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Paul A Hoope - One of the best experts on this subject based on the ideXlab platform.
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cyclic plasticity and fatigue damage of crmnfeconi high entropy alloy fabricated by laser Powder Bed Fusion
Additive manufacturing, 2020Co-Authors: A. Piglione, Paul A Hoope, Ogda Dovgyy, E Hosseini, S R Holdsworth, Minhso PhamAbstract:Abstract In-depth understanding of cyclic plasticity and fatigue damage is crucial for structural application of CrMnFeCoNi which is found to be highly printable. This study provides insights into the link between print processes, solidification microstructure, cyclic plasticity and fatigue damage evolution in the alloy fabricated by laser Powder Bed Fusion. Thermodynamics-based predictions and experimental validation showed that Cr, Co and Fe partition to the core of the solidification cells, whilst Mn and Ni to the cell boundaries in all considered print parameters. Both dislocation slip and deformation twinning were found to be responsible for plastic deformation under monotonic loading. However, the former was found to be the single dominant mechanism for cyclic plasticity. The surface finish helped to substantially delay the crack initiation and cause lack-of-Fusion porosity to be the main source of crack initiation. Most significantly, the scan strategies significantly affect grain arrangements and grain dimensions, leading to noticeable effects on fatigue crack propagation; in particular, the highest resistance crack propagation was seen in the meander scan strategy with 0° rotation thanks to the most columnar grains and the smallest spacing of grain boundaries along the crack propagation path.
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cyclic plasticity and fatigue damage of crmnfeconi high entropy alloy fabricated by laser Powder Bed Fusion
arXiv: Applied Physics, 2020Co-Authors: A. Piglione, Paul A Hoope, Ogda Dovgyy, E Hosseini, S R Holdsworth, Minhso PhamAbstract:The CrMnFeCoNi high-entropy alloy is highly printable and holds great potential for structural applications. However, no significant discussions on cyclic plasticity and fatigue damage in previous studies. This study provides significant insights into the link between print processes, solidification microstructure, cyclic plasticity and fatigue damage evolution in the alloy fabricated by laser Powder Bed Fusion. Thermodynamics-based predictions (validated by scanning transmission electron microscopy (STEM) energy dispersive X-ray spectroscopy (EDX)) showed that Cr, Co and Fe partition to the core of the solidification cells, whilst Mn and Ni to the cell boundaries in all considered print parameters. Both dislocation slip and deformation twinning were found to be responsible for plastic deformation under monotonic loading. However, the former was found to be the single dominant mechanism for cyclic plasticity. The surface finish helped to substantially delay the crack initiation and cause lack-of-Fusion porosity to be the main source of crack initiation. Most significantly, the scan strategies significantly affect grain arrangements and grain dimensions, leading to noticeable effects on fatigue crack propagation; in particular, the highest resistance crack propagation was seen in the meander scan strategy with 0° rotation thanks to the most columnar grains and the smallest spacing of grain boundaries along the crack propagation path.
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revealing relationships between porosity microstructure and mechanical properties of laser Powder Bed Fusion 316l stainless steel through heat treatment
Materials & Design, 2020Co-Authors: Tobias Ronneberg, C M Davies, Paul A HoopeAbstract:Abstract The understanding of relationships between processing, microstructure and mechanical properties in laser Powder Bed Fusion is currently incomplete. Microstructure-property relations in 316L stainless steel are revealed in this study using isothermal heat treatments as an investigative tool. As-built material was heat treated to selectively remove microstructural features such as melt pool boundaries, microsegregations and the as-built grain structure to evaluate their influence on yield and failure behaviour. Anisotropic yield behaviour was found to be caused by microstructural features alone and not influenced by porosity. However, ductility and failure were dominated by lack of Fusion porosity. The alignment of pores between tracks along layer boundaries was found to cause anisotropic ductility. Three strengthening mechanisms in as-built material were identified as grain boundaries, chemical segregation and dislocation density. Heat treatments were categorised into three regimes: recovery, homogenisation and annealing. The findings of this study show that the shape, size, orientation and distribution of pores are crucial parameters for evaluating the structural integrity of parts produced by laser Powder Bed Fusion.
