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Thompson, John RyanRELATING MICROSTRUCTURE TO PROCESS VARIABLES IN BEAM-BASED ADDITIVE MANUFACTURING OF INCONEL 718
Master of Science (MS), Wright State University, 2014, Mechanical Engineering
The advancement of laser or electron beam-based additive manufacturing requires the ability to control solidification microstructure. Previous work combined analytical point source solutions and nonlinear thermal finite element analysis (FEA) to explore the effects of deposition process variables on Ti-6Al-4V solidification microstructure. The current work seeks to extend the approach to Inconel 718, with the addition of Cellular Automaton-Finite Element (CAFE) models. Numerical data from finite element results are extracted in order to calculate accurate melt pool geometry, thus leading to corresponding cooling rates and thermal gradients. The CAFE models are used to simulate grain grown and nucleation, providing a link between additive manufacturing process variables (beam power/velocity) and solidification microstructure. Ultimately, a comparison of results between Ti-6Al-4V and Inconel 718 is expected to lay the ground work for the integrated control of melt pool geometry and microstructure in other alloys.

Committee:

Nathan Klingbeil, Ph.D. (Advisor); Raghavan Srinivasan, Ph.D., P.E. (Committee Member); Jaimie Tiley, Ph.D. (Committee Member)

Subjects:

Aerospace Engineering; Aerospace Materials; Engineering; Materials Science; Mechanical Engineering

Keywords:

Additive Manufacturing Beam Laser FEA CAFE ProCAST Inconel 718 Ti-6Al-4V melt pool process variables microstructure power velocity gamma prime 3D printing Rosenthal

Liutkus, Timothy JamesDigital Image Correlation in Dynamic Punch Testing and Plastic Deformation Behavior of Inconel 718
Master of Science, The Ohio State University, 2014, Mechanical Engineering
A custom punch-die fixture allowing full field three-dimensional Digital Image Correlation (DIC) measurements on the rear surface of the specimen is introduced for dynamic and quasi-static punch experiments. The punch fixture design methodology is described. Results from punch experiments on 5.08 mm Ti-6Al-4V disk specimens using three different punch geometries in both dynamic and quasi-static conditions are presented and discussed. These experiments can be used to generate material failure data under complex stress states. Such data is essential in developing and calibrating complex material models, like those developed for precipitate hardened Inconel 718. The plastic behavior of precipitate hardened Inconel 718 under various strain rates, orientations, and temperatures is examined; and a punch experiment that uses 3D-DIC measurements of the punch specimen is presented. The research presented herein is part of an ongoing project to develop and calibrate a material model in a finite element code, LS-DYNA. Such models are valuable for the simulation of dynamic events, such as blade off failure in aircraft engines. The equipment, theory, and methodologies used to complete experiments in tension and compression at different strain rates and temperatures are presented. Quasi-static experiments are conducted using a biaxial servo-hydraulic load frame and dynamic experiments using two split Hopkinson bars. A specially designed furnace and adapters are used to complete experiments at elevated temperatures. DIC is an optical method for measuring full field deformations and strains on the specimen surface that is utilized extensively in this work. Experimental results for precipitate hardened Inconel 718 are presented and discussed. The material shows significant strain hardening and some strain rate sensitivity in tension. Data from experiments at elevated temperature show complex temperature dependence. The material shows decreasing flow stress with increasing temperature and decreasing ductility between 21°C and 600°C. Between 600° and 800°C the ductility increases significantly. Compression experiments at various strain rates show similar strain hardening and less rate sensitivity than in tension. The material is anisotropic in the ±45° from rolling directions and shows anisotropy between tension and compression loadings in the transverse direction. These data are used to determine parameters for a Johnson-Cook plasticity model, and yield criteria are discussed. Additional work is presented for the design of plane stress, plane strain, and axisymmetric fracture specimens. These specimens will be used in future work in the generation of a failure surface based on stress triaxiality and lode parameter – two stress-state parameters which govern material failure.

Committee:

Amos Gilat (Advisor); Mark Walter (Committee Member)

Subjects:

Aerospace Materials; Engineering; Mechanical Engineering

Keywords:

Experimental Mechanics, Plasticity, High Rate Testing, Inconel 718, Punch Testing

Dike, Shweta SrikantDynamic Deformation of Materials at Elevated Temperatures
Master of Sciences (Engineering), Case Western Reserve University, 2010, EMC - Mechanical Engineering
High Strength Low Alloy steel, grade 65 (HSLA-65) plates used by the US Navy for ship building are to be joined by Friction Stir Welding (FSW) which subjects the work-piece material to high strain rates at high temperatures. The strength of materials varies with the strain-rate and temperature to which they are subjected. Development of constitutive models to get the optimum FSW weld parameters requires experimental determination of the dynamic behaviour of a material at different strain-rates and temperatures. In the current study, experiments using the Split Hopkinson Pressure Bar (SHPB) were conducted on HSLA-65 at high temperatures to generate the true stress-strain curves in compression. In addition, two other materials, which are used in practical applications where high strain rate loading occurs at high temperatures, namely Inconel-718 superalloy (precipitation hardened and annealed) and Aluminum alloy 7075-T6 were also tested using the SHPB.

