Heat treatment of highly dispersed electrolytic iron and Fe-Co alloy powders with a composite coating

Conclusions A necessary condition for improving the magnetic properties of powers is improvement of the metal phase structure, elimination of nonmagnetic impurities, and destruction of a chemisorbed coating. Annealing in hydrogen at 633–653 K makes it possible to retain the main geometric size of particles within the limits 0.8–1.0 m, to reduce dendrites and to increase the coercive force by a factor of 1.5–2 and the residual specific magnetization of iron and Fe-Co alloy powders up to 95 and 105 A·m²/kg, respectively.Translated from Poroshkovaya Metallurgiya, No. 4(340), pp. 74–78, April, 1991.     

Methods of increasing the magnetic energy of sintered platinum-cobalt magnets

Conclusions A process has been developed for the production of nonporous sintered platinum-cobalt alloy specimens having a density of 15.1–15.2 g/cm³. A heat treatment schedule is proposed enabling the magnetic energy of such specimens to be increased to 34.2 kJ/m³.Translated from Poroshkovaya Metallurgiya, No. 10 (142), pp. 33–36, October, 1974.     

Magnetic analysis as a means of determining the degree of ferritization of barium ferrite powder

Conclusions It has been demonstrated in this work that the magnetic analysis technique is in principle suitable for determining the completeness of ferritization of barium ferrite powders. At a specific saturation-magnetization intensity of 56 G-cm³/g or more, anisotropic magnets with an energy of about 3 · 10⁶ G-Oe are obtained; at _s=52 G-cm³/g or more, anisotropic magnets are obtained having an energy of more than 2 · 10⁶ G-Oe. The particles of ferritized powders used for such magnets should be approximately single-domain in size.Translated from Poroshkovaya Metallurgiya, No. 3 (87), pp. 57–60, March, 1970.     

Effect of electrolysis conditions on the formation,structure, and magnetic properties of a finely divided iron-cobalt alloy

Conclusions An investigation was carried out into the effect of electrolyte concentration and current density on current efficiency in the electrodeposition of Fe, Co, and Fe-Co alloy powders. It was established that raising the electrolyte concentration from 6.65 to 26.62 g/liter of Fe²⁺ + Co²⁺ increases current efficiency, whose maximum value is about 90%. The highest current efficiency is attained at i_c of 20–30 A/dm². Changing the electrolyte concentration and current density does not significantly affect the composition of alloy deposits. At an iron-to-cobalt ion content ratio in the electrolyte of 11 the rate of discharge of Fe²⁺ during alloy formation in the twolayer bath is greater than that of Co²⁺. X-ray structural analysis revealed that the greatest changes in the internal structure of a very finely divided iron-cobalt alloy take place at low electrolyte concentrations. That raising the electrolyte concentration facilitates alloy formation is confirmed by a decrease in the degree of defectiveness of the particles and a stabilization of the crystal lattice parameter of the alloy; i_c does not have such an effect on the structure of the alloy. Magnetometric measurements demonstrated that the coercive force of alloy powders is greater at higher densities of dislocations in their particles.Translated from Poroshkovaya Metallurgiya, No. 8(224), pp. 5–11, August, 1981.     

Manufacture of magnetic cores from various iron powders

Conclusions Coercive force measurements were made on grades PZh4M3, PZhCh3SV, PZhCh3MV, NC 100.24, PZhR(0) and PZhÉ iron powders and magnetic cores heat treated in the temperature range 750–1200°C. Iron powders of large specific surface are characterized by greater coercive forces compared with powders of small specific surface. Grades PZhCh3SV, PZhCh3MV, NC 100.24, and PZhR(0) iron powders are suitable for the manufacture of magnetic cores after they have been alloyed with elements decreasing internal stresses in alloys. Sintered magnetic cores from PZhÉ electrolytic iron powder meet all the requirements of TU 16-538.225-74 without alloying. The properties of grades EMP300M, PM282N, KiP 270.MS, and SC 100.26 iron powders were assessed. KiP 270.MS and SC 100.26 powders possess the same properties as PZhCh3SV, PZhCh3MV, and NC 100.24 powders, but in grade SC 100.26 powder high oxygen contents are not permissible. Consequently, magnetic cores made from this powder will exhibit high coercivity. Grades EMP300M and PZhR(0) iron powders are similar in all their properties, and the magnetic characteristics of cores made from them will therefore also be comparable. Grade PM282N iron powder is produced by the electrolysis of solutions and characterized by a dendritic particle shape. Owing to the large specific surface of the particles of this powder, its coercive force will be 25–30 A/m greater than that of PZhÉ. In the manufacture of magnetic cores from this powder recourse must therefore be had to alloying with silicon in order to decrease their coercivity.Translated from Poroshkovaya Metallurgiya, No. 6(234), pp. 73–78, June, 1982.     

