2023 Annual International Solid Freeform Fabrication Symposium (SFF Symp 2023): Materials: Metals-Processing Strategies I
Program Organizers: Joseph Beaman, University of Texas at Austin
Tuesday 1:40 PM
August 15, 2023
Room: 616 AB
Location: Hilton Austin
Session Chair: Christopher Ledford, Oak Ridge National Laboratory
1:40 PM
The Development of a Directed Energy Deposition (DED) Printability Framework for Improving Part Density and Performance in High Strength Martensitic Steels: Matthew Vaughan1; Michael Elverud1; Jiahui Ye1; Raiyan Seede2; Sean Gibbons3; Philip Flater3; Bernard Gaskey3; Alaa Elwany1; Raymundo Arroyave1; Ibrahim Karaman1; 1Texas A&M University; 2Lawrence Livermore National Laboratory; 3Air Force Research Laboratory
While the additive manufacturing (AM) directed energy deposition (DED) technology provides a novel and efficient method for printing high strength steels to novel geometries, its inherent complexity merits a need for the development of a systematic DED framework that quickly identifies the ideal printability space for a given steel, and subsequently enables one to print the material to full density and dimensional accuracy. Afterwards, achieving optimal strengthening in novel high strength martensitic steels via DED and the Hall-Petch effect would be much more straightforward. To address this need, the present study develops a DED printability framework, where an advanced high strength martensitic steel known as AF9628 is printed to full density, high strength, and respectable ductility (ρ > 99%, UTS > 1.2 GPa, εf > 10%). The introduced process optimization framework is easily adaptable to other high-end steels and alloys and should prove quite valuable to the AM research community.
2:00 PM
AM Process Development of NASA HR1 Alloy using Laser Powder Direct Energy Deposition (LP-DED).: Javier Lares1; Paul Gradl2; Colton Katsarelis,2; Francisco Medina1; Ryan Wicker1; Dana Godinez1; 1W.M. Keck Center; 2National Aeronautics and Space Administration
NASA HR1 alloy is an iron-nickel based material designed by NASA and derived from A286 and JBK-75 alloys. At extreme conditions, NASA HR1 possess high strength, high fatigue resistance, and high resistance to corrosion and hydrogen embrittlement resistance. The main applications include structural components and liquid rocket engine nozzles with internal cooling channels. NASA has produced HR1 using vacuum induction melting (VIM), a considerably expensive fabrication method. Aimed to explore other more affordable and accessible manufacturing methods, HR1 specimens were fabricated under different parameters using LP-DED and were heat treated through stress relief, homogenization, solution treatment and aging. The feasibility of this AM process was investigated by evaluating mechanical and microstructural analyses on specimens. This work finalizes with discussion and remarks on tensile and low-cycle fatigue properties and its relationship with microstructural features.
2:20 PM Cancelled
Laser Powder Bed Fusion Process Feedback Control Based on In-situ Powder Layer Thickness: Jorge Neira1; Ho Yeung1; 1National Institute of Standards and Technology
Metal laser powder bed fusion (LPBF) is a promising additive manufacturing technique for producing complex metal parts. However, the quality of the final product can be affected by various factors such as laser power, scanning speed, powder spreading quality, and layer thickness. In this study, we propose a real-time feedback control method based on the powder spreading quality and layer thickness. We employ a laser 3D scanner to measure the surface profile of each layer before and after the powder has been spread. A powder re-spreading will be triggered if an abnormality is detected on the spread powder surface. The difference between the profile is taken as the actual powder layer thickness and used to adjust the scan strategy for the next layer. The feedback control system is integrated into the customized-built LPBF testbed, and the effectiveness of the proposed feedback control system is demonstrated through a series of experiments.
2:40 PM
Towards High-throughput Assessment
of Printability in Refractory Alloys Systems for Laser-powder Bed Fusion: Peter Morcos1; Brent Vela1; Cafer Acemi1; Alaa Elwany1; Ibrahim Karaman1; Raymundo Arroyave1; 1Texas A&M University
Due to the brittle nature of refractory alloys, their development has been limited by difficulties associated with their processing by conventional means. However, due to their high melting temperature and high cracking susceptibility, their Laser-powder bed fusion (L-PBF) processing is challenging. Therefore, predicting the printability of refractory alloys rank order is critical. In this work, we present a framework capable of predicting the printability of alloys in-silico. We demonstrate this framework by co-designing alloys for performance and amenability to L-PBF. Performance metrics are evaluated in a high-throughput manner within the alloy space then the alloys were filtered, yielding a tractable number of candidate alloys so they can be synthesized via arc-melting. Using CALPHAD-based property models and analytical thermal models, a suite of process-parameter informed printability criteria were calculated. These criteria were then used to rank the printability of the alloys using technique for order preference by similarity to ideal solution.
