In principle, boron (B) as a material has many excellent surface properties, including corrosion resistance, very high hardness, refractory properties, and a strong tendency to bond with most substrates. The potential technological benefits of the material have not been realized, because it is difficult to deposit it as coatings. B is difficult to evaporate, does not sputter well, and cannot be thermally sprayed. In this article, first successful deposition results from a robust system, based on the vacuum (cathodic) arc technology, are reported. Adherent coatings have been produced on 1100 Al, CP–Ti, Ti–6Al–4V, 316 SS, hard chrome plate, and 52 100 steel. Composition and thickness analyses have been performed by Rutherford backscattering spectroscopy. Hardness (H) and modules (E) have been evaluated by nanoindentation. The coatings are very pure and have properties characteristic of B suboxides. A microhardness of up to 27 GPa has been measured on a 400-nm-thick film deposited on 52 100 steel, with a corresponding modulus of 180 GPa. This gives a very high value for the H/E ratio, a figure-of-merit for impact resistance of the film. A number of applications are contemplated, including corrosion/abrasion protection for die-casting dies and improved wear resistance for biomedical implants.
The magnetic properties of rapidly quenched FeRM alloys where R=La,Y,Pr,Nd,Gd and M=B,Si,Al,Ga,Ge have been investigated over a wide range of chemical compositions. The samples are generally magnetically soft in the as-quenched state. Magnetic hardening is produced by annealing the samples around 700 °C. The best properties have been obtained in samples containing Pr and Nd together with B and Si. An energy product of 13 MGOe and a coercive field of 15 kOe have been obtained in a Fe76Pr16B5Si3 sample. The higher Fe content samples appear to be more promising with a potential energy product of 49 MGOe. Thermomagnetic data show that a structural transformation takes place upon heating the samples to 700 °C. The Curie temperature of the as-quenched phase is around 160 °C while that of the new phase is around 320 °C. Transmission electron microscope studies show fine precipitates (∼100 Å) dispersed in a matrix of different chemical composition. X-ray and electron diffraction data indicate that the precipitates have the Fe21R3B tetragonal structure. The high anisotropy of this phase together with its fine size and distribution give rise to the observed high coercive fields.
The magnetic and structural properties of rapidly quenched FePr(BSi) alloys are presented. The samples are usually magnetically soft in the as-quenched state. However, large coercive fields in the range of 5–20 kOe are developed upon heating the samples to a temperature around 700 °C. The best properties have been obtained on a Fe76Pr16B5Si3 sample with a maximum energy product (BH)m≂12 MGOe. This value is much better than that of AlNiCo and makes these materials outstanding as cobalt-free permanent magnets.
Plasma dynamics are characterized in a long-conduction time plasma opening switch [Phys. Fluids B 4, 2368] operated with densities and currents near the theoretical intersection of the magnetohydrodynamic (MHD) [IEEE Trans. Plasma Sci. PS-19, 400 (1991)] and electromuagnetohydrodynamic (EMH) [Phys. Fluids B 3, 1908] regimes. In agreement with MHD theory, a hydrodynamic snowplow is observed to translate axially and reach the load end of the switch at opening. The axial motion of the front agrees with one-dimensional analytic predictions if the carbon plasma possesses an average ionization of 1, but is significantly less than theory if higher ionization levels are present. The axial motion of the plasma center-of-mass is significantly less than that expected from theory for any ionization level. The reduced center-of-mass motion is attributed to an ion loss mechanism in the unconfined switch plasma, an effect also observed in the total particle inventory, which saturates while the source plasma flux remains relatively constant. An ion lifetime of 450+15 ns (290?23 nsj for Z= 1 (Z=2) results in a predicted center-of-mass motion in agreement with the measurements. Only minimal EMH effects are observed indicating, in contrast to theoretical predictions, that the switch is MHD dominated in this regime. 0 1995 American Institute of Physics.
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