Laser-based Additive Manufacturing Research Articles

Investigation on Optical Absorption and Reflection of Carbon Nanotubes Mixed Copper Composites for Laser Sintering Process Improvement

Selective laser sintering (SLS) of copper components manufactured via powder metallurgy is widely studied due to minimal material wastage. However, copper has poor optical absorption when exposed to infrared (IR) lasers, such as in laser-based additive manufacturing or laser surface processing. To address this issue, an innovative approach to enhance the optical absorption of copper powders during infrared laser sintering is presented in this study. Carbon nanotubes (CNTs) have several unique properties, including their high surface area, plasmonic response, excellent conductivity, and optical absorption properties. CNTs were mixed with copper powders at different weight percentages using an acoustic method. The resulting Cu-CNT compositions were fabricated into pellets. The Box-Behnken Design of Experiments methodology was used to optimize the IR laser processing conditions for sintering. Spectroscopic analysis was conducted to evaluate the reflection and thermal absorption of the IR wavelengths by the Cu-CNT composites. Density and hardness measurements were taken for the laser-sintered Cu-CNT pellets. The coating of copper powders with CNTs demonstrated enhanced optical absorption and correspondingly reduced reflection. Due to the enhanced optical absorption, increased control and sensitivity of the laser sintering process was achieved, which enabled improvement in the mechanical properties of strength, hardness, and density, while also enabling control over the composite thermal expansion coefficient. A maximum average hardness of 66.5 HV was observed. Indentation test results of the samples revealed maximum tangential and radial stresses of 0.148 MPa and 0.058 Mpa, respectively.

Laser-Based Selective Material Processing for Next-Generation Additive Manufacturing.

The connection between laser-based material processing and additive manufacturing is quite deeply rooted. In fact, the spark that started the field of additive manufacturing is the idea that two intersecting laser beams can selectively solidify a vat of resin. Ever since, laser has been accompanying the field of additive manufacturing, with its repertoire expanded from processing only photopolymer resin to virtually any material, allowing liberating customizability. As a result, additive manufacturing is expected to take an even more prominent role in the global supply chain in years to come. Herein, an overview of laser-based selective material processing is presented from various aspects: the physics of laser-material interactions, the materials currently used in additive manufacturing processes, the system configurations that enable laser-based additive manufacturing, and various functional applications of next-generation additive manufacturing. Additionally, current challenges and prospects of laser-based additive manufacturing are discussed.

High-speed direct energy deposition as a high-throughput design tool for laser-based additive manufacturing

A wide range of additive manufacturing (AM) processing conditions can be rapidly realized within a single specimen via high-speed direct energy deposition laser based (DED-LB), due to a variety of cooling conditions and in-situ powder mixing. Since existing approaches are inefficient in exploring the vast material and process design space in AM, high-speed DED-LB can be employed as a novel technology for high-throughput alloy design tool. However, an evaluation of the process transferability of the high-speed DED-LB process with respect to the currently dominating metal AM technologies, namely laser powder bed fusion (PBF LB/M) and conventional DED-LB, is required. In this study, high-speed DED-LB is applied for the high-throughput sample production, using the nickel alloy IN718 as reference material as well as the AM processes PBF LB/M and DED-LB as reference processes. The resulting microstructures are characterized and compared using optical microscopy and large-area scanning electron microscopy (SEM) analysis combined with energy-dispersive X-ray spectroscopy (EDS). Furthermore, a model for calculation of the volumetric energy density is developed to compare the applied AM processes. The significant influence of the processing conditions on the solidification behavior of the investigated material allows for efficient exploration of the microstructure and phase composition. Specific high-speed DED-LB-process conditions achieved the average solidification cell size and laves phase content as observed in the PBF LB/M- and DED-LB -produced counterparts. The applicability of the high-speed DED-LB process for rapid alloy and process development, i.e., process transferability, is critically evaluated. The results show that high-speed DED-LB can be used to emulate cooling conditions of PBF-LB/M and DED-LB and, therefore, be used as tool for rapid alloy development.

