Laser Beam Melting Research Articles

Tribocorrosion Performance and Cytotoxicity of Additive Manufactured CoCrMo: A Benchmark Against Wrought CoCrMo

Additive Manufacturing (AM) has increasingly gained attention as a tool for the fabrication of complex biomedical components, due to the flexibility of the technique for accounting to the patient individuality. Additive manufacturing techniques, like laser beam melting, often result in highly anisotropic microstructures that greatly differ from those obtained in conventionally manufactured alloys. This study evaluates the potential of AM manufactured CoCrMo for body implants as an alternative to the wrought CoCrMo, especially considering tribocorrosion performance in buffered fluid. Its biocompatibility is also assessed via in-vitro cytotoxicity assays. The results show that both materials have a comparable tribocorrosion performance, independently of the manufacturing process, despite their radically different initial microstructure. This results from the microstructural convergence arising from the plastic deformation imparted by sliding motion. While the initially elongated grains of the AM CoCrMo tend to grain refinement, the microstructure of the wrought CoCrMo undergoes grain coarsening, resulting in a similar final grain size detected after the tribocorrosion experiments. The addition of albumin to the phosphate buffer testing fluid, simulating body fluid applications, reduces the grain refinement, particularly under constant 0.21 V, due to lower shear stresses caused by the lower coefficient of friction. Therefore, the initial dissimilarity found in the untested microstructure between the materials does not affect the wear rate nor lead to an increased metal release. As the cytotoxicity is neither impaired by the manufacturing process, the use of AM CoCrMo could be recommended on those biomedical applications requiring wear resistance in body fluid environment.

Wetting behaviour of nickel-based brazing alloy BNi-5a on conventionally cast and laser-melted austenitic stainless steel 316L

Laser beam melting is an additive manufacturing process that enables the production of highly complex components. In this process, metal powder is locally melted using a laser beam and built up layer by layer to form a physical component. Due to the layer-by-layer process manufacturing technique of the additive manufacturing process, the microstructure of a laser-melted 316L austenitic stainless steel differs from that of a conventionally cast material. For brazing technology, the different microstructure morphology is important because it affects the known wetting and diffusion behavior with a brazing filler metal, which affects the ability to produce high-strength brazed joints. Brazeability can be determined by examining the wetting of the brazing filler metal with the material to be joined. Therefore, this study investigates the wetting behavior of nickel-base brazing alloy BNi-5a on conventionally cast and laser-melted 316L austenitic stainless steel. Wetting tests were performed to evaluate the spreading area and wetting angle of BNi-5a on both 316L substrates. The wetting tests were performed in a high-temperature vacuum furnace at 1190 °C for 15 min. The results show that the laser-melted 316L stainless steel exhibits enhanced wettability compared to the conventionally cast material. This is related to a higher surface energy and a more pronounced diffusion mechanism called grain boundary grooving on the surface of the material.

Influence of Process Parameters on Selected Properties of Ti6Al4V Manufacturing via L-PBF Process.

This study investigates the microstructural effects of process parameters on Ti6Al4V alloy produced via powder bed fusion (PBF) using laser beam melting (LB/M) technology. The research focuses on how variations in laser power, exposure velocity, and hatching distance influence the final material's porosity, microhardness, and microstructure. To better understand the relationships between process parameters, energy density, and porosity, a simple mathematical model was developed. The microstructure of the alloy was analyzed in the YZ plane using a confocal microscope. The study identified optimal parameters-302.5 W laser power, 990 mm/s exposure velocity, and 0.14 mm hatching distance-yielding the lowest porosity index of 0.005%. The material's average hardness was measured at 434 ± 18 HV0.5. These findings offer valuable insights for optimizing printing parameters to produce high-quality Ti6Al4V components using PBF-LB/M technology, shedding light on the critical relationship between process parameters and the resulting microstructure.

17-4 PH Steel Parts Obtained through MEX and PBF-LB/M Technologies: Comparison of the Structural Properties.

The material extrusion (MEX) method utilizing highly filled metal filament presents an alternative to advanced additive metal manufacturing technologies. This process enables the production of metal objects through deposition and sintering, which is particularly attractive compared to powder bed fusion (PBF) technologies employing lasers or high-power electron beams. PBF requires costly maintenance, skilled operators, and controlled process conditions, whereas MEX does not impose such requirements. This study compares research on 17-4 PH steel manufactured using two different commercially available techniques: MEX and powder bed fusion with laser beam melting (PBF-LB/M). This research included assessing the density of printed samples, analyzing surface roughness in two printing planes, examining microstructure including porosity and density determination, and measuring hardness. The conducted research aimed to determine the durability and quality of the obtained samples and to evaluate their strength. The research results indicated that samples produced using the PBF-LB/M technology exhibited better density and a more homogeneous structure. However, MEX samples exhibited better strength properties (hardness).

