Selective Laser Melting Technique Research Articles

Crashworthiness Study of Functional Gradient Lattice-Reinforced Thin-Walled Tubes under Impact Loading.

Creating lightweight and impact-resistant box structures has been an enduring pursuit among researchers. A new energy-absorbing structure consisting of a bionic gradient lattice-enhanced thin-walled tube is presented in this article. The gradient lattice and thin-walled tube were prepared using selective laser melting (SLM) and wire-cutting techniques, respectively. To analyze the effects of gradient pattern, mass ratio, diameter range and impact speed on structural crashworthiness, low-speed impact at 4 m/s and finite element simulation experiments were conducted. The study demonstrates that the design of inward radial gradient lattice-reinforced thin-walled tubes can effectively enhance structure's energy-absorption efficiency and provide a more stable mode of deformation. It also shows a 17.44% specific energy-absorption advantage over the uniformly lattice-reinforced thin-walled tubes, with no significant overall gain in peak crushing force. A complex scale evaluation method was used to determine the optimum structure and the structure type with the best crashworthiness was found to be a gradient lattice-filled tube with a thickness of 0.9 mm and a slope index of 10. The gradient lattice-reinforced thin-walled tube suggested in this investigation offers guidance for designing a more efficient thin-walled energy-absorption structure.

Lightweight design of lattice structure of boron steel prepared by selective laser melting

Three-cycle minimum surface structures show excellent lightweight and energy absorption capabilities, and additive manufacturing techniques provide a unique degree of freedom for lattice structure design. Therefore, in this study, three-period minimum surface (TPMS) structures of Schwarz-P boron steel alloys were prepared by Selective Laser Melting (SLM) technique. By investigating the effect of lattice structure design, we have analyzed the deformation behaviour, mechanical properties and energy absorption capacity under compression. In addition, tensile properties and fracture morphology were analyzed to gain insight into the performance characteristics of these structures, and the effect of structural design on hardness was explored. The results of the study show that the structural design has a small effect on the microstructure and hardness. Under compressive loading, the P (0.5 1) structure exhibits a uniform deformation behaviour, while the other four structures show a crushing deformation pattern. In particular, the P (0.5 1) structure exhibits excellent compressive performance, with an energy absorption work per unit mass as high as 296.2 J/mmˆ3, and its stiffness reaches 1627 MPa. Meanwhile, the P (0.35 1) structure exhibits excellent tensile performance with the tensile strength of 687 MPa. The morphological analysis of the tensile fracture reveals that the fracture mainly occurs in the strut nodes, and it mainly exhibits ductile tensile fracture.

Preparation of Zr-based metallic glasses gradient composites with designable amorphous fraction by laser powder bed fusion

Introducing ductile crystals in situ into the matrix is an efficient approach for enhancing the mechanical properties of bulk metallic glasses (BMGs). However, controlling the volume of the crystalline phase is challenging, and the introduction of crystals may be detrimental to its strength and ductility trade-off. In addition, BMGs prepared by conventional casting process suffers from the disadvantages of size limitation, inhomogeneous crystallization, and uncontrollable crystallization fraction. In this study, Zr48Cu47.5Al4Co0.5 amorphous powder with better forming ability was utilized as raw material and printed by selective laser melting (SLM) technique with high cooling rate. Through parameter adjustments and proactive design of amorphous fractions, gradient metallic glasses (GMGs) based on Zr has been successfully prepared. Micro-morphology, DSC tests, micro-area XRD, optical calculations and nanoindentation experiments all indicate the presence of gradient structures. The microstructure reveals that the crystalline phases in the heat affected zone (HAZ) are mainly B2 phase. In addition, the results of room temperature compression show that the yield strength (1.2 GPa) and plastic deformation (0.8 %) of the gradient structure are better than those of the samples prepared with a single parameter. The theme of amorphous fraction gradient structure design, realized by SLM technology, opens a new window for the large-scale development of high-performance BMGs.

Enhancing oral function: A case report on mandibular overdenture utilization with custom-made subperiosteal implant.