Enhancing industry 5.0 goals through laser based additively Manufactured High-Performance Metals

In the current industry 4.0 (I4.0) and emerging Industry 5.0 (I5.0) eras, the integration of digitalization and sustainable goals is driving nature-centric and human-centric products. The production of these products are also creating digital supply chain that boosts agility and resiliency in operations, management, and supply chain interlinks. Additive manufacturing (AM), an element of I4.0, for instance, offers an integrated connection of all process steps and value chains using computer-based designing, data-driven simulations, cloud-based processing, storing, and managing software along seamless digital threads to create agile and resilient supply chain. The integration of AM and other I4.0 technologies enables greater flexibility offering intrinsic sustainable, human-centric and resilience advantages. Laser based additive manufacturing (LBAM), one of the subcategories of AM, offers opportunities to manufacture new intricate and conventionally impractical metal product designs in an ecological and economic competitive stance. High performance metals (HPMs) suited for high-stress and corrosive demanding applications are tough to machine and prone to thermal cracking in case of welding. Conventionally difficult and lengthy to manufacture yet unavoidable HPMs such as nickel alloys and titanium alloys are effortlessly possible via LBAM. Different industrial sectors that utilize these grades of metal alloys continue to adopt AM for the offered design flexibility for achieving goals such as customization, lightweight, on-demand manufacturing, raw material efficiency and cost saving. This study uses literature review and manufacturing case studies to demonstrate the flexibility and digital nature of LBAM towards I5.0 goals. The study objectively highlights the promising responsiveness of AM in the eventuality of supply disruptions that may be caused by sudden changes. The novelty of the study lies in the pragmatic emphasis on the potentials of LBAM and paired I4.0 technologies in revolutionizing the industry towards industry 5.0 goals. The study shows how I4.0 elements can be paired to enable operational efficiencies, lower carbon emissions, and foster sustainability in promoting I5.0 transformation. This study offers a fundamental understanding of the role of LBAM in the advancement of sustainability, human-centricity, and resilience.

Coaxial Wire Laser-based Additive Manufacturing of AA7075 with TiC Nanoparticles

AA7075 is a heat treatable aluminium alloy widely used in aerospace and automotive applications due to its outstanding high strength-to-weight ratio. However, the implementation of this alloy in Additive Manufacturing (AM) processes has been limited due to its susceptibility to hot cracking. Moreover, selective evaporation of low boiling point elements Zn and Mg can cause gas porosity and diminish the mechanical properties of AM parts. Recent research revealed the effectiveness of nanoparticles additives to change the solidification behaviour of high-strength aluminium alloys and improve their weldability/printability. In this study, AA7075 enhanced with TiC nanoparticles was utilized as wire feedstock to create single and multi-layer samples with coaxial laser-directed energy deposition (L-DED). The response of the samples to precipitation hardening was studied, evaluating the microstructure and the microhardness before and after T6 heat treatment. Specimens were characterized using optical and electron microscopy and electron backscatter diffraction (EBSD). Crack-free and virtually porosity-free samples were fabricated, which exhibit a refined equiaxed grain structure with grain size <10μm. This confirms the ability of TiC nanoparticles to prevent columnar dendritic growth and promote heterogeneous nucleation. Microhardness values increased by 51 HV after T6 heat treatment and were uniform across the sample. Energy Dispersive Spectroscopy (EDS) analysis showed that there are evaporation losses of Zn and Mg. Considering the boiling temperatures of these elements, it is inferred that the molten pool reaches temperatures above 1090°C, and the partially melted zone temperature is between 907°C and 1090°C.

