Indentation hardness of 3D-printed metals

In this research, laser powder bed fusion (LPBF) technology was utilized to fabricate FeCoCrNiMn high-entropy alloys (HEAs). An integrated approach combining simulation and experimental research was employed to investigate the influence of process parameters on the columnar-to-equiaxed transition (CET) within the molten pool during the LPBF process. Initially, a finite element model was developed to simulate the multi-layer LPBF printing process. This study delved into the effects of various printing parameters, namely laser power, scanning speed, and hatch spacing, on the solidification parameters. Experimental characterization was conducted to provide specific solidification model parameters, thereby validating the accuracy and reasonability of the simulation model. The research systematically and quantitatively constructed a solidification map, which correlates LPBF printing parameters with temperature gradient and solidification rate. This map unveiled a potential relationship between the LPBF solidification parameters and the microstructural morphology of the HEAs. Ultimately, mechanical property tests were performed, confirming that adjustments to the parameters could facilitate the CET to a certain extent, leading to an effective enhancement in the microhardness of the HEAs produced using LPBF technology. This study systematically investigated the LPBF printing of HEA, fine-tuned process parameters to control microstructure, and studied the effects on printed parts. This provides a valuable foundation for optimizing LPBF printing HEAs.

A method to find the optimum process parameters for manufacturing nickel-based superalloy Inconel 738LC by laser powder bed fusion (LPBF) technology is presented. This material is known to form cracks during its processing by LPBF technology; thus, process parameters have to be optimized to get a high quality product. In this work, the objective of the optimization was to obtain samples with fewer pores and cracks. A design of experiments (DoE) technique was implemented to define the reduced set of samples. Each sample was manufactured by LPBF with a specific combination of laser power, laser scan speed, hatch distance and scan strategy parameters. Using the porosity and crack density results obtained from the DoE samples, quadratic models were fitted, which allowed identifying the optimal working point by applying the response surface method (RSM). Finally, five samples with the predicted optimal processing parameters were fabricated. The examination of these samples showed that it was possible to manufacture IN738LC samples free of cracks and with a porosity percentage below 0.1%. Therefore, it was demonstrated that RSM is suitable for obtaining optimum process parameters for IN738LC alloy manufacturing by LPBF technology.

Utilization of additive manufacturing, particularly Laser Powder Bed Fusion (L-PBF), has garnered considerable interest in recent times owing to its capacity to produce intricate geometries and functional components possessing enhanced mechanical characteristics. This review provides a thorough examination of the sustainability and environmental implications associated with the production of as-built Ti-6Al-4V parts using Laser Powder Bed Fusion (L-PBF) technology in additive manufacturing. This study aims to assess the sustainability dimensions of Laser Powder Bed Fusion technology, specifically in relation to material efficiency, energy usage, and waste production. Furthermore, this study evaluates the environmental ramifications associated with L-PBF Ti-6Al-4V components across their entire life cycle, encompassing activities such as extraction of raw materials, processing, utilization, and end-of-life management. This review critically examines the existing body of knowledge pertaining to the sustainability and environmental implications associated with as-built L-PBF Ti-6Al-4V components. The objective of this study is to determine the primary factors that impact sustainability, offer a comprehensive understanding of the environmental consequences associated with L-PBF technology, and delineate the existing constraints, difficulties, and prospects for future investigations in the domain of sustainable additive manufacturing.

Recent progress on the additive manufacturing of aluminum alloys and aluminum matrix composites: Microstructure, properties, and applications

Additive manufacturing (AM) enables fully dense biomimetic implants in the designed geometries from preferred materials such as titanium and its alloys. Titanium aluminum vanadium (Ti6Al4V) is one of the pioneer metal alloys for bone implant applications, however, the reasons for eliminating the toxic effects of Ti6Al4V and maintaining adequate mechanical strength have increased the potential of commercially pure titanium (cp-Ti) to be used in bone implants. This literature review aims to evaluate the production of cp-Ti and Ti6Al4V biomedical implants with laser powder bed fusion (L-PBF) technology, which has a very high level of technological matureness and industrialization level. The optimization of L-PBF manufacturing parameters and post-processing techniques affect the obtained microstructure leading to various mechanical, corrosion and biological behaviors of the manufactured titanium. All of the features are considered in the light of specifications and needs of bone implant applications. The most critical disadvantages of the L-PBF technology, such as residual stresses and leading deformations are introduced and the potential solutions are discussed. Moreover, the manufacturability of porous bone implants that causes benefit and harm in L-PBF applications are assessed.

