摘要:

The structure of surface oxide layers formed during annealing of non‐oriented silicon‐aluminum electrical steels has been studied. For alloys containing from 1.5 to 2.5 percent silicon, a transition from internal to external oxidation is observed as the oxygen potential of the annealing atmosphere is decreased at constant temperature or as the temperature is increased in a constant atmosphere. Surface oxide structure has a significant effect on the rate at which decarburization and nitrogen absorption occur during annealing, the formation of an external oxide scale inhibiting both of these processes. The presence of a subscale (zone of internal oxidation) in electrical steel sheet results in an increase in core loss in comparison with subscale free sheet.

ISSN:0021-8979    

DOI:10.1063/1.324787

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Directional solidification of the eutectic Mn‐Bi alloy (2 at&percent; Mn) produces an aligned array of ferromagnetic Mn‐Bi needles, 0.1 to 1.5 &mgr;m in diameter, in a matrix of diamagnetic Bi. Samples grown at about 50 cm/hr and then annealed at 200 °C contain two magnetic phases. One phase is normal equilibrium MnBi, known in the recent literature as the low‐temperature phase (LTP). The second phase is crystallographically similar to the high‐temperature phase (HTP) Mn1.08Bi, but has a much lower Curie temperature of 240 K. Low‐temperature hysteresis loops measured parallel and perpendicular to the axis of freezing are of unusual form. If the magnetization due to the normal MnBi phase is subtracted the resulting loop in the parallel direction hasHci≳100 kOe, suggesting single‐domain behavior. The resulting loop in the perpendicular direction can be accounted for by the presence of a relatively large fourth‐order anisotropy.

ISSN:0021-8979    

DOI:10.1063/1.324788

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Cr‐Co‐Fe permanent magnet alloys have been investigated for potential replacement of Remalloy in the U‐type ring armature telephone receiver. Of particular interest would be an alloy which could be cold drawn into cup shape. Small additions of Al, V, Nb, Ti and Zr were added to the basic 28&percent;Cr–15&percent;Co–Fe ternary in an attempt to suppress &ggr; phase formation and improve cold formability. As a result of extensive investigation we have discovered two Zr bearing alloys that are highly promising for fabrication as receiver magnets. One alloy consists of 0.25&percent;Zr–1&percent;Al and the other 0.25&percent;Zr–0.25&percent;Ti–1&percent;Nb. After suitable heat treatment they yield values ofBr=9600 G,Hc=460 Oe,BHmax=1.9×106GOe andBr=8900 G,Hc=440 Oe,BHmax=1.8×106GOe respectively.

ISSN:0021-8979    

DOI:10.1063/1.324789

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The relationship between the microstructure and magnetic properties of heat treated Fe–23 wt&percent;Cr–15 wt&percent; Co–5 wt&percent;V has been studied by transmission electron microscopy and Lorentz microscopy. Three different heat treatments were adopted for the present investigations, viz., (1) isothermal aging, (2) thermomagnetic treatment (TMT) + step‐aging, (3) continuous cooling. It has been found that the magnetic properties of the alloy are very sensitive to the temperature of the TMT. Step‐aging gave the best magnetic properties, producing an elongated ferromagnetic phase, 300 A˚ in diameter and 1200 A˚ in length. Lorentz microscopy revealed domain walls and these lie within the Cr‐rich phase and pinned by the Fe‐rich phase in the isothermally aged alloy at 650 °C. Magnetic domains of optimally step‐aged alloys, 0.5 &mgr;m in width, are elongated along the direction of the applied magnetic field. The results suggest that the magnetic anistropy is introduced parallel to the direction of the applied magnetic field during TMT and step‐aging treatments.

ISSN:0021-8979    

DOI:10.1063/1.324701

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A value of 67.5 kOe has been measured for the room temperature coercivity of an isotropic, heat treated, 1‐5 samarium‐cobalt plasma sprayed deposit. This value is believed to be the largest published, so far, for a permanent magnet. Sprayed magnets are generally found to be better than 93 percent dense with coercivities of 35 to 60 kOe. Deposits comprised of fine microstructures yield broad, unresolved x‐ray diffraction peaks. Low temperature crystallization of these deposits yields diffraction patterns representative of the high temperature equilibrium structure. The emergence of peaks, ascribed to SmCo5, from a low temperature 700 °C heat treatment implies both formation and stability of the SmCo5phase at this temperature. These results dispute the existence of the generally accepted eutectoid decomposition reaction for SmCo5at 750–800 °C. If such a reaction were present the products of crystallization should have included Sm2Co7and not SmCo5. High temperature investigations on sprayed magnets indicate that temperatures of 1100 °C result in low values of coercivity, possibly due to grain growth.