Laser-based Metal Additive Manufacturing at the Faculty of Mechanical Engineering, University of Ljubljana

Laser-based Metal Additive Manufacturing at the Faculty of Mechanical Engineering, University of Ljubljana

Oxide dispersion strengthening in CrCoNi medium entropy alloy built by selective laser melting with oxygen-rich powder

In laser-based additive manufacturing for metallic materials, the high standard for alloy powder quality significantly increases cost, energy, and time consumption, which hinders further practical applications. In this study, we focus on the influence of oxygen impurity of the powder feedstock for the additive manufacturing approach of selective laser melting, using equimolar CrCoNi medium entropy alloy (MEA) as an example. We synthesized both pristine CrCoNi powder and its oxygen-rich counterpart (MEAO). We thoroughly characterized the microstructural evolution during tensile loading using a series of characterization methods, including XRD, SEM, EBSD, and TEM. The results revealed a well-preserved deformation mechanism of nano-twinning, along with elevated strength achieved by the oxide dispersion strengthening in the LPBF-built MEAO sample. This research demonstrates the potential for cost reduction in the powder fabricating process for additive manufacturing.

Laser-Based Additive Manufacturing and Mechanical Surface Post-Processing: Comparison of Barrel Finishing, Shot and Ultrasonic Peening for Corrosion Resistance Improvement of Superalloy

Laser-Based Additive Manufacturing and Mechanical Surface Post-Processing: Comparison of Barrel Finishing, Shot and Ultrasonic Peening for Corrosion Resistance Improvement of Superalloy

Revealing the effects of laser beam shaping on melt pool behaviour in conduction-mode laser melting

Laser beam shaping offers remarkable possibilities to control and optimise process stability and tailor material properties and structure in laser-based welding and additive manufacturing. However, little is known about the influence of laser beam shaping on the complex melt-pool behaviour, solidified melt-track bead profile and microstructural grain morphology in laser material processing. A simulation-based approach is utilised in the present work to study the effects of laser beam intensity profile and angle of incidence on the melt-pool behaviour in conduction-mode laser melting of stainless steel 316L plates. The present high-fidelity physics-based computational model accounts for crucial physical phenomena in laser material processing such as complex laser–matter interaction, solidification and melting, heat and fluid flow dynamics, and free-surface oscillations. Experiments were carried out using different laser beam shapes and the validity of the numerical predictions is demonstrated. The results indicate that for identical processing parameters, reshaping the laser beam leads to notable changes in the thermal and fluid flow fields in the melt pool, affecting the melt-track bead profile and solidification microstructure. The columnar-to-equiaxed transition is discussed for different laser-intensity profiles.

Innovative liquid metal strategy for real-time thermal control in additive manufacturing

Metal additive manufacturing (AM) involves rapid cycles of melting and solidification, often resulting in significant thermal stress variations, microcrack formation, and compromised structural integrity, especially for complex structures. Effective strategies are crucial for regulating temperature and stress distribution during laser-based metal AM processes; however, traditional thermal management approaches suffer from limitations in action area and response speed. In this study, the novel Liquid Metal-Assisted Additive Manufacturing (LMAAM) process is developed to enhance real-time temperature and stress control during deposition. This is the first known attempt to utilize liquid tin as an auxiliary thermal management material for AM. Numerical simulations and experimental analysis are performed to determine the relationship between LMAAM process conditions and resultant material microstructural properties. The results show that compared to AM without active thermal management, the incorporation of liquid tin yields an approximate 20 % increase in the cooling rate, a roughly 30 % reduction in residual tensile stress, a decrease in part grain size, and a roughly 30 % enhancement in microhardness. LMAAM technology opens up new possibilities for metal AM of highly reliable and intricate structures like multi-chambers, multi-channels, and deep blind holes.

Phase and thermodynamics-informed predictive model for laser beam additive manufacturing of a multi-principal element alloy

The complex solidification cycles experienced by multi-principal element alloys (MPEAs) during laser-based additive manufacturing (LBAM) often lead to structural defects that affect the build quality. The underlying thermal processes and phase transformations are a function of the process parameters employed. With a moving Gaussian heat source to mimic LBAM and leveraging material thermodynamics guidelines from CALculation of PHAse Diagrams (CALPHAD), we estimate the temperature-dependent thermal properties, phase fractions, and melt pool geometry using an experimentally validated computational fluid dynamics model. The results substantiate that the peak temperatures are inversely correlated to the scan speeds, and the melt pool dimensions can assist in the predictive selection of process parameters such as hatch distance and layer thickness. A relatively low cooling rate recorded during the process is ascribed to the preheating of the substrate to ensure printability of the alloy.

