Materials Science Forum Vol. 815

Abstract: For the past few years, nanocrystalline soft magnetic alloy has become hot topic in the field of strategic functional materials based on its excellent magnetic properties and advantages of energy saving, low cost, etc. With rapid innovationof various new type soft magnetic materials, FeCuNbSiB soft magnetic powder cores havebeen gradually turning into researching focusin soft magnetic material field for its excellent high frequency properties, such as high magnetic permeability (μ) and quality factor (Q), low core loss (P_c) and coercivity (H_c), etc.This paper mainly reviews the recent advances and technological achievements of FeCuNbSiB nanocrystalline soft magnetic powder cores, and also provides a brief introduction of FeCuNbSiB/Mn-Zn ferrite powder core, one new type composite magnetic powder core. Finally, future developing trend for FeCuNbSiB nanocrystalline powder cores isalso prospectedcompendiouslyin the paper.

Abstract: Mesoporous sulfated TiO₂-graphene oxide composites were prepared by hydrothermal method. The samples were analyzed by using scanning electron microscope (SEM), X-ray diffraction (XRD), FT-IR spectroscopy (IR) and Brunauer-Emmett-Teller (BET) method. photocatalytic activities of sulfated titania-GO samples were evaluated using the photooxidation of methylene blue in aqueous solutions by ultraviolet-visible (UV-via) spectroscopy. The results indicated that oxygen-containing carbonaceous groups in the GO are incorporated into the network of C\O\Ti and coordinated to titania in bidentate model, Sulfur species in the form of sulfate are incorporated into the network of Ti\O\Ti, resulting in the strong inductive effect, large specific surface area, and mesoporous structure. All these are beneficial to improve the photocatalytic activities of the mesoporous sulfated TiO₂-graphene oxide composites. The formation mechanism of sulfated mesoporous titania-graphene oxide composites was explored. Joint electronic system of reduced graphene oxide, SO₄²⁻ and TiO₂ was also predicted.

Abstract: Three types of V-Ti (vanadium-titanium) iron concentrate powder were studied on their features as well as their influences on the properties of cold-bonded iron ore pellets. The research results indicated that the relations between the fineness modulus of the three types of V-Ti iron concentrate is in the order of LM>HL>SX, and SX has the smallest fineness modulus and particle sizes. The relations between average wetting speed of the three types of iron concentrate powder is in the order of HL>LM>SX, and the wettability of HL powder is the highest. The relations between mixing time of the three types of iron concentrate powder is in the order of SX≈LM>HL. Under the same briquetting pressure, SX had the best pelletizing performance.

Abstract: In this paper the process of direct reduction of vanadium slag was adopted. The main factor was determined by uniform experimental design and single factor analysis, and then the optimum process condition was drawn by the test. The test results showed that the regression equation curve fitting of the experiment data was very significant, the main factors affecting the vanadium slag reduction (according to the primary and secondary order) was the content of anhydrous sodium carbonate, roasting temperature, roasting time and reduction of carbon content. The factors for the reduction of the optimum process conditions are the carbon coefficient 1.04, roasting temperature 1100°C, roasting reduction time 4h, 4% mass percent of anhydrous sodium carbonate and slag. Under the optimum conditions, the actual rate of weight loss and theory rate of weight were close to 0, the results could be reproduced, and the vanadium slag metallization rate was 75%~83%.

Abstract: In this work, hot compression tests on columniform TC18 titanium alloy specimens were performed with a Gleeble^® 3500 thermal and mechanical simulator in the temperature range of 820-875 °C and at constant strain rates of 0.01, 0.1 and 1 s⁻¹. Relationship model of true stress versus true strain as well as peak stress versus deformation temperature were established, and microstructural micrographs of TC18 titanium alloy were analyzed. The results showed that the flow stress decreased as the deformation temperature increased or the strain rate decreased. Besides, the deformation resistance at temperature above T_β (β transus temperature) was obviously lower than that at below T_β. In addition, flow stresses kept almost constant when it deformed in β region where hot deformation mechanism is DRV, but significant flow softening occurred in α+β region, where deformation mechanism is mainly dominated by DRX. And in α+β region, DRX is prone to occur at a low strain rate, and it is difficult for DRX to occur at high strain rate.

