Process-Microstructure-Properties Relationships in DED Ti-6Al-4V
Abstract
Jack Beuth, Sneha Narra and Tony Rollett propose to investigate the effect of process conditions and heat treatment on laser hot wire (LHW) directed energy deposition (DED) additive manufacturing (DED-AM) of Ti-6Al-4V in collaboration with NSWCCD. The progressivedeposition of molten metal inherent in LHW-DED means that substantial thermal shrinkage is applied to the material below. Dependingon the part geometry, this leads to a planar or linear stress that often approaches the yield stress, which in turn may generate cracks as indeed observed in QM builds with Ti-6Al-4V. Cracking depends on a wider range of material properties such as yield strengthand fracture toughness, both of which depend on microstructure, which further depends on temperature and thermal history. Thus, controlling the process enables both mitigation of residual stress and optimization of materials properties. Taking thin walls as the test case geometry, our hypothesis is that we can use diffraction experiments to validate predictions of the as-deposited stress state to within 20 % (in magnitude) and vary the process conditions to control microstructure and improve the resistance to cracking by10%.The overarching effort will address the main hypothesis of mitigating residual stress via process-microstructure-properties control. Our technical approach will be grounded in Integrated Computational Materials Engineering (ICME) which in this context means that we will compute as many aspects of the behavior as possible and treat experimental data as either calibration (equivalent to training) or as validation (testing). The tasks listed in the body of the proposal include enhanced tools for process optimization and monitoring, along with process-microstructure-properties relationships. The task on establishing process-structure-properties mainlycomprises residual stress measurement via neutron diffraction of walls on plates, residual stress prediction using finite element analysis (FEA) such as the Netfabb software, predicting the microstructure from the thermal history and accounting heat treatment, refine constitutive model for flow stress, mechanical testing of AM materials and development of materials models for temperature dependent flow stress for use in the FEA. Complementary to these, the task on process optimization focuses on developing a multi-scale process design and simulation platform. This includes bead-level cross-alloy parameter development, layer-level thermal modeling of fill patterns, part-level thermal modeling of part heating, and part-level stress prediction. Both these tasks combined will advance the prediction of microstructure and properties as well as measuring and mitigating residual stress. We will collaborate in detail with personnel at NSWCDD to perform builds and analyze samples from these builds. Further, this effort will make full use of the equipment acquired by CMU through DURIP grants including the LHW-AM system from Lincoln, automated hardness tester, x-ray diffraction contrast tomography system, and Gleeble mechanical test system. The Navy has new vehicles to design and build, as well as a very largerange of platforms to maintain. Given a diverse fleet of ships and boats, the need for high quality, low part count manufacturing is obvious, which strongly motivates the development and deployment of additive manufacturing for all materials. Nevertheless, there are challenges associated with substantial residual stress that was enough to induce macroscopic cracks microstructures showed complex features linked to the local thermal history and the tensile properties were anisotropic. Addressing these issues is relevant to future Navy use of DED whether in Ti64 or other alloys such as commercial purity Ti and Navy-relevant steels. The work proposed herein will address these gaps and support the everyday use of the technology.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 11, 2023
- Source ID
- N000142312815
Entities
People
- Anthony Rollett
Organizations
- Carnegie Mellon University
- Office of Naval Research
- United States Navy