Progress of Sm-Fe-N Anisotropic Magnets

A reduction and diffusion method (R/D) is used to make a mother alloy of Sm-Fe-N anisotropic magnets. Reduction of 0.5wt% of samarium content compared to the conventional powder increases magnetization. Milling condition and surface treatment improve the squareness of demagnetization curve, the aging property and the heat resistance. The maximum energy product of 292 kJ/m³ is obtained with the powder. High coercive force is maintainable even if the powder is exposed for 300h in 80 °C 90%RH. The maximum energy product of 141 kJ/m³ is obtained with an injection molded anisotropic magnet. The aging property estimated by irreversible flux loss is comparable to the conventional MQP-B magnets. The heat resistance temperature (T_−5%) at which die initial irreversible flux loss becomes −5% is 125-more than 150 °C for Sm-Fe-N magnets and 150–170 °C for hybrid magnets. The magnetic properties of bonded HDDR Nd-Fe-B magnet were improved by substituting for Nd-Fe-B powder with Sm-Fe-N powder. A new technology to make anisotropic bonded Sm-Fe-N thin cylinder magnets by an injection molding using unsaturated polyester (UP) resin was developed.     

Effect of Gallium Addition on Magnetic Properties of Nd2Fe14B-Based/ α-Fe Nanocomposite Magnets

The influence of Ga addition on the crystallization behavior and the magnetic properties of nanocomposite Nd2Fe14B-based/α-Fe magnets was investigated. It was found that the addition of 0.2% did not change the crystallization temperature of amorphous alloy, but the magnetic properties were improved significantly because of the strong exchange coupling interaction between the hard and soft magnetic phases. The optimum magnetic properties with iHc = 600. 3 kA· m^-1, B r = 0.75 T, and （BH）max = 88.03 kJ· m^-3 were obtained in bonded Nd9.5（FeCoZr）83.8 Ga0.3 B6.5 magnet with 15 m·s^- 1 wheel speed and 670 ℃ annealing treatment. The apparent improvement of magnetic properties originates from the grain refinement calculated using the Scherrer formula from corresponding XRD patterns and the excellent rectangularity of the demagnetization curve.     

Control over the particle size of stainless-steel powders

Conclusions Replacing some of the metallic iron by ferric oxide, Fe₂O₃, in the charge for the preparation of Kh18N15 and Kh23N28 stainless-steel powders by the calcium-hydride reduction process increases (two- to threefold) the yield of the fine fraction (-0.063 mm) without affecting the apparent density of the powders (1.4–1.85 g/cm³) or the sponge shape of their particles. At the present time, stainless-steel powders are being manufactured using a charge in which 20–30% of metallic iron has been replaced by the oxide Fe₂O₃.Translated from Poroshkovaya Metallurgiya, No. 2 (134), pp. 1–8, February, 1974.     

Properties of composite powder coatings based on iron and ultrafine silicon nitride

Conclusions Composite-powder plasma coatings based on iron and ultrafine silicon nitride consist of a structure made up of iron matrix with inclusions of solid particles of silicon-containing compounds.The coatings have a high wear-resistance (wear rate 6.10^–11 m per l m of tracking) and are not inferior to coatings made of thermally active PN85Yul5 powders.The coatings material has a low cost, good workability with traditional methods, and demonstrates excellent working properties in actual conditions for friction units.Translated from Poroshkovaya Metallurgiya, No. 3(339), pp. 65–68, March, 1991.     

