Journal of Alloys and Compounds
Nd-Fe-(B.C) alloys have been synthesized by mechanical alloying and subsequent heat-treatment, with B4C as one of the starting materials. It is found that when the pure B4C is milled alone, it proves difficult to decompose. When the B4C compound is milled with Nd and Fe, the complete decomposition of B4C and the formation of Nd2Fe14(B,C) phase is observed. Furthermore, the competition between B and C atoms for entering the Nd2Fe14B lattice. the effects of the B4C content on the structure and the magnetic properties of Nd2Fe14(B,C)-based alloys are investigated. A coercivity as high as 18.3 kOe and the maximum energy product of 10.4 MGOe have been achieved for the Nd-Fe-(B,C) alloys. (c) 2005 Elsevier B.V. All rights reserved.
关键词:
permanent magnets;mechanical alloying;fe-c alloys;permanent-magnets;r2fe14c;nd
Journal of Alloys and Compounds
Effects of B or C addition on phase transformation and magnetic properties of Pr17CO83-xTx (T=13 or C, x=0-10) alloys, prepared by mechanical alloying and subsequent annealing, have been studied systematically. The X-ray diffraction results show that after annealing at 650 degrees C for 2 min, the main phase of Pr17Co83 alloy is a crystalline PrCo5 phase with hexagonal CaCU5-type structure. The Pr2CO14B phase with tetragonal Nd2Fe14B-type structure appears when the B content increases. The formation of the Pr2CO14B phase is also confirmed by observing its spin reorientation transition temperature T-sr (=390 degrees C)on ac susceptibilities versus temperature curves. The amount of the Pr2Co14B phase increases with increasing B content. Further increasing the B content leads to the formation of another magnetically hard PrCo4B phase with hexagonal CeCo4B-type structure with its Curie temperature about 190 degrees C. In the Pr17CO73B10 alloys, PrCo4B phase becomes the main phase. Remanences decrease monotonously with increasing B content, whereas the coercivities increase, reaching a maximum of 17.9kOe in Pr17Co81B2 powders milled for 5 h and annealed at 650 degrees C for 2 min, and then decrease for the higher B content. In the case of C addition, however, the alloys are composed of a mixture of a major PrCO5 phase and secondary Pr2Co17 and PrCo2Cx Phases. No expected Pr2Co14C phase has been observed in all of the C-containing powders. The magnetic properties of the C-containing alloys have not been improved evidently. (c) 2006 Published by Elsevier B.V.
关键词:
alloys;phase transformation;magnetic properties;mechanical alloying;rare-earth;permanent-magnets;fe;coercivity
A. Alizadeh
材料科学技术（英文）
In this study, aluminum alloy (Al-2 wt% Cu) matrix composites reinforced with 1, 2 and 4 wt% boron carbide nanoparticles fabricated through mechanical milling with average size of 100 nm were fabricated via stir casting method at 850°C. Cast ingots of the matrix alloy and the composites were extruded at 500°C at an extrusion ratio of 10:1 to investigate the effects of hot extrusion on the mechanical properties of the composites. The microstructures of the as-cast and the extruded composites were investigated by scanning electron microscopy (SEM). Density measurement, hardness and tensile tests were carried out to identify the mechanical properties of the composites. The extruded samples revealed a more uniform distribution of B4C nanoparticles. Also, the extruded samples had strength and ductility values superior to those of the as-cast counterparts. In the as-cast and the extruded samples, with increasing amount of B4C nanoparticles, yield strength and tensile strength increased but elongation to fracture decreased.
关键词:
Stir casting
LIANG Minxian XIA Fei Institute of Metal Research
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Academia Sinica
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Shenyang
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China
金属学报(英文版)
The microstructure and mechanical properties of TiB_2 /B_4C composites have been investi- gated.It was found that both the strength and hardness for TiB_2 greatly increase with the ad- dition of 20 to 30 wt-% B_4C,and the fracture toughness K_(IC) value remaines on the original high level.The flexure strength,Vicker's hardness and fracture toughness are 782 MPa,26.2 GPa and 7.2 MPam~(1/2),respectively,for the TiB_2-30 wt-% B_4C composite,compared to 450 MPa,21 GPa and 7.0 MPam~(1/2) for monolithic TiB_2.The toughening and strengthening mechanisms,have also been discussed.