Microstructural Investigation of Process Parameters Dedicated to Laser Powder Bed Fusion of AlSi7Mg0.6 Alloy.

This study presents a microstructural investigation of the printing parameters of an AlSi7Mg0.6 alloy produced by powder bed fusion (PBF) using laser beam melting (LB/M) technology. The investigation focused on the effects of laser power, exposure velocity, and hatching distance on the microhardness, porosity, and microstructure of the produced alloy. The microstructure was characterized in the plane of printing on a confocal microscope. The results showed that the printing parameters significantly affected the microstructure, whereas the energy density had a major effect. Decreasing the laser power and decreasing the hatching distance resulted in increased porosity and the increased participation of non-melted particles. A mathematical model was created to determine the porosity of a 3D-printed material based on three printing parameters. Microhardness was not affected by the printing parameters. The statistical model created based on the porosity investigation allowed for the illustration of the technological window and showed certain ranges of parameter values at which the porosity of the produced samples was at a possible low level.

Investigations into the mechanical properties of TA6V Dode-Thin lattice sandwich beams fabricated by powder bed laser beam melting process

Investigations into the mechanical properties of TA6V Dode-Thin lattice sandwich beams fabricated by powder bed laser beam melting process

Laser remelting of regolith in vacuum: Reducing porosity for enhanced lunar resource utilization

The use of lunar regolith, the powdery soil found on the Moon, is crucial for utilizing the Moon as a stepping stone for future space exploration. Laser beam melting of regolith on the lunar surface is a promising technique for constructing infrastructure on the Moon. When regolith simulants are melted using a laser beam under Earth’s atmosphere, the resulting samples are dense with a porosity below 5%. However, melting it under vacuum results in porosities of up to 75%. In order to enhance the mechanical strength and dimensional accuracy of the samples, it is necessary to develop an approach to reduce the porosities.Therefore, in this work, two-dimensionally manufactured samples, approximately 25 mm x 25 mm in size, made of solidified regolith simulant were remelted with a laser beam (wavelength: 940 nm and 980 nm) using laser powers of 100-150 W and a scanning speed of 1 mm/s under a vacuum of approximately 3 ∙ 10-3 mbar. The study found that remelting reduces the porosity of two-dimensional samples to 19% and that the laser power applied primarily influences the size of the remelted area. It was also observed that remelting resulted in thinner samples that exhibited partial translucency. The surface roughness was reduced by 77%, and the surface appeared smoother. The hardness of the samples remained unchanged.

Recent advances of metallic bio-materials in additive manufacturing in biomedical implants–A review

During the last three decades, metal additive manufacturing (metal-AM) has evolved significantly. It has become possible to produce prototypes of products using metal-AM in combination with various manufacturing processes since the technology has matured enough to be used for complex geometries. Recent advancements in biomedical implants have attracted increasing attention to additive manufacturing (AM). The use of titanium and its alloys in biomedical implants, cobalt alloys, stainless steel 316L, nickel-titanium, and others is explored. A number of metal additive manufacturing processes are available, including Selective Laser Melting (SLM), Selective Laser Sintering (SLS), and Electron Beam Melting (EBM). Moreover, the paper discusses the latest developments in metal-AM via direct metal laser sintering and the fabrication and characterization of a three-dimensional scaffold. There is increasing use of laser or electron beam melting techniques in the manufacture of metal implants, among all methods of additive manufacturing (AM). In the future, metal-AM is expected to provide various benefits to the biomedical industry.

New approach for multi-material design: Combination of laser beam and electromagnetic melt pool displacement by induced Lorentz forces

