ferrite to decline and crystal grain size to decrease, therefore it was useful to improve density and mechanic strength of Mn-Zn ferrite by this way. The results show that proper addition of NiO can bring higher density and more perfect mechanic strength of Mn-Zn ferrite used for inertial gyroscope.