Investigation of TI6AL4V microstructure effects on process material interaction during micro milling
Author
Ahmadi, Masoud
Advisor
Karpat, Yiğit
Date
2018-01Publisher
Bilkent University
Language
English
Type
ThesisItem Usage Stats
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Abstract
The interrelationship between material microstructure and process parameters
must be well understood in order to improve the machinability. In micro milling,
the process parameters including depth of cut, feed and cutting edge radius are
comparable to grain size of the material which significantly affects the mechanics
of machining. This thesis investigates the contribution of microstructural characteristics
including grain size, grain morphology and phase fractions/distributions
of dual phase Ti6Al4V titanium alloy in micro scale milling. Various heat treatments
were performed on the Ti6Al4V samples obtaining five different microstructures
including fine equiaxed plus elongated, two size enlarged equiaxed, lamellar
and martensitic microstructures. The influences of microstructures on built upedge
(BUE) formation, cutting forces, surface quality and burr formation were
studied. It was observed that smaller grain size leads to larger BUE and burr formation
and higher cutting forces. However, when feed is set properly it also yields
better surface roughness. The crystallographic texture and microstructure of the
machined surface of selected samples were investigated using electron backscatter
diffraction (EBSD) analysis which revealed that at low feed rates can result in
occurrence of dynamic recrystallization (DRX) on the microstructure of the machined
surfaces. It was observed that up and down milling stages led to different
crystallographic texture of the machined samples during micro scale milling. The
findings of this study are important in terms of developing predictive modeling
of machining based on material microstructure.