Magnetic Hysteretic and Mechanical Properties of a 31Kh20K3M Alloy with an Increased Carbon Content

An Fe–31Cr–20Co–3Mo (31Kh20K3M) alloy containing 0.09 wt % C, which is almost twice as much as its maximum content according to GOST 24897–81, has been studied to verify the influence of the carbon content on the magnetic hysteretic properties of hard magnetic high-chromium Fe–Cr–Co alloys. The optimal heat treatment, including thermomagnetic treatment, results in the average values of residual magnetic induction B_r = 0.96 T and coercive force H_cB = 63 kA/m and the maximum energy product (BH)_max = 29 kJ/m³. Some heat treatment regimes give B_r = 1.03 T, H_cB = 72 kA/m, and (BH)_max = 31 kJ/m³. In addition, for isotropic alloy samples, the following average values are obtained: B_r = 0.71 T, HcB = 56 kA/m, and (BH)_max = 15 kJ/m³. These magnetic hysteretic properties of the 31Kh20K3M alloy with an increased carbon content are similar to those of a powder 30Kh21K3M alloy with the minimum carbon content.     

PERMANENT MAGNETS FROM ELONGATED SINGLE-DOMAIN PARTICLES

Abstract

A process is described for producing elongated single-domain (ESD) fine-particle magnets. The 150-Å. ESD iron or iron–cobalt alloy particles are prepared by controlled electrodeposition into mercury, followed by thermal growth and treatment with a third metal to attain optimum particle shape and magnetic properties. The particles are then aligned by a magnetic field, compacted under pressure, freed of mercury by vacuum distillation, and embedded in a suitable matrix. This is ground to a coarse powder and fed into automatic presses for realigning and compacting to the final magnet shape. The factors controlling each step of the process are discussed, and the advantages of magnets with artificial microstructures synthesized by this approach are pointed out. The process described produces commercial ESD iron and iron–cobalt magnets with energy products of 2·2 and 3·5 million gauss-oersteds, and laboratory ESD iron and iron–cobalt magnets of 4·2 and 5·0 million gauss-oersteds.     

Change in Iron Powder Properties with Treatment in Rolls

Conditioned iron powders are prepared by carbothermal reduction of “Blue Dust” (India) ore concentrate followed by compaction treatment in rolling mill and a decarburizing anneal. The properties of powder prepared by grinding in a vibration and rolling mill are determined. The method makes it possible to control the bulk density of the powder from 1.75 to 2.75 g/cm³. Determination of the production properties of the powders obtained and powder NC.100.24 by the same procedure established satisfactory conformity of the results. The technological desirability of preparing conditioned iron powder by treatment in a rolling mill is demonstrated.__________Translated from Poroshkovaya Metallurgiya, Nos. 3–4(442), pp. 12–16, March–April, 2005.     

Effect of surface-active agents on the properties of a copper powder produced by the autoclave method

Conclusions Carboxyl-containing water-soluble polymers have the strongest influence on the properties of copper powders and are the most effective in reducing their deposits on the inside reactor surface. The optimum SAA consumption rate is 0.003–0.007 g per 1 g of copper. Higher consumption rates intensify the flocculatton of powder particles and increase the carbon content of the powder, which is undesirable, since it makes the latter's subsequent processing more difficult. The carboxyl-containing substances currently produced by industry can be used as SAAs, but, because of their low carboxyl-group content (not more than 45–60%), powders produced in their presence become fairly severely contaminated with carbon owing to destruction of inert radicals. By suitable choice of type of carboxyl-containing SAA it is possible to vary the properties of powders in the following ranges: specific surface 0.02–0.18 m²/g, apparent density 0.9–2.9 g/cm³, mean particle size 20–42m, and flowability 0–2.6 g/sec.Translated from Poroshkovaya Metallurgiya, No. 7(283), pp. 5–8, July, 1986.     

Reduction annealing of very fine electrolytic iron powders with organic coatings

Conclusions Very fine iron powders produced by electrolysis in a two-layer bath are not suitable in the as-deposited condition for the manufacture of micropowder magnets. Heat treatment for 4 h in very dry hydrogen at a temperature of 600°K removes the excess of the organic component, reduces surface oxides, and brings about structural changes which impart to such powders an optimum particle shape and good compressibility. This enables micropowder magnets of excellent properties to be obtained.Translated from Poroshkovaya Metallurgiya, No. 7(235), pp. 1–7, July, 1982.     

