SUBJECT: Ph.D. Proposal Presentation
BY: Ranadip Acharya
TIME: Monday, December 2, 2013, 9:00 a.m.
PLACE: MRDC Building, 4211
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. Arun Gokhale (MSE)
Dr. Surya Kalidindi (ME)
Dr. JianJun Shi (ISYE)


Scanning Laser Epitaxy (SLE) is a new laser-based layer-by-layer generative manufacturing process being developed in the Direct Digital Manufacturing Laboratory at Georgia Tech that allows creation of three-dimensional complex geometry with as-desired microstructure through controlled melting and solidification of stationery metal-alloy powder on top of like-chemistry substrate. Prior methods of the repair showed limited success in the range of Ni-based superalloy, failed to consistently maintain epitaxy in the repaired part and suffered from several mechanical and metallurgical defects. The use of fine laser beam, close thermal control and overlapping raster scan pattern allows the SLE process to perform significantly better on a range of Ni-base superalloy. The process produced dense, crack-free and epitaxial deposit for both single-crystal (CMSX4) and equiaxed (René-80, IN 100) superalloy. However, to enable consistent production of defect-free part and subsequent commercialization of the technology several concerns related to process capabilities and fundamental physics need to be addressed. An in-house active-contour based image analysis technique has been developed to obtain several microstructural responses from the optical microscopy of sample cross-section and optimization of the process parameter is carried out through subsequent design of experiments. The development work hence focuses on studying process response to different superalloy material and implementing a multivariate statistical process control that allows efficient management and optimization of the design parameter space. The simulation-based study is aimed at developing a multiphysics model that can explain the fundamental physics of the fabrication process and allows the generation of constitutive equation for the microstructural transition and properties. The flow-thermal model is further tied to empirical microstructural model through the active-contour based optical image analysis and allowed redefining several microstructural transition criteria for laser beam describing a raster scan pattern. 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 microstructure.