N15A-T007 TITLE: Real-Time Additive Manufacturing Process Models Applied to Wire Fed Electron Beam Processed 4340 Steel

TECHNOLOGY AREAS: Materials/Processes

OBJECTIVE: Develop innovative, integrated additive manufacturing (AM) structure, processing, and property-geometry modeling concepts that will facilitate the qualification and certification of AM-fabricated 4340 steel alloy parts and enable their rapid deployment.

DESCRIPTION: There has been much progress during the past few years with the advancement of AM techniques. There has been much progress during the past few years with the advancement of AM techniques. Multiple processing techniques are being developed to produce metallic parts. It is anticipated that some of these techniques, if properly engineered, could be used to produce parts that enhance aircraft performance and operational readiness while reducing sustainment costs. This tool-less, on-demand manufacturing technology will facilitate rapid overhauling, servicing, and repair of desired components.

In order to produce parts that can be used on Navy aircraft they must obtain flight certification. To accomplish this, the material properties of the parts manufactured using AM must be fully understood and repeatable to meet flight qualification and certification requirements. Specific concerns include the microstructure and properties of the AM parts, which involves the development of process-microstructural models, sensor technology, and control methods and algorithms.

AM is a uniquely complex process of layer-by-layer deposition. During this process, the thermal history of a layer may involve multiple re-melt and solidification cycles as well as multiple solid state phase transformations. Melt pool size and shape are features that should be controlled in order to produce materials of consistent quality. Beuth and Klingbeil (Ref 1) have developed process maps for predicting melt pool size and related these properties to deposition rate and laser power for the Ti-6Al-4V alloy. By doing so, it was shown that it is possible to maintain a constant melt pool size over a range of deposition rates. The microstructural evolution of Ti-6Al-4V has been investigated and modeled for a variety of AM and thermal mechanical processes (Ref 2). The combined effect of rapid solidification, directional cooling, and phase transformations induced by repeated thermal cycles has a profound influence on the microstructures of the materials deposited. Rapid solidification reduces elemental partitioning and extends solid solubility and can result in metastable phase formation. Directional heat extraction may result in preferred directionality in grain growth. Repeated thermal cycles have a possible complex set of effects, including microstructural banding, i.e., microstructural differences between depositions layers (Ref 3). Thus, in order to rapidly transition this technology, the development of validated models is needed to accurately predict the structure and properties of the 4340 alloy deposit throughout the wire feed electron beam AM process.

The proposed modeling software should be able to predict real-time melt pool size, thermal history in the build, microstructures resulting from rapid solidification, and related mechanical properties at any location in the build corresponding to various process parameters. The software package should include modeling of melt pool dimensions (e.g., diameter and length/depth) and temperature (e.g., melt pool and substrate) throughout the build process in terms of machine parameters such as beam energy, stand-off distance, bead spacing, and build travel speed. Issues with current metallic AM techniques will be identified and included in the software package.

PHASE I: Define and develop a concept for innovative real-time process models for AM of 4340 electron beam wire feed materials. Demonstrate the feasibility to monitor and model the fabrication process and predict the resulting material microstructures and mechanical properties of the fabricated materials.

PHASE II: Develop a prototype control system based upon the modeling and monitoring demonstrated in Phase I. Demonstrate ability to predict the melt pool size and temperature profiles, to fabricate parts using 4340 material with properties equivalent to parts forged with 4340 alloys.

PHASE III: Further improve the software to accurately predict the microstructure and mechanical properties by producing various parts and verifying if the produced properties match with the design requirements. Transition the control system/software package to Navy depots or commercial companies for producing aircraft parts.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: These new approaches can be used for production of large commercial aircraft and other facilities.

REFERENCES:
1. Beuth, J. & Klingbeil, N. (2001). The role of process variables in laser-based direct metal solid freeform fabrication. Journal of the Minerals, Metals & Materials Society, 53, 36�39. doi: 10.1007/s11837-001-0067-y

2. Kelly, S.M. & Kampe, S.L. (2004). Microstructural evolution in laser-deposited multilayer Ti-6Al-4V builds: Part II. Thermal modeling. Metallurgical and Materials Transactions, A, 35A, 1869�1879. doi: 10.1007/s11661-004-0095-7

3. Murr, L.E., Martinez, E., Gaytan, S.M., Ramirez, D.A., Machado, B.I., Shindo, P.W., Martinez, J.L., Medina, F., Wooten, J., Ciscel, D., Ackelid, U., & Wicker, R.B. (2011). Microstructural architecture, microstructures, and mechanical properties of a nickel-base superalloy fabricated by electron beam melting. Metallurgical and Materials Transactions, A, 42A, 3491�3508. doi: 10.1007/s11661-011-0748-2

4. United States Navy. (2014, February). Naval aviation vision 2014-2025, 25. Retrieved from http://www.navy.mil/strategic/Naval_Aviation_Vision.pdf

KEYWORDS: Direct Digital Manufacturing; Additive Manufacturing; Metallic; Electron beam; process modeling; 4340 alloys

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