Lattice structures in additive manufacturing of 316L stainless steel have gained increasing attention due to their well-suited mechanical properties and lightweight characteristics. Infill structures such as honeycomb, lattice, and gyroid have shown promise in achieving desirable mechanical properties for various applications. However, the design process of these structures is complex and time-consuming. In this study, we propose a machine learning-based approach to optimize the design of honeycomb, lattice, and gyroid infill structures in 316L stainless steel fabricated using laser powder bed fusion (L-PBF) technology under different loading conditions. A dataset of simulated lattice structures with varying geometries, wall thickness, distance, and angle using a computational model that simulates the mechanical behavior of infill structures under different loading conditions was generated. The dataset was then used to train a machine learning model to predict the mechanical properties of infill structures based on their design parameters. Using the trained machine learning model, we then performed a design exploration to identify the optimal infill structure geometry for a given set of mechanical requirements and loading conditions. Finally, we fabricated the optimized infill structures using L-PBF technology and conducted a series of mechanical tests to validate their performance under different loading conditions. Overall, our study demonstrates the potential of machine learning-based approaches for efficient and effective designing of honeycomb, lattice, and gyroid infill structures in 316L stainless steel fabricated using L-PBF technology under different loading conditions. Furthermore, this approach can be used for dynamic loading studies of infill structures.

Experimental investigation on shear strength of laser powder bed fusion AlSi10Mg under quasi-static and dynamic loads

Nondestructive investigation on close and open porosity of additively manufactured parts using an X-ray computed tomography

Low performance is considered one of the main drawbacks of laser powder bed fusion (LPBF) technology. In the present work, the effect of the AlSi10Mg powder layer thickness on the laser melting process was investigated to improve the LPBF building rate. A high-fidelity simulation of the melt pool formation was performed for different thicknesses of the powder bed using the Kintech Simulation Software for Additive Manufacturing (KiSSAM, version cd8e01d) developed by the authors. The powder bed after the recoating operation was obtained by the discrete element method. The laser energy deposition on the powder particles and the substrate was simulated by ray tracing. For the validation of the model, an experimental analysis of single tracks was performed on two types of substrates. The first substrate was manufactured directly with LPBF technology, while the second was cast. The simulation was carried out for various combinations of process parameters, predominantly with a high energy input, which provided a sufficient remelting depth. The calculations revealed the unstable keyhole mode appearance associated with the low absorptivity of the aluminum alloy at a scanning speed of 300 mm/s for all levels of the laser power (325–375 W). The results allowed formulating the criteria for the lack of fusion emerging during LPBF with an increased layer thickness. This work is expected to provide a scientific basis for the analysis of the maximum layer thickness via simulation to increase the performance of the technology.