Subperiosteal implants, previously set aside because of complications, are now emerging again as effective treatments for severe mandibular atrophy, aided by recent improvements in digital dentistry. Traditional dentures in such cases often face challenges with support and retention, necessitating complex regenerative procedures. This paper presents a case report of a 54-year-old male patient with significant mandibular atrophy who received a custom-made subperiosteal implant, showcasing promising results. The implant was precisely designed utilizing computed tomography (CT) scans, a 3D-printed model, the selective laser melting (SLM) technique, and constructed with biocompatible Ti6Al4V material. This innovative approach offered a practical solution, resulting in high patient satisfaction and no complications over a year of use.

A review of the microstructure and tensile behavior of additively manufactured metastable β Ti alloys

AbstractThis review summarizes and critically discusses the current knowledge on the microstructures and tensile properties of metastable β Ti alloys fabricated by selective laser melting and laser metal deposition techniques. The effects of post‐heat treatments are also addressed. The spatial variations in the microstructure and properties are linked with the processing parameters. The review also compares the additively manufactured and post heat‐treated metastable β Ti alloys with their wrought counterparts. It highlights the research questions for further investigations.

The Effects of Heat Treatment on the Microstructure and Mechanical Properties of a Selective Laser Melted AlCoFeNi Medium-Entropy Alloy.

A single body-centered cubic (BCC)-structured AlCoFeNi medium-entropy alloy (MEA) was prepared by the selective laser melting (SLM) technique. The hardness of the as-built sample was around 32.5 HRC. The ultimate tensile strength (UTS) was around 1211 MPa, the yield strength (YS) was around 1023 MPa, and the elongation (El) was around 10.8%. A novel BCC + B2 + face-centered cubic (FCC) structure was formed after aging. With an increase in aging temperature and duration, the number of fine grains increased, and more precipitates were observed. After aging at 450 °C for 4 h, the formed complex polyphase structure significantly improved the mechanical properties. Its hardness, UTS, YS, and El were around 45.7 HRC, 1535 MPa, 1489 MPa, and 8.5%, respectively. The improvement in mechanical properties was mainly due to Hall-Petch strengthening, which was caused by fine grains, and precipitation strengthening, which was caused by an increase in precipitates after aging. Meanwhile, the FCC precipitates made the alloy have good toughness. The complex interaction of multiple strengthening mechanisms leads to a good combination of strength, hardness, and toughness.

Effect of post-processing and variation of the building angle of Ti-6Al-4 V disks obtained by selective laser melting: A comparison of physical, chemical and mechanical properties to machined disks

Additive Manufacturing (AM) is driving the development of dental implants with freedom of design, material savings, and predictable properties. The modification of a single parameter, and post-processing treatments affects the final macro and microstructure. The aim was to evaluate the effect of changing the building angle, using the Selective Laser Melting (SLM) technique, on the physical, chemical, and mechanical properties and to compare them with sanded manufacturing surfaces and machined surfaces, with and without chemical surface treatment. There were 8 groups of Ti-6Al-4 V discs (Ø 10 mm×2 mm), classified as machined (M), machined with acid-alkali treatment (TM), SLM 0° (AM0), SLM 0° with sanding (SAM0), SLM 45° (AM45), SLM 45° with sanding (SAM45), SLM 90° (AM90), and SLM 90° with sanding (SAM90). The tests used were Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), roughness, wettability, surface free energy, X-ray diffraction (XRD), and Vickers hardness. The normality of the data was checked using the Shapiro-Wilk test followed by Kruskal-Wallis and ANOVA, with Dunn and Tukey post-tests, with a significance level of 5%. SEM revealed angle dependence in the number of unmelted powder particles and topographical heterogeneity, and EDS reported the elemental composition of the base alloy. AM90 showed the highest wettability among the manufactured groups, and the chemical surface treatment increased the wettability of the machined sample (p<0.001). In the roughness analysis, the higher the building angle, the higher the surface roughness . Sanding provided homogeneity in roughness, wettability, surface free energy, and microhardness. It was concluded that the production routes, change in angle, sanding and surface treatment affect the macro and microstructure of titanium surfaces. Changing the building angle influenced all of the topographical characteristics of the material, a parameter that can be changed and improved that is important for determining properties.