Assessment of self-lubricating coated cutting tools fabricated by laser additive manufacturing technology for friction-reduction

Dry cutting acting as a green machining technology is a promising manufacturing process in industrial applications; however, severe friction under dry cutting conditions aggravates tool wear and reduces tool life. Self-lubricating cutting tools exhibit excellent benefits in improving cutting properties and that can be used in sustainable machining. The complex process, low efficiency and thin coating thickness limit the production and use of present self-lubricating cutting tools with traditional methods. To enhance the lubricating effect and motivate the development of fabrication methods for self-lubricating cutting tools, Ni-based powders dispersed with MoS2 and Al2O3 particles were preset on the tool substrate; afterward, the self-lubricating coatings were deposited by laser powder-bed fusion additive manufacturing (AM) with a nanosecond fiber laser for cutting application. The self-lubricating coatings were characterized, and the friction and cutting performances of the AM self-lubricating coated tools (SLCs) were evaluated by sliding friction and dry machining tests. The results show that the developed SLC tools reduced the friction coefficient by 8.8–11.7%, cutting forces by 17.6–29.6%, and cutting power by 17.3–22.0% compared to conventional high-speed steel cutting tools (HSS). Built-up edge formation and tool wear were also significantly reduced. The observed mechanisms were attributed to the release of MoS2 particles from the coatings forming a lubricating film at the tool-chip interface, while the Al2O3 particles enhanced surface hardness. The results revealed the practicability of self-lubricating coated cutting tools fabricated by laser-based AM for friction-reduction, and that provide a cleaner process for dry cutting applications.

Effects of laser rescanning on microstructure and mechanical properties of Al-10Si-1Mg alloy produced by laser-directed energy deposition

Laser-based additive manufacturing (AM) is a powerful tool for the production of complex metal parts. In this study, the Al-10Si-1Mg (wt%) alloy was fabricated using the laser-based directed energy deposition (L-DED) process. Additionally, the laser rescanning (LRS) process was used to fabricate samples under the same L-DED processing parameters. The microstructure and mechanical properties of the samples were investigated. Microstructural analysis showed the presence of a unique microstructure containing relatively coarse dendrites near the laser melt-pool boundary and fine equiaxed grains inside the melt pool. LRS was shown to effectively alter the grain size and texture of the alloy. Tensile tests in directions vertical and transverse to the L-DED BD showed that only the L-DED-processed alloys exhibited strong anisotropy in their mechanical properties. The LRS-processed samples exhibited significant improvements in strength and elongation with significantly reduced anisotropy compared to the L-DED-only processed samples. Under the same laser volumetric energy density conditions, increasing the laser scanning speed could effectively reduce the porosity, which resulted in a significant improvement in the mechanical properties with and without the LRS.

Microstructure Design of Semi-Solid Slurry for Metal Direct Writing

Metal direct writing in semi-solid slurry is an innovative technology to realize low-cost printing of load-bearing parts in contrast to laser-based additive manufacturing. However, it is challenging to achieve near net-forming of 3D parts in the current stage because of the out of controlled microstructure and hence the unstable macro extrusion of the used semi-solid slurry. Here, mixed powder remelting (MPR) is introduced to actively design the characteristics of solid phases, i.e., solid fraction, shape factor, and size distribution. Specifically, high-melting-point pure Al powder served as the dispersed solid phases in the liquid phase that transformed from Al-Si alloy powder after remelting, leading to hypoeutectic Al-Si semi-solid slurry. The effectiveness of this approach was experimentally examined and kinetically modelled, to prepare semi-solid slurry with pre-set microstructure. The improved extrusion stability of semi-solid slurry can be anticipated, and it is universal for manufacturing of metal matrix composites slurry.

