Grain Boundary Engineering in Additive Manufacturing (AM)

Proposal develops a comprehensive AM metal-powder Grain-Boundary-Engineering (GBE) toolset (hardware/software) to improve material failure strain. Phase I will demonstrate polycrystalline stainless-steel powder with inclusion, formation of coincidence-site-lattice (CSL) grain boundaries, low-angle-grain-boundaries (LAGB), and crystallization of AM coupons by: 1) post build heat-treatment, 2) analyze/optimize post build performance using machine-driven data, and integrated-computational-material-engineering (ICME); and 3) Optimize CSL/LAGB during AM by thermal-heating, fast-cooling, melt-excitation, and inclusion technique. First, feasibility of grainboundary modeling (GBM) will demonstrate several successful GE post heat-treatments using commercial AM machine. Second, Analysis by ICME, entailing: (i) Micro-thermal-management, to determine the thermal-history (melt-pool depth/width, superheated-cooling), Material state (voids/density), %crystallization, process-map of stable and unstable print regions (ii) grain-boundary-modeling (GBM) using creep-diffusion algorithms, predicting surfaceroughness, residual stress/strain, cracks (inter-granular/trans-granular), oxidation, and supported by visualization of construct 3D Voxel Electron-beam-scatter-diffraction (EBSD), (iii) Nano-Micro-mechanical analytical modeling, predicting mechanical properties (stresses-strain), layers distortion/curvature, considering inclusion, defects and uncertainties. Third, Optimization of machine parameters for formation of CSL/LAGB during/post AM coupon performance, and progressive-failure-analysis of improved mechanical properties (failure-strain, yield/ultimate strength).  ICME driven design will be compared/validated with tests including: a) printing stainless-steel coupon specimens using machine equipped in-Situ-monitored sensors, and NDE measurement, failure-strains, and b) use of SEM/TEM microscopy, EBSD imaging.