Heat Treatment In Hydrogen Atmosphere Research Articles

Synthesis of iron–tungsten alloy on mild steel by laser surface alloying

Laser surface alloying (LSA) was used to synthesize iron–tungsten alloy on mild steel substrate. The slurry of tungsten powder 1.28 μm in average diameter was made and a uniform layer of the slurry was applied onto substrate using thin layer chromatography method. Thickness of powder layer was varied from 0.2 mm to 0.6 mm. The surface was melted using beam oscillated CO 2 laser. When impinged energy density is selected to be 93 W mm −2 or 81 W mm −2, the microhardness of the obtained iron-rich alloying layer is 330–430 HV. It increases up to 630 HV through heat treatment in hydrogen atmosphere at a temperature of 873 K for 5 h and successively at 973 K for 5 h.

Microstructure and magnetic properties of Zn- or Sn-bonded Sm2Fe17Nx magnets

Hard magnetic Sm2Fe17Nx alloy powders with a coercivity of 5.6 kA/cm and a remanent polarization of 1 T, related to the density of 7.7 g/cm3, could be achieved by a combined heat treatment in hydrogen atmosphere and a successive nitrogenation. During nitrogenation SmFe3 and SmFe2 constituents decompose into SmN and αFe immediately. The density of die-pressed anisotropic Sm2Fe17Nx magnets containing 5 wt % Zn amounts to ∼5 g/cm3 and increases to 5.25 g/cm3 for additions of 20 wt % Zn. After annealing at 390 °C for 10 h, the remanent polarization of 0.66 T and the coercivity of 8.8 kA/cm result in a maximal energy density of 67 kJ/m3. Annealing at temperatures of ∼420 °C achieves additional αFe due to a decomposition of Sm2Fe17Nx by Zn: Sm2Fe17Nx+Zn→Sm2FeZn2+αFe+N2. Additions of 10 wt % Sn result in a density of 4.6 g/cm3 of isostatically compacted magnets. The remanent polarization amounts to ∼0.6 T, but the coercivity Hcj of ∼4 kA/cm is inferior to Zn-bonded Sm2Fe17Nx magnets.

EPR investigations on Cr 3+ modified PbTiO 3 ceramics

EPR studies show axial Cr 3+ centres in Cr-doped ferroelectric PbTiO 3 ceramic after heat treatment in hydrogen atmosphere. The fine-structure splitting at room temperature was interpreted on the basis of the Newman superposition model. The temperature dependence of the fine-structure splitting has been measured and discussed. A hopping model was introduced to interpret these results.

Fe-C-O amorphous thin film by plasma CVD

Fe-C-O thin films were prepared by plasma CVD. The films were amorphous and had columnar structures. The magnetic characteristics measured in the plane were 4πMs=13.65 kgauss, 4πMr=1.84 kgauss and Hc= 40 Oe, but the coercive force measured vertically to the plane was nearly zero. On the other hand, Mossbauer measurement indicated that the average direction of magnetization was inclined at 30 degrees from the normal of the film. By a heat treatment in hydrogen atmosphere, the film transformed to αFe and Fe 3 C crystalline phases with a granular structure, and the directions of magnetization became random.

High Magnetic Permeability Alloys “Hardperm” in the Ni–Fe–Nb–W and Ni–Fe–Ta–W Systems

Ni–Fe–Nb–W and Ni–Fe–Ta–W alloys were heated in pure hydrogen atmosphere at 1150°C for 3 hr and then cooled at various rates from a temperature above their order-disorder transformation points. In the Ni–Fe–Nb–W system, an alloy of 79.4% Ni, 11.54% Fe, 8.51% Nb and 0.50% W cooled at the rates of 240 and 300°C/hr showed the highest initial permeability of 109000 and the highest maximum permeability of 463000. In the Ni–Fe–Ta–W system, the highest initial permeability of 101000 is obtained with an alloy of 73.40% Ni, 10.96% Fe, 14.11% Ta and 1.53% W cooled at the rate of 200°C/hr, and the highest maximum permeability of 557000 with an alloy of 73.50% Ni, 10.96% Fe, 14.99% Ta and 0.55% W cooled at 300°C/hr. The hardness and electrical resistivity of these alloys are considerably higher than those of Permalloy-type alloys. The high permeability of these alloys is largely due to the major contribution of high-temperature heat treatment in hydrogen atmosphere to the homogenization, removal of impurities, and the very low saturation magnetostriction and crystal magnetic anisotropy in a proper state of ordering.

Ni-Fe-Ta-W系高透磁率合金Hardpermについて

Ni-Fe-Ta-W alloys were heated in hydrogen atmosphere at 1150°C for 3 hr and then cooled at various rates from a temperature above their order-disorder transformation points. The highest initial permeability of 101000 is obtained with the alloy of 73.40%Ni, 10.96%Fe, 14.11%Ta and 1.53%W cooled at the rate of 200°C/hr, and the highest maximum permeability of 557000 with the alloy of 73.50%Ni, 10.96%Fe, 14.99%Ta and 0.55%W cooled at 300°C/hr. The alloy having the highest initial permeability exhibited the electrical resistivity of 71.4 μΩ-cm, with 210 Vickers hardness. The high permeability of the Ni-Fe-Ta-W alloys is largely due to the effective contributions of the high-temperature heat treatment in hydrogen atmosphere to the homogeneity of alloys and removal of impurities, associated with the low values of saturation magnetostriction and crystal magnetic anisotropy in a proper state of ordering.

The mechanism of color center production in iron doped photochromic sodalites

Bromide sodalites doped with iron (0.75 mg/cm 3) have been studied by the Mossbauer technique, before and after heat treatment in hydrogen atmosphere and after coloration by u.v. light and by electron bombardment. The measurements show that u.v. or electron irradiation causes Fe 2+ ions to convert to Fe 3+. The number of converted ions (≁ 10 17/cm 3 for u.v. irradiation, and 5 × 10 17/cm 3 for electron irradiation) agrees with the expected number of F centers estimated from optical measurements. The thermal recovery time at room temperature of the Fe 3+ ions back to their Fe 2+ state was found to be several months.

Effect of High-Temperature Heat Treatment on the Properties of Hardperm in the Ni–Fe–Ta System

Considerable improvements of the magnetic properties of Ni–Fe–Ta alloys having a range of composition from 70.03 to 77.41% Ni, 9.50 to 15.96% Fe, and 9.57 to 17.80% Ta have been effected by heating in hydrogen atmosphere at high temperatures of 1050 to 1350°C, followed by cooling at rates from 100 to 8100°C/hr. The highest value of 75000 in initial permeability and of 650000 in maximum permeability can be obtained with a composition of 73.00% Ni, 11.60% Fe, and 15.40% Ta by cooling at the rate of 800°C/hr after heating at 1250°C for 30 min and 3 hr, respectively. The alloy subjected to the latter heat treatment exhibits the electrical resistivity of 70.1 μΩ-cm and the Vickers hardness 211. The high permeability of the Ni–Fe–Ta alloys is largely due to the effective contributions of high-temperature heat treatment in hydrogen atmosphere to the homogeneity of the alloys, removal of impurities and grain growth, associated with the low value of magnetostriction caused by the atomic arrangement in the ordered state.