3:00 PM
Effects of Preheating and Multi-laser Melting of Refractory Alloys in Laser Powder Bed Fusion: Frank Brinkley1; Christopher Ledford1; Michael Kirka1; 1Oak Ridge National Laboratory
Processing of refractory materials and alloys via laser powder bed fusion (L-PBF) has proven difficult due to the high melting temperature, high ductile-to-brittle transition temperature, and the high cooling rates present. This work investigates the effects of high temperature build plate heating (up to 1200°C) and heat input from multiple lasers (a focused master laser and a defocused slave laser) on the melt morphology and cracking behavior of refractory alloys (Mo and W) using single laser track experiments. The effects of laser power, scan speed, beam pathing, and preheating temperature on processability are investigated.
3:20 PM
The Use of Laser Preheating for Microstructural Customization of Ti6Al4V Processed Using Diode Point Melting System: Alkim Aydin1; Kamran Mumtaz1; 1The University of Sheffield
The Laser Powder Bed Fusion (LPBF) process generates high-temperature gradients within a build due to the rapidly traversing high-intensity laser beam. These temperature gradients and rapid solidification rates can increase component residual stress and limit the type of microstructure that can be formed. This research aims to investigate the use of a de-focused 140W 915 Nm diode laser with beam shaping optics to pre-heat an area of 150 mm2 between 150C and 750C. It was found that using laser pre-heating reduced the cooling rate of the LPBF melt pool, cracks could be prohibited, residual stresses were decreased and Ti6Al4V microstructure and mechanical properties improved.
3:40 PM
Influence of Silane-doped Argon Processing Atmosphere on Powder Recycling and Part Properties in L-PBF of Ti-6Al-4V: Nicole Emminghaus1; Robert Bernhard1; Jörg Hermsdorf1; Ludger Overmeyer2; Stefan Kaierle1; 1Laser Zentrum Hannover e. V.; 2Leibniz Universität Hannover, Institut für Transport- und Automatisierungstechnik
In the additive manufacturing of metal powders the residual oxygen in the processing atmosphere plays a crucial role, especially highly reactive materials like titanium alloys. Besides oxidation of the built parts, it leads to oxygen pick-up into the unmolten powder. Since oxidized particles cannot be removed during recycling, the powder properties deteriorate after multiple uses. In this work, Ti-6Al-4V powder was processed under conventional argon atmosphere (residual oxygen content < 0.01 vol.-%) as well as silane-doped argon atmosphere (< 0.001 vol.-% silane in argon). The silane-doping leads to a residual oxygen content of < 10-20 vol.-%. The powder was sieved and reused 5 times for each atmosphere. The powder properties morphology, chemical composition and flowability were analyzed for virgin as well as reused powder. Furthermore, the roughness and relative density of the built parts was evaluated. It is hypothesized that oxygen-free production improves recyclability and thus resource efficiency.
4:00 PM Cancelled
Effect of Build Height on Microstructure and Mechanical Behavior of Ti-6Al-4V Fabricated via Laser Powder Bed Fusion (LPBF): MohammadBagher Mahtabi1; Saeed Ataollahi2; Aref Yadollahi1; Mohammad J. Mahtabi2; 1Purdue University Northwest; 2University of Tennessee at Chattanooga
Additive manufacturing is a process that involves the layer-by-layer fabrication of parts, which can result in different thermal histories (i.e. cooling rates and thermal gradients) for each layer. Consequently, the microstructural and mechanical properties of parts can be affected as the build height increases. This research aims to investigate the influence of build height on the structural integrity of Ti-6Al-4V specimens fabricated via laser powder bed fusion (LPBF). Microstructural features, microhardness values, and defect characteristics (e.g., size, location, and distribution of defects) were analyzed along the build direction. Tensile and fatigue tests were performed to determine if there is a relationship between the location of the fatigue and tensile failures and the build height. The findings of this study indicate that the build height can significantly affect the structural integrity of the part, as the majority of the fatigue specimens failed in the top half of the gage section.