Crystal structure and magnetic properties of SmCo5 permanent magnets produced by deformation sintering

Conclusions The phase composition and structure requirements for the optimization of the magnetic properties of SmCo₅ magnets are largely fulfilled in deformation sintering. Deformation sintering of magnets from single-phase powder enables, by ensuring the formation of an optimum structure, magnets of good magnetic properties [B^HC=7.5–8 kOe, (BH)_max=21–22 MG-Oe] to be obtained. The optimum deformation sintering conditions are: deformation load P_d=0.59 GPa; sintering temperature T_d=550°C; and sintering time _d=10–30 min.Translated from Poroshkovaya Metallurgiya, No. 1(217), pp. 75–82, January, 1981.     

A novel technique for manufacturing metal-bonded Nd-Fe-B magnets by squeeze casting

A new method was developed for forming Nd-Fe-B rapidly quenched ribbon to metal-bonded magnets. The process was carried out by a squeeze casting technique. The A356 aluminum alloy and zinc alloy (ZAS) were used as metal binders. The energy product (BH) of A356-bonded magnet was 62.2 k J/m³ and that of ZAS-bonded magnet was 61.2 k J/m³. The maximum bending strength of ZAS-bonded magnets (259 MPa) was greater than that of A356-bonded magnets (148 MPa). The corrosion behavior of both magnets was studied in the salt spray test and the magnetization flux loss was measured. The magnetization flux loss of ZAS-bonded magnets is less than that of A356-bonded magnets due to Zn as a sacrificial anode to protect MQ powders.     

Production of pure iron powder by a chemicometallurgical method

Conclusions The new process for the production of pure iron powder with an iron content of the order of 99.9% is simple and can be mechanized. The resulting powder has excellent processing characteristics and in particular, as demonstrated by tests conducted at various organizations, can be successfully utilized for the production of sintered magnets, magnetic cores, high-density constructional parts, etc. In addition, the powder is also likely to find application as a charge material in the manufacture of steel powders and in the production of alloys with special electrical, magnetic, and physical properties.Translated from Porosh-kovaya Metallurgiya, No. 9(69), pp. 1–9, September, 1968.     

Production of metal powders from melts by centrifugal atomization

Conclusions A study was made of centrifugal atomization of molten metals in argon at low argon consumption rates [(5.2–7.5) · 10^–3 NTP m³/kg]. Output with a single injector attained 30–40 kg/h. Increasing the molten metal head to 0.6–0.8 MPa and decreasing the nozzle diameter to 0.3 mm substantially increased the fineness of the powders. Raising the head still further influenced the effectiveness of atomization to a smaller extent, and decreasing the nozzle diameter to less than 0.3 mm coarsened the powders. Powders of magnesium, aluminum, and Br020 alloy. (20% Sn-Cu bronze) produced by centrifugal atomization of superheated (by about 30–50°K) melts in an inert atmosphere (argon) had spherical particle shapes, which imparted to them good flowability. The oxygen content of the powders was low (less than 0.08%).Translated from Poroshkovaya Metallurgiya, No. 12(276), pp. 5–10, December, 1985.     

Mechanism of additional reduction of metallic powders in a falling layer

Conclusions The specific rate of additional reduction of the oxides films on the particles of iron in a falling layer of the powder in the temperature range 800–1000°C calculated for the initial specific surface was 0.036–0.078 g[O]/m²· sec. The activation of the reduction process was equal to 54.16 kJ/mole.The rate of additional reduction of the iron powder in the falling layer is high. For example, in the temperature range 800–1000°C it is 1.2–3.1% [O]/sec.The experimental results as well as the comparison with the available data make it possible to conclude that the process of reduction of the surface oxides in the falling layer in the temperature range 800–1000°C takes place in the kinetic range of reaction and is limited by the reaction of interaction of hydrogen with the surface oxides of iron.Translated from Poroshkovaya Metallurgiya, No. 9-(345), pp. 1–5, September, 1991.