ISSN:0021-8979    

DOI:10.1063/1.324790

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Structural, metallographic and magnetic properties of Y2Co17−xNixand Sm2Co17−xNixhave been established to ascertain the effect of nickel on the permanent magnet properties of Sm2Co17. The results indicate that the 2 : 17 compositions exist in the concentration limits 0<x<8 in Y2Co17−xNixand 0<x<6 in Sm2Co17−xNix. Metallographic examination of these materials confirms the absence of secondary phases. Magnetic properties were examined in the temperature range 4.2–1200 K in external fields up to 21 kOe. The ordering temperatures of Sm2Co17−xNixand Y2Co17−xNixdecrease with increasing concentration of nickel. Examination of saturation magnetization results indicates a smooth variation with the addition of nickel. The easy direction of magnetization at room temperature was established for the samples by examining the x‐ray diffraction patterns of aligned powders. The results show that the axial anisotropy exhibited by Sm2Co17is retained with the substitution of nickel. For a few nickel‐rich compositions of Sm2Co17−xNix, thermomagnetic hysteresis effects were observed. The results are interpreted on the basis of a strong competition between the exchange field and the crystal field interaction. Calculations were performed to support this interpretation.

ISSN:0021-8979    

DOI:10.1063/1.324737

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Giant intrinsic magnetic hardness is found at low temperatures in structurally homogeneous materials SmNi5−xCux. Magnetic hardness peaks at a composition SmNi2.5Cu2.5where the crystal field disorder due to compositional randomization is at a maximum. By comparison with SmCo5−xNix, where giant intrinsic magnetic hardness originates, in part, from fluctuations from site to site of the magnitude of moment and strength of exchange of the transition metal, magnetic hardness in the SmNi5−xCuxis predominantly due to anisotropy and concomitant exchange fluctuations on Sm sites.

ISSN:0021-8979    

DOI:10.1063/1.324738

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The phenomenon of giant intrinsic magnetic hardness in SmCo5−xNixand SmCo5−yCuyis investigated in applied fields up to 23.5 T. At 4.2 K, the average propagation field (approximate coercive field)Hpis ≃13.0 T, 22.0 T and 18.2 T forx=3, 3.6 and 4.2 respectively, andHpis ≃12.0 and ≃23.0 T fory=2.5 and 3.6 respectively. At 77 K, values ofHp≃5.0 and ≃5.5 T fory=2.5. Some values ofHpat 4.2 K are the largest observed to date for any material. The results are consistent with models for thermally activated domain wall motion. For several materials the irreversible portion of the magnetization is not saturated at 23 T and 4.2 K. In these cases the maximum magnetization is less than that observed at 77 K.

ISSN:0021-8979    

DOI:10.1063/1.324739

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Demagnetization curves of Sm(CoFeCuMn)7with applied fields up to 127 kOe both parallel and perpendicular to thecaxis were measured at several temperatures from 4.2 K to 600 K. The ratio ofIHc(400 K)/IHc(300 K) was found to be 0.83 which is a factor of two larger than that of Sm2(CoFeMnCr)17. The anisotropy constant was also determined in the temperature range from 4.2 to 480 K. The relationship betweenIHc(T) andK1(T) was discussed.

ISSN:0021-8979    

DOI:10.1063/1.324740

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Transmission electron microscopy is being used to characterize the microstructural features in some 1 : 5 and 2 : 17 RE‐Co magnets. In 2 : 17 compounds containing Fe and Mn, lamellae of hexagonal and other polytypic regions embedded in the rhombohedral matrix are observed. It is shown that the interface between the hexagonal and rhombohedral phases can be described as a stacking fault with fault vector normal to the interfacial plane. APB’s parallel to the prism planes in the rhombohedral structure have also been identified and characterized. In contrast, no planar faults have been observed in the 1 : 5 materials containing misch metal as the major rare‐earth component. In these alloys extensive twinning and precipitation of a 2 : 17 rhombohedral phase are the major microstructural features observed. The influence of these microstructures on the magnetic properties are discussed.

ISSN:0021-8979    

DOI:10.1063/1.324741

出版商:AIP    

年代:1978

数据来源: AIP