Brian E. Meacham

Microstructures and phase formation in rapidly solidified Sm-Fe alloys

Abstract Sm–Fe-based alloys were produced by melt spinning with various melt spinning parameters and alloying additions. The structural and microstructural evolution varied and strongly depended on processing and alloy composition. The microstructural scale was found to vary from micron to nanometer scale depending on the solidification rate and alloying additions. Additions of Si, Ti, V, Zr and Nb with C were all found to refine the scale, and the degree of refinement was dependent on the atomic size of the alloying agent. The alloying was also found to affect the dynamical aspects of the melt spinning process, although in general the material is characterized by a poor melt stream and pool, which in part contributes to the microstructural variabilities. The alloying additions also suppressed the long-range ordering, leading to formation of the TbCu 7 -type structure. The ordering was recoverable upon heat treatment, although the presence of alloying agents suppressed the recovery process relative to the binary alloy. This was attributed to the presence of Ti (V, Nb, Zr) in solid solution, which limited the diffusion kinetics necessary for ordering. In the binary alloy, the ordering led to the development of antiphase domain structures, with the antiphase boundaries effectively pinning Bloch walls.

Order–disorder effects in nitrided Sm–Fe permanent magnets

Rapidly solidified Sm11Fe89 was observed to form partially ordered Sm2Fe17. The ordering increased systematically with annealing temperature, reaching an order parameter of 0.8 after annealing at 950 °C for 15 min. The coercivity of the corresponding interstitial compound Sm2Fe17Nx varied with annealing temperature and thus order parameter. The coercivity reached a maximum for an order parameter of 0.45–5, then dramatically decreased as the order increased. This behavior is characteristic of demagnetization controlled by domain wall pinning by antiphase boundaries.

Control of ordering and microstructure in Pr-Co and Sm-Fe alloys for permanent magnets

In this study, the structural state and microstructural scale of Pr/sub 2/Co/sub 17/ and Sm/sub 2/Fe/sub 17/ were modified by rapid solidification and alloying. Partial suppression of the dumbbell ordering was accomplished by melt spinning, and more effective suppression, leading to the formation of the TbCu/sub 7/-type structure, was accomplished by the addition of Ti or Ti and C. Annealing recovered the order, although Ti and TiC significantly affected the kinetics in the Sm-Fe system. The addition of Ti and C refines the grain size in both Pr-Co and Sm-Fe. The degree of order was found to influence the coercivity in the nitrided Sm-Fe alloys. The Pr-Co alloys were found to have a planar easy magnetization direction at all levels of ordering.

Phase formation in hypostoichiometric Sm2Fe17 alloys modified with Ti and C

The phase formation, crystallization products, microstructure, and magnetic behavior of Fe-rich Sm–Fe alloys modified with Ti and C have been determined. Alloys of nominal composition (Sm0.11−xFe0.89+x)94Ti3C3 with x=0, 0.02, and 0.04 were produced by melt spinning. Crystalline phases observed included SmFe7 and α-Fe and an increasing amorphous fraction was observed with increasing x. Upon crystallization the amorphous fraction converted to Sm2Fe17 and α-Fe, with a grain size of 30 nm for the sample with x=0.02. The magnetic measurements of nitrided alloys revealed a remanent ratio above 0.5 for x=0 and 0.02, although the coercivity was rather low.

Effect of combined metal-carbon additions on the microstructure and structure of Sm2Fe17

The effect of combined alloying additions on the structure and scale of rapidly solidified Sm-Fe alloys was investigated. Transition metal additions tend to promote the formation of the disordered TbCu 7 -type structure inSm 2 Fe 1 7 alloys, as determined by monitoring the long-range order parameter. Essentially no order was observed for M = Ti, Zr, V, or Nb. Thus, the structure was close to the prototypical TbCu 7 -type structure. With M = Si, a large amount of order was observed (S = 0.62), resulting in a structure closer to the well-ordered Th 2 Zn 1 7 -type. The microstructural scale was also affected by alloying. In this case, refinement depended on the substituent and also on carbon for microstructural refinement. The scale of the as-solidified grain structures ranged from 100 nm for SiC-modified alloys to 13 nm for NbC-modified alloys. The degree of refinement was directly related to the atomic size of the M addition. The refinement was the result of solute partitioning to grain boundaries, resulting in a solute drag effect that lowered the growth rates.

High hysteresis in a homogeneous metallic glass

In this article, we demonstrate high hysteresis in a well characterized homogeneous Tb–Al glass which contained no crystallites or crystalline embryos as verified using conventional and synchrotron diffraction, neutron diffraction, and direct observation in the transmission electron microscope. At low temperature (2 K), the metallic glass structure exhibited intrinsic coercivities approaching 23 kOe and high isotropic energy products of 12.4 MGOe. After crystallization into a three-phase nanoscale structure, the hard magnetic properties were found to be far inferior to that obtainable in the glass structure. From the well defined intrinsic magnetic properties (Msat,Tc), it is clear that the glass contains one or more types of well defined associations (i.e., clusters) and that these associations lead to ferromagnetic coupling/ordering. From the large random magnetic anisotropy, it is probable that the domain size is much larger than the structural cluster size. The measured single-phase loop shapes and th...

Chemical Ordering and Microstructural Affects on Magnetic Properties of Sm 2 Fe 17 and Sm 2 Fe 17 N x

The effect of chemical order and defect structure on the magnetization process in Sm 2 Fe 17 and Sm 2 Fe 17 N x has been investigated. In Sm 2 Fe 17 , chemical disorder results in the development of random anisotropy and a small degree of magnetic hardness. The anisotropy is reduced as long-range order increases. The motion of domain walls in Sm 2 Fe 17 N x is more dependent on the antiphase domain structure than on the amount of long-range order.

Introduction of New Tensile Specimen Geometry for Property Evaluation in Stamped Parts

Reliable tensile data are crucial in the automotive design process, particularly for the implementation of new Advanced High Strength Steel grades that can be used in new intricate shapes. The property evaluation of specific subsections of a complex part, such as a metal stamping, requires deviation from standard-sized specimens because of material quantity limitations which force the use of smaller specimens. A new tensile geometry is introduced for testing regions within parts that were previously difficult to characterize. However, the specimen size effect is not consistent between different steels, as demonstrated for this new geometry herein. Tensile property measurements taken with noncontact extensometers from specimens of three different sizes from three different sheet steels showed varying material responses to changes in specimen geometry.