Browsing by Subject "porosity"
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Item Competing Influence of Porosity and Microstructure on the Fatigue Property of Laser Powder Bed Fusion Stainless Steel 316L(University of Texas at Austin, 2017) Zhang, Meng; Sun, Chen-Nan; Zhang, Xiang; Chin Goh, Phoi; Wei, Jun; Li, Hua; Hardacre, DavidCrack initiation constitutes a large portion of the total life for parts under high cycle fatigue loading. Materials made by the laser powder bed fusion (L-PBF) process contain unavoidable process-induced porosity whose effect on the mechanical properties needs to be considered for fatigue applications. Results from this work show that not all pores in L-PBF parts promote fatigue crack initiation. The length scale of local microstructure defects, i.e. grain boundary, could be larger than the pores and in such cases they are the primary cause for crack initiation. Samples were produced in this work to demonstrate the critical defect size responsible for the transition between the porosity-driven and microstructure-driven failure modes.Item Defect Morphology in Ti-6Al-4V Parts Fabricated by Selective Laser Melting and Electron Beam Melting(University of Texas at Austin, 2013-08-16) Gong, Haijun; Rafi, Khalid; Karthik, N.V.; Starr, Thomas; Stucker, BrentIn order to investigate the morphology of defects present in Selective Laser Melting (SLM) and Electron Beam Melting (EBM) processes, Ti-6Al-4V specimens were fabricated with varying porosity using non-optimum processing parameters. Defective specimens were sectioned and polished for microscopy. Image processing was adopted for statistically analyzing the characteristics of defects, such as distribution of defect area and dimensional proportion of each defect. It is found that defect morphology is influenced by process parameters as a result of a variation in the melt pool. Image processing of a cross-section could be a feasible way for calculating porosity of specimens.Item DEVELOPMENT OF HIGHLY FILLED BIO-BASED COMPOSITES FOR SUSTAINABLE, LOW-COST FEEDSTOCK: PROCESSING EFFECTS ON POROSITY AND FIBER ALIGNMENT(University of Texas at Austin, 2023) Copenhaver, Katie; Lamm, Meghan; Hubbard, AmberA poly(lactic acid) composite with a high loading of bio-based fibers was developed using a combination of high-aspect ratio (AR) wood pulp and low-AR wood flour along with viscosity modifiers to maximize mechanical performance, maintain processability, and lower the cost and embodied energy of the resulting feedstock. An optimized composite formulation containing 40 wt.% of a blend of high- and low-AR natural fibers with a rice bran-based wax processing aid was scaled up to produce pellet feedstock using twin screw extrusion, and materials were compression and injection molded to investigate the effect of fiber alignment on material performance. The feedstock was then printed on the Big Area Additive Manufacturing system at Oak Ridge National Laboratory. Print parameters including temperature gradients, screw and gantry speeds, layer times, and nozzle designs were varied to minimize sharkskinning, warpage, and porosity of the final parts. A strong effect of the nozzle size on the resulting porosity was observed, and consistent trends between decreasing porosity, increasing fiber alignment, and increasing mechanical performance were identified after printing with different nozzles, compression molding, and injection molding.Item Effect of Architecture and Porosity on Mechanical Properties of Borate Glass Scaffolds Made by Selective Laser Sintering(University of Texas at Austin, 2013) Kolan, Krishna C.R.; Leu, Ming C.; Hilmas, Gregory E.; Comte, TaylorThe porosity and architecture of bone scaffolds, intended for use in bone repair or replacement, are two of the most important parameters in the field of bone tissue engineering. The two parameters not only affect the mechanical properties of the scaffolds but also aid in determining the amount of bone regeneration after implantation. Scaffolds with five different architectures and four porosity levels were fabricated using borate bioactive glass (13–93B3) using the selective laser sintering (SLS) process. The pore size of the scaffolds varied from 400 to 1300 µm. The compressive strength of the scaffolds varied from 1.7 to 15.5 MPa for porosities ranging from 60 to 30%, respectively, for the different architectures. Scaffolds were soaked in a simulated body fluid (SBF) for one week to measure the variation in mechanical properties. The formation of the Hydroxyapatite and in-vitro results are provided and discussed.Item Effect of Heat Treatment and Hot Isostatic Pressing on the Morphology and Size of Pores in Additive Manufactured Ti-6Al-4V Parts(University of Texas at Austin, 2017) Zhang, Bin; Ham, Kyungmin; Shao, Shuai; Shamsaei, Nima; Thompson, Scott M.Additive manufactured parts suffer from porosity, among other defects. The slit-shaped pores due to lack of fusion are the most detrimental to fatigue and mechanical properties. Their sharp edges generate severe stress concentration and serve as preferred sites for crack initiation. The sharp edges also have low formation energy of surface adatoms, increasing their tendency to spheroidize under elevated