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

Abstract

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 Zr50Cu40Al10 and Zr49Cu46Al5 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 Zr50Cu40Al10 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 Zr49Cu46Al5 alloy, in the particle diameter range of 400–1100 µm, the solidified microstructure consists of primary B19'-ZrCu phase, a small amount of Cu10Zr7 phase and Zr14Cu51 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 Zr50Cu40Al10 and Zr49Cu46Al5 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 Zr50Cu40Al10 particles are always better than those of Zr49Cu46Al5 particles.