关键词:
TiB_2-B_4C composites
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null
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null
Journal of Physics-Condensed Matter
The structure, phase transformation and magnetic properties of mechanically alloyed (MA) samples of Dy(m)Fe(92-m)Z(8) (Z = C, B) (13 less than or equal to m less than or equal to 20) have been studied systematically. The tetragonal Dy2Fe14C compound can be formed within a wide composition range, 15 less than or equal to m less than or equal to 18. When m greater than or equal to 19 or m less than or equal to 14, Dy2Fe17Cx with different Curie temperatures forms accompanying the Dy2Fe14C phase. An fee structure Dy-rich phase emerges during the annealing process and its amount increases with the increment of Dy content. The composition range for the formation of Dy2Fe14B is rather narrower than that of Dy2Fe14C. When m greater than or equal to 16, Dy6Fe23 is formed. When m less than or equal to 14, a certain amount of alpha-Fe that is unreacted with Dy and C is left. No Dy-rich phase if found in the Dy-Fe-B series of alloys. The highest intrinsic coercivities obtained in Dy-Fe-C and Dy-Fe-B systems are 93 kOe and 70 kOe respectively.
关键词:
sintered magnets;iron;carbon
Journal of Applied Physics
Two different reaction mechanisms for Ti50C50 and Ti33B67 have been observed respectively during milling in a planetary ball mill. It is shown that a gradual reaction occurred during milling Ti50C50, while a self-sustained reaction was obtained during milling Ti33B67 under the same milling condition. Compared with the results of milling Ti50C50 in a spex mill, the difference in mechanism is suggested to be caused by the effect of plastic deformation on the changes of fine grains and internal strain during milling, and the different formation heat of TiC and TiB2, which is the driving force for the reactions. (C) 1996 American Institute of Physics.
关键词:
amorphous-alloys;powders;physics
Journal of Physics-Condensed Matter
The structure, phase transformation and magnetic properties of mechanically alloyed (MA) alloys Nd16Fe76-mCm (7 less than or equal to m less than or equal to 11) and Nd16Fe84-mCm-yBy (0 less than or equal to y less than or equal to m, m = 7, 8, 9) have been studied systematically. The Nd2Fe14C compound can be formed within a wide window for the range of composition and annealing temperature. More carbon than the stoichiometric content for Nd2Fe14C is necessary to stabilize the tetragonal structure. Substitution of boron for carbon can accelerate the phase transformation from Nd2Fe17Cx to Nd2Fe14(C, B) and increase the magnetic properties drastically. There is an fee structure Nd-rich phase in the mechanically alloyed Nd-FeC alloy. The lattice constant of the Nd-rich phase decreases as the boron content increases. Nd2Fe14(C, B) compounds formed in the alloys with same boron content and different carbon contents have different Curie temperatures. The Curie temperatures also vary with the variation of annealing temperature. The best magnetic properties achieved in Nd16Fe76B5C3 alloy are H-i(c) = 1480 kA m(-1), M(r) = 0.71 T and(BH)(max) = 91.5 kJ m(-3).
关键词:
nd2fe14c;phase
Junbao ZHANG
,
Guangwu WEN
,
Tingquan LEI
,
Dechang JIA
,
Jiancun RAO
材料科学技术（英文）
Si-B-O-N powder without B-O bonds synthesized by polymeric precursor were hot-pressed into ceramics at different temperatures. The variations of microstructure and mechanical properties of Si-B-O-N ceramics have been investigated. Crystallization of Si-B-O-N ceramics occurred at about 1400°C. Density, elastic modulus, and flexural strength of the ceramics increased with the increasing sintering temperatures, and reached to their maximum values at 1600°C. By contrast,hardness and fracture toughness of the ceramics monotonically changed with increasing sintering temperatures. Hardness decreased, while the fracture toughness increased. The principal toughening mechanisms including crack deflection, crack bridging and plate grain pulling-out effects are discussed
关键词:
Si-B-O-N ceramics
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null
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null
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null