temperatures, such as during heat treatment (HT). In hot isostatic pressing (HIP), the combined action of high temperature/pressure also reduces the size of the pores. In this work, HT and HIP were performed on Ti-6Al-4V parts manufactured from laser-based powder bed fusion to investigate the effect of HT and HIP on morphology/size of pores. Using scanning electron microscopy combined with X-ray computed tomography, special attention is paid to the evolution of the shape of the pore1s under controlled exposures to elevated temperature during HT. The results will be used, in our subsequent work, to validate a phase field porosity evolution model based on density functional theory.Item Effect of pore structure on capillary condensation in a porous medium(2009-02) Deinert, M. R.; Parlange, J. Y.; Deinert, M. R.; Deinert, M. R.The Kelvin equation relates the equilibrium vapor pressure of a fluid to the curvature of the fluid-vapor interface and predicts that vapor condensation will occur in pores or irregularities that are sufficiently small. Past analyses of capillary condensation in porous systems with fractal structure have related the phenomenon to the fractal dimension of the pore volume distribution. Recent work, however, suggests that porous systems can exhibit distinct fractal dimensions that are characteristic of both their pore volume and the surfaces of the pores themselves. We show that both fractal dimensions have an effect on the thermodynamics that governs capillary condensation and that previous analyses can be obtained as limiting cases of a more general formulation.Item Effect of Porosity on Electrical Insulation and Heat Dissipation of Fused Deposition Modeling Parts Containing Embedded Wires(University of Texas at Austin, 2018) Billah, Kazi Md Masum; Coronel, Jose Luis Jr; Wicker, Ryan B.; Espalin, DavidWhile the effects of porosity on the mechanical strength of fused deposition modeling (FDM) parts have been thoroughly investigated, there exists a need for evaluating electrical and thermal properties. This work describes the method of determining the effect of porosity that resembles 3D printed electronics. In addition to mechanical strength, determination of desirable limit of electrical insulation and heat dissipation will allow the additive manufacturing community to fabricate power electronics components with reduced cost and improved performance. For experimentation, three different sets of coupons were fabricated using Polycarbonate (PC) thermoplastic with embedded bare copper wire. Characterization included high electrical stresses and thermal testing to determine the effect of porosity on insulation and heat dissipation, respectively. During electrical characterization, higher wire density resulted in reduced breakdown strength. In thermal test, the comparisons between as fabricated and heat-treated specimen showed that heat dissipation increased by an average of 30 % to 40 %.Item Effect of Post-Processing on the Microstructure and Mechanical Properties of Ultra-Low Carbon Steel Fabricated by Selective Laser Melting(University of Texas at Austin, 2015) Almangour, B.; Yang, J.M.In this study, the effects of heat treatments and hot-isotactic pressing (HIP) on the microstructure and mechanical properties of ultra-low carbon steel produced using selective laser melting (SLM) were investigated. Powder and prototypes characterizations including XRD phase analysis, microstructural observations, and hardness were performed. It was found that heat treatments at 1000 ºC and HIP process improved inter-particle bonding very slightly. Significant increases in the grain size were observed for the annealed specimens at 600ºC and above as well as after HIP due to recrystallization and further grain growth, which coincide with the drop in hardness.Item Effect of Preheating Build Platform on Microstructure and Mechanical Properties of Additively Manufactured 316L Stainless Steel(University of Texas at Austin, 2019) Nezhadfar, P.D.; Soltani-Tehrani, Arash; Shamsaei, NimaThis study aims to understand the effect of build platform preheating on the microstructural features and mechanical properties of 316L stainless steel (SS) fabricated via laser beam powder bed fusion (LB-PBF) process. Two sets of specimens were fabricated on a non-preheated build platform and the build platform preheated to 150 °C. Thermal simulations are carried out using ANSYS using additive manufacturing module to investigate the variation in thermal history experienced by the specimens in each condition. Microstructural features are analyzed via simulation, and the results are validated experimentally. In addition, the effect of preheating on the porosity size and distribution is evaluated using digital optical microscopy. Mechanical properties of specimens from each condition are further assessed and correlated to the variations in microstructure and defect size distributions.Item Effect of Scanning Methods in the Selective Laser Melting of 316L/TiC Nanocomposites(University of Texas at Austin, 2016) AlMangour, B.; Grzesiak, D.; Yang, J.M.Selective laser melting (SLM) is a promising additive manufacturing process that allows for the fabrication of complex functional components by the selective layer-by-layer