Processing of iron-based glass-forming alloys by the uniform-droplet spray process

The uniform-droplet spray (UDS) process involves the capillary jet break-up via sonic perturbations and the subsequent solidification of the resulting mono-size droplets into deposits or powders. The unique ability to precisely control the thermal history and the resulting microstructure has been harnessed in several studies of process-structure relationships in metals and alloys.In the present work, the fundamental aspects of the phenomenon of jet break-up is revisited and a methodology is developed for estimating the UDS processing parameters such as applied pressure, frequency, orifice diameter and jet velocity for a target droplet size. Numerical studies of these parameters are carried out. The current models for droplet dynamics and thermal transport are appropriately modified. Modifications in the existing models for the droplet nucleation and solidification are presented. New models are presented for the metallographic determination of the dual phase heat transfer in oil-quenched droplets and motion-thermal characteristics of droplet arrays subjected to gas jets. In-flight solidification simulations were carried out on, 200-1000 mum droplets of a Sn-5 (mass %) Pb droplets using a software developed in this work.UDS experiments were carried out on glass-forming alloys, Fe75.5 C10.5B6.3Si5.3P1.3Mo, Fe 72C8B7.3Cr4.3Si5.3P 2Mo, Fe67.3C11V3.7Cr 12.5Si5P2Mn0.7 and Fe45Ni 22.5Co7.5Mo3B14Si8. The Fe75.5C10.5B6.3 Si5.3P1.3Mo alloy droplets solidify with the formation Fe9SiC0.4 dendrites, followed by that of the bcc matrix with the microstructural evolution in them in accordance with the thermal histories predicted by the in-flight solidification model. Fully and partially amorphous balls of Fe45Ni22.5Co7.5Mo3B 14Si8 alloy were produced at different UDS processing conditions the glass formation in these droplets was verified by XRD and DSC measurements. Stalagmites, 3 to 5 cm in length, were processed by the deposition of Fe 45Ni22.5Co7.5Mo3B14Si 8 alloy droplets in oil with superheated and mushy droplets. The deposits showed a fine, equiaxed structure at the root and an as cast morphology at the top. Further adjusting process parameters would facilitate epitaxial growth of columnar crystals.