Browsing by Subject "defects"
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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 Pre-Repair Machining Strategies for Laser-Aided Metallic Component Remanufacturing(University of Texas at Austin, 2018) Zhang, Xinchang; Cui, Wenyuan; Hill, Leon; Li, Wei; Liou, FrankRemanufacturing worn metallic components can prolong the service life of parts that need frequent replacement but are extremely costly to manufacture, such as aircraft titanium components, casting dies. Additive manufacturing (AM) technology enables the repair of such valuable components by depositing filler materials at the worn area layer by layer to regenerate the missing geometry. In general, damaged parts would be inspected and pre-machined prior to material deposition to remove oil, residue, oxidized layers or defects located in inaccessible regions. Therefore, the motivation of this paper is to introduce pre-repair machining strategies for removing contaminated materials from damaged components and materials surrounding inaccessible defects to ensure that the target damage is repairable. The current research targets at common failures comprising surface indentations, erosion, corrosion, wear and cracking, and the machining strategies for each defect were proposed. Each strategy takes the 3D scanned damaged model as input and the cut-off volume around the defects is defined by using different approaches. Pre-repair machining toolpath and program were generated based on the defined cut-off volume and finally, damaged parts were machined using the proposed strategies.Item Discussion On Device Structures And Hermetic Encapsulation For SiOx Random Access Memory Operation In Air(2014-10) Zhou, Fei; Chang, Yao-Feng; Wang, Yanzhen; Chen, Yen-Ting; Xue, Fei; Fowler, Burt W.; Lee, Jack C.; Zhou, Fei; Chang, Yao-Feng; Wang, Yanzhen; Chen, Yen-Ting; Xue, Fei; Lee, Jack C.An edge-free structure and hermetic encapsulation technique are presented that enable SiOx-based resistive random-access memory (RRAM) operation in air. A controlled etch study indicates that the switching filament is close to the SiOx surface in devices with an exposed SiOx edge. Electrical test of encapsulated, edge-free devices in 1 atmosphere air indicates stable switching characteristics, unlike devices with an edge. This work demonstrates that SiOx RRAM is able to operate in air with proper encapsulation and an edge-free structure. The resistive switching failure mechanism when operating in air is explained by the oxidation of hydrogen-complexed defects in the switching filament. (C) 2014 AIP Publishing LLC.Item Effects of Spatial Energy Distribution on Defects and Fracture of LPBF 316L Stainless Steel(University of Texas at Austin, 2019) Jost, Elliott; Miers, John; Robinson, Aron; Moore, David; Saldana, ChristopherMeasures of energy input and spatial energy distribution during laser powder bed fusion additive manufacturing have significant implications for the build quality of parts, specifically relating to formation of internal defects during processing. In this study, scanning electron microscopy was leveraged to investigate the effects of these distributions on the mechanical performance of parts manufactured using laser powder bed fusion as seen through the fracture surfaces resulting from uniaxial tensile testing. Variation in spatial energy density is shown to manifest in differences in defect morphology and mechanical properties. Computed tomography and scanning electron microscopy inspections revealed significant evidence of porosity acting as failure mechanisms in printed parts. These results establish an improved understanding of the effects of spatial energy distributions in laser powder bed fusion on mechanical performance.Item Fatigue Life Prediction of Additively Manufactured Metallic Materials Using a Fracture Mechanics Approach(University of Texas at Austin, 2018) Torries, Brian; Shrestha, Rakish; Imandoust, Aidin; Shamsaei, NimaThe present study aims to model the fatigue strength of additively manufactured metallic materials employing a fracture mechanics approach. Specimens with different build orientations were subjected to strain controlled fatigue testing. Upon failure, the defect(s) responsible for crack initiation were identified by fractographic analysis. From these defects an equivalent internal defect size is calculated using the √𝑎r𝑒𝑎 method based on Murakami model. Using this parameter, the elastic-plastic energy release rate (𝛥𝐽𝐽𝑒𝑓𝑓) was determined, and the relationship between 𝛥𝐽𝑒𝑓𝑓 and fatigue life was investigated. The results showed that this method improves the predictability of the fatigue strength of additively manufactured materials when the defects size and