Additive manufacturing technology has emerged over the past decade as one of the best solutions for building prototypes and components with complex geometries and reduced thicknesses. Its application has rapidly spread to various industries, such as motorsport, automotive, aerospace, and biomedical. In particular, titanium alloy Ti-6Al-4V, due to its exceptional mechanical properties, low density, and excellent corrosion resistance, turns out to be one of the most popular for the production of parts with additive manufacturing technology across all the market segments listed above. However, when producing components using Laser Powder Bed Fusion (LPBF) technology, it is always necessary to perform appropriate heat treatments whose main purpose is to reduce the residual stresses typically generated during the manufacturing process. Post-process heat treatments on Ti6Al4V components obtained by way of additive technology have been extensively studied in the literature, with the aim of identifying optimal thermal cycles, which may allow for the effective reduction of residual stresses combined with proper microstructural conditions. However, despite the usual target of maximizing relevant mechanical properties, it is mandatory for industrial production to achieve a robust process, i.e., minimizing the sensitivity to noise-induced variation. Therefore, the aim of the present work is to compare several post-process heat treatment strategies by performing different thermal cycles in the temperature range of 750–955 °C and investigating how these affect the average mechanical properties and their variance. The treated samples are then analyzed running a complete mechanical and microstructural characterization, and the latter particularly focused on the determination of the typical microstructure present in the treated samples by using the XRD technique.

ABSTRACTHardness and elastic modulus can be derived from instrumented sharp indentation curves by considering the effects of materials pile-up and sink-in and tip blunting. In particular, this study quantifies pile-up or sink-in effects in determining contact area based on indentation-curve analysis. Two approaches, finite-element simulation and theoretical modeling, were used to describe the detailed contact morphologies. The ratio of contact depth to maximum indentation depth was proposed as a key indentation parameter and was found to be a material constant independent of indentation load. In addition, this parameter can be determined strictly in terms of indentation-curve parameters, such as loading and unloading slopes at maximum depth and indentation energy ratio. This curve-analysis method was verified by finite-element simulations and nanoindentation experiments.

High strain-rate response of additively manufactured light metal alloys

Influence of heat treatments on low-power-LPBFed CuCrZr for nuclear fusion applications

Metal additive manufacturing (AM) promises functional flexibility in the production of engineering components, and great progress has been made with respect to part geometry and overall performance criteria. The fracture and fatigue behaviors of metals depend on the sample microstructure, an aspect of metal AM for which many challenges remain. Here, we report on progress with respect to the rolling contact fatigue (RCF) performance of metal AM bearing rollers. A set of rollers was created using laser powder bed fusion from 8620HC steel powder. The print parameters were first studied with respect to laser power, laser scan speed, laser spot size, and layer thickness. A set of tapered cylindrical rollers was then manufactured using build parameters that were selected based on material density, optical microscopy, ultrasound, and residual stress measurements. The rollers were then heat-treated while still on the build plate to relieve any residual stresses. The rollers were removed from the build plate, machined to the typical product geometry, case-hardened, carburized, and ground to a final surface finish. Finally, the rollers were integrated within railroad tapered roller bearings and tested in two ways. The accelerated life test subjected the rollers to high-stress RCF that generated significant spalling on both types of rollers. The simulated service life test was designed with RCF at levels typical of in-service bearings. At the conclusion of this test, equivalent to 250,000 miles, the performance of the AM rollers was judged to be in line with rollers manufactured using traditional methods, and visual inspections showed no surface damage to any rollers. The results of this study provide a clear foundation for additional AM roller designs that can exploit the unique capabilities of the AM process.

Additive manufacturing offers a wide range of possibilities for the design and optimization of lightweight and application-tailored structures. The great design freedom of the Laser Powder Bed Fusion (LPBF) manufacturing process enables new design and production concepts for heat pipes and their internal wick structures, using various metallic materials. This allows an increase in heat pipe performance and a direct integration into complex load-bearing structures. An important influencing factor on the heat pipe performance is the internal wick structures. The complex and filigree geometry of such structures is challenging in regards to providing high manufacturing quality at a small scale and varying orientations during the printing process. In this work, new wick concepts have been developed, where the design was either determined by the geometrical parameters, the process parameters, or their combination. The wick samples were additively manufactured with LPBF technology using the lightweight aluminum alloy Scalmalloy®. The influence of the process parameters, geometrical design, and printing direction was investigated by optical microscopy, and the characteristic wick performance parameters were determined by porosimetry and rate-of-rise measurements. They showed promising results for various novel wick concepts and indicated that additive manufacturing could be a powerful manufacturing method to further increase the performance and flexibility of heat pipes.