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the role of side branching in microstructure development in laser Powder Bed Fusion
Nature Communications, 2020Co-Authors: Minhso Pham, Paul A Hoope, Christopher M. Gourlay, Ogda Dovgyy, A. PiglioneAbstract:In-depth understanding of microstructure development is required to fabricate high quality products by additive manufacturing (for example, 3D printing). Here we report the governing role of side-branching in the microstructure development of alloys by laser Powder Bed Fusion. We show that perturbations on the sides of cells (or dendrites) facilitate crystals to change growth direction by side-branching along orthogonal directions in response to changes in local heat flux. While the continuous epitaxial growth is responsible for slender columnar grains confined to the centreline of melt pools, side-branching frequently happening on the sides of melt pools enables crystals to follow drastic changes in thermal gradient across adjacent melt pools, resulting in substantial broadening of grains. The variation of scan pattern can interrupt the vertical columnar microstructure, but promotes both in-layer and out-of-layer side-branching, in particular resulting in the helical growth of microstructure in a chessboard strategy with 67° rotation between layers.
Panagiotis Michaleris - One of the best experts on this subject based on the ideXlab platform.
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model based feedforward control of laser Powder Bed Fusion additive manufacturing
Additive manufacturing, 2020Co-Authors: Qia Wang, Panagiotis Michaleris, Abdalla R Nassa, Jeffrey E Irwi, Christophe StutzmaAbstract:Abstract Control of laser power to improve part quality is critical for fabrication of complex components via Laser Powder Bed Fusion (LPBF) additive manufacturing (AM) processes. If the laser power is too low, it will result in a small melt pool and lack of Fusion; on the other hand, if the laser power is too high, it will result in keyhole and material evaporation. This paper examines a model-based feed-forward control for laser power in LPBF to improve build quality by avoiding the onset of keyhole formation or reducing over-melting. First, an analytical, control-oriented model on the dynamics of melt-pool cross-sectional area in scanning a multi-track part was developed, and then a nonlinear inverse-dynamics controller was designed to adjust laser power such that the melt-pool cross-sectional area can be regulated to a constant set point during the build process. The resulting control trajectory on laser power from the simulated closed-loop controller was then implemented in a LPBF process as a feed-forward (FF) controller for laser power. Multiple bead-on-plate samples of Inconel 625, with different number of tracks and track lengths, were then built on an EOSINT M 280 AM system to evaluate the performance of the resulting FF-Analytic controller. Experimental results demonstrated that the proposed FF-Analytic control of laser power was able to avoid the onset of keyhole formation that occurred under a constant laser power for certain samples. Furthermore, the proposed FF-Analytic control was demonstrated to have significantly reduced over-melting at the returning ends of the laser scan path in scanning a multi-track part compared to applying a constant laser power, albeit with some over-compensation due to modeling imperfection. Overall, the proposed FF-Analytic control of laser power had 23–40% lower average error rate than applying a constant laser power in regulating the melt-pool cross-sectional area to a constant reference value, in terms of measurements of cross-sections at track ends.
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Comparisons of laser Powder Bed Fusion additive manufacturing builds through experimental in situ distortion and temperature measurements
Additive Manufacturing, 2017Co-Authors: Alexander Jay Dunbar, Erik R Denlinger, Michael F. Gouge, Timothy W Simpson, Panagiotis MichalerisAbstract:In situ experimental measurements of the laser Powder Bed Fusion build process are completed with the goal gaining insight into the evolution of distortion in the Powder Bed Fusion build process. Utilizing a novel enclosed instrumented system, five experimental builds are performed. Experimental builds compare materials: Ti–6Al–4V and Inconel®718, differing build geometries, and manufacturing machines: EOS M280 and Renishaw AM250. A combination of in situ measurements of distortion and temperature and post-build measurements of final part geometry are used to compare and contrast the different experiments. Experimental results show that builds completed using Inconel®718 distort between 50% and 80% more relative to Ti–6Al–4V depending on substrate size and build geometry. The experimental build completed on the Renishaw AM250 distorted 10.6% more in the Z direction when compared with the identical build completed on the EOS M280 machine. Comparisons of post-build XY cross-sectional area show a 0.3% contraction from the predefined build geometry for the Renishaw AM250 as compared with the 4.5% contraction for the part built using the EOS M280. Recommendations and future work are also discussed.