Multimaterial structures are a promising solution to reduce vehicle weight and save fuel or electric energy in automotive design. However, thermal joining of steel and aluminum alloys is a challenge to overcome due to different material properties and the formation of brittle intermetallic phases. In this study, a new joining approach for producing overlap line-shaped joints is presented. The lower joining partner (EN AW 5754) is melted by a laser beam, and this melt is displaced into a line-shaped cavity of the upper joining partner (1.0330) by induced Lorentz forces. The melt solidifies in the cavity to a material and form-fitting joint. This approach needs no auxiliary joining elements or filler materials. Previous investigation to produce spot-shaped joints by using this approach showed that quality and reproducibility were limited by known melt pool dynamics of aluminum alloys (keyhole collapses). For line-shaped joints, the melt displacement can take place behind the keyhole. This allows the displacement process to be spatially uncoupled from the influence of keyhole collapses. The study shows that this improved the process stability and the quality of the joint. The created line-shaped joints were microstructurally characterized by transversal sections. Intermetallic phases were identified by electron backscatter diffraction and EDX analysis. The detected intermetallic phases consist of a 5–6 μm compact phase seam of Al5.6Fe2 and a needle-shaped phase of Al13Fe4. Tensile shear tests were carried out to quantify the load capacity. It was possible to create a joint with a load capacity of about 2 kN.

Additive Manufacturing of Soft Ferromagnetic Fe 6.5%Si Annular Cores: Process Parameters, Microstructure, and Magnetic Properties

The laser beam melting (LBM) additive manufacturing (AM) technology is used for processing a high silicon steel (Fe 6.5%wtSi). The effects of LBM machine parameters over microstructure and magnetic properties are studied. Particular attention is dedicated to determining the influence of a normalized energy density over the material density, the grain size, and the crystallographic texture and their impact on the magnetic properties: magnetic flux density and coercivity.

High-Temperature Mechanical Properties of Stress-Relieved AlSi10Mg Produced via Laser Powder Bed Fusion Additive Manufacturing.

The present study is dedicated to the evaluation of the mechanical properties of an additively manufactured (AM) aluminum alloy and their dependence on temperature and build orientation. Tensile test samples were produced from a standard AlSi10Mg alloy by means of the Laser Powder Bed Fusion (LPBF) or Laser Beam Melting (LBM) process at polar angles of 0°, 45° and 90°. Prior to testing, samples were stress-relieved on the build platform for 2 h at 350 °C. Tensile tests were performed at four temperature levels (room temperature (RT), 125, 250 and 450 °C). Results are compared to previously published data on AM materials with and without comparable heat treatment. To foster a deeper understanding of the obtained results, fracture surfaces were analyzed, and metallographic sections were prepared for microstructural evaluation and for additional hardness measurements. The study confirms the expected significant reduction of strength at elevated temperatures and specifically above 250 °C: Ultimate tensile strength (UTS) was found to be 280.2 MPa at RT, 162.8 MPa at 250 °C and 34.4 MPa at 450 °C for a polar angle of 0°. In parallel, elongation at failure increased from 6.4% via 15.6% to 26.5%. The influence of building orientation is clearly dominated by the temperature effect, with UTS values at RT for polar angles of 0° (vertical), 45° and 90° (horizontal) reaching 280.2, 272.0 and 265.9 MPa, respectively, which corresponds to a 5.1% deviation. The comparatively low room temperature strength of roughly 280 MPa is associated with stress relieving and agrees well with data from the literature. However, the complete breakdown of the cellular microstructure reported in other studies for treatments at similar or slightly lower temperatures is not fully confirmed by the metallographic investigations. The data provide a basis for the prediction of AM component response under the thermal and mechanical loads associated with high-pressure die casting (HPDC) and thus facilitate optimizing HPDC-based compound casting processes involving AM inserts.

Susceptibility to Pitting and Environmentally Assisted Cracking of 17-4PH Martensitic Stainless Steel Produced by Laser Beam Melting.

Materials produced by additive manufacturing (AM) often have different microstructures from those obtained using conventional metallurgy (CM), which can have significant impacts on the materials’ durability, and in particular, resistance to corrosion. In this study, we were concerned with the susceptibility to pitting and environmentally assisted cracking (EAC) of 17-4PH martensitic stainless steel (MSS). We focused on the evolution from pitting to EAC, and the behaviour of MSS produced by AM was compared with that of its CM counterpart. Potentiodynamic polarisation tests were combined with chronoamperometry measurements performed without and with mechanical loading to study both stable and metastable pitting and the influence of stress on these processes. EAC tests were carried out and combined with observations of fracture surfaces. MSS produced by AM was more resistant to pit initiation due to fewer and finer NbC particles. However, the propagation kinetics of stable pits were higher for this MSS due to a higher amount of reversed austenite. The stress was found to stabilise the metastable pits and to accelerate the propagation of stable pits, which resulted in an increased susceptibility to EAC of the MSS produced by AM. These results clearly highlighted the fact that the reversed austenite amount has to be perfectly controlled in AM processes.