A state-of-the-art digital factory integrating digital twin for laser additive and subtractive manufacturing processes

PurposeThis study aims to discuss the state-of-the-art digital factory (DF) development combining digital twins (DTs), sensing devices, laser additive manufacturing (LAM) and subtractive manufacturing (SM) processes. The current shortcomings and outlook of the DF also have been highlighted. A DF is a state-of-the-art manufacturing facility that uses innovative technologies, including automation, artificial intelligence (AI), the Internet of Things, additive manufacturing (AM), SM, hybrid manufacturing (HM), sensors for real-time feedback and control, and a DT, to streamline and improve manufacturing operations.Design/methodology/approachThis study presents a novel perspective on DF development using laser-based AM, SM, sensors and DTs. Recent developments in laser-based AM, SM, sensors and DTs have been compiled. This study has been developed using systematic reviews and meta-analyses (PRISMA) guidelines, discussing literature on the DTs for laser-based AM, particularly laser powder bed fusion and direct energy deposition, in-situ monitoring and control equipment, SM and HM. The principal goal of this study is to highlight the aspects of DF and its development using existing techniques.FindingsA comprehensive literature review finds a substantial lack of complete techniques that incorporate cyber-physical systems, advanced data analytics, AI, standardized interoperability, human–machine cooperation and scalable adaptability. The suggested DF effectively fills this void by integrating cyber-physical system components, including DT, AM, SM and sensors into the manufacturing process. Using sophisticated data analytics and AI algorithms, the DF facilitates real-time data analysis, predictive maintenance, quality control and optimal resource allocation. In addition, the suggested DF ensures interoperability between diverse devices and systems by emphasizing standardized communication protocols and interfaces. The modular and adaptable architecture of the DF enables scalability and adaptation, allowing for rapid reaction to market conditions.Originality/valueBased on the need of DF, this review presents a comprehensive approach to DF development using DTs, sensing devices, LAM and SM processes and provides current progress in this domain.

Effect of Fe additions on microstructure and mechanical properties in near-eutectic Al–Ce alloys

The effects of adding 1 or 3 wt % Fe to a near-eutectic Al–10Ce alloy are investigated in terms of their as-cast and aged microstructures, thermal stability, and creep resistance. A 1 wt% Fe addition forms fine, Chinese-script Al10CeFe2 and Al11Ce3 eutectic phases without loss of microhardness as compared to the Fe-free Al–10Ce alloy, unlike in traditional cast Al-alloys where detrimental coarse phases are observed when adding Fe. Adding 3 wt% Fe increases hardness significantly while forming primary Al10CeFe2 in a coarse rod morphology. These near-eutectic Al–10Ce–1Fe and hyper-eutectic Al–10Ce–3Fe alloys, after thermal exposure at 400 and 425 °C for up to 384 h, show only a small loss in microhardness, indicating excellent coarsening resistance. Compressive creep measurements performed at 300 °C show similar trends: (i) near-eutectic Al–10Ce–1Fe performs quite similarly to near-eutectic Al–10Ce and (ii) hyper-eutectic Al–10Ce–3Fe exhibits much improved creep resistance, similar to near-eutectic Al–10Ce–5Ni with costly Ni additions, and much better than hyper-eutectic Al–13Ce. After surface laser remelting to simulate laser powder-bed fusion, the near-eutectic Al–10Ce–1 Fe alloy exhibits greatly refined Al10CeFe2 and Al11Ce3 eutectic phases with a doubling in microhardness, indicating a strong potential for laser-based additive manufacturing. Cast Al–Ce–Fe-based alloys show great promise as low-cost alloys with high creep- and coarsening-resistance for use at high temperatures, with the high Fe tolerance enabling the use of recycled aluminum with high Fe contamination.

