Powder Casting: Producing Bulk Metal Components from Powder Without Compaction
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https://doi.org/10.1007/s11837-020-04261-x Ó 2020 This is a U.S. government work and not under copyright protection in the U.S.; foreign copyright protection may apply
ADDITIVE MANUFACTURING: BEYOND THE BEAM TECHNOLOGY
Powder Casting: Producing Bulk Metal Components from Powder Without Compaction JAMES D. PARAMORE ,1,2,3 MATTHEW K. DUNSTAN BRADY G. BUTLER ,1,2,5 and DANIEL O. LEWIS 1,6
,1,4
1.—United States Army Research Laboratory, 575 Ross St (3003 TAMU), College Station, TX 77843-3003, USA. 2.—Department of Materials Science and Engineering, Texas A&M University, 575 Ross St (3003 TAMU), College Station, TX 778433003, USA. 3.—e-mail: [email protected]. 4.—e-mail: matthew.k.dunstan.civ@ mail.mil. 5.—e-mail: [email protected]. 6.—e-mail: [email protected]
Powder casting was developed to produce metal components with near-theoretical density from low-cost, loose powder using hydrogen sintering and phase transformation. This has significant implications for non-beam metal additive manufacturing processes (e.g., metal extrusion AM, binder jetting, and ordered powder lithography), which produce green parts with relatively low densities. Additionally, powder casting can enable the production of geometries typically not suitable for powder processing, such as plate and bar stock. In the current study, Ti-6Al-4V, Zr, and Hf were densified to 99.2%, 95.7%, and 94.0% of their respective theoretical densities, when sintered from loose powder at 1200°C for 4 h. The relative density and pore size distributions of Ti-6Al-4V produced by powder casting were very similar to those produced by press-and-sinter HSPT. The powder-cast Ti-6Al-4V samples also displayed ductility consistent with press-and-sinter HSPT. However, they exhibited lower strength due to unintentional overheating during the dehydrogenation step.
INTRODUCTION While hydrogen is detrimental to the mechanical properties of finished components, the presence of hydrogen during powder metallurgy (PM) processing has several benefits, including its ability to improve densification.1–4 Additionally, when hydrogen is added to titanium, it enables new phase transformations that allow for microstructural engineering without requiring mechanical working.2,5 Introducing hydrogen in the form of TiH2-containing feedstocks has been used for over 50 years in PM.6–8 However, similar results are obtained by using a H2-containing atmosphere, instead of vacuum or inert gas, to sinter elemental Ti powders.9–11 Over the last decade, the authors and their collaborators have developed a process named hydrogen sintering and phase transformation (HSPT), a blended elemental press-and-sinter PM process.12–14 This process was developed to produce high-performance titanium alloys with wrought-like microstructures and properties using only low-cost
feedstocks and processing. To date, this process has been reported to produce tensile strength exceeding 1 GPa, ductility exceeding 20%EL and 45%RA, and fatigue endurance limits of 50–60% of the ultimate tensile streng
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