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,N sub 2, or He) on the formation tendency of amorphous alloy powders and their Curie temperature (T sub c), structural relaxation, glass transition T sub g), and crystallization T sub x) 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 in 25 to 44microns for Ar and 44 to 100microns for He. The average particle size is considerable smaller for He than for Ar and N sub 2 probably because of large kinematic viscosity of He. No appreciable differences in T sub c, T sub g and T sub x of Fe sub 77 P sub 13 C sub 10 amorphous powders with the kind of atomizing gas are seen and these values are the same as those of the amorphous ribbon with 20microns thickness. However, He-atomized Fe sub 77 P sub 13 C sub 10 powders exhibit a lower onset temperature of relaxation and larger heats of relaxation and crystallization as compared with the Ar- and N sub 2 -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.