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Experimental validation of finite element modeling for laser Powder Bed Fusion deformation
Additive Manufacturing, 2016Co-Authors: Alexander Jay Dunbar, Erik R Denlinger, Michael F. Gouge, Panagiotis MichalerisAbstract:Experimental measurements are a critical component of model development, as they are needed to validate the accuracy of the model predictions. Currently, there is a deficiency in the availability of experimental data for laser Powder Bed Fusion made parts. Here, two experimental builds of cylindrical geometry, one using a rotating scan pattern and the other using a constant scan pattern, are designed to provide post-build distortion measurements. Measurements are made using a coordinate-measuring machine which provides distortion profiles along the height of the part at four separate locations. Measurements show that for these cylindrical thin wall builds, there is no discernable effect on distortion from using the rotating versus constant scan patterns. Project Pan finite element modeling software is used to model each of the experimental builds. The simulation results show good agreement with experimental measurements of post-build deformation, within a 12% percent error as compared to experimental measurements. Using the FE model, the effect of a flexible versus a rigid substrate on distortion profile is examined. The FE model is validated against in situ experimental measurements of substrate distortion. The simulated results are used to study stress and distortion evolution during the build process. Internal stresses calculated by the model throughout the part are used in explaining the final part distortion. The combination of experimental and simulation results from this study show that the distortion of the top layer is relatively small (less than 30%) throughout the duration of the build process compared to the peak distortion, which occurs several layers below the most recently deposited layer. For these geometries once the part is built to a sufficient height, the peak distortion magnitude does not change.
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Thermal modeling of Inconel 718 processed with Powder Bed Fusion and experimental validation using in situ measurements
Additive Manufacturing, 2016Co-Authors: Erik R Denlinger, Vijay Jagdale, Tahany El-wardany, G. V. Srinivasan, Panagiotis MichalerisAbstract:A model for predicting the thermal response of Inconel® 718 during laser Powder-Bed Fusion processing (LPBF) is developed. The approach includes the pre-placed Powder layer in the analysis by initially assigning Powder properties to the top layer of elements before restoring the solid properties as the heat source traverses the layer. Different linear heat inputs are examined by varying both laser power and scan speed. The effectiveness of the model is demonstrated by comparing the predicted temperatures to in situ experimental thermocouple data gathered during LPBF processing. The simulated temperatures accurately capture the measured peak temperatures (within 11% error) and temperature trends. The effect of neglecting the pre-placed Powder layer in the simulations is also investigated demonstrating that conduction into the Powder material should be accounted for in LPBF analyses. The simulation neglecting the Powder predicts temperatures more than 30% higher than the simulation including the Powder.
Shawn P. Moylan - One of the best experts on this subject based on the ideXlab platform.
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a review on measurement science needs for real time control of additive manufacturing metal Powder Bed Fusion processes
International Journal of Production Research, 2017Co-Authors: Mahesh Mani, Alkan Donmez, Brandon M. Lane, Shaw C. Feng, Shawn P. MoylanAbstract:Additive manufacturing technologies are increasingly used in the development of new products. However, variations in part quality in terms of material properties, dimensional tolerances, surface roughness and defects limit its broader acceptance. Process control today based on heuristics and experimental data yields limited improvement in part quality. In an effort to identify the needed measurement science for real-time closed-loop control of additive manufacturing (AM) processes, this paper presents a literature review on the current AM control schemes, process measurements and modelling and simulation methods as it applies to the Powder Bed Fusion process, though results from other processes are reviewed where applicable. We present our research findings to identify the correlations between process parameters, process signatures and product quality. We also present research recommendations on the key control issues to serve as a technical basis for standards development in this area. Complimentary deta...
