Ni Powder Mixture Research Articles

放電焼結によるＴｉＮｉ形状記憶合金の作製

Ti-Ni shape memory alloys were fabricated by a pulse current sintering process from two types of starting powders prepared through different processes: mechanical alloying of TiH and Ni powders mixture and dehydrogenation(MA powder), and pre-mixed of Ti and Ni powders (mixed powder).The MA powder was composed of mainly TiNi phase and a small amout of Ti2Ni and TiNi3 phases. The composition of this powder remained unchanged after the pulse current sintering at 973-1173K for 300s, while the relative density of 100% was attained for the sintering body. On the contrary, the pulse current sintering of the mixed powder at 1273K for 60-300s, led to a distinguished compositional change and the relative density of 100%. The TiNi3 phase in the sintered body could be removed on the condition of longer sintering period or by heat treatment at 1273K for 18ks; however, the Ti2Ni phase could not be removed. The composition and the thermal characteristics (Ms=318K) of these sintered bodies were found to be almost the same as those of commercially available Ti-Ni shape memory alloys.

Formation of Mg<SUB>2</SUB>Ni from Mg and Ni Powder Mixtures by the Use of a Planetary Ball Mill

Mg2Ni powder material can be synthesized from a mixture of Mg and Ni by its mechanical alloying using a planetary ball mill. The particle size of the mechanically alloyed Mg2Ni powder decreases with an increase in milling time, and the Mg2Ni phase in the milled mixture tends to change into poor crystalline structure in the prolonged milling operation. No significant exothermic reaction takes place during heating of the mechanically alloyed Mg2Ni powder except for the recrystallizing reaction at 430 K, while a considerable exothermic reaction due to the self-combustion is detected at around 860 K for the unmilled mixture followed by the ignition behavior of the starting powders at 780 K. There is no significant difference in the characteristic of hydrogen storage in the PCT diagram between the mechanically alloyed Mg2Ni powder and the thermally synthesized one.

Metastable bcc Ni produced by rod milling and chemical leaching

Nanocrystalline Al 60Ni 40 and Ni have been obtained by rod milling Al and Ni powder mixtures and chemical leaching Al atoms from the rod-milled Al 60Ni 40, respectively. The rod-milled alloy powders retained their bcc structure after being treated at room temperature and at 85 °C with a 25–30 wt.% KOH solution. The leached powders are very active and easily explode when they come into contact with air. The leached powders were transformed to a ferromagnetic fcc phase at high temperature. On cooling of the specimen from 600 °C, spontaneous magnetization M sharply increased at about 350 °C, indicating that the bcc phase was transformed to an fcc phase. It has been confirmed that the leaching temperature and annealing temperature and KOH concentration have a considerable effect on structural and magnetic properties.

Injection Molding of Electrolytic Copper Powder.

In this study, products obtained using Cu-Ni alloy powder and a Cu, Ni powder mixture in injection molding were compared. Both the alloy powder and the powder mixture were composed of 69.4 mass% Cu and 30.6 mass% Ni. Both feedstocks were composed of 56.0 vol% metal powder and 44.0 vol% organic binder. The binder system consisted of 25.0 vol% polybutylmethacrylate (PBMA), 35.0 vol% ethylene-vinyl acetate copolymer (EVA), and 40.0 vol% paraffin wax (PW) for both feedstocks. Sintered bodies of Cu-Ni alloy were produced from Cu-Ni alloy powder or Cu, Ni powder mixture using metal injection molding (MIM) technology. In nitrogen sintering, the density of sintered bodies produced using the Cu, Ni powder mixture was higher than that of sintered bodies produced using the Cu-Ni alloy powder. In vacuum sintering, the density of sintered bodies produced using the alloy powder was higher than that of sintered bodies produced using the powder mixture. Contents of oxygen and carbon in sintered bodies, and density depended on hydrogen treatment temperature. The maximum density, tensile strength and Vickers hardness (Hv) of sintered bodies produced using alloy powder were 8.39 g⋅cm-3, 213 MPa and 56.9-87.2, respectively. On the other hand, those of sintered bodies produced using the powder mixture were 8.36 g ⋅CM-3, 199 MPa and 86.9-123, respectively.

Comparison between Cu-Ni Alloy Powder and Cu, Ni Powder Mixture by Metal Injection Molding.

Comparison between Cu-Ni Alloy Powder and Cu, Ni Powder Mixture by Metal Injection Molding.

Mechanical alloying of the NiAl(M) (MTi,Fe) system

The mechanical alloying of intermetallic compounds has attracted much attention in recent years. The formation of NiAl with B2 structure by mechanical alloying of Ni and Al powder mixture has been found to be an explosive exothermic reaction. In this paper, Ti and Fe elements were substituted for Al and their effects on the mechanical alloying process and the final products of the NiAl(M) (MTi, Fe) system were studied in detail by in situ thermal analysis, X-ray diffraction and scanning electron microscopy. The results showed that the addition of as much as 15 at.% Ti or 5 at.% Fe for Al prolonged the milling time prior to the explosive reaction, which indicated the abrupt formation of β phase NiAl(Ti) or NiAl(Fe). The addition of 20 at.% Ti eliminated the abrupt explosive formation of β phase NiAl(Ti) completely. The addition of 25 at.% Ti induced an NiAlTi amorphous-like phase. The prolongation of the milling time prior to the explosive reaction might be attributed to the addition of Ti or Fe preventing the formation of a fine homogeneous layered structure of Ni, Al and Ti or Fe, thus enhancing the energy threshold for the formation of the β NiAl(M) (MTi,Fe) compound. With an increase in Ti content the degree of ordering of the β phase NiAl(Ti) compounds decreased, whereas the crystal lattices expanded and the particle size increased. The particle size of the amorphous-like phase was much larger than that of the explosive-formed β phase NiAl(Ti) compounds.

Transmission electron microscopy on the process of mechanical alloying in NiTi binary systems

In this paper, the Ni and Ti powder mixture with equiatomic ratio was high energy ball milled and then consolidated by explosive compaction. The microstructures of as-compacted and heat treated bulk samples after explosive consolidation are investigated in detail by transmission electron microscopy (TEM) and high resolution electron microscopy (HREM). The experiment results reveal the microstructure variation during mechanical alloying in NiTi binary systems. It is found that a metastable phase denoted as I phase formed during ball milling and the structure of I phase was determined by both electron diffraction and HREM. Finally, the mechanism of amorphization induced by ball milling was discussed.

Shock-induced chemical reactions and synthesis of nickel aluminides

Chemical reactions in Ni and Al powder mixtures, initiated by the passage of shock waves, are used for the synthesis of nickel aluminides. Mechanistic investigations reveal that the extent of these shock-induced chemical reactions and the type (stoichiometry) of shock-synthesized compound formed depend on shock-loading conditions and the initial powder particle morphology. More intense shock conditions and irregular powder morphology assist in attaining an intimately (mechanically) mixed and activated closed-packed mass, thereby favoring bulk chemical reactions and resulting in the synthesis of compounds. While the Ni3Al compound is the preferred reaction product at lower shock conditions, more intense shock conditions favor the formation of the equiatomic B2-phase NiAl compound (having highest melting temperature and highest heat of reaction in contrast to other nickel aluminides), in spite of the starting powders mixed in a volumetric ratio corresponding to the Ni3Al compound.

Macrokinetics of reaction and thermal explosion in Ni and Al powder mixtures

Macrokinetics of reaction and thermal explosion in Ni and Al powder mixtures