Chizuko Maeda

Nonoriented electrical steel sheet with low iron loss for high-efficiency motor cores

A new material was studied for high-efficiency motor cores that need higher magnetic flux density, lower iron loss, and lower mechanical hardness. Excessively high Si content tends to decrease magnetic flux density of nonoriented electrical steel sheets. The composite addition of rare-earth metals (REM) and Al into molten steel was found to make inclusions coarse and remarkably improve grain growth during stress relief annealing, which resulted in decreased iron loss. A new nonoriented electrical steel sheet (50RMA350) with Si, Al, and REM has been successfully developed to give a higher efficiency to inverter drive model motors than a conventional material.

Transmission Kossel study of the formation of (110) [001] grains after an intermediate annealing in grain oriented silicon steel containing a small amount of Mo

The transmission Kossel (TK) technique was applied in an attempt to elucidate the formation of (110) [001] grains in the recrystallized texture of high induction and low core loss grain oriented silicon steel containing a small amount of Mo after an intermediate annealing. Prior to the detailed TK examination, the etch pit technique was also used for seeking the representative areas of (110) [001] grains. The average matrix grain size of an intermediate annealed steel containing a small amount of Mo is slightly smaller than that with no Mo. The formation of (110) [001] grains in the vicinity of the steel surface is also strengthened due to the addition of Mo. The diameters of single (110) [001] grains are comparable to or slightly larger than those of other matrix grains, but those of the colonized (110) [001] grains occupy extremely large areas (about 40 pet at the maximum area). The areal fraction of (110) [001] grains of the intermediate annealed sheets containing a small amount of Mo is approximately 1 to 5 times as large as that with the conventional inhibitors such as MnSe and Sb. The colonies of (110) [001] grains formed during an intermediate annealing are compatible with the volume fraction inherited from small and well-defined (110) [001] areas with the sharpened TK patterns in the hotrolled sheet containing a small amount of Mo. It is believed that the preferential formation of (110) [001] grains during an intermediate annealing is inherited by the structure memory from the original hot-rolled texture, and it is noticeably strengthened with the addition of Mo.

Magnetic properties and surface crystallization induced by selective oxidation in Fe-B-Si amorphous alloy

The relationship between the annealing atmosphere and the magnetic properties of Fe78.5B13Si8.5 amorphous alloy has been studied, showing that annealing in nitrogen, argon, hydrogen and air significantly improved the iron loss of the amorphous ribbon, giving much better results than annealing in an H2 + H2O atmosphere. A boron-depletion zone with the alloy composition O to 3 mol % B and 9 to 11 mol% Si was detected by Auger electron spectroscopy under the oxide film formed during annealing in H2 + H2O. The iron crystalline phase is formed only on the ribbon surface after annealing in H2 + H2O. A mechanism is proposed explaining the deleterious effect of annealing in the H2 + H2O, whereby the H2O in this atmosphere selectively oxides boron in the amorphous alloy to form a B2O3 film and the boron-depletion zone, and the alloy in this zone is then crystallized into α-Fe. This surface crystalline layer induces out-of-plane magnetic anisotropy in the amorphous alloy ribbon (which was observed by transmission Mössbauer spectroscopy) and thus deterioration of the iron loss.

Electromigration lifetime as a function of line length or step number

The dependence of electromigration-induced (EM) failure time on line length and step number in the line has been investigated. Theoretical equations for the dependence are derived assuming that EM failure obeys the Weibull failure distribution function. The EM failure time distribution of 2.4 mu m-wide AlSi(1%) lines of different lengths or with different step numbers agreed well with the equations. Also confirmed experimentally was the theoretical prediction that the shape parameter m in the Weibull distribution function is the key parameter for estimating the EM lifetime of an LSI product based on lifetime measurements of test structures. A lower EM resistance at the step location than that of the flat lines has been investigated quantitatively and has been interpreted in terms of the difference in step coverage, joule heating, grain size, and stress. A unifying equation to include both straight and step locations for EM lifetime is derived.<<ETX>>