Rationalization of Liquid/Solid and Solid/Solid Interphase Instabilities During Thermal-Mechanical Transients of Metal Additive Manufacturing
Abstract
Recent thermal analyses have confirmed that steady-state conditions assumed for traditional manufacturing are not valid for additive manufacturing (AM), due to spatial and temporal transients in energy delivery. These transients lead to varied thermal gradients (103 to 107 K/m) and their reversals (> 10 Hz) across liquid/solid (l/s) and solid/solid (s/s) interfaces. These transient thermomechanical boundary conditions are not consistent with the principles of physical metallurgy developed for isothermal (0 K/m) and/or steady-state boundary conditions. In the proposed research, the technical approach will focus on addressing these deficiencies through in-situ and ex-situ measurements of material behaviors in model nickel and titanium alloys. These measurements will be made using a suite of analytical tools that use phonons, photons, electrons, and neutrons for probing materials while they are being subjected to controlled thermomechanical conditions typical to that of metal AM, i.e., powder bed fusion and direct energy deposition. The outcomes will include comprehensive three-dimensional information of initial and final microstructure, as well as paths taken by the above metal samples in terms of geometrical changes, morphology of grains defined by size, shape and distribution, composition, crystal structure, phase orientation, and defect densities with reference to imposed boundary conditions. These measurements will be used for verification and validation of existing integrated computational materials engineering (ICME) models, as well as guiding and informing the emerging Exascale computational initiatives for AM. The proposed research is critical to the US Department of Defense (DoD), because AM of metallic objects is being considered as an affordable engineering solution for (1) effective replacement of existing components within an aging fleet and custom tooling, thereby shortening the supply chain, and (2) the production of new components with improved performance and functionality through designed complexity, along with reduced cost and shorter delivery times. However, to qualify these processes for high-value-added metallic components, it is necessary to understand the physical metallurgy of these builds at different length- and time- scales. This research will validate ICME tools through data generated by in-situ and ex-situ characterization for AM, as well as provide a framework that can be hosted by Navy enterprises that collate the 3D geometry, thermomechanical boundary conditions, defects, and microstructure at unprecedented spatial and temporal resolutions. This holistic approach can be deployed to qualify AM builds for DoD applications. The impact of this fundamental research will be crosscutting and crucial to all metal AM processes including large-scale direct energy deposition processes involving arc, plasma, and laser, and electron beam, and powder bed fusion processes with laser and electron beam, both involving solidification and solid-state transformations.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Sep 04, 2018
- Source ID
- N000141812794
Entities
People
- Sudarsanam Babu
Organizations
- Office of Naval Research
- United States Navy
- University of Tennessee