Year of Publication

2020

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Engineering

Department

Mechanical Engineering

First Advisor

Dr. Ibrahim S. Jawahir

Second Advisor

Dr. David A. Puleo

Abstract

The excellent properties of titanium alloys such as high strength, as well as good corrosion and fatigue resistance are desirable for the biomedical and aerospace industry. However, the same properties that make titanium alloys desirable in high-performance applications also make these space-age materials “difficult-to-machine” materials, as the titanium alloys exhibit high cutting temperatures because of their high strength and low thermal conductivity.

Cryogenic machining is a severe plastic deformation (SPD) processes which uses liquid nitrogen as the coolant to take away the heat generated during machining in a relatively short time. Cryogenic machining can significantly reduce the cutting temperatures at the tool-workpiece interface, thereby improving the surface integrity of the manufactured components. This dissertation presents the results of experimental and numerical investigations of the effects of different cooling conditions on the machining performance and machining-induced surface integrity of Ti-6Al-7Nb and Ti-5553 alloys. Surface integrity and residual stresses induced by cryogenic machining are studied and compared with dry machining. Corrosion tests were also conducted to study the influence of machining parameters on the corrosion resistance of machined Ti-6Al-7Nb alloy.

The results of the numerical and experimental studies show that compared with dry machining, cryogenic machining generates superior surface finish, along with higher surface layer hardening. The sub-surface residual stress profile is more compressive after cryogenic machining, and evidence of nanostructured grains is also observed in the influenced surface layer under both cooling conditions. Also, cryogenically-cooled machined sample showed better corrosion resistance compared with dry machined sample.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2020.186

Funding Information

Grant from National Science Foundation (NSF) (Project ID: 1405129), from 2014-2017.

Available for download on Tuesday, November 17, 2020

Included in

Manufacturing Commons

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