AMORPHOUS AL-BASED THICK SHEETS PRODUCED BY RAPID SOLIDIFICATION OF SUPERCOOLED LIQUID DROPLETS

Al84Ni10Mm6 (Mm = mischmetal) amorphous sheets with a maximum thickness of 7.0 mm were produced by the two-stage quenching technique consisting of high-pressure argon atomization and the subsequent incremental impact deposition on a rotator. The amorphous sheets had a thickness of 0.1 to 7.0 mm and an average width and length of 40 and 100 mm, respectively, and the thickness was controlled by changing the amount of the molten alloy in one ejection. The formation of an amorphous sheet with a large thickness up to 7.0 mm is quite different from the result by melt spinning that the amorphous ribbon is formed in the thickness range below about 0.13 mm and is thought to result from an incremental deposition at an interval of the order 10(-3) s of the supercooled liquid droplets with high kinetic energies produced by high-pressure gas atomization. The glass transition and crystallization behavior remained unchanged over the entire thickness range of 0.1 to 7.0 mm and were the same as that of the melt-spun ribbon, but the density and hardness of the sheets were slightly lower than those of the ribbon probably because of the inclusion of pores. The thermal stability allows us to conclude that there is no distinct difference in amorphicity between the sheet with a thickness of 7.0 mm and the ribbon with a thickness of 0.02 mm. It is concluded therefore, that the present two-stage quenching technique provides an appropriate cooling condition for the formation of an amorphous thick sheet.