Osseointegrative and immunomodulative 3D-Printing Ti6Al4V-based implants embedded with biogenic hydroxyapatite

Although titanium-based metal implants have become a game changer in dental and orthopedic therapies, they still have several problems such as late osseointegration and immune response. In this study, we present a novel strategy to develop Ti6Al4V-based implants embedded with biogenic hydroxyapatite derived from equine bone to overcome these problems. A selective laser melting technique was employed for facile fabrication with flexible fusing feedstock and regular uniform distribution of equine bone. The physicochemical characteristics, cell attachment and proliferation, osteogenic differentiation, osseointegration, inflammatory response, and metabolomics of the developed Ti6Al4V/equine bone composite were then investigated. The Ti6Al4V-based composite integrated with equine bone at a certain concentration has improved the crystalline structure (β-Ti) suitable for implantation and exhibited higher hydrophilicity and protein adsorption. They significantly promoted cell attachment, osteogenic differentiation, and anti-inflammatory effects in vitro. In vivo study confirmed the osseointegration and alleviated inflammatory responses. Furthermore, the Ti6Al4V-based implants integrated with equine bone significantly reduced metabolites associated with inflammatory responses both in vitro and in vivo. The observed reduction in inflammatory responses suggests a subsequent promotion of osteogenesis. These promising results position the Ti6Al4V-based implant integrated with equine bone as a potential candidate for replacing conventional dental and orthopedic implants.

A new cutting tool filled with metallic lattice and design method for vibration suppression in milling

Enhancing the vibration suppression performance of cutting tools is crucial for achieving high-performance cutting of difficult-to-machine materials. This paper presents a novel cutting tool as well as its design method for vibration suppression in milling process. By incorporating a high-damping lattice structure into the cutting tool, the dynamic stiffness of the spindle-holder-tool system can be effectively increased based on the dynamic absorber effect. To achieve this goal, the natural frequency of the cutting tool filled with metallic lattice is tuned with the spindle-holder subassembly by altering the geometric parameters of the metallic lattice. A comprehensive dynamic model of the spindle-holder-tool system, considering the complex tool geometries, is developed to accurately analyze this system’s behavior and a design procedure is proposed to optimize the cutting tool. The geometric parameters of the lattice structure in the cutting tool are optimized based on the dynamic model, while the cell type of the high-damping lattice is selected by experiments. The proposed cutting tool is additively manufactured using the selective laser melting technique, and a comparison is made with a conventional indexable cutting tool with a solid tool body. Both simulations and impact hammer tests demonstrate an increase of 18.3% in the dynamic stiffness of the proposed cutting tool filled with metallic lattice compared with the conventional indexable cutting tool. Furthermore, a large number of milling tests are carried out on titanium alloy Ti-6Al-4V to validate the vibration suppression performance of the cutting tool filled with metallic lattice. Experimental results show that the stability limit corresponding to the proposed cutting tool can be doubled compared with the conventional indexable cutting tool.

Parametric Optimization of Selective Laser Melted 13Ni400 Maraging Steel by Taguchi Method

Parametric Optimization of Selective Laser Melted 13Ni400 Maraging Steel by Taguchi Method

Study of the effect of bio-inspired surface texture on the shear strength of bonded 3D-printed materials: Comparison between stainless steel and polycarbonate joints