Modification of Iron with Degradable Silver Phases Processed via Laser Beam Melting for Implants with Adapted Degradation Rate

In medical technology, implants are used to improve the quality of patients’ lives. The development of materials with adapted properties can further increase the benefit of implants. If implants are only needed temporarily, biodegradable materials are beneficial. In this context, iron‐based materials are promising due to their biocompatibility and mechanical properties, but the degradation rate needs to be accelerated. Apart from alloying, the creation of noble phases to cause anodic dissolution of the iron‐based matrix is promising. Due to its high electrochemical potential, immiscibility with iron, biocompatibility, and antibacterial properties, silver is suited for the creation of such phases. A suitable technology for processing immiscible material combinations is powder‐bed‐based procedure like laser beam melting. This procedure offers short exposure times to high temperatures and therefore a limited time for diffusion of alloying elements. As the silver phases remain after the dissolution of the iron matrix, a modification is needed to ensure their degradability. Following this strategy, pure iron with 5 wt% of a degradable silver–calcium–lanthanum alloy is processed via laser beam melting. Investigation of the microstructure yields achievement of the intended microstructure and long‐term degradation tests indicates an impact on the degradation, but no increased degradation rate.

Microstructure and Properties of a Novel Carbon‐Martensitic Hot Work Tool Steel Processed by Laser Additive Manufacturing without Preheating

Laser additive manufacturing (LAM) techniques, such as laser‐powder bed fusion (L‐PBF) or laser‐directed energy deposition (L‐DED), allow for the production of complex‐shaped parts by either the local melting of a metallic powder bed by a laser beam (L‐PBF) or a local application and laser beam melting of powder material by a nozzle (L‐DED). In the case of carbon‐martensitic tool steels, their cold crack susceptibility limits their LAM processability and is usually counteracted by substrate preheating. As preheating can increase the oxygen take‐up of the powder and alter the part microstructure, it can be disadvantageous for part quality and powder reusability. In this study, it is investigated a carbon‐martensitic steel designed for the production of parts with low crack density by LAM without preheating, focusing on the microstructure and hardness of the L‐PBF‐ and L‐DED‐manufactured steel. The steel can be LAM‐processed without preheating, resulting in specimens with low crack densities and martensitic microstructure with retained austenite. The hardness of the as‐built material (L‐PBF: 542HV30 and L‐DED: 623HV30) is increased by quenching and tempering up to 693HV30. Direct tempering of the as‐built specimen without previous quenching leads to a shift of the secondary hardness maximum from 500 to 530 °C.

A Study of the Mechanical Properties of Al6061-Zr1,2 Alloy Processed by Laser Beam Melting

A Study of the Mechanical Properties of Al6061-Zr1,2 Alloy Processed by Laser Beam Melting

Adjustment of AgCaLa Phases in a FeMn Matrix via LBM for Implants with Adapted Degradation

For many applications, implants overtake body function for a certain time. Bioresorbable implants reduce patient burden as they prevent adverse consequences due to remaining implants or operations for removal. Such materials are in clinical use but do not fulfill the requirements of all applications. Iron (Fe) is promising to develop further bioresorbable materials as it offers biocompatibility and good mechanical properties. Alloying, e.g., with manganese (Mn), is necessary to adapt the mechanical behavior and the degradation rate. However, the degradation rate of FeMn is too low. The creation of phases with high electrochemical potential evokes anodic dissolution of the FeMn, increasing the degradation rate. Therefore, silver (Ag), which is insoluble with Fe, has high potential, is biocompatible, and offers antibacterial properties, can be used. Powder-based processes such as laser beam melting (LBM) are favorable to process such immiscible materials. A degradable Ag alloy has to be used to enable the dissolution of Ag phases after the FeMn. This study reports first about the successful processing of FeMn with 5 wt.% of a degradable Ag–calcium–lanthanum (AgCaLa) alloy and enables further targeted adaption due to the gained understanding of the effects influencing the morphology and the chemical composition of the Ag phases.