melting of particles on a powder bed using a high-energy laser beam. In this study, the SLM process was used to fabricate components of TiC/ 316L stainless steel nanocomposite using various laser scanning methods. The results showed that the laser-scanning method used for the SLM process affects the degree of densification, microstructure, and the hardness of the components produced. We believe that the alternative fabrication route presented in this study should significantly increase the use of nanocomposites.Item The effects of powder feedstock and process parameters on the material characteristics of Ti6Al4V thin strut features fabricated by laser powder bed fusion additive manufacturing(2022) Koju, Naresh; Hermes, Jonah; Paul, Sumit; Saghaian, Sayed Ehsan; Yang, LiIn this work, three different types of Ti6Al4V powder feedstock of different particle size ranges (fine, medium, and coarse) were utilized to fabricate thin strut lightweight features using laser powder bed fusion additive manufacturing (L-PBF-AM) using different process parameter settings. Thin strut features of varying dimensions from 0.1mm to 0.5mm were fabricated. The resulting sample sets allow for the analysis of the compound powder feedstock-process- geometry-material (PPG-M) characteristics for lightweight features fabricated by L-PBF-AM, which have not been previously explored. Various material characteristics were experimentally determined and analyzed, including success rate, geometry quality, porosity, pore size, grain size, and mechanical properties of the lightweight thin strut samples. The results clearly demonstrated the significance of the compound PPG-M relationships for lightweight structures, which calls for further studies to “re-establish” the knowledge base for L-PBF-AM materials at small dimension scales.Item A Hierarchical, Heterogeneous Material CAD Model with Application to Laser Sintering(University of Texas at Austin, 2010) Rosen, David W.; Jeong, Namin; Wang, YanVariations in laser irradiance and local temperatures in laser sintering cause variations in porosity and material microstructure, which can affect mechanical properties of a part. From the design perspective, it is important to model microstructures, mechanical properties, and their relationships so that parts can be analyzed and designed taking into account their as-manufactured condition. In this paper, we propose the modeling of part geometry and microstructure by using a new hierarchical modeling method. A surfacelet transform is introduced to model microstructure. The application of image processing methods enables multi-resolution representations of microstructure. Combined with methods from computational materials design, low resolution microstructure representations can be used to compute effective mechanical properties. The models and methods are demonstrated on two examples, a simple fiber-reinforced composite and a laser sintered nylon-12 material.Item Hydraulic conductivity measurement of permeable friction course (PFC) experiencing two-dimensional nonlinear flow effects(Center for Research in Water Resources, University of Texas at Austin, 2010-05) Klenzendorf, Joshua Brandon; Charbeneau, Randall J.; Barrett, Michael E.Item In-Situ TiC Particle Reinforced 316L Stainless Steel Matrix Nanocomposites: Powder Preparation by Mechanical Alloying and Selective Laser Melting Behavior(University of Texas at Austin, 2016) AlMangour, B.; Grzesiak, D.; Yang, J.M.Item Increasing Process Speed in the Laser Melting Process of Ti6Al4V and the Reduction of Pores During Hot Isostatic Pressing(University of Texas at Austin, 2017) Ahlers, D.; Koppa, P.; Hengsbach, F.; Gloetter, P.; Altmann, A.; Schaper, M.; Tröster, T.Additive manufacturing of titanium alloys has gained intensive attraction from industry and academia. Moreover, for additively fabricated parts consisting of Ti6Al4V, hot isostatic pressing (HIP), is widely used as a post treatment in order to increase the relative density of the built parts. However, one aspect which has rarely been addressed so far, is the increase of process speed, accompanied by a reduced relative density in the as-built condition and a subsequent hot isostatic pressing process to achieve the desired dense material. The approach here is to use the standard process route as described, but intentionally increase the process speed and accept a certain value of porosity. The focal objective of this study is the identification of a parameter-set with the highest potential for an increase of process speed and subsequently reduce the internal defects during the hot isostatic pressing process to achieve completely dense components.Item Individual and Coupled Contributions of Laser Power and Scanning Speed Towards Process-Induced Porosity in Selective Laser Melting(University of Texas at Austin, 2018) Shrestha, Subin; Starr, Thomas; Chou, KevinPorosity is an undesirable characteristic of selective laser melting (SLM) process and keyhole pores are formed when the energy density is very high which leads to deep penetration melting. In this study, single-track SLM experiments using Ti-6Al-4V powder were designed and conducted with combination of varied levels of the laser power and the scanning speed, intended