Date of Award

1-2011

Degree Name

Doctor of Philosophy

Department

Mechanical and Aeronautical Engineering (to 2013)

First Advisor

Dr. John Patten

Abstract

Ceramics and semiconductors are hard, strong, inert and lightweight. They also have good optical properties, wide energy bandgap and high maximum current density. This combination of properties makes them ideal candidates for tribological, semiconductor, MEMS and optoelectronic applications respectively. Manufacturing these materials without causing surface and subsurface damage is extremely challenging due to their high hardness, brittle characteristics and poor machinability. However, ductile regime machining of these materials is possible due to the high-pressure phase transformation occurring in the material caused by the high compressive stresses induced by the single point diamond tool tip. In this study, to further augment the ductile response of the machined material, single point scratch tests are coupled with a micro-laser assisted machining (μ-LAM) technique. The high pressure phase is preferentially heated and thermally softened by using concentrated energy sources (i.e. laser beams) to enhance the ductile response of the material. The focus here is to develop an efficient manufacturing technique to improve the surface quality of ceramics and semiconductors to be used as optical devices (mirrors and windows). Machining parameters such as the depth of cut, feed, cutting speed and laser power are optimized in order to make the manufacturing process more time and cost effective. Also, the science behind the thermal softening effect during the formation of high-pressure phases is experimentally studied by isolating the temperature and pressure effect. Micro-laser assisted scratch tests successfully demonstrate the enhanced thermal softening in silicon (Si), silicon carbide (SiC) and sapphire resulting in greater depths of cuts (when compared to similar applied loads for cuts with no laser), greater ductile-to-brittle transition depths and smaller cutting forces. Imaging and characterization techniques such as optical microscopy, light interferometry, XRD, surface profilometry, OIM, AFM, scanning acoustic microscopy, electron microscopy and Raman spectroscopy are utilized to quantify the ductile mode material removal process. Ductile mode machining is experimented on nine ceramics and semiconductors including Si, SiC (three polytypes: 4H, 6H and 3C), sapphire, quartz, spinel, AlON and AlTiC.

Access Setting

Dissertation-Open Access

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