Formation of insoluble silver-phases in an iron-manganese matrix for bioresorbable implants using varying laser beam melting strategies

The combination of immiscible metals is targeted to fulfil the requirements for certain technical and biomedical applications. The degradation behavior of iron (Fe) is adjustable by the insertion of silver (Ag) phases with high electrochemical potential causing anodic dissolution of the Fe-based matrix. To process such immiscible materials, powder-based processes like laser beam melting (LBM) can be applied. The continuous fusion process characterized by a small melt pool, strong melt flow, and rapid solidification enables the creation of well-dispersed Ag phases. To enable the adaption of insoluble phases this study aims to understand the mechanism responsible for the incorporation of insoluble phases within the matrix. Based on the characterization of FeMn with 5 wt.-% Ag processed via LBM the surface tension is determined as the essential influencing factor and a model of the melt pool including melt flow is developed. The Ag forms an almost closed layer on the top surface with an increased thickness between adjacent melt tracks. The lower surface tension of Ag compared to FeMn keeps Ag on the top and the outward-directed melt flow of underlying FeMn transports the Ag to the sides of the melt pools. During the generation of the next slice, deep parts of the Ag layer remain in the bulk material. By adaption of process conditions, e. g. the hatch distance, the size and shape of Ag phases are influenced. Moreover, the chemical composition depends on the LBM strategy, since the diffusion of alloying elements is differently pronounced.

Evolution of an industrial-grade Zr-based bulk metallic glass during multiple laser beam melting

Selective laser melting (SLM), taking advantage of its inherent rapid cooling rates and near-net-shape forming ability, has been employed to fabricate bulk metallic glasses (BMGs). However, crystallization is frequently triggered during the SLM process, which results in the loss of advantageous properties of BMGs, such as extremely high hardness and near-theoretical yield strength. Although many studies have been conducted to investigate SLM of BMGs, there is still a lack of knowledge about the microstructural and compositional evolution during the laser beam processing, particularly the micromechanical property response upon crystallization.In the present work, a systematic investigation is performed to gain a much better understanding about the evolution of microstructure and composition as well as the corresponding micromechanical property change during multiple laser beam melting. The material used in this study is an industrial-grade Zr-based BMG Zr59.3Cu28.8Al10.4Nb1.5 (AMZ4) with two different oxygen levels. AMZ4 demonstrates its good thermal stability by the fact that observable crystalline structure appears around the melt pool only after more than once laser beam treatment. The compositional stability of AMZ4 is manifested by the homogeneous elemental distribution on the melt pool area after even twenty-five laser beam remelting. The laser-metal interaction, melting and subsequent solidification are not effectively influenced by the emerging and expanding of crystallization zone (or heat affected zone, HAZ). Higher oxygen content results in not only a larger HAZ but also more quenched-in nuclei at the melt pool bottom. The HAZ does not exhibit a fully crystallized structure, but rather has a mixture of amorphous and crystalline phases. Crystallization of AMZ4 leads to an increase in hardness and Young’s modulus of the material.

Melt pool monitoring in laser beam melting with two-wavelength holographic imaging

Over the past two decades, laser beam melting has emerged as the leading metal additive manufacturing process for producing small- and medium-size structures. However, a key obstacle for the application of this technique in industry is the lack of reliability and qualification mainly because of melt pool instabilities during the laser-powder interaction, which degrade the quality of the manufactured components. In this paper, we propose multi-wavelength digital holography as a proof of concept for in situ real-time investigation of the melt pool morphology. A two-wavelength digital holographic setup was co-axially implemented in a laser beam melting facility. The solidified aluminum tracks and melt pools during the manufacturing of 316L were obtained with full-field one-shot acquisitions at short exposure times and various scanning velocities. The evaluation of the complex coherence factor of digital holograms allowed the quality assessment of the phase reconstruction. The motion blur was analyzed by scanning the dynamic melt pool.

Biofilm accumulation on additive manufactured Ti-6Al-4V alloy surfaces.

This study investigated whether additive manufactured (AM) surfaces inhibit accumulation of bacterial biofilm on the surfaces of Ti-6Al-4V alloy dental implants. Bacterial biofilms are thought to cause peri-implant disease, which develops in mucosa surrounding titanium (Ti) and Ti alloy dental implants and can lead to bone loss and implant failure. Accumulation of a Streptococcus mutans (ATCC 25175) biofilm on Ti-6Al-4V alloy was compared in relation to fabrication method, ie, AM using electron beam melting (EBM) or laser beam melting (LBM). Conventional lost-wax casting was used as positive control, and Teflon was used as negative control. Biofilm accumulation on the alloys and negative control (each n = 10) was conducted at 37°C under anaerobic conditions. After 4 h, the number of metabolically active S. mutans bacteria adhering to the alloy was determined with a bioluminescence assay. The quantitative roughness values of the specimens, before exposure to bacteria, ranked EBM > LBM > cast > Teflon. The amount of biofilm accumulation on the investigated AM metals and cast metal controls did not significantly differ.