Effect of Annealing on the Magnetic Properties of FeCoNiCuNbSiB Soft Magnetic Alloys

A series of nanocrystalline soft magnetic alloys with nominal compositions of Fe66.8-xCo10NixCu0.8Nb2.9Si11.5B8 (x = 1–15 at%) were developed and studied. Effects of annealing on the soft magnetic properties, crystallization behavior, and domain structure were investigated. The alloys with higher Ni content were prone to exhibit stronger magnetic anisotropy. The Fe66.8Co10Ni10Cu0.8Nb2.9Si11.5B8 alloy exhibited excellent soft magnetic properties, including the low permeability of 2000, low coercivity of about 0.6 A/m, and low remanence of 2.4 mT, together with a temperature gap of 128 K between two crystallization onset temperatures. It has been found that the Ni content and the annealing process possess significant effects on the soft magnetic property of the nanocrystalline alloys. It shows that the developed Fe66.8Co10Ni10Cu0.8Nb2.9Si11.5B8 nanocrystalline alloy exhibits great potentials for applying in the field of common mode chokes or current transformers, due to its ability to resist the direct current.

Physicochemical properties of ternary Fe-Si-Nb and Fe-Al-Nb metallic systems

The Russian Federation has a sufficient number of promising deposits of niobium raw materials which can satisfy the niobium and tantalum demands of Russian metallurgical enterprises for many decades. Ferroalloy technologists are faced with the difficult tasks of developing from various types of ore raw materials not only effective processes for its processing but also new acceptable rational compositions of niobium-containing ferroalloys. The chemical composition of niobium ferroalloy should, on the one hand, correspond to the product obtained by benefication (concentrate) and, on the other hand, satisfy the requirements of steelmakers for ferroalloys intended for microalloying niobium steel. To develop rational compositions of new niobium-containing ferroalloys in this work the physicochemical characteristics (which include crystallization temperature and density) of alloys containing 10-50% Nb, 10-40% Si, and 5-30% Al were studied. Two-component Fe-Nb metal alloys have a rational crystallization onset temperature (<1400 °С) only when the niobium content is not more than 10%. To achieve rational crystallization onset temperatures it is necessary to use complex alloys with silicon and aluminum. Studies have shown that a decrease in the crystallization onset temperature of complex niobium alloys occurs when the niobium content decreases with an increase in the concentration of silicon or aluminum. Three-component alloys Fe-Si-Nb and Fe-Al-Nb with a content of 15-20% Nb, 32-40 Si% or 12-30% Al belong to the category of low-melting ferroalloys. To achieve rational density values light metals such as silicon or aluminum must be introduced into a two-component system. The studied three-component alloys with a content of 25-40% Si or 15-30% Al have rational density values both from the point of view of their production and application to the processing of steel melt. The best physicochemical characteristics providing high service properties are possessed by complex niobium (15-20% Nb) FeNbSi alloys with 32-40% Si and FeNbAl with 15-30% Al which are recommended for widespread use in ladle microalloying of steels.

Thermal Stability of High k Layers

ABSTRACTThermal stability of amorphous phases in various high-k layers (Al2O3, ZrO2, HfO2, ZrAlOx, HfAlOx and HfSiOx) and the phase transformation of crystalline ZrO2 and HfO2 were studied experimentally, as functions of surface preparation, deposition conditions, material composition and post deposition thermal treatment. It is found that pure ZrO2 and HfO2 show relatively low crystallization onset temperatures. The crystalline ZrO2 or HfO2 phases are tetragonal or monoclinic, depending on the layer thickness. The phase transformation of metastable t-phase into stable m-phase has been observed in ZrO2 and HfO2. Crystallization behavior of Al2O3 depends on the surface preparation of the substrate. ALCVD grown Al2O3 layers on an oxide-based surface remain amorphous after 1100°C spike annealing, while those on HF-last surface crystallize at temperatures around 800°C. Alloying Al2O3 into ZrO2 and HfO2 can improve their resistance to crystallization under thermal exposure. The kinetics of the crystallization in the alloys can be described by linear TTT curves. Hf-aluminates show better thermal stability than Zr-aluminates. A defect model relative to the phase transformation is discussed, based on the above observations.

Correlation Between Structure And The Magnetic Properties Of Amorphous And Nanocrystalline Fe74Cu0.5Nb3Si13.5B9 Alloys

Structural and magnetic measurements have been performed on the FINEMET type of ribbons with nominal composition of Fe74Cu0.5Nb3Si13.5B9 synthesized by rapid solidification technique. The crystallization behavior and the nanocrystal formation have been studied by differential thermal analysis (DTA) and X-ray diffraction (XRD). The crystallization onset temperatures determined by XRD are in good agreement with DTA results. Magnetic permeability and magnetization measurements have been carried out using inductance analyzer and vibrating sample magnetometer (VSM). Magnetic permeability sensitively depends on the annealing temperature which increases sharply with the increase of annealing temperature. Maximum permeability corresponding to optimum annealing temperature (Ta) was observed at Ta = 575°C. Saturation magnetization, Ms, increases with Ta for the sample and finally decreases for annealing at a temperature much higher than peak crystallization temperature. The results show that the amounts of Cu and Nb are very important for the soft magnetic properties of FINEMET alloys. Key words: FINEMET; XRD; Grain size; Permeability; Saturation; Magnetization DOI: http://dx.doi.org/10.3329/jbas.v35i2.9423 JBAS 2011; 35(2): 187-195