location is known. The 𝛥𝐽𝑒𝑓𝑓 − 𝑁𝑓 relationship appeared to better fit the fatigue data of the experimental materials as compared to the 𝜀𝑎 − 𝑁𝑓 relationship and contributed to a reduction in data scatter.Item Formation, Nature, And Stability Of The Arsenic-Silicon-Oxygen Alloy For Plasma Doping Of Non-Planar Silicon Structures(2014-12) Ventzek, Peter L. G.; Kweon, Kyoung E.; Ueda, Hirokazu; Oka, Masahiro; Sugimoto, Yasuhiro; Hwang, Gyeong S.; Kweon, Kyoung E.; Hwang, Gyeong S.We demonstrate stable arsenic-silicon-oxide film formation during plasma doping of arsenic into non-planar silicon surfaces through investigation of the nature and stability of the ternary oxide using first principles calculations with experimental validations. It is found that arsenic can be co-mingled with silicon and oxygen, while the ternary oxide exhibits the minimum energy phase at x approximate to 0.3 in AsxSi1-xO2-0.5x. Our calculations also predict that the arsenic-silicon-oxide alloy may undergo separation into As-O, Si-rich As-Si-O, and Si-O phases depending on the composition ratio, consistent with experimental observations. This work highlights the importance of the solid-state chemistry for controlled plasma doping. (C) 2014 AIP Publishing LLC.Item Frequency Inspection of Additively Manufactured Parts for Layer Defect Identification(University of Texas at Austin, 2019) Allen, Aimee; Johnson, Kevin; Blough, Jason; Barnard, Andrew; Hartwig, Troy; Brown, Ben; Soine, David; Cullom, Tristan; Bristow, Douglas; Landers, Robert; Kinzel, EdwardAdditive manufactured (AM) parts are produced at low volume or with complex geometries. Identifying internal defects is difficult as current testing techniques are not optimized for AM processes. The goal of this paper is to evaluate defects on multiple parts printed on the same build plate. The technique used was resonant frequency testing with the results verified through Finite Element Analysis. From these tests, it was found that the natural frequencies needed to detect the defects were higher than the excitation provided by a modal hammer. The deficiencies in this range led to the development of other excitation methods. Based on these results, traditional methods of resonant part inspection are not sufficient, but special methods can be developed for specific cases.Item Luminescent CulnSe2-Based Core/Shell Nanocrystals: Characterizing Defects in CulnSe2 Nanocrystals(2015-05) Sher, Soa-Jin; Korgel, Brian A.As interest continues to grow in new materials for next-generation photovoltaic (PV) devices (i.e. solar cells), it is important to understand the mechanisms and limitations of promising materials. Many researchers are focused on the use of semiconductor nanocrystals (NCs) in PV devices because of their potential to be deposited in thin films via solution, which is more cost-effective than traditional methods. This study focuses on CuInSe2 (CISe) NCs, which are part of a larger class of materials known as CuInxGa1-xSe2 (CIGS). CIGS is well-known in the PV industry, especially for its use on flexible substrate materials, which have significant cost and processing advantages over traditional, bulky, glass-based solar cells. However, defects within or on the surface of the CIGS NCs limit the movement of holes and electrons, affecting the ability of the NCs to extract charge carriers; these defects ultimately result in lower-efficiency PV devices. The purpose of this study is to better understand the defects within CISe NCs by coating them with ZnS shells. A Zn-based shell was successfully formed around a CISe NC without compromising the integrity of the CISe NC. The shell also successfully passivated the surface defects and increased the efficiency of the CISe NCs. By creating luminescent CISe-based core/shell NCs, this study examines the nature of CISe NC defects and the implications of these defects on the future of CISe in the PV industry.Item Towards Defect Detection in Metal SLM Parts Using Modal Analysis "Fingerprinting"(University of Texas at Austin, 2017) Urban, James; Capps, Nick; West, Brian; Hartwig, Troy; Brown, Ben; Landers, Robert; Bristow, Douglas; Kinzel, EdwardThe validation of Additively Manufactured (AM) materials is a difficult and expensive process because the local engineering properties are a function of the thermal history. The thermal history varies with the process parameters, as well as the part geometry. This paper presents a case study using modal testing to identify defects in realistic AM parts. A setup consisting of a Scanning Laser Doppler Vibrometer (LDV) was used to identify the resonant frequencies for several geometrically identical parts on a build plate. Parts with suboptimal process parameters from purposely varying the