Committee:

Vikas Prakash (Advisor); John Lewandowski (Advisor); Joseph Mansour (Committee Member)

Subjects:

Engineering; Experiments; Mechanical Engineering; Mechanics; Metallurgy

Keywords:

Dynamic compressive response of HSLA-65 steel at high temperature; Dynamic compressive response of Inconel-718 at high temperature; High temperature SHPB experiments

Sheridan, Luke CharlesAn Adapted Approach to Process Mapping Across Alloy Systems and Additive Manufacturing Processes
Master of Science in Mechanical Engineering (MSME), Wright State University, 2016, Mechanical Engineering
The continually growing market for metal components fabricated using additive manufacturing (AM) processes has called for a greater understanding of the effects of process variables on the melt pool geometry and microstructure in manufactured components for various alloy systems. Process Mapping is a general approach that traces the influence of process parameters to thermal behavior and feature development during AM processing. Previous work has focused mainly on Ti-6Al-4V (Ti64), but this work uses novel mathematical derivations and adapted process mapping methodologies to construct new geometric, thermal, and microstructural process maps for Ti64 and two nickel superalloy material systems. This work culminates in the production of process maps for both Inconel 718 (IN718) and Inconel 625 (IN625) that were developed via both experimental and analytical data, and the tools used in the established process mapping approach have been thoroughly explored. This has resulted in a non-dimensional template for solidification behavior in terms of material solidification parameters and AM process parameters. The optimized non-dimensional approach presented here will increase the efficiency of future process map development and will facilitate the comparison of process maps across alloy systems and AM processes, laying the ground work for integrated AM feature control and evaluation of current and future materials for AM application.

Committee:

Nathan Klingbeil, Ph.D. (Advisor); Joy Gockel, Ph.D. (Committee Member); Raghavan Srinivasan, Ph.D. (Committee Member)

Subjects:

Engineering; Materials Science; Mechanical Engineering

Keywords:

additive manufacturing; Inconel; Inconel 718; Inconel 625; Ti-6Al-4V; process mapping; microstructure; melt pool; finite elements; closed-form process maps; solidification maps

Makiewicz, Kurt TimothyDevelopment of Simultaneous Transformation Kinetics Microstructure Model with Application to Laser Metal Deposited Ti-6Al-4V and Alloy 718
Master of Science, The Ohio State University, 2013, Materials Science and Engineering
Laser based additive manufacturing has become an enabling joining process for making one-of-a-kind parts, as well as, repairing of aerospace components. Although, the process has been established for more than a decade, optimization of the process is still performed by trial and error experimentation. At the same time, deployment of integrated process-microstructure models has remained as a challenge due to some of the reasons listed below: (1) lack of good process models to consider the laser-material interactions; (2) inability to capture all the heat transfer boundary conditions; (3) thermo-physical-mechanical properties; and (4) robust material model. This work pertains to the development of robust material model for predicting microstructure evolution as a function of arbitrary thermal cycles (multiple heating and cooling cycles) that can be integrated into a process model. This study focuses on the development of a material model for Ti-6Al-4V and Alloy 718. These two alloys are heavily used in turbine engines and undergo complex phase transformations, making them suited to developing a material model for laser metal deposition (LMD). The model uses simultaneous transformation kinetics (STK) theory to predict the transformation of one parent phase into several products. The model uses calculated thermodynamic properties of the alloys for portions of the respective transformation characteristics. Being a phenomenological model there are several user defined calibration parameters to fit the predicted output to experimental data. These parameters modify the nucleation and growth kinetics of the individual transformations. Analyses of experimental LMD builds are used to calibrate the material model. A Ti-6Al-4V build made on a room temperature substrate showed primarily colony alpha morphology in the bottom half of the build with a transition to basketweave alpha in the top half. An increase in hardness corresponding to the microstructural transition was observed. This sample had an average of 340 HV hardness. Analysis of the calculated thermal profiles at the location of the morphology transition showed a transition from cooling below the beta transus to cooling above the beta transus. The Ti-6Al-4V STK model was calibrated using the experimental data from this sample. The substrate of a second build was heated above the Ti-6Al-4V beta transus. This build showed predominantly basketweave alpha without a microstructural transition. Large prior beta grains (>1mm) were observed growing epitaxially from the substrate. These large grains promoted the basketweave formation. Hardness testing showed an average of 344 HV. Samples built in this way were also fatigue tested in the as built condition. Results show that they match previous builds that had been stress relieved. A third build was performed at room temperature on a substrate with large prior beta grains. This build showed basketweave morphology like the second build even though the substrate was not thermally controlled. The hardness for this build averaged 396 HV which is ~50 HV higher than the previous two. This build shows that it may be possible to produce better mechanical properties by controlling the beta grain size rather than heating the substrate. Eighteen Alloy 718 builds were made using proprietary processing conditions. All of these builds were analyzed for nano-scale γ’ and γ’’ precipitates. Two of the builds were similar but had different laser powers. The low laser power build did not show nano-scale precipitates. The higher power build did show small amounts (<3%) of nano-scale precipitates and a corresponding increase in hardness at their locations. The higher power build was used to develop the STK model for Alloy 718. Sixteen of these builds were part of a design of experiments and are referred to as DOE samples. Eight of them have a single layer while the other eight have multiple layers. They were examined for nano-scale precipitates. The amounts of precipitates were correlated to hardness values and thermal profiles.

Committee:

Sudarsanam Babu (Advisor); Wolfgang Windl (Committee Member)

Subjects:

Aerospace Materials; Materials Science; Metallurgy

Keywords:

Simultaneous Transformation Kinetics; STK; Microstructure Modeling; Laser Additive Manufacturing; Laser Metal Deposition; aerospace repair; Ti-6Al-4V; Inconel 718; Alloy 718; Additive Manufacturing; LAM; LMD;