Browsing by Subject "L-PBF"
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Item A Comparison of Microstructure and Mechanical Performance of Inconel 718 Manufactured via L-PBF, LP-DED, and WAAM Technologies(University of Texas at Austin, 2023) Ahmad, Nabeel; Bidar, Alireza; Ghiaasiaan, Reza; Gradl, Paul R.; Shao, Shuai; Shamsaei, NimaThe microstructure and mechanical properties of additively manufactured (AM) alloys can be significantly affected by variations in cooling rates, resulting from different process conditions across different additive manufacturing (AM) platforms. Therefore, it is crucial to understand the effect of manufacturing process on the microstructure and mechanical properties of AM Inconel 718. This study examines three AM processes: laser powder bed fusion, laser powder directed energy deposition, and wire arc additive manufacturing. Results show that fully heat treated laser powder bed fused (L-PBF) and wire arc additively manufactured (WAAM) Inconel 718 specimens exhibit higher strength compared to laser powder directed energy deposited (LP-DED) ones due to finer grain structure in L-PBF and retained dendritic microstructure in WAAM. The ductility in LP-DED Inconel 718 was slightly higher compared to WAAM and L-PBF due to relatively small carbide size, which causes stress concentration in a small material volume, leading to delayed fracture.Item A Comparative and Experimental Study on the Effect of Heat Treatment Cycles for PBF Ti6Al4V(University of Texas at Austin, 2021) Karasoglu, M.; Yasa, E.; Tan, E.; Yağmur, A.Powder bed fusion (PBF) presents the highest level of technological maturity and industrialization level for metallic materials among other Additive Manufacturing technologies. The advantages of high geometrical complexity, ability to produce internal cavities, reduced lead time and buy-to-fly ratio enables a wide range of application areas from aerospace to biomedical. Laser-PBF and Electron-PBF present different limitations and opportunities while they can both build from Ti6Al4V powder. The performance of the E-PBF and L-PBF parts highly depends on the resulting microstructures and differs significantly due to various mechanisms such as preheating temperatures and processing environment. Moreover, the obtained material properties generally necessitate heat treatments for reducing residual stresses, enhancing mechanical properties and changing the microstructure. This study aims to investigate the effect of the same heat treatment cycles on the E-PBF and L-PBF microstructure evolution and microhardness by a comparative experimental work with several combinations of exposure durations, temperatures and cooling rates.Item A Comparative Study on the Microstructure and Texture Evolution of L-PBF and LP-DED 17-4 PH Stainless Steel during Heat Treatment(University of Texas at Austin, 2021) Nezhadfar, P.D.; Gradl, Paul R.; Shao, Shuai; Shamsaei, NimaThis study aims to characterize the microstructure and crystallographic texture of 17-4 PH stainless steel (SS) manufactured with laser powder directed energy deposition (LP-DED) and laser powder bed fusion (L-PBF), in both non-heat treated and heat treated conditions. It is found that the non-heat treated LP-DED 17-4 PH SS possesses coarse columnar ferrite grains decorated with Widmanstätten ferrite grains, whereas the L-PBF counterpart has very fine and mostly equiaxed ferrite grains along with lath martensite. An identical stress relief (SR) temperature is obtained for both the L-PBF and LP-DED 17-4 PH SS samples based on the phase diagrams generated using Thermo-Calc. software. The SR step prior to CA-H1025 heat treatment resulted in texture weakening and slightly refined the grain structure. The non-heat treated L-PBF 17-4 PH SS sample possesses strong cube and γ-fiber textures, while the texture transfers to weaker γ-fiber components after performing SR-CA-H1025 heat treatment.Item CONTROLLING CHEMICAL COMPOSITION CHANGES IN LASER POWDER BED FUSION OF ALSI10MG(University of Texas at Austin, 2023) Liu, Bochuan; Gibbons, Gregory J.Due to the large energy input during the laser powder bed fusion process, some elements of metal alloy will reach vaporisation temperature. Significant differences between the volatility of various elements in the alloy may change the chemical composition after manufacturing. This study used this preferential evaporation effect to control the final