Akira Fujiki

Isotropic bulk exchange-spring magnets with 34 kJ/m/sup 3/ prepared by spark plasma sintering method

Densification of exchange-spring magnet ribbons of Nd/sub x/Fe/sub 85-x/Co/sub 8/V/sub 1/B/sub 6/ (x=7-11) alloys has been investigated. The starting ribbon powders containing amorphous parts were prepared by melt spinning and were compacted by using a spark plasma sintering (SPS) method. SPS is a type of solid compression sintering similar to hot-pressing and the sintering promotion factor is self-heat generation by electric discharges between particles when the on-off DC pulse is applied. The bulk magnets indicated the springback phenomenon, pointing to multiple phases of the Nd/sub 2/Fe/sub 14/B type and the /spl alpha/-Fe type, and had isotropic magnetic properties. With increasing Nd content, B/sub r/ decreased from 1.05 T to 0.82 T and H/sub cJ/ increased from 256 kA/m to 832 kA/m. These changes were equivalent to those of the starting ribbons following annealing. The grain sizes of these bulk magnets were about 40 nm when x=7-11. Under optimum preparation conditions, bulk Nd/sub 10/Fe/sub 75/Co/sub 8/V/sub 1/B/sub 6/ magnet indicated (BH)/sub max/=134 kJ/m/sup 3/ (16.8 MGOe).

Properties of /spl alpha/-Fe/Nd/sub 2/Fe/sub 14/B-type Nd-Fe-Co-V-B system bulk exchange-spring magnets prepared by spark plasma sintering

We have made a detailed examination of the microstructure, crystallization process, volume ratio of hard/soft phases, and magnetic properties of Nd/sub x/Fe/sub 85-x/Co/sub 8/V/sub 1/B/sub 6/ (x = 7-11) bulk exchange-spring magnets having a hard Nd/sub 2/Fe/sub 14/B phase and a soft /spl alpha/-Fe phase. The bulk exchange-spring magnets were made by applying the spark plasma sintering (SPS) method to rapidly quenched ribbons containing amorphous parts. The SPS method is a type of solid compression sintering and can be performed at lower temperatures with a shorter hold time. The obtained bulk compacts showed excellent isotropic magnetic properties of (BH)/sub max/ greater than 130 kJ/m/sup 3/, equal to those of the rapidly quenched ribbons. In the densification process by SPS, crystallization of compounds close to Fe/sub 3/B was followed by nearly simultaneous crystallization of the hard Nd/sub 2/Fe/sub 14/B phase and the soft /spl alpha/-Fe phase. The magnetization state of the hard phase must be considered in order to quantify the hard/soft phase ratio. The phase ratio calculated for a saturation state of the hard phase agreed well with the predicted value. The bulk magnets densified without any crystal grain growth between the grains of the starting ribbon powders, and a grain boundary region of about 150-200 nm in thickness formed between the ribbon powders. There was no composition segregation in the grain boundary region, and its mechanical strength was equal to that of the interior of the powder grains. Fine crystal grains smaller than 50 nm occurred in the interior of the starting powders, and the grain size decreased with increasing compressive pressure during the sintering process.

Tougher valve seats use two hard particles but no cobalt

Japanese researchers have produced a new material for internal combustion engine valve seats that is more environmentally friendly, and cheaper…

Properties of α-Fe/Nd2Fe14B-Type Nd-Fe-Co-V-B system bulk exchange-spring magnets prepared by spark plasma sintering

We have made a detailed examination of the microstructure, crystallization process, volume ratio of hard/soft phases, and magnetic properties of Nd/sub x/Fe/sub 85-x/Co/sub 8/V/sub 1/B/sub 6/ (x = 7-11) bulk exchange-spring magnets having a hard Nd/sub 2/Fe/sub 14/B phase and a soft /spl alpha/-Fe phase. The bulk exchange-spring magnets were made by applying the spark plasma sintering (SPS) method to rapidly quenched ribbons containing amorphous parts. The SPS method is a type of solid compression sintering and can be performed at lower temperatures with a shorter hold time. The obtained bulk compacts showed excellent isotropic magnetic properties of (BH)/sub max/ greater than 130 kJ/m/sup 3/, equal to those of the rapidly quenched ribbons. In the densification process by SPS, crystallization of compounds close to Fe/sub 3/B was followed by nearly simultaneous crystallization of the hard Nd/sub 2/Fe/sub 14/B phase and the soft /spl alpha/-Fe phase. The magnetization state of the hard phase must be considered in order to quantify the hard/soft phase ratio. The phase ratio calculated for a saturation state of the hard phase agreed well with the predicted value. The bulk magnets densified without any crystal grain growth between the grains of the starting ribbon powders, and a grain boundary region of about 150-200 nm in thickness formed between the ribbon powders. There was no composition segregation in the grain boundary region, and its mechanical strength was equal to that of the interior of the powder grains. Fine crystal grains smaller than 50 nm occurred in the interior of the starting powders, and the grain size decreased with increasing compressive pressure during the sintering process.

