Advisor(s)

Teichi Ando

Contributor(s)

Charalabos Doumanidis (University of Cyprus), Yung Joon Jung

Date of Award

2008

Date Accepted

8-2008

Degree Grantor

Northeastern University

Degree Level

Ph.D.

Degree Name

Doctor of Philosophy

Department or Academic Unit

College of Engineering. Deparment of Mechanical and Industrial Engineering

Keywords

UDS, jet break-up, droplet dynamics

Subject Categories

Alloys--Thermal properties

Disciplines

Mechanical Engineering

Abstract

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 µm droplets of a Sn-5 (mass %) Pb droplets using a software developed in this work. UDS experiments were carried out on glass-forming alloys, Fe75.5C10.5B6.3Si5.3P1.3Mo, Fe72C8B7.3Cr4.3Si5.3P2Mo, Fe67.3C11V3.7Cr12.5Si5P2Mn0.7 and Fe45Ni22.5Co7.5Mo3B14Si8. The Fe75.5C10.5B6.3Si5.3P1.3Mo 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 Fe45Ni22.5Co7.5Mo3B14Si8 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 Fe45Ni22.5Co7.5Mo3B14Si8 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.

Document Type

Dissertation

Rights Holder

Suresh Kumar S. Pillai


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