Corrigendum: Additive manufacturing of Al2O3 ceramics with MgO/SiC contents by laser powder bed fusion process.

[This corrects the article DOI: 10.3389/fchem.2023.1034473.].

Additive manufacturing of Al2O3 ceramics with MgO/SiC contents by laser powder bed fusion process.

Laser powder bed fusion is a laser-based additive manufacturing technique that uses a high-energy laser beam to interact directly with powder feedstock. LPBF of oxide ceramics is highly desirable for aerospace, biomedical and high-tech industries. However, the LPBF of ceramics remains a challenging area to address. In this work, a new slurry-based approach for LPBF of ceramic was studied, which has some significant advantages compared to indirect selective laser sintering of ceramic powders. LPBF of Al2O3 was fabricated at different MgO loads up to 80 wt%. Several specimens on different laser powers (70 W-120 W) were printed. The addition of magnesia influenced the microstructure of the alumina ceramic significantly. The findings show that when the laser power is high and the magnesia load is low, the surface quality of the printing parts improves. It is feasible to produce slurry ceramic parts without binders through LPBF. Furthermore, the effects of SiC and MgO loads on the microstructure and surface morphology of alumina are compared and analysed.

Printability for additive manufacturing with machine learning: Hybrid intelligent Gaussian process surrogate-based neural network model for Co-Cr alloy.

AM has revolutionized the manufacturing industry, involving several operating parameters that may affect the properties of the final manufactured part. In AM, LPBF has proved its reliability in producing dense components; however, process development for every material necessitates extensive testing. Even the tiniest change can negate all the data for the same material. It is vital to have a P-P correlation that can train itself following a change in powder or machine to achieve defects-free parts and optimal properties. These goals cannot be met alone by multi-physics. One of the ways to address this issue is to apply ML, but it requires a huge data set for training and testing purposes. A framework has been developed for Co-Cr S-S curves to resolve this issue. Twenty-two experimental S-S curves have been generated to produce YS, TS, and EL data points. In combination with DNN, these data points have been applied to the validated and tested GPS-surrogate model to develop a smart processing window to achieve desired YS, TS, and EL. LP, LSS, HD, and PLT have been selected during the whole framework as inputs, while YS, TS, and EL have been classified as outputs. The output of the smart window was verified experimentally. It is found that the highest YS (1110.91 MPa) is attained using LP = 180 W, LSS = 600 mm/s and HD = 70 µm, while least YS (645.05 MPa) is identified using LP = 160 W, LSS = 900 mm/s and HD = 70 µm. For TS, the maximum (165.91 MPa) and minimum (689.73 MPa) values have been achieved using LP = 180 W, LSS = 900 mm/s and HD = 70 µm, and LP = 180 W, LSS = 1000 mm/s and HD = 70 µm, respectively. In the case of EL, LP = 180 W, LSS = 700 mm/s and HD = 70 µm, and LP = 180 W, LSS = 600 mm/s and HD = 70 µm, resulted 23.04% and 0.789% EL, respectively. Using CC, LP and HD did not significantly affect the TS, YS, and EL, while a negative relationship has been found for LSS with TS, YS, and EL. The smart processing window showed that the YS and TS could be achieved at low-high LP and low LSS at the cost of EL. This study provides a technique for framework development in the case of P-P relation based on the provided inputs and the corresponding outputs, leading toward process smartification.

Advances in Laser Additive Manufacturing of Cobalt-Chromium Alloy Multi-Layer Mesoscopic Analytical Modelling with Experimental Correlations: From Micro-Dendrite Grains to Bulk Objects.

This study presents two analytical models for the laser powder bed fusion (LPBF) process. To begin, the single layer's dimensions were measured using principal operating conditions, including laser power, laser scanning speed, powder layer thickness, and hatch distance. The single-layer printing dimensions were transformed into multi-layer printing using the hatch distance. The thermal history of the printed layers was used as an input to the Johnson-Mehl-Avrami-Kolmogorov model to estimate the average dendrite grain size. LPBF experiments were conducted for a Cobalt-chromium (Co-Cr) alloy to validate the developed model. The average dendrite grain size was estimated using a scanning electron microscope (SEM) combined with "Image J" software. The Vickers hardness test was performed to correlate the average dendrite grain size and operating conditions. A 10-15% mean absolute deviation was presented between experiments and simulation results. In all samples, a Co-based γ-FCC structure was identified. An inverse correlation was established between the laser power and smaller average dendrite grain, while a direct relationship has been determined between laser scanning speed and average dendrite grain size. A similar trend was identified between hatch distance and average dendrite grain size. A direct link has been determined between the average dendrite grain size and hardness value. Furthermore, a direct relationship has connected the laser volume energy density and hardness value. This study will help experimentalists to design operating conditions based on the required grain size and corresponding mechanical characteristics.

Influence of Silicon Carbide on Direct Powder Bed Selective Laser Process (Sintering/Melting) of Alumina.

The powder bed selective laser process (sintering/melting) has revolutionised many industries, including aerospace and biomedicine. However, PBSLP of ceramic remains a formidable challenge. Here, we present a unique slurry-based approach for fabricating high-strength ceramic components instead of traditional PBSLP. A special PBSLP platform capable of 1000 °C pre-heating was designed for this purpose. In this paper, PBSLP of Al2O3 was accomplished at different SiC loads up to 20 wt%. Several specimens on different laser powers (120 W to 225 W) were printed. When the SiC content was 10 wt% or more, the chemical interaction made it difficult to process. Severe melt pool disturbances led to poor sintering and melting. The structural analysis revealed that the micro-structure was significantly affected by the weight fraction of SiC. Interestingly, when the content was less than 2 wt%, it showed significant improvement in the microstructure during PBSLP and no effects of LPS or chemical interaction. Particularly, a crack pinning effect could be clearly seen at 0.5 wt%.

Laser Melting Deposition Additive Manufacturing of Ti6Al4V Biomedical Alloy: Mesoscopic In-Situ Flow Field Mapping via Computational Fluid Dynamics and Analytical Modelling with Empirical Testing.

Laser melting deposition (LMD) has recently gained attention from the industrial sectors due to producing near-net-shape parts and repairing worn-out components. However, LMD remained unexplored concerning the melt pool dynamics and fluid flow analysis. In this study, computational fluid dynamics (CFD) and analytical models have been developed. The concepts of the volume of fluid and discrete element modeling were used for computational fluid dynamics (CFD) simulations. Furthermore, a simplified mathematical model was devised for single-layer deposition with a laser beam attenuation ratio inherent to the LMD process. Both models were validated with the experimental results of Ti6Al4V alloy single track depositions on Ti6Al4V substrate. A close correlation has been found between experiments and modelling with a few deviations. In addition, a mechanism for tracking the melt flow and involved forces was devised. It was simulated that the LMD involves conduction-mode melt flow only due to the coaxial addition of powder particles. In front of the laser beam, the melt pool showed a clockwise vortex, while at the back of the laser spot location, it adopted an anti-clockwise vortex. During printing, a few partially melted particles tried to enter into the molten pool, causing splashing within the melt material. The melting regime, mushy area (solid + liquid mixture) and solidified region were determined after layer deposition. This research gives an in-depth insight into the melt flow dynamics in the context of LMD printing.

Keyhole Formation by Laser Drilling in Laser Powder Bed Fusion of Ti6Al4V Biomedical Alloy: Mesoscopic Computational Fluid Dynamics Simulation versus Mathematical Modelling Using Empirical Validation.

In the laser powder bed fusion (LPBF) process, the operating conditions are essential in determining laser-induced keyhole regimes based on the thermal distribution. These regimes, classified into shallow and deep keyholes, control the probability and defects formation intensity in the LPBF process. To study and control the keyhole in the LPBF process, mathematical and computational fluid dynamics (CFD) models are presented. For CFD, the volume of fluid method with the discrete element modeling technique was used, while a mathematical model was developed by including the laser beam absorption by the powder bed voids and surface. The dynamic melt pool behavior is explored in detail. Quantitative comparisons are made among experimental, CFD simulation and analytical computing results leading to a good correspondence. In LPBF, the temperature around the laser irradiation zone rises rapidly compared to the surroundings in the powder layer due to the high thermal resistance and the air between the powder particles, resulting in a slow travel of laser transverse heat waves. In LPBF, the keyhole can be classified into shallow and deep keyhole mode, controlled by the energy density. Increasing the energy density, the shallow keyhole mode transforms into the deep keyhole mode. The energy density in a deep keyhole is higher due to the multiple reflections and concentrations of secondary reflected beams within the keyhole, causing the material to vaporize quickly. Due to an elevated temperature distribution in deep keyhole mode, the probability of pores forming is much higher than in a shallow keyhole as the liquid material is close to the vaporization temperature. When the temperature increases rapidly, the material density drops quickly, thus, raising the fluid volume due to the specific heat and fusion latent heat. In return, this lowers the surface tension and affects the melt pool uniformity.

Laser Powder Bed Fusion (LPBF) of In718 and the Impact of Pre-Heating at 500 and 1000 °C: Operando Study.

The morphology of a melt pool has a critical role in laser powder bed fusion (LPBF). Nevertheless, directly characterizing the melt pool during LPBF is incredibly hard. Here, we present the melt pool flow of the entire melt pool in 3D using mesoscopic simulation models. The physical processes occurring within the melt pool are pinpointed. The flow patterns throughout the same are exposed and measured. Moreover, the impact of pre-heating at 500 and 1000 °C has been described. The study findings offer insights into LPBF. The findings presented here are critical for comprehending the LPBF and directing the establishment of improved metrics for process parameters optimization.

Full-Field Mapping and Flow Quantification of Melt Pool Dynamics in Laser Powder Bed Fusion of SS316L.