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Predictive modeling and optimization of multi-track processing for laser Powder Bed Fusion of nickel alloy 625
Additive Manufacturing, 2017Co-Authors: Luis E. Criales, Tuǧrul Özel, Brandon Lane, Shawn P. Moylan, Alkan Donmez, Yiǧit M. Arisoy, Tugrul OzelAbstract:This paper presents an integrated physics-based and statistical modeling approach to predict temperature field and meltpool geometry in multi-track processing of laser Powder Bed Fusion (L-PBF) of nickel 625 alloy. Multi-track laser processing of Powder material using L-PBF process has been studied using 2-D finite element simulations to calculate temperature fields along the scan and hatch directions for three consecutive tracks for a moving laser heat source to understand the heating and melting process. Based on the predicted temperature fields, width, depth and shape of the meltpool is determined. Designed experiments on L-PBF of nickel alloy 625 Powder material are conducted to measure the relative density and meltpool geometry. Experimental work is reported on the measured density of built coupons and meltpool size. Statistically-based predictive models using response surface regression for relative density, meltpool geometry, peak temperature, and time above melting point are developed and multi-objective optimization studies are conducted by using genetic algorithm and swarm intelligence.
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Effect of Process Parameters on the Surface Roughness of Overhanging Structures in Laser Powder Bed Fusion Additive Manufacturing
Procedia CIRP, 2016Co-Authors: Jason C. Fox, Shawn P. Moylan, Brandon M. LaneAbstract:The development of additive manufacturing has allowed for increased flexibility and complexity of designs over formative and subtractive manufacturing. However, a limiting factor of additive manufacturing is the as-built surface quality as well as the difficulty in maintaining an acceptable surface roughness in overhanging structures. In order to optimize surface roughness in these structures, samples covering a range of overhang angles and process parameters were built in a laser Powder Bed Fusion system. Analysis of the surface roughness was then performed to determine a relationship between process parameters, angle of the overhanging surface, and surface roughness. It was found that the analysis of surface roughness metrics, such as Rpc, Rsm, and Rc, can indicate a shift between surfaces dominated by partially melted Powder particles and surfaces dominated by material from the re-solidified melt track.
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Measurement of Powder Bed density in Powder Bed Fusion additive manufacturing processes
Measurement Science and Technology, 2016Co-Authors: Gregor Jacob, Alkan Donmez, John A. Slotwinski, Shawn P. MoylanAbstract:Many factors influence the performance of additive manufacturing (AM) processes, resulting in a high degree of variation in process outcomes. Therefore, quantifying these factors and their correlations to process outcomes are important challenges to overcome to enable widespread adoption of emerging AM technologies. In the Powder Bed Fusion AM process, the density of the Powder layers in the Powder Bed is a key influencing factor. This paper introduces a method to determine the Powder Bed density (PBD) during the Powder Bed Fusion (PBF) process. A complete uncertainty analysis associated with the measurement method was also descriBed. The resulting expanded measurement uncertainty, U PBD ( k = 2), was determined as 0.004 g · cm −3 . It was shown that this expanded measurement uncertainty is about three orders of magnitude smaller than the typical Powder Bed density. This method enables establishing correlations between the changes in PBD and the direction of motion of the Powder recoating arm.
Hua Li - One of the best experts on this subject based on the ideXlab platform.
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Predictive models for fatigue property of laser Powder Bed Fusion stainless steel 316L
Materials and Design, 2018Co-Authors: Meng Zhang, David Hardacre, Xiang Zhang, Hua LiAbstract:The selection of appropriate processing parameters is crucial for producing parts with target properties via the laser Powder Bed Fusion (L-PBF) process. In this work, the fatigue properties of L-PBF stainless steel 316L under controlled changes in laser power and scan speed were studied by employing the statistical response surface method. Processing regions corresponding to different fatigue failure mechanisms were identified. The optimum fatigue properties are associated with crack initiation from microstructure defect, which, by acting as the weakest link, creates enhanced porosity-tolerance at applied stress approaching the fatigue limit. Deviations from the optimum processing condition lead to strength degradation and porosity-driven cracking. Based on the observed relations between microstructural features and failure behaviour, a processing-independent fatigue prediction model was proposed. The microstructure-driven failure was modelled by a reference S-N curve where the intrinsic effect of microstructure inhomogeneity was accounted for by applying a reduction factor on fatigue life. For the porosity-driven failure, high cycle fatigue life follows an inverse-square-root relation with porosity fraction. This relation was incorporated into the Basquin equation for predicting the fatigue strength parameters.