composition to a targeted value, potentially for alloy and component tracing. Different laser process parameter sets were studied, and the mechanical properties changes associated with various compositions were investigated.Item Effect of Shield Gas on Surface Finish of Laser Powder Bed Produced Parts(University of Texas at Austin, 2018) Montgomery, Colt; Farnin, Christopher; Mellos, Greg; Brand, Michael; Pacheco, Robin; Carpenter, JohnAdditive manufacturing (AM) of metals is a novel manufacturing technique that allows for net-shape or near net-shape parts to be produced quickly. Within additive manufacturing a large concern is the produced surface finish, especially for upward and downward facing surfaces on complex geometries. Surface finish is of utmost importance for many engineering applications. In melting of powders, the gas used dominates the thermal conductivity of the metal powder. Manipulation of the type of shield gas may provide a means to modify the surface finish without adjustment of established lasing parameters and thereby produce a higher quality part with minimal post processing. These results have potential applications in aerospace, automotive, and biomedical sectors where surface finish requirements coupled with complex geometries are extremely common.Item Effects of Design Parameters on Thermal History and Mechanical Behavior of Additively Manufactured 17-4 PH Stainless Steel(University of Texas at Austin, 2018) Shrestha, Rakish; Nezhadfar, P. Dastranjy; Masoomi, Mohammad; Simisiriwong, Jutima; Phan, Nam; Shamsaei, NimaIn this study, the effects of part size on thermal history and mechanical properties of additively manufactured 17-4 PH stainless steel were investigated under monotonic tensile and strain-controlled fatigue loadings. Two sets of specimens were machined from square rods and oversized specimens, which were fabricated using a laser bed powder fusion (L-PBF) process, to introduce variation in specimen geometry and consequently thermal history. Monotonic tensile tests were conducted at a strain rate of 0.001 s-1 . Fully-reversed (Rε = -1), strain-controlled fatigue tests were performed at 0.003 and 0.0035 mm/mm, and varying test frequency to maintain a constant average strain rate in all tests. Experimental results indicated minimal effect of specimen geometry on the tensile properties of L-PBF 17-4 PH SS, which were also found to be comparable to the wrought material. On the other hand, some influence of specimen geometry on fatigue behavior was observed. Specimens machined from square rods exhibited slightly higher fatigue resistance as compared to specimens machined from oversized specimens. Furthermore, thermal simulations demonstrated higher bulk heating in specimens machined from oversized specimens as compared to those from square rods, which indicated the effect of part geometry on thermal history experienced by the fabricated part.Item Effects of Heat Treatment and Fast Neutron Irradiation on the Microstructure and Microhardness of Inconel 625 Fabricated via Laser-Powder Bed Fusion(University of Texas at Austin, 2021) Keya, T.; O'Donnell, V.; Lieben, J.; Romans, A.; Harvill, G.; Andurkar, M.; Gahl, J.; Thompson, S.M.; Prorok, B.C.The microstructure of Inconel 625 fabricated via Laser-Powder Bed Fusion (L-PBF) was investigated in as-printed and heat-treated conditions. The very high cooling rates inherent to the L-PBF process generally result in fine microstructures and complex residual stress fields which requires annealing to reduce stress and tailor the microstructure to obtain the desired mechanical properties. Inconel 625 alloy, a nickel-based superalloy, continues to be a common material employed with the L-PBF process. The unique microstructure produced by the L-PBF process and different phases introduced by different heat treatment processes require investigation to facilitate the material’s wide range of applications. This paper investigates the influence of heat treatments at 700°C, 900°C and 1050°C for one hour on the microstructure and microhardness of the L-PBF parts. The parts were irradiated using ‘fast’ neutrons in University of Missouri Research Reactor Center (MURR). The microhardness before and after radiation are also compared.Item Effects of Powder Reuse and Spatial Location Dependency on the Powder Characteristics and Defect Structure of Additively Manufactured Ti-6Al-4V Parts(University of