Additive Manufacturing (AM) is one of the important technological pillars of Industry 4.0. Thanks to its tool-free manufacturing and extreme flexibility, AM has the potential to respond to individual customer preferences with a customized final product. Nevertheless, the size of 3D printed products is limited by the size of the build chamber of commercially available printers. In addition, deformations, stability, tolerances, and especially cost are highly dependent on the maximum size of the parts. Therefore, a larger final product can only be realized as an assembly group. Therefore, adhesive bonding appears to be an attractive solution for assembling parts made by AM. In this paper, a comparison of the influence of surface texture on the shear strength of 3D-printed metallic and polymeric adhesive joints was performed. A fish scale (FS) bio-inspired surface texture was chosen to examine how surface patterning influences the strength of joints. Fused deposition modeling (FDM) and selective laser melting (SLM) techniques were used to produce polycarbonate (PC) and stainless steel (17-4 PH) specimens, respectively. The effect of bio-surface and material type on the shear strength of adhesive joints was assessed using the ASTM D4501 standardized block shear testing method. The morphological analysis revealed that FDM exhibits reduced resolution and accuracy, making it less suitable for the additive manufacturing of complex surface features in 3D-printed parts when compared to SLM technology. In addition, bio-surface texturing significantly improved the wettability of stainless steel, requiring the synergy of higher surface free energy and increased surface roughness (FS bio-surface) for super-hydrophilicity, while a combination with lower surface free energy (PC material) and the same surface roughness resulted in hydrophobic behavior. On the other hand, the bio-surface texture greatly enhanced the shear strength (+31%) of stainless steel specimens, compared to PC specimens, due to the increase of physical adsorption forces and the enhancement of the mechanical interlocking effect. The analysis of variance (ANOVA) results highlight the predominant influence of material type on surface wettability (84%), while surface texture has a more pronounced impact on the shear strength of bonded joints (71%).

ABRASIVE SURFACE TREATMENT OF ALSI10MG PARTS MADE BY L-PBF

The scientific community has been intensively studying how to improve the level of surface roughness on 3D-printed parts, particularly metallic parts made using the selective laser melting (SLM) technique. Various research papers on this subject have revealed that accurate surface roughness data can be generated using several methods that are, in fact, not cost-effective. For this reason, the finishing processes are an integral part of the overall production, especially for those components where the primary concern is not only appearance but also functional properties (e.g., lower friction, reduced noise, etc.). This work deals with the measurement of the surface roughness of tumbled parts produced with SLM after surface treatment with centrifugal and vibratory methods. Tumbling was performed with ceramic, plastic, and porcelain mediums. At the end, there is an evaluation of the measurement data based on the required surface roughness of the components.

High cycle fatigue behaviour of AlSi10Mg alloy processed by selective laser melting technique

ABSTRACT Selective laser melting (SLM) is progressing rapidly with promising applications in both scientific and industrial areas. AlSi10Mg is currently used in automotive and aerospace industries. While most of the existing literature on fatigue study was based on artificially made defects, various roughness levels and densified or hot isostatic pressed conditions, the present study aims to understand the high cycle fatigue (HCF) behaviour of SLMed AlSi10Mg alloy which was not subjected to any machining to remove the surface roughness. The as-built condition was high cycle fatigue tested at various stress amplitudes, and the S-N plot was drawn. OM image of the AlSi10Mg alloy in the as-built condition revealed the scan track pattern and pores in the longitudinal plane and fish scale morphology in the transverse plane. The SEM image showed a fine aluminium cell surrounded with eutectic silicon inside the melt pool. It was observed from the S-N curve that the number of cycles reduced on increasing the stress amplitude and the as-built AlSi10Mg can be used safely below 70 MPa. SEM fractography confirmed that the surface roughness, surface and subsurface pores were found to be the source of crack nucleation irrespective of the stress amplitude.

Effect of process parameters on the densification of SLM-produced Mg–Y–Sm–Zn–Zr alloy

In this study, Mg–Y–Sm–Zn–Zr samples were prepared using the selective laser melting technique. The influence of process parameters on the densification and mechanical properties of samples was systematically studied from a single-melt track to double melt tracks to block, and the formation mechanism of defects was analysed. Research results show that the appropriate laser power and scanning speed resulted in excellent single-melt path formability. When the scanning spacing was 80 μm, adjacent trajectories were closely connected without spheroidised particles and porosity defects. The densