Search

This research explores how variations in laser powder bed fusion (LPBF) parameters—laser power (P), scanning speed (v), and base plate preheating temperature (ϑp)—affect the mechanical properties of the EOS Co-Cr SP2 dental alloy. A central composite design (CCD) was used to optimize the process parameters. Mechanical testing focused on crucial properties for dental applications, including yield strength (Rp0.2), elongation (ε), toughness (KVa), and flexural strength (Rms). Microstructural analysis was conducted using light and electron microscopy, while XRD identified microstructural phases. Statistical analysis (ANOVA, Scheffé post hoc test, α = 0.05) revealed significant effects of P, v, and ϑp on the mechanical properties. Response surface models (RSMs) were developed, and optimal parameters were determined to achieve maximum toughness and flexural strength. Maximum values were obtained with laser power above 205 W and base plate preheating at 310 °C. The mathematical model predicted toughness values with less than 5% deviation from experimental results, indicating high accuracy. [ABSTRACT FROM AUTHOR]

For the improvement of surface roughness, titanium joint arthroplasty (TJA) components are grit-blasted with Al2O3 (corundum) particles during manufacturing. There is an acute concern, particularly with uncemented implants, about polymeric, metallic, and corundum debris generation and accumulation in TJA, and its association with osteolysis and implant loosening. The surface morphology, chemistry, phase analysis, and surface chemistry of retrieved and new Al2O3 grit-blasted titanium alloy were determined with scanning electron microscopy (SEM), X-ray energy-dispersive spectroscopy (EDS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and confocal laser fluorescence microscopy, respectively. Peri-prosthetic soft tissue was studied with histopathology. Blasted retrieved and new stems were exposed to human mesenchymal stromal stem cells (BMSCs) for 7 days to test biocompatibility and cytotoxicity. We found metallic particles in the peri-prosthetic soft tissue. Ti6Al7Nb with the residual Al2O3 particles exhibited a low cytotoxic effect while polished titanium and ceramic disks exhibited no cytotoxic effect. None of the tested materials caused cell death or even a zone of inhibition. Our results indicate a possible biological effect of the blasting debris; however, we found no significant toxicity with these materials. Further studies on the optimal size and properties of the blasting particles are indicated for minimizing their adverse biological effects. [ABSTRACT FROM AUTHOR]

PBF-LB/M is a metal additive manufacturing process that enables the production of complex-shaped products with very low porosity and excellent mechanical properties. However, different laser beam shapes and varying energy inputs during the LPBF process affect the solidification rate and microstructure development. We investigated and compared the microstructures using samples made with the standard Gaussian laser beam and two laser beams in the shape of a Donut. It was found that changing the laser beam shape and volume energy input increases the grain size and texture. However, the cellular dendritic structure remains very similar, as does the fraction of the Laves phase. The samples were heat-treated at different temperatures, and we tracked the microstructure development, which revealed that carbides begin to form at specific temperatures. These carbides can be undesirable for mechanical properties due to their notch effect. At higher laser energy inputs, somewhat larger segregations may occur, which can influence carbide precipitation. [ABSTRACT FROM AUTHOR]

Nickel Alloy IN718 belongs to the nickel-based superalloys, which have excellent corrosion resistance and mechanical properties at elevated temperatures. This is due to the specific microstructure, consisting of an austenitic gamma matrix with a large number of 0' and 0" precipitates, which impede dislocation movement and thus stabilise the microstructure even at high temperatures. As part of the Horizon Europe InShaPe project, we compared microstructures using PBF-LB/M, producing samples with a standard Gaussian laser beam and modified laser beam shapes such as Donut, C-shape, Chair, etc. It was found that the microstructure of the printed samples has a cellular dendritic structure, which, in addition to the austenitic matrix, contains Laves phase at the boundaries of the nanodendrites. This phase is undesirable and is eliminated by heat treatment. However, we were interested in the quantitative analysis of the Laves phase, which is quite challenging. Conventional image analysis, based on phase segmentation by grayscale, is not feasible. Therefore, we used artificial intelligence and neural networks to train a program for phase determination. The development of the program is still in progress. [ABSTRACT FROM AUTHOR]

Products made with additive manufacturing technologies do not reach the market mainly because of the long production time and, consequently, high cost. Within the Horizon Europe InShaPe project, we are exploring the possibility of increasing production speed and productivity by changing the shape of the laser. The modified laser shape contributes to faster product building, which may result in larger crystal grains and stronger texture. The IN718 nickel alloy is always heat-treated before use, which involves annealing to dissolve the Laves phase and other segregations, followed by a two-stage ageing process to precipitate / and y'' in the microstructure. However, the final microstructure can significantly depend on the initial microstructure before heat treatment. Not all segregations are removed if the heat treatment temperature is too low, and the Laves phase may remain. On the other hand, an excessively high heat treatment temperature can lead to significant grain growth. Another major issue is the formation of carbides during annealing. Therefore, conducting the heat treatment process just below the recrystallisation temperature is crucial to avoid the precipitation of undesirable carbides. Since different laser beam shapes and energy inputs were used for sample production, the heat treatment temperature had to be adjusted to achieve optimal mechanical properties. [ABSTRACT FROM AUTHOR]