to obtain the same energy density. Three energy densities: 0.32 J/mm, 0.4 J/mm and 0.48 J/mm were selected to investigate the influence of laser power versus scanning speed on porosity. Pore numbers and volumes was analyzed using micro-scale computed tomography. The results indicated that the pore formation is affected more by the change in the power than the scanning speed while keeping the energy density constant. As the power increased from around 20 W to 140 W, total pore volume increased, whereas pore volume decreased when power increased from 140 W to 195W.Item Influences of Energy Density on Porosity and Microstructure of Selective Laser Melted 17- 4PH Stainless Steel(University of Texas at Austin, 2013) Gu, Hengfeng; Gong, Haijun; Pal, Deepankar; Rafi, Khalid; Starr, Thomas; Stucker, BrentEnergy density, which directly impacts the properties of as-built parts, is a key factor in the metal selective laser melting (SLM) process. This paper studies the influences of energy density on porosity and microstructure of SLM 17-4PH stainless steel parts. Experiments were carried out by varying processing parameters to change energy density. Porosity was estimated using the Archimedes method and image analysis. Microstructures were investigated through optical and electron microscopy. The experimental results were discussed regarding porosity formation and microstructure characterization.Item Investigating the Build Consistency of a Laser Powder Bed Fused Nickel-Based Superalloy, Using the Small Punch Technique(University of Texas at Austin, 2019) Haigh, B.; Lancaster, R.J.; Johnston, R.; White, M.; Minshull, J.Inconel 718 (IN718) is a nickel-based superalloy that possesses impressive corrosion resistance and high strength properties at elevated temperatures, making it an ideal choice for aerospace applications. However, with the continuous evolution of the jet engine, there is a strong desire to fabricate more intricate components with less stress-raising features to enable higher engine efficiencies to be achieved. To overcome this issue, aerospace engineers are looking at Additive Manufacturing (AM) as a potential solution. A limitation of AM is the transient nature of the microstructure, and it is difficult to produce representative laboratory scale mechanical test specimens that closely replicate the microstructure of the finished component. Therefore, it can be beneficial to utilise small-scale test methods, such as the Small Punch (SP) test, which can obtain mechanical property information from miniaturised specimens extracted directly from the finished part. In this paper, the small punch test technique has been adopted to characterise and evaluate the mechanical response of laser powder bed fused (LPBF) Inconel 718. Results showed a high consistency across builds and certain orientations exhibited superior properties.Item Microstructural Sensitive Fatigue Modeling of Additively Manufactured Ti-6Al-4V(University of Texas at Austin, 2015) Sterling, Amanda J.; Torries, Brian; Shamsaei, Nima; Thompson, Scott M.; Daniewicz, Steven R.A common issue in powder-based Additive Manufacturing (AM) techniques is porosity. While process parameters can be controlled to limit this occurrence, complete elimination without post-processing is difficult. Because porosity can significantly affect fatigue behavior of AM parts, it is important to understand and model this material trait. In this study, the porosity in various Ti-6Al-4V specimens fabricated via Laser Engineered Net Shaping (LENS) was determined prior to fatigue testing. Void distribution and morphology was quantified. Fractography was performed to determine the specimen’s transition through crack initiation and propagation stages. These results were used to calibrate a microstructure-sensitive fatigue model for predicting the fatigue behavior of as-built and heat treated LENS Ti-6Al-4V.Item Numerical and Experimental Study on the Effect of Artificial Porosity in a Lattice Structure Manufactured by Laser Based Powder Bed Fusion(University of Texas at Austin, 2018) du Plessis, Anton; Yadroitsava, Ina; Kouprianoff, Dean; Yadroitsev, IgorAdditively manufactured lattice structures are used in various applications due to their unique properties, especially low weight with relatively good strength and stiffness. While lattices have been investigated widely, the effect of manufacturing flaws on the lattice performance was not yet analyzed in detail. One important type of manufacturing flaw which can be relatively easily analyzed numerically and experimentally is unwanted voids or porosity. In this work, using a simple cubic lattice structure as a test case, pores with varying sizes were induced in a single strut and compressive loading simulated. Ti6Al4V ELI (extra low interstitial) lattices produced by laser powder bed fusion, with and without induced pores, were subjected to mechanical compression tests. MicroCT images validated the presence and size of the induced voids in produced samples. The mechanical compression results show that even relatively large pores in individual loadbearing struts do not affect the ultimate compressive strength of these lattices, for these particular lattice shapes studied and for individual large pores.