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Fatigue and fracture behaviour of laser Powder Bed Fusion stainless steel 316L: Influence of processing parameters
Materials Science and Engineering A, 2017Co-Authors: Meng Zhang, Phoi Chin Goh, David Hardacre, Xiang Zhang, Hua LiAbstract:The laser Powder Bed Fusion (L-PBF) process involves a large number of processing parameters. Extending the intricate relationship between processing and structure to mechanical performance is essential for structural L-PBF materials. The high cycle fatigue properties of L-PBF parts are very sensitive to process-induced porosities which promote premature failure through the crack initiation mechanisms. Results from this work show that for stainless steel 316 L, porosity does not impinge on the high cycle fatigue properties when processing is kept within a ±30% tolerance band. In this ‘optimum’ processing region, crack initiation takes place due to defects at the solidification microstructure level. Beyond the ‘optimum’ processing region, over-melting and under-melting can lead to porosity-driven cracking and inferior fatigue resistance. In addition, regardless of the processing condition, fatigue resistance was found to follow a direct linear relationship with ductility and tensile strength in the low and high stress fatigue regimes respectively.
Richard Leach - One of the best experts on this subject based on the ideXlab platform.
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surface topography investigations on nickel alloy 625 fabricated via laser Powder Bed Fusion
The International Journal of Advanced Manufacturing Technology, 2018Co-Authors: Tugrul Ozel, Ayca Altay, Alka Donmez, Richard LeachAbstract:Laser Powder Bed Fusion as an additive manufacturing process produces complex surface topography at multiple scales through rapid heating, melting, directional cooling, and solidification that are often governed by laser path and layer-to-layer scanning strategies and influenced by process parameters such as power, scan velocity, hatch distance, and resultant energy density. Investigations on manufactured surfaces, as-built and after applying electropolishing, are performed using stylus profilometry, digital optical microscopy, and scanning electron microscopy techniques to reveal the complex surface texture of the nickel alloy 625 test cubes that are produced by following an experimental design. Surface texture is further explored using image processing together with machine learning-based algorithms. Measurement uncertainty is also discussed briefly. The results reveal a complex nature of laser Powder Bed Fusion created surface topography and textures as exposed with electropolishing that may further lead to a quantitative understanding of such textures and their formations influenced by different scanning strategies and process parameters.
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Feature-based characterisation of signature topography in laser Powder Bed Fusion of metals
Measurement Science and Technology, 2018Co-Authors: Nicola Senin, Adam Thompson, Richard LeachAbstract:The use of state-of-the-art areal topography measurement instrumentation allows for a high level of detail in the acquisition of topographic information at micrometric scales. The three-dimensional geometric models of surface topography obtained from measured data create new opportunities for the investigation of manufacturing processes through characterisation of the surfaces of manufactured parts. Conventional methods for quantitative assessment of topography usually only involve the computation of texture parameters; summary indicators of topography-related characteristics that are computed over the investigated area. However, further useful information may be obtained through characterisation of signature topographic formations, as more direct indicators of manufacturing process behaviour and performance. In this work, laser Powder Bed Fusion of metals is considered. An original algorithmic method is proposed to isolate relevant topographic formations and to quantify their dimensional and geometric properties, using areal topography data acquired by state-of-the-art areal topography measurement instrumentation.
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Internal surface measurement of metal Powder Bed Fusion parts
Additive Manufacturing, 2018Co-Authors: Adam Thompson, Nicola Senin, Lars Körner, Ian Maskery, Simon Lawes, Richard LeachAbstract:Recent advances in X-ray computed tomography (XCT) have allowed for measurement resolutions approaching the point where XCT can be used for measuring surface topography. These advances make XCT appealing for measuring hard-to-reach or internal surfaces, such as those often present in additively manufactured parts. To demonstrate the feasibility and potential of XCT for topography measurement, topography datasets obtained using two XCT systems are compared to those acquired using coherence scanning interferometry and focus variation microscopy. A hollow Ti6Al4V part produced by laser Powder Bed Fusion is used as a measurement artefact. The artefact comprises two component halves that can be separated to expose the internal surfaces. Measured surface datasets are accurately aligned and similarly cropped, and compared by various qualitative and quantitative means, including the computation of ISO 25178-2 areal surface texture parameters, commonly used in part quality assessment. Results show that XCT can non-destructively provide surface information comparable with more conventional surface measurement technologies, thus representing a viable alternative to more conventional measurement, particularly appealing for hard-to-reach and internal surfaces.