Based on the density functional theory (DFT), using full-potential linearized augmented plane wave and improved local orbital (APW+lo) method, the structure and magnetism of the rare-earth permanent magnetic materials YFe11Ti are analyzed and calculated. The formation energy of YFe12，Y2Fe17 and YFe11Ti are calculated, The stabilization effect and the possible positions of the substituted atom Ti are discussed. The magnetic moments for the system and respective atoms are obtained. The calculated result is consistent with the experiment. The contributions of the density of states of the electrons to the magnetism are discussed.

The R(Fe, Mo)12 (R=Nd, Y, Dy) samples have been prepared and measure d by x-ray diffraction at different temperatures. The crystal lattice constant s and degree of the thermal expansion along the different axes are calculated. As a result, we consider that the abnormally thermal expansion of R(Fe, Mo)12 compounds is mainly determined by the Fe-Fe interaction. According to structural parameters of Nd(Fe, Mo)12, the anomaly is caused not on ly by the short Fe-Fe interaction as the previous explanation on other R-Fe inte rmetallic compounds but also by the other strongly positive Fe-Fe interactions. The mechanism of the substitution by Mo affecting the thermal expansion anomal ies is also discussed.

Using density functional theory, the structural parameters of α-U and bcc phases were obtained separately, in reasonable agreement with previous experimental and theoretical results. The enthalpy-pressure curve showed that the phase transition pressure was approximately 111 GPa. The structural behavior of γ-U under extreme loading conditions was exhibited by the ideal strength calculations. In addition, by analyzing the energy-strain relationship we found that the strain corresponding to the shear modulus c’ could decrease the total energy of U-Nb (6.25 at.%) alloy, indicating the instability of this structure.

The high-strain dynamic behavior of NiTi shape memory alloy has significant applications in several fields such as military af- fairs, aerospace. In order to investigate the transformation behavior in NiTi alloy, induced by dynamic mechanics, the shock-loading experiments are performed using a single stage gas gun at different temperatures and different shock velocities. Differential scanning calorimeter (DSC) and comprehensive physical property measurement system are employed to analyze the phase transformation in- duced by residual effects of shock waves in NiTi alloy. Three endotherms are observed in the first heating cycle, showing the presence of three-step reverse phase transformation; whereas during the second heating only one endotherm is seen, because the other two en- dotherms attributed to stress-induced martensite have disappeared. The exothermic and endothermic peak, owing to the transformation of shock-treated specimens, become small and their transformation temperature regions are broadened. This tendency indicates that the internal defects in the specimens, introduced by shock-treated, increase the resistance of phase transformation. The exothermic peaks of specimens, shock-treated at low velocity and high velocity, all shift to the low-temperature-zone, because the dislocations increase the hindrance to martensitic transformation. However, the endothermic peaks of specimens with low velocity shock-treated shift to high-temperature-zone, illustrating that the reverse martensitic transformation is also opposed by dislocations; while the endothermic peaks shift to low-temperature-zone for high velocity shock-treated, due to the decrease of transformation energy, caused by the re-duction of recoverable martensite. A small shoulder is detected in exothermic peak, whose shape becomes sharper with shock rate increasing. This result reveals that the intermediate phase (R-phase) results in two-stage phase transformation. The electrical resistivity measurement result further confirms that the two types of phase transformations associated with austenite to rhombohedral (A→R) and rhombohedral to martensite (R→M) can occur at the same time in a certain temperature range.

In the NiTi shape memory alloys (SMAs), the macro-mechanical deformations and the microstructural evolutions at different strain-rates (0.001-1200 s-1) are investigated. It is found that the detwinning stress of martensitic twin increases with strain-rate increasing, which indicates that the detwinning stress has the positive strain-rate dependence. A large number of detwinning regions are found in the NiTi specimen which is deformed at the strain-rate of 10 s-1 under tension. However, with the strain-rate further increasing up to 100 s-1 and 1200 s-1, no detwinning region is observed and many twins still exist. It is shown that the detwinning rates of martensitic twin in NiTi SMAs are in a range of 10-100 s-1. Simultaneously, thermally-induced austenite is detected in the NiTi specimens deformed at high strain-rates (≥qslant10 s-1). It is ascribed to the fact that there is a change from the isothermal process to the adiabatic process when the tensile strain-rate goes up to a critical value. Additionally, a small shoulder peak is detected in differential scanning calorimeter peak of 1200 s-1 strain-rate specimen, indicating that the two-stage phase transformation occurs.