SUBJECT: Ph.D. Dissertation Defense
BY: Ranadip Acharya
TIME: Monday, November 10, 2014, 12:00 p.m.
PLACE: MRDC Building, 4115
TITLE: Multiphysics Modeling and Statistical Process Optimization of the Scanning Laser Epitaxy Process Applied to Additive Manufacturing of Turbine engine Hot Section Superalloy Components
COMMITTEE: Dr. Suman Das, Chair (ME)
Dr. Yogendra Joshi (ME)
Dr. Jianjun Shi (ISYE)
Dr. Arun Gokhale (MSE)
Dr. Surya Kalidindi (ME)


Scanning Laser Epitaxy (SLE) is a new laser-based layer-by-layer generative manufacturing technology being developed in the Direct Digital Manufacturing Laboratory at Georgia Tech. SLE allows creation of geometrically complex three-dimensional components with as-desired microstructure through controlled melting and solidification of stationary metal-alloy powder placed on top of like-chemistry substrates. The proposed research seeks to garner knowledge about the fundamental physics of SLE through simulation-based studies and apply this knowledge for hot section turbine component repair, ultimately for reduction to practice in commercial settings. The use of a fine focused laser beam, close thermal control and overlapping raster scan pattern allows SLE to perform significantly better on a range of so-called “non-weldable” Ni-base superalloys. The process produces dense, crack-free and epitaxial deposit for single-crystal (SX) (CMSX4), directionally-solidified (DS) (René 142) and equiaxed (René 80, IN 100) Ni-based superalloys. To explore the process capability, the fabricated components are characterized in terms of several geometrical, mechanical and metallurgical parameters. An active-contour based image analysis technique has been developed to obtain several microstructural responses from the optical metallography of sample cross-sections and the process goes through continuous improvement through optimization of the process parameters through subsequent design of experiments. The simulation-based study is aimed at developing a multiphysics model that captures the fundamental physics of the fabrication process and allows the generation of constitutive equations for microstructural transitions and properties. The research thus allows extending the SLE process to different superalloy materials, performs statistical monitoring of the process, and studies the fundamental physics of the process to enable formulation of constitutive relations for use in closed-loop feedback control; thus imparting ground breaking capability to SLE to fabricate superalloy components with as-desired microstructures.