Abstract: Nickel coated Zr-V-Fe non-evaporable getter (NEG) powders were prepared using electroless plating. The microstructure and composition of the Ni-coated Zr-V-Fe powders were analyzed by XRD, SEM and EDS. The hydrogen absorption performance of Ni-coated Zr-V-Fe powders and as-prepared powders were analyzed by dynamic method after an activation at 300°C for 2 hours. The hydrogen absorption performance of Ni-coated Zr-V-Fe powders and as-prepared powders at 100°C, 200°C, 300°C, 400°C, and 500°C were also analyzed. The results indicated that Ni existed as crystalline phase. The Ni coating played an important role as a catalyst which favored the dissociation of hydrogen on surface and Ni lowers the hydrogen diffusion energy for the Zr-V-Fe powders. The hydrogen absorption kinetics of Ni-coated Zr-V-Fe powders was improved in comparison with that of the as-prepared powders, and a relatively higher absorption rate was exhibited.

Abstract: Two kinds of 2:17R Sm-Co alloys, Sm₂(Fe,Cu,Zr,Co)₁₇ and pure binary Sm₂Co₁₇ were prepared, and the amorphous powder was prepared by high-energy ball milling Sm-Co alloys. The bulk nanocrystalline SmCo₇ was prepared by hot-pressing the amorphous powder, and the magnetic properties and phase composition were studied. Initial Sm₂(Fe,Cu,Zr,Co)₁₇ showed a large value of coercivity while the pure Sm₂Co₁₇ almost showed no coercivity. However, after ball milling the grain size of alloys decreased dramatically until completely amorphous. Two kinds of alloys showed the different phase composition and magnetic properties after hot-pressing. It was found that the pure Sm₂Co₁₇ bulk magnet showed a high coercivity H_c and had the 1:7H phase. On the other hand, the Sm₂(Fe,Cu,Zr,Co)₁₇ showed high saturation magnetization M_s and very low H_c since the Fe-Co and Sm₂Co₃ phase were precipitated from the alloy.

Abstract: The Nd-Fe-B powder was prepared to bulk by cold pressing, and then was hot-deformed by the vacuum hot-pressing machine. Effects of hot-deformation temperature and rate on the density, anisotropy, performance and microstructure were studied. The results showed that the grain size was small, but the density and orientation degree was low, thus leading to poor performance when the deformation temperature was too low or deformation rate was too large. When the temperature was higher than 750 °C or the rate was lower than 0.1mm/s, the anisotropic magnets with good density and texture could be obtained. However, the magnetic properties of hot-deformed magnets deteriorated due to the present of coarse grains. From the microstructure of hot-deformed magnets it could be seen that there were plenty of coarse and irregular grains, which have a higher Nd content than the plate-like grains. The optimum magnetic properties could be obtained at deformation temperature of 700 °C and rate of 0.1 mm/s.

Abstract: A novel process was developed to obtain high content of ceria powder directly from bastnasite mineral. The bastnasite was roasted with NaHCO₃ at 550 oC for 2 h, washed with water and dilute HCl respectively to remove impurities, and finally calcined in air. TG-DTA, XRD, XRF, SEM was used to characterize the decomposition process of bastnasite, crystalline phase, the chemical composition, and morphology of the product. The results showed that the concentration of HCl solution was the most important factor in the leaching process, and the calcining temperature of bastnasite mineral should be controlled below 600 oC. The optimal technological parameters were suggested as follows: leaching temperature at 45 oC, for 45min in 3 mol/L HCl, with the weight ratio of solid to liquid of 1:5, and the calcining of the leachate at 600 oC for 2 h. And the high content of ceria (T_REO > 80wt %, Ceria/T_REO > 85wt %) nanosized (20~100 nm) powder was obtained succeffully, which showed potential application in polishing materials.

Abstract: The V(C,N) nanometer powder master alloy was added into a low carbon high strength bainite steel to refine grain size, and its refinement action with that of Ti addition was compared. The experimental specimens were melted in 25kg induction furnace with 0.03%Ti, 0.15%, 0.24%, 0.31% and 0.50% V(C,N) addition, respectively. The specimens were observed by optical microscope, XRD and EDS. The results showed that 0.03%Ti addition refined to the grain size to 13μm-18μm in the research steel, but to 6.5μm-10μm in the case of 0.31% V(C,N) master alloy. And the 0.31% V(C,N) addition has better refining effect than 0.15, 0.24% and 0.50%V(C,N) addition. The microstructure of research steels was lower bainite and martensite for all specimens.