Crystalline and amorphous microstructure evolution of Zr-Cu-Al ternary alloys solidified in drop tube.

High undercooling rapid solidification process has a significant impact on the solidified microstructure and mechanical properties of materials. In this study, particles with a diameter range between 100 and 1100 µm of ternary Zr 50 Cu 40 Al 10 and Zr 49 Cu 46 Al 5 alloys were prepared by a drop tube. The evolution process of particle-solidified microstructure with decreasing particle diameter was analyzed using XRD, SEM, and TEM. For Zr 50 Cu 40 Al 10 alloy, the solidified microstructure in the particle diameter ranges of 200–1100 µm is composed of an amorphous phase and a primary B2-ZrCu high-temperature metastable phase. As the particle diameter reduces, the retained crystalline phase in the solidified microstructure decreases progressively, and the dendrite grain length gradually becomes finer. When the particle diameter is reduced to below 200 µm, the crystalline phase has completely disappeared, and the solidified microstructure evolves into a completely amorphous structure. For Zr 49 Cu 46 Al 5 alloy, in the particle diameter range of 400–1100 µm, the solidified microstructure consists of primary B19'-ZrCu phase, a small amount of Cu 10 Zr 7 phase and Zr 14 Cu 51 phase. As the particle diameter reduces, a grain refinement phenomenon also occurs in the solidified microstructure and the dendritic morphology changes from equiaxed grain to rod-shaped dendrite. The amorphous phase appears when the particle diameter is lowered to 470 µm and solidified microstructure evolves into a completely amorphous structure as the particle diameter is reduced to 146 µm. The nanoindentation results show that the micromechanical properties of amorphous composite microstructures are superior to the single component composition of crystalline or amorphous phase for Zr 50 Cu 40 Al 10 and Zr 49 Cu 46 Al 5 alloys. The reinforcement effect on the amorphous phase is related to the content of the second crystalline phase. Moreover, under similar particle diameters, the mechanical properties of Zr 50 Cu 40 Al 10 particles are always better than those of Zr 49 Cu 46 Al 5 particles. • In-situ preparation of amorphous composite particles using containerless rapid solidification technique. • Comparison of the amorphous forming ability between the two Zr-Cu-Al alloys. • Characterization of the phase constitution and solidified microstructure evolution under different diameters. • Amorphous composite materials exhibit higher hardness and elastic modulus properties. [ABSTRACT FROM AUTHOR]