process parameters, are identified by a shift in the mode peak frequency. Results from this study are compared to Finite Element Analysis (FEM) models and generalized for identifying defects in parts created with AM on the basis vibration/modal “fingerprinting.”Item Understanding Sources of Defects in Polyimide Films Using Aerosol Based Printing(University of Texas at Austin, 2016) Lavin, J.M.; Keicher, D.M.; Whetten, S.R.; Moore, P.B.; Mani, S.S.A study of the sources of defects in films of commercially available polyamic acid fabricated using aerosol based printing was carried out. Printing was conducted using a Sono-Tek spray nozzle on multi-modular Direct Write Additive Manufacturing System. The driving force behind this work stemmed from the need to form smooth, defect free films to be used in electronic components. While numerous process conditions give rise to defects such as the obvious substrate cleanliness, efforts here focused on the more subtle conditions such as deposition temperature, deposition speed, nozzle height from the substrate and cure temperature. The results of this study led to the identification of the most critical source of defects and to a set of optimal process conditions in the printing of polyimide films using aerosol based printing.Item Unsupervised Defect Classification of 2D SEM and 3D X-Ray CT Images from Laser Powder Bed Fusion(University of Texas at Austin, 2021) Lang, Andrew; Ortiz Rios, Cesar; Newkirk, Joseph; Landers, Robert G.; Castle, James; Bristow, Douglas A.This work discusses a method to classify defects in laser powder bed fusion using 2D images of layer samples taken by Scanning Electron Microscope (SEM) and 3D image stacks of a full part by X-Ray Computed Tomography (XCT). Images using SEM are taken of a sampled layer in a printed part and unsupervised classification of defects in the SEM images is performed with Otsu’s thresholding method, K-means classification, and the Robust Automatic Threshold Selection algorithm. The performance of the classifiers, measured against human-generated ground truth defect labels, is improved by registering and fusing multiple SEM images taken under different settings and detector locations. Otsu’s method is shown to be the best classifier for the 3D XCT dataset. Finally, the 2D sample is located in the 3D XCT array and the reliability of the 3D defect classification technique is validated.Item Use of SWIR Imaging to Monitor Layer-to-Layer Part Quality During SLM of 304L Stainless Steel(University of Texas at Austin, 2018) Lough, Cody S.; Wang, Xin; Smith, Christopher C.; Adeniji, Olaseni; Landers, Robert G.; Bristow, Douglas A.; Kinzel, Edward C.This paper evaluates using in-situ SWIR imaging to monitor part quality and identify potential defect locations introduced during Selective Laser Melting (SLM) of 304L stainless steel. The microstructure (porosity, grain size, and phase field) and engineering properties (density, modulus, and yield strength) depend on the thermal history during SLM manufacturing. Tensile test specimens have been built with a Renishaw AM250 using varied processing conditions to generate different thermal histories. SWIR imaging data is processed layer-to-layer to extract features in the thermal history for each process condition. The features in the thermal history are correlated with resulting part engineering properties, microstructure, and defects. The use of SWIR imaging is then discussed as a potential for processes monitoring to ensure part quality and develop layer-to-layer control in SLM.Item Volume Effects on the Fatigue Behavior of Additively Manufactured Ti-6Al-4V Parts(University of Texas at Austin, 2018) Pegues, Jonathan; Roach, Michael; Williamson, R. Scott; Shamsaei, NimaRecent interest to implement additive manufactured parts into structural applications has created a critical need to better understand the fatigue behavior of these parts. Alloys such as Ti-6Al-4V are popular in the aerospace and biomedical industries due to their superior strength to weight ratio and biocompatibility. In these two industries, part sizes can range from very small surgical implants to large structural components, all of which are subjected to cyclic loading conditions. The fatigue behavior of additively manufactured parts may show more sensitivity to part size than their wrought counterparts due to the defects that are inherent to the fabrication process. This research investigates the sensitivity of additively manufactured Ti-6Al-4V parts to volume size by comparing the stress-life fatigue curves of three geometries with increasing gage volumes. Results indicate that additive Ti-6Al-4V parts show reduced fatigue lives because of an increase in surface or near-surface defects.