Texas at Austin, 2021) Soltani-Tehrani, Arash; Yasin, Mohammad Salman; Shao, Shuai; Shamsasei, NimaIn laser powder bed fusion additive manufacturing (L-PBF AM), different powder characteristics including particle size and morphology may yield different packing states and thus different defect content in the resulting parts. As the powder is spread by the recoater, the packing state may not be uniform on the powder bed, giving rise to location-dependent part performance. In addition, as the powder is reused (a common practice in AM industry), its characteristics continuously evolve, causing the defect content to change from build to build. This study aims to investigate the effects of powder reuse and part location on powder characteristics as well as the defect structure of the parts. Results indicate powder reuse in an L-PBF system may reduce the number of defects in the as-fabricated parts due to the superior packing state of reused powder. Part density was also found to be location-dependent, with more defects near the gas outlet.Item Effects of Scanning Strategy on Residual Stress Formation in Additively Manufactured Ti-6Al-4V Parts(University of Texas at Austin, 2017) Masoomi, Mohammad; Thompson, Scott M.; Shamsaei, Nima; Haghsenas, MeysamParts fabricated via directed energy additive manufacturing (AM) can experience very high, localized temperature gradients during manufacture. These temperature gradients are conducive to the formation of a complex residual stress field within such parts. In the study, a thermo-mechanical model is employed for predicting the temperature distribution and residual stress in Ti-6Al-4V parts fabricated using laser-powder bed fusion (L-PBF). The result is utilized for determining a relationship between local part temperature gradients with generated residual stress. Using this numerical model, the effects of scan patterns are investigated.Item Effects of Stripe Width on the Porosity and Mechanical Performance of Additively Manufactured Ti-6Al-4V Parts(University of Texas at Austin, 2021) Soltani-Tehrani, Arash; Yasin, Mohammad Salman; Shao, Shuai; Shamsaei, NimaIn laser powder bed fusion (L-PBF) additive manufacturing, parts are manufactured in a layer-by-layer pattern. In each layer, cross-sections can be scanned with or without partitioning by the laser, which are commonly known as “stripe” and “meander” patterns, respectively. Under the two scanning strategies, the thermal history experienced by the part can be considerably different. Accordingly, defect distribution, microstructure, and mechanical properties may be affected. In this study, two sets of Ti-6Al-4V specimens were fabricated using L-PBF: in one set, the tracks were partitioned in 5-mm stripes, while in the other set, they were partitioned at 100 mm resulting in no stripe seams in the cross-section. It was found that altering the stripe width can considerably affect the laser penetration depth, the defect content, and consequently fatigue performance. However, tensile strength was not much sensitive to changing the stripe width.Item Optimization of Inert Gas Flow Inside Laser Powder Bed Fusion Chamber with Computational Fluid Dynamics(University of Texas at Austin, 2018) Chen, Yu; Vastola, Guglielmo; Zhang, Yong WeiIt is crucial to maintain a uniform and fast enough inert gas flow inside build chamber to obtain high-quality final products (e.g. low porosity) without oxidation. The current study investigated the behaviors of the inert gas flow inside a chamber with CFD simulations, as well as its evaluation and optimization. The gas flow pattern inside the chamber was evaluated in terms of the uniformity of velocity across the build plate. It was shown that the gas channels and locations of inlet openings significantly affected the flow inside the chamber. So the design of gas channels/inlets and flow rates was carefully adjusted to generate uniform gas flow across the chamber to remove emissions from the melt pool efficiently. Furthermore, the re-circulation of emission inside chamber was significantly reduced to keep the chamber walls clean and minimize the damage to the optical surface. In conclusion, CFD benefits in improving quality of products and reducing life-cycle cost for laser powder-bed fusion process (L-PBF).Item Powder Reuse Effects on the Tensile Behavior of Additively Manufactured Inconel 718 Parts(University of Texas at Austin, 