Laser powder bed fusion (LPBF) has a wide range of uses in high-tech industries, including the aerospace and biomedical fields. For LPBF, the flow of molten metal is crucial; until now, however, the flow in the melt pool has not been described thoroughly in 3D. Here, we provide full-field mapping and flow measurement of melt pool dynamics in laser powder bed fusion, through a high-fidelity numerical model using the finite volume method. The influence of Marangoni flow, evaporation, as well as recoil pressure have been included in the model. Single-track experiments were conducted for validation. The temperature profiles at different power and speed parameters were simulated, and results were compared with experimental temperature recordings. The flow dynamics in a single track were exposed. The numerical and experimental findings revealed that even in the same melting track, the melt pool's height and width can vary due to the strong Marangoni force. The model showed that the variation in density and volume for the same melting track was one of the critical reasons for defects. The acquired findings shed important light on laser additive manufacturing processes and pave the way for the development of robust, computational models with a high degree of reliability.

Enhanced bioconversion of dairy and chicken manure by the interaction of exogenous bacteria and black soldier fly larvae.

Generation of insects' biomass from lignocellulose rich organic wastes is of significant challenges in reducing the environmental impact of wastes and in sustaining feed and food security. This research looked at the effects of lignocellulotic exogenous bacteria in the black soldier fly (BSF) organic waste conversion system for biomass production and lignocellulose biodegradation of dairy and chicken manures. Six exogenous bacteria were investigated for cellulolytic activity with carboxymethyl cellulose and found that these tested bacterial strains degrade the cellulose. In this study; a co-conversion process using Hermetia illucens larvae to convert the previously studied best mixing ratio of dairy manure (DM) and chicken manure (CHM) (2:3) and cellulose degrading bacteria was established to enhance the larval biomass production, waste reduction and manure nutrient degradation. BSF larvae assisted by MRO2 (R5) has the best outcome measures: survival rate (99.1%), development time (19.0 d), manure reduction rate (48.7%), bioconversion rate (10.8%), food conversion ratio (4.5), efficiency of conversion of ingestion (22.3), cellulose (72.9%), hemicellulose (68.5%), lignin (32.8%), and nutrient utilization (protein, 71.2% and fat, 67.8%). By analyzing the fiber structural changes by scanning electron microscopy and Fourier-transformed infrared spectroscopy (FT-IR), we assume that exogenous bacteria assist the BSF larvae that trigger lead to structural and chemical modification of fibers. We hypothesized that these surface and textural changes are beneficial to the associated gut bacteria, thereby helping to larval growth and reduce waste. The finding of the investigation showed that enhanced conversion of DM and CHM by BSF larvae assisted with lignocellulotic exogenous bacteria could play key role in the manure management.

Successful retrieval of a Figulla Occlutech septal occluder - embolized device stability and potential solutions.

Go to: We report a case of an atrial septal defect where a Figulla Occlutech device embolized into the right ventricle. As this device has no left atrial hub, we brought the bare device into the inferior vena cava and used a novel two-snare technique to slenderize the device into the sheath. This report highlights additional tips in transcatheter device retrieval.

Covered stents in the management of native coarctation of the aorta--intermediate and long-term follow-up.

OBJECTIVES: To evaluate the results of covered Cheatham-Platinum stent implantation in the management of native coarctation of the aorta and report intermediate and long-term follow-up. BACKGROUND: Covered stents are being used increasingly in severe and complex coarctation of the aorta mainly to reduce risk of aortic wall complications. There is, however, limited data on the intermediate and long-term outcome. PATIENTS AND METHODS: Fifty-six patients received 59 covered Cheatham-Platinum stents (January 2002-December 2011) at a single center-in 54 patients as primary treatment and in 2 as a rescue. Mean age was 22.25 ± 1.2 (11-56) years and mean weight 58.6 ± 2.1 (32-99) kg. Primary end points were reduction in systolic pressure gradient and an increase in coarctation segment diameter. Changes in antihypertensive medicines and complications were recorded on follow-up. RESULTS: Mean coarctation segment diameter increased from 4.69 ± 0.20 to 15.1 ± 3.2 mm (P < 0.0001). The systolic gradient decreased from mean of 51.4 ± 3.4 to 4.6 ± 0.7 mm Hg (P < 0.0001). There was one death 3 days postprocedure due to cerebral anoxia. There was one dissection diagnosed 24-hr postprocedure. At a mean follow-up of 45.9 ± 3.9 (3-120) months, all stents were patent and in good position on computed tomography. Four (7.1%) patients underwent successful redilation. Antihypertensive medication was decreased or stopped in 37 (66%) patients. CONCLUSIONS: Covered Cheetham-Platinum stents may be used effectively as therapy of choice in selected patients with severe coarctation of the aorta. Aortic wall complications occur even with covered stents. Covered stents provide a safe alternative to conventional stenting in the intermediate and long-term and can be redilated safely to keep pace with somatic growth.

Analysis of infective endarteritis in patent ductus arteriosus.

This study reports on infective endarteritis in 14 children with patent ductus arteriosus over a period of 6 years. Infective endarteritis mostly involved the small ducts and was previously undiagnosed. These patients were given antibiotic treatment for a variable period of 4 to 10 weeks, and all except 1 underwent subsequent closure.