THE SCHOOL OF MATERIALS SCIENCE AND ENGINEERING

GEORGIA INSTITUTE OF TECHNOLOGY

Under the provisions of the regulations for the degree

DOCTOR OF PHILOSOPHY

on Thursday, December 7th, 2017

10:00 AM

in Love 295

will be held the

DISSERTATION PROPOSAL DEFENSE

for

Jason P. Allen

"Modeling the Texture and Property Evolution in Subtractive and Additive Manufacturing of Ti-6Al-4V and Low Carbon Steel Alloys"

Committee Members:

Prof. Hamid Garmestani, Advisor, MSE

Prof. Steven Liang, ME

Prof. Naresh Thadhani, MSE

Prof. David McDowell, ME/MSE

Prof. Preet Singh, ME

Abstract:

Common effects of subtractive and additive manufacturing processes are the development of residual stresses, the evolution of texture and change in mechanical properties, often to the detriment of the workpiece. High speed turning operations on Ti-6Al-4V parts often subjects the workpiece surface to increased temperatures, high strains and strain rates and can lead to phase transformations, recrystallization, growth and grain size gradients while additive manufacturing of low carbon steels, via processes such as the Wire-Fed Directed Energy Deposition (DED), can subject the workpiece to large thermal gradients and thermal gyrations leading to cyclic remelting/solidification, phase transformations, residual stresses, recrystallization, etc. Crystal plasticity modeling, with suitable flow stress models, have been shown to have good predictive capabilities with regards to modeling the evolution of texture and anisotropic mechanical properties of many different polycrystalline metallic systems (e.g. copper, aluminum alloys, and titanium alloys) for various processes, such as wire drawing or rolling. This proposal seeks to utilize a Viscoplastic Self Consistent (VPSC) crystal plasticity simulation framework to evaluate the evolution of texture and mechanical properties of Ti-6Al-4V undergoing turning operations and low carbon steels undergoing Wire-Fed DED operations. Due to the variability of strain rates and temperatures throughout processing and its inclusion within the VPSC framework, the Mechanical Threshold Stress (MTS) constitutive model is proposed to model the flow stress behavior of these material systems. It is the ultimate goal of this proposed work to identify the processing parameters that yield the most favorable texture and material properties and investigate the possibilities of leveraging current manufacturing processes to tailor the microstructure and material properties in a beneficial manner.