This research aims to optimize the process parameters and material composition to enhance the Laser Powder Bed Fusion (LPBF) processability of EN AW 7075. The high-strength aluminium alloy EN AW 7075 poses significant challenges due to the alloy's susceptibility to hot cracking and porosity. Experimental investigations were conducted to explore the influence of varying laser power, scan speed, and preheating temperatures on the microstructure and mechanical properties of the alloy. Initial results revealed that conventional SLM parameters resulted in significant microstructural defects, including hot cracks and high levels of porosity. Preheating, intended to reduce thermal gradients and mitigate these defects, showed limited effectiveness. To address these challenges, a novel approach involving the modification of the alloy's chemical composition by adding silicon was employed. This modification aimed to reduce the solidification range and enhance the material's resistance to cracking. Silicon addition was found to refine the microstructure and promote the formation of a more uniform grain structure, which is less prone to hot cracking. Comprehensive microstructural analysis using Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM), along with mechanical testing, confirmed the enhanced processability and mechanical properties of the modified alloy. The analyses revealed that the modified alloy exhibited a finer and more homogenous microstructure, with significantly reduced porosity and crack density. Mechanical testing showed improvements in both tensile strength and ductility, indicating that the modified alloy could better withstand the thermal stresses associated with the LPBF process. These findings provide critical insights into the optimization of processing for high-performance aluminium alloys, highlighting the importance of alloy composition in achieving desirable microstructural and mechanical properties. The research outcomes suggest that by carefully adjusting the chemical composition and optimizing process parameters, it is possible to overcome the inherent challenges associated with LPBF of EN AW 7075. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) of metals is growing ever more commonplace. Industries such as Aeronautics and medicine have already embraced it as a method of producing parts with difficult geometries. Now, the technology is spreading to other applications such as tools and die-making. The benefits of AM to these industries are twofold: it opens the door for more complex tool design with integrated cooling channels that conform to the shape of the die while also reducing the waste material produced in the manufacturing process, as the unspent powder can easily be reused. Of the various AM methods, laser powder bed fusion (LPBF) is the best suited for this application, as it has some of the highest productivity among all the AM methods, along with high printing accuracy. One of the most frequently used materials in tool and die manufacturing is AISI H13. It's a chromium, vanadium, and molybdenum-based hot work tool steel with good hardness at elevated temperatures, softening, and wear resistance. Its excellent properties at elevated temperatures, along with good price performance, make H13 a prime candidate for LPBF. However, AM production of H13 is relatively difficult, as the high cooling rate and martensitic transformation induce a lot of retained stress in the printed parts. These stresses have a negative impact on the produced parts, as they can deform them or induce cracking. An effective way of managing such stresses is to produce the parts with base plate preheating. With the fusion process occurring on a surface that is already at an elevated temperature, the cooling rate and, subsequently, the solidification rate are reduced. This causes less solidification stress to be retained. The elevated temperature also has a mild stress-relieving effect, as the build parts tend to be exposed to it for longer periods of time. The parts produced using LPBF must meet or surpass the specific properties of conventionally produced tools. While the enhanced control over geometry and reduction of waste material are significant advantages of the LPBF production method, the hardness, toughness, thermal conductivity, and tool lifespan must exceed those of traditionally produced parts to justify the higher initial cost and lower production rate. In this study, our goal is to demonstrate that Laser Powder Bed Fusion (LPBF) is a feasible method for creating tools that can match or exceed tools manufactured using traditional methods. We produced H13 samples with and without preheating, analyzed their microstructure, and tested their mechanical and physical properties. We also compared these samples with reference samples produced using conventional methods to assess their performance. [ABSTRACT FROM AUTHOR]

Austenitic stainless steels are promising materials for next generation nuclear reactors due to their excellent mechanical properties and reasonable corrosion resistance compared to ferritic and ferritic-martensitic steels. However, they suffer from lower strength and void swelling resistance. Oxide dispersion strengthening (ODS) addresses these issues by incorporating nano-sized oxides, which pin dislocation motion and prevent grain coarsening, thus enhancing mechanical strength and creep resistance at high temperatures. Additionally, the matrix-oxide interfaces act as sinks for radiation-induced defects, improving swelling resistance. In this study the preparation of oxide dispersion-strengthened austenitic steel 316L involved mechanical alloying of the steel powder with Y2O3. Elemental Y was also introduced to dissolve within the Fe matrix as an alternative method. These powder precursors were then compacted using Spark Plasma Sintering (SPS) and analysed for their microstructure. The mechanical properties of the resulting compacts were assessed, revealing an initial formation of chromium-containing carbides, likely due to carbon diffusion from the graphite tools used. Both Y2O3 and Y were successfully incorporated into a solid solution during mechanical alloying, with precipitation occurring during compaction. The mechanical properties varied based on chemical composition and specific SPS conditions. Homogeneously distributed Y2O3 particles were successfully achieved through this powder metallurgy process. Future research will aim to optimize SPS conditions to prevent carbide formation. [ABSTRACT FROM AUTHOR]