2021) Soltani-Tehrani, Arash; Shamsaei, Nima; Surya, Adapa Venkata; Mallory, Jaikp; Ramakrishnan, RameshInconel 718 (IN718), with a wide range of applications in aerospace industries and good weldability, is a popular powder feedstock in the laser beam powder bed fusion (LB-PBF) additive manufacturing (AM) process. Due to fabrication, handling, and storage costs, powder feedstock is commonly reused several times. Therefore, it is important to understand how the mechanical properties of LB-PBF parts can be affected by powder reuse given that powder characteristics may change after repeated recycling. This study aims to investigate the effect of powder reuse on the tensile properties of LB-PBF IN718 parts. Powder characteristics such as cohesion and compressibility will be quantified in order to shed light on the variations observed in the part performances. In addition, by correlating the state of the reused powder with tensile properties, the most critical metrics for quality aspects in powder reuse will be determined.Item Prediction of Fatigue Lives in Additively Manufactured Alloys Based on the Crack-Growth Concept(University of Texas at Austin, 2017) Yadollahi, Aref; Mahtabi, Mohammad J.; Doude, Haley R.; Newman, James C. JrThis paper aims to predict the fatigue behavior of additively manufactured alloys using crack-growth data. Among different sources of damage under cyclic loadings, fatigue due to cracks originated from voids is the most life-limiting failure mechanism in powder-based metal additive manufacturing (AM) parts. Hence, the ability to predict the fatigue behavior of AM materials based on the void features is the first step toward improving AM part reliability. Test results from the literature on AM alloys are analyzed herein to model fatigue behavior based on the semi-circular surface flaws. The fatigue-life variations in the specimens are captured using the distribution of defect size. The results indicate that knowing the statistical distribution of the defect size can provide the opportunity of predicting the scatter in the fatigue-life of the AM materials, using an appropriate fatigue analysis code.Item Process-controlled Grading of the Young's Modulus of AlSi10Mg Components Using L-PBF(2022) Geis, J.; Reichwein, J.; Merschroth, H.; Kirchner, E.; Weigold, M.Laser Powder Bed Fusion (L-PBF) increases freedom in the design of components and is therefore well suited for the manufacturing of complex geometries tailored to their function. In addition, it is possible to influence the microstructural characteristics of the components by varying the process parameters during the L-PBF process. This allows shifting the load from areas with high stresses to less heavily loaded areas in order to exploit the full potential of the material. For this purpose, the process window in which the Young‘s modulus of the material AlSi10Mg can be varied was investigated. Subsequently, test geometries were analyzed by finite element method with respect to their critical component areas and a design for grading the Young‘s modulus to distribute stress more uniformly was developed. These specimens were then manufactured and compared with components manufactured using homogeneous parameters.Item The Variation of Mechanical Properties of M300 Maraging Steel Manufactured with Varying Process Parameters in Laser Powder Bed Fusion(University of Texas at Austin, 2023) Petersen, Haley E.; Sampson, Brad J.; Failla, David P.; Priddy, Matthew W.; McClelland, Zackery B.Laser power bed fusion (L-PBF) is a type of additive manufacturing (AM) that uses layers of powdered metal and a laser to manufacture a part in a layer-by-layer fashion. L-PBF uses a variety of process parameters that ultimately determine the overall quality and mechanical properties of a print. The ability to alter parameters allows for the utilization of various metals in this form of AM. Maraging 300 steel (M300) is a material of particular interest due to its combined tensile strength and high strength-to-weight ratio. By using an assortment of parameters and comparing the resulting mechanical properties it can be determined which process parameters result in a more favorable part to be used in a variety of applications. A favorable process parameter set was selected for future use. This study aims to determine which process parameters result in the best overall mechanical properties of M300 manufactured using L-PBF.