Properties of α-Fe/Nd/sub 2/Fe/sub 14/B-type Nd-CFe-Co-V-B system bulk exchange-spring magnets prepared by spark plasma sintering

We have made a detailed examination of the microstructure, crystallization process, volume ratio of hard/soft phases, and magnetic properties of Nd/sub x/Fe/sub 85-x/Co/sub 8/V/sub 1/B/sub 6/ (x = 7-11) bulk exchange-spring magnets having a hard Nd/sub 2/Fe/sub 14/B phase and a soft /spl alpha/-Fe phase. The bulk exchange-spring magnets were made by applying the spark plasma sintering (SPS) method to rapidly quenched ribbons containing amorphous parts. The SPS method is a type of solid compression sintering and can be performed at lower temperatures with a shorter hold time. The obtained bulk compacts showed excellent isotropic magnetic properties of (BH)/sub max/ greater than 130 kJ/m/sup 3/, equal to those of the rapidly quenched ribbons. In the densification process by SPS, crystallization of compounds close to Fe/sub 3/B was followed by nearly simultaneous crystallization of the hard Nd/sub 2/Fe/sub 14/B phase and the soft /spl alpha/-Fe phase. The magnetization state of the hard phase must be considered in order to quantify the hard/soft phase ratio. The phase ratio calculated for a saturation state of the hard phase agreed well with the predicted value. The bulk magnets densified without any crystal grain growth between the grains of the starting ribbon powders, and a grain boundary region of about 150-200 nm in thickness formed between the ribbon powders. There was no composition segregation in the grain boundary region, and its mechanical strength was equal to that of the interior of the powder grains. Fine crystal grains smaller than 50 nm occurred in the interior of the starting powders, and the grain size decreased with increasing compressive pressure during the sintering process.

Basic Research on the TiO2 Electrode and the Coloring Effect of Dye-Sensitized Solar Cell

The dye-sensitized solar cell (DSSC) is a device for the conversion of visible light into electricity which uses the photoelectrochemical system that is made up of a semiconductor that is formed between a photosensitized anode and an electrolyte. It is based on the sensitization of wide bandgap semiconductors. The DSSCs are categorized as the solar cells of the next generation for their low manufacturing costs compared with the silicon type of solar cells. In DSSC, titanium dioxide (TiO2) is one of the suitable material used for nano-porous thin film since it has appropriate energy levels, high dye adsorption ability, and low cost, and it is easy to prepare. Extensive research on the photochemistry and photophysics of TiO2-based DSSCs has shown that the light-harvesting efficiency of TiO2 is influenced by its crystalline phase, particle size, as well as its surface area, dye affinity, and film porosity. In this research, we have focused on the dye and its effect on the light scattering of TiO2 particles and the best condition of TiO2 particles in order to improve solar energy conversion efficiency. The best condition for TiO2 particles, which were sintered at 450 °C for 60 min, resulted from the use of the spin-coating method. On the other hand, the best dye is anthocyanin (blueberry), and the best condition was to keep it for 6 h, at 21 °C, in a dark environment.

Study of Elastic Moduli of Sintered Low Alloy Steels by Acoustic Pulse Method

The influence of porosity (P) on Young’s modulus (E) and Poisson’s ratio (υ) of sintered steels produced from four types of steel powders were investigated. The values of E and υ depends mainly on the value of P, and those were a little affected by alloying elements. The relationship between compacting pressure (CP) and P and the relationships between E, υ, and P were described as following equations: P = P1 + P2 exp(- CP / P3), E = E0 (1 - kEP)2, and υ = (υ0 - υsub)(1 - kυP)2 + υsub, where subscript 0 means P = 0, and P1 - 3, kE, kυ and υsub were empirical constants. It was clarified that if powder and sintering temperature is defined, the elastic moduli of sintered steel can be calculated as a function of compacting pressure.

Influences of alloy elements in infiltrant on mechanical properties of copper-alloy infiltrated P/M high speed steels

Elements in Infiltrant on Mechanical Properties of Copper-alloy Infiltrated P/M High Speed SteelsMechanical properties of copper-alloy infiltrated M42, T42 P/M high speed steels were studied.The green compacts were sintered in vacuum at 1433, 1443, 1453 K to make skeletons. The skeletons were infiltrated with Cu-Cr, Cu-Co and Cu-Fe-Mn alloy infiltrants in hydrogen or argon at 1423 K for 1.8 ks.The result obtained were summarized as follows.1)All the infiltrated specimens shrinked.The Cu-Fe-Mn infiltrated M42, T42 P/M high speed steels had the least amount of dimentional change values during infiltration.The Cu-Fe-Mn infiltrated M42, T42 P/M steels had comparatively high hardness, but low strength.2)Cu-Cr, Cu-Co infiltrated P/M high speed steels showed high strength, especially the P/M M42 steel having a skeleton sintered at 1453 k in vacuum and infiltrated with the Cu-Co alloy infiltrant in hydrogen had 2450 MPa of transverse rupture strength and HRC 48 of hardness as infiltrated.