High Pressure Gas Atomization Research Articles

Preparation of Fe-, Co-, and Ni-Based amorphous alloy powders by high-pressure gas atomization and their structural relaxation behavior

By using newly constructed high-pressure gas atomization equipment, the effect of atomizing gas (Ar, N2, or He) on the formation tendency of amorphous alloy powders and their Curie temperature(Tc), structural relaxation, glass transition(Tg), and crystallization(Tx) was examined for Fe-P-C, Fe-Si-B, Fe-Cr-Mo-P-C, Co-Si-B, Ni-Si-B, Ni-Pd-P, and Cu-Zr alloys with easy glass-forming capacity. Amorphous powders are formed in all the alloy systems and the critical diameter for the formation of amorphous powders is 25 to 44 µm for Ar and 44 to 100 µm for He. The average particle size is considerably smaller for He than for Ar and N2, probably because of large kinematic viscosity of He. No appreciable differences inTc,Tg, andTx of Fe77P13C10 amorphous powders with the kind of atomizing gas are seen and these values are the same as those of the amorphous ribbon with 20 µm thickness. However, He-atomized Fe77P13C10 powders exhibit a lower onset temperature of relaxation and larger heats of relaxation and crystallization as compared with the Ar- and N2-atomized powders, and the values of the He-atomized powders are comparable to those of the ribbon sample, indicating that He-gas atomization has a higher cooling capacity and results in the formation of a more disordered amorphous structure. This difference agrees with the tendency estimated under the assumption that heat removal from atomized droplets occurs by Newtonian cooling caused only by the convective heat transfer. Accordingly, the greater heat removal capacity of He gas is concluded to be a dominant factor for the formation of amorphous alloy powders with a more unrelaxed atomic configurations.

A technique for evaluating aluminium alloys for high pressure gas atomization

Cooling rates similar to those in gas atomization have been estimated at the tip of a wedge-shaped copper chill mould. For aluminium alloys a relationship has been established between the thickness of the casting and the critical powder size at which the solidification microstructure changes from microcellular to one containing intermetallics. The technique allows the prediction of the critical powder size in a given alloy or can be used to test predictions of other alloy compositions that would give powders of a desired critical size without having to perform gas atomization.

Solidification microstructures in rapidly solidified, gas atomized aluminium-lithium alloy powders

The examination of the solidification behaviour and resultant microstructures in an Al-Li-Cu-Mg-Zr alloy processed by high-pressure inert gas atomization is reported. Using analytical transmission electron microscopy some quantification of the segregation behaviour is possible which allows the comparison with a simple solute redistribution model (Scheil analysis). It is shown that for powder sizes likely to be of commercial interest (10 to 20 μm), cellular solidification structures are to be expected on atomization, and methods of utilizing such structures are discussed.

Production of Ultrafine Aluminium Powder by High Pressure Gas Atomization

The paper is concerned with the production of ultrafine aluminium alloy powder by the relatively novel route of gas atomization at high pressures (4–8 MPa). It is shown that such a process is capable of the bulk production of rapidly solidified alloy powder having a median diameter below 20 μm. Some process variables are discussed and preliminary results obtained from the operation of a high pressure gas atomizer at the University of Surrey are presented. In addition, some results concerning the consolidation behaviour of such rapidly solidified powder are discussed. PM/0371

Bulk production of ultrafine metallic powder by high pressure gas atomization

Bulk production of ultrafine metallic powder by high pressure gas atomization