91 publications from this institution
This paper studies the influence of metallic element composition on the formation ability, thermal stability and magnetic properties of melt-spun (Fe1-xCox)B15–19Si1 (x =0.2–0.4) amorphous alloy ribbons. The maximum metal concentration at which an amorphous phase is formed during melt spinning has been determined in conjunction with the metal content dependence of crystallization processes and crystallized phases. The amorphous (Fe0.8Co0.2)84B15Si1 alloy with the highest metal content in an optimally annealed state exhibits an extremely high saturation induction (MS) of 2.0 T, low coercive force of 7.6 A m−1, high effective permeability of 13500 at 1 kHz and low core losses of 5.5 W kg−1 at 100 mT and 19.7 W kg−1 at 200 mT at 10 kHz which have not been simultaneously obtained for all kinds of soft magnetic materials up to date. The replacement of Fe with Co significantly increases the Curie temperature of the amorphous phase, resulting in very high thermal stability of the high MS alloys. The combination of excellent soft magnetic properties with ultrahigh MS value makes them candidates for use in highly loaded high-speed electric motors capable of operating at temperatures up to 473 K.
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A glassy phase with glass transition (GT) was formed in a wide B content range of 12‒31 at% for (Co0.75Cr0.125Mo0.125)100-xBx alloys. The appearance of GT at the low metalloid content of 12%B among Co-, Fe- and Ni-based alloys is the first, in contrast to the absence of GT for (Fe0.75Cr0.125Mo0.125)88B12 and (Ni0.75Cr0.125Mo0.125)88B12 alloys. The Co-based 12%B glassy alloy crystallized through unique three stages, i.e., glass (G) → [G + hcp + fcc] → [G + fcc] → [fcc + M23B6]. The appearance of GT is due to the necessity of long-range rearrangement of constituent elements for the simultaneous precipitation of hcp and fcc phases from glassy phase. The glass transition temperature, crystallization temperature, Vickers hardness (Hv) and Young's modulus for the Co-based glassy alloys increase linearly with increasing B content and reach 904 K, 946 K, 1566 and 188 GPa, respectively, at 31%B. The good bending plasticity is retained up to 29%B. The crystallization of the 27‒29%B alloy occurs through G → [G + M23B6] → [M23B6 + M2B] and the ultrahigh Hv above 2000 is attained for the metastable [G + M23B6] phase state. The glassy alloy rod with a diameter of 1 mm was prepared for the 27%B alloy and exhibited ultrahigh yield strength of 4700 MPa, plastic strain of 1% and high oxidation resistance up to about 1200 K. The Co-based bulk glassy alloy with simultaneously high strength, ultrahigh hardness and high oxidation resistance, is promising for the future high hardness and heat-resistance materials.
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An exciton-exciton collisional annihilation was studied with the naphthalene-tetracyanobenzene complex crystal by observing and analyzing the fluorescence decay curve; the second-order decay constant was determined to be 3 × 10−13 cm3 sec−1 at 77°K. A new type of inhomogeneous broadening effect was found for the fluorescence from the complex crystal excited in high density and was interpreted to be due to the strong electrostatic interaction between the charge-transfer excitons with large dipole moments.
New Fe82-85B13-16Si1Cu1 amorphous alloys with low B content and high B/Si content ratios were synthesized by melt spinning for developing good soft magnetic and high strength materials. The crystallization occurs through two stages and the first-stage onset temperature increases from 673 K to 705 K with increasing B content, while the second-stage temperature remains nearly constant. The first and second stages are due to the precipitation of the α-Fe(Si) phase with a size of about 30 nm and the decomposition of the remaining amorphous phase to α-Fe(Si)+Fe3B+Fe2B, respectively. The Fe-based alloys exhibited good soft magnetic properties both in annealed amorphous and nanocrystallized amorphous+α-Fe(Si) phases. The saturated magnetic flux density, coercivity and permeability at 1 kHz are 1.7 T, 4.92 A/m and 7100, respectively, for the annealed amorphous 14B alloy and 1.74 T, 5.62 A/m and 10100, respectively, for the nanocrystallized 13B alloy. The Vickers hardness (H v) is 803–867 for the as-spun state and it increases with decreasing B content. The H v increases significantly by crystallization to α-Fe+amorphous phases and reaches 997–1550 for the alloys annealed at 693–763 K just before T x2. The ultrahigh H v is presumably due to the combination of fine nanoscale mixed phases, high volume fraction of α-Fe(Si) without internal defects and the enrichment of B into the remaining amorphous phase. Such ultrahigh H v has not been obtained for Fe-based amorphous and crystallized alloys before and the addition of 1%Cu is essential for the ultrahigh H v and the amorphous phase formation for the Fe-rich 85%Fe alloy. The new Fe-based alloys are encouraging as future soft magnetic and ultrahigh strength materials with low material cost.
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