3D characterization of magnetic phases through neutron polarization contrast tomography

The advancement of laser-based metal additive manufacturing has enabled the production of near net shape complex geometries. Understanding the microstructural features of materials is crucial for accurate modeling of their mechanical behavior, particularly with regard to strain- or thermal-induced martensitic phase transformations in ferrous alloys and steels. For example, the formation of BCC α′-martensite can strengthen materials while preserving ductility of the dominating austenitic phase. However, in components where the shape memory effect is attributed to the reversible formation of ε-martensite, the accumulation of deformation-induced α′-martensite is an undesired, irreversible degradation mechanism. This study presents a novel tomographic approach utilizing polarization contrast neutron imaging for the 3D volumetric characterization of magnetic crystallographic phases, especially those present in low phase fractions that are typically undetectable with traditional techniques. The technique is applied to the study of strain-induced martensitic phase transformations in additively manufactured lattice structures made of high-Mn steels, which form small fractions of α′-martensite upon deformation. The results demonstrate the value of this technique for characterizing entire components and complex geometries found in numerous technological applications.

Plastic strain visualization and analysis of Laser-Processed nickel single crystals

The capability to characterize the inelastic response of a material induced by laser processing is particularly relevant within the context of laser-based additive manufacturing. While many efforts have been directed toward elastic residual field measurements, determining the extent of plastic deformation significant experimental challenges. The present effort seeks to offer direct insight into the nature of plastic strain generation in nickel single crystals subjected to melt-mediated laser processing. Ultra-high purity nickel single crystals were chosen for their FCC crystal structure and their lack of potential for dislocation interactions with either grain boundaries or solutes, thus significantly simplifying their analysis.

Influence of PBF-LB Process Atmosphere on the Fatigue Strength of Hot Isostatically Post-Densified Duplex Steel Parts Produced via the Shell Core Approach.

Laser-based additive manufacturing is a great manufacturing technology for producing parts of any geometry. To also increase the strength and reliability of parts produced via powder bed fusion with laser beam (PBF-LB), hot isostatic pressing (HIP) is often used to densify residual porosity or lack-of-fusion defects. When components are post-densified via HIP, they do not require a high density beforehand, only a closed porosity or a dense shell. By building up samples with increased porosity, the PBF-LB process can be accelerated and productivity increased. HIP post-treatment gives the material its full density and good mechanical properties. However, with this approach, the influence of the process gases becomes important. Either argon or nitrogen is used in the PBF-LB process. It is assumed that these process gases are trapped in the pores and thus have an influence on the HIP process and also the mechanical properties after HIP. In this study, the influence of argon and nitrogen as process gases on the properties of duplex AISI 318LN steel after powder bed fusion with laser beam and hot isostatic pressing is investigated for the case of very high initial porosities.

Microstructural Evolution of a High-Strength Zr-Ti-Modified 2139 Aluminum Alloy for Laser Powder Bed Fusion

The demand for high-performance aluminum components drives research into the design of novel alloys that can be processed by laser-based additive manufacturing. In recent years, the addition of grain refiners proved to be an effective strategy to reduce the hot-cracking of high-strength Al alloys. In this study, the solidification and aging behavior of an Al2139 alloy doped with additions of Zr and Ti for L-PBF was investigated. These elements favored the formation of a fine-grained structure free of cracks. The formation of Al3(Zr,Ti) inoculants was predicted by Scheil simulations and observed as cuboidal particles in the center of α-Al grains. The microstructure of the as-built material featured fine and fully equiaxed grains, which appeared comparatively finer at the edge (300–600 nm) and coarser (0.8–2.0 μm) at the center of the molten pools. In both cases, there was evidence of Cu and Mg micro-segregations at the grain boundaries. The microhardness of 109.7 HV0.5 in the as-built state was increased to 186.1 HV0.5 after optimized T4 heat treatment, responsible for the precipitation of many rod-shaped Zr- and Ti-based second phases and quasi-spherical Cu-, Mn-, and Fe-rich particles. Prolonged exposure carried out to simulate high-temperature service caused a drop in microhardness and marked modification of the microstructure, evidenced by the rearrangement and subsequent spheroidization of Cu- and Mg-rich particles at the grain boundaries.