Abstract: The effects of Cu addition on the crystal structure, phase stability and magnetic properties of Ni8Mn4-xGa4Cux (x=0, 0.5, 1, 1.5 and 2) ferromagnetic shape memory alloys are systematically investigated by first-principles calculations. The formation energy results indicate that the added Cu preferentially occupies the Mn sites in Ni2MnGa alloy. The formation energy results indicate that ferromagnetic austenite is more stable than the paramagnetic one. The ferromagnetic state becomes instable and paramagnetic state becomes more stable when Mn is gradual substituted by Cu. Furthermore, the electronic density of states gives rise to the difference in the magnetic properties.
Abstract: Ni-Mn-In is a novel type of magnetic shape memory alloy, its shape memory effect has been realized through magnetic field induced reverse martensitic transformation. A variety of point defects would be generated during composition adjustment process, such as antisite defect, vacancy and exchange. The first–principles calculations within the framework of the density functional theory using the Vienna ab initio software package (VASP) have been used in this paper to investigate the defect formation energy and electronic configuration of the off-stoichiometric Ni-X-In (X= Mn, Fe and Co) alloys. The In antisite on the X sublattice (InX) and the Ni antisite on the X sublattice (NiX) have the lowest formation energies in the investigated series. The formation energy of the Ni vacancy is the lowest, while that of the in vacancy is the highest. It is confirmed that the in constituent plays a dominant role for stabilizing the austenitic phase.
Abstract: The effects of Cr addition on the crystal structure, phase stability and magnetic properties of Ni8Mn4-xGa4Crx (x=0, 1 and 2) ferromagnetic shape memory alloys are systematically investigated by ab-initio calculations. The formation energy results indicate that the added Cr preferentially occupies the Mn sites in Ni2MnGa alloy due to the lowest formation energy. The evaluated Curie temperature decreases with increasing Cr content are derived from the decrease of the total energy difference between the paramagnetic and the ferromagnetic austenite.
Abstract: The equilibrium alloys closed to Mg-Nd side in the Mg-rich corner of the Mg-Zn-Nd system at 400°C have been investigated by scanning electron microscopy, electron probe microanalysis and X-ray diffraction. The binary solid solutions Mg12Nd and Mg3Nd with the solubility of Zn have been identified. The maximum solubility of Zn in Mg12Nd is 4.8at%, and Mg12Nd phase can be in equilibrium with Mg solid solution. However, only when the solubility range of Zn in 26at%~32.2at%, Mg3Nd can be in two-phase equilibrium with Mg solid solution. As the results, two two-phase regions as Mg+Mg12Nd and Mg+Mg3Nd and a three-phase region as Mg+Mg12Nd+Mg3Nd in Mg-Nd-Zn ternary isothermal section at 400°C have been identified.
Abstract: Fe83.5B15Cu1.5Cax (x= 0.04, 0.07, 0.1 and 0.13) alloy ribbons were fabricated by melt spinning. The effects of Ca addition on electrical resistivity and soft magnetic properties were investigated. The results show that with increasing Ca content from 0.04 to 0.13 the electrical resistivity monotonously increases from 0.51 μΩ·m to 0.99 μΩ·m while the core loss reduced by 39% and 28% at 10 kHz and 20kHz under an applied magnetic field of 200 mT, respectively. After annealing at 420°C for 10min, sample with x=0.13 obtains the peak saturation induction density (Bs) of 1.82 T and coercive force (Hc) of 18 A/m. Especially, the core loss of sample x=0.13 decreased by 13% and 34% than that of x= 0.04 at 200 kHz under an applied magnetic field of 25 mT and 50 mT respectively. Therefore, the soft magnetic properties and core loss can be tuned by addition of Ca in Fe-B-Cu alloy ribbons.
Abstract: This paper uses ProCast software to simulate Mg-Gd alloy solidification process, calculates temperature field and solidification field for Mg-9.76Gd at different stages and compares the influence of different heat transfer coefficient on the solidification structure. The results show that the crystallization process which is simulated is consistent with the actual crystallization process; as the heat transfer coefficient increases, the average grain size decreases. With the result, the reasonable casting formation control parameters can guide the practical production, which can reduce human and financial resources.
Abstract: In this study, we investigated the aging strengthening of Mg-Zn-Cu alloy based on component optimization design by FactSage software, optical microscope (OM), X-ray diffraction (XRD) and Vickers hardness tester. The results show that the precipitation rate of MgZn2 phase in Mg-6Zn-1Cu is significantly higher than that of the other alloys. When Mg-6Zn-1Cu alloy is subjected to aging at 160°C for different time, the phase consists of α-Mg, MgCu2 and MgZn2. The content of main strengthening phase MgZn2 is increasing with the prolonging of aging time. When Mg-6Zn-1Cu alloy aged at 160°C for 10h, the kinetics of precipitation is considerably accelerated. The results indicate that the hardening produced in the Cu-containing alloy is considerably higher than in the Mg-Zn alloy. Therefore, based on component optimization design to establish Mg-Zn-Cu alloy solidification database, and to predict the phase equilibrium and thermodynamic properties of the alloy, is an effective method for the development of new magnesium alloy.
Abstract: Antisite defects are common defects in nanotube materials and have seriously impacts on their electronic properties. Based on density-functional theory calculations, the electronic structures of the antisite defective chiral (6, 2) SiCNTs are investigated. C antisite and Si antisite lead to the formation of a depression and a bump in the surface of the nanotube, respectively. In the band gap of the SiCNT with a C antisite defect, the occupied level near the top of the valence band is formed, while the unoccupied level originating from the Si antisite defect enters the conduction band of the SiCNT.
Abstract: Research object of this article is a type of oriented silicon steel in 3.07% silicon content. By comparing samples under normalization and non-normalization respectively after primary recrystallizing annealing and secondary recrystallizing annealing, we have figured out how normalization influenced the recrystallizing behavior. The EBSD data of samples showed that normalization can half the grain size after primary recrystallizing, raise the percentage content of favored grain boundaries and high-angle grain boundaries, increase the content of Goss orientation grains by 5 times. And normalization coarsens the secondary recrystallizing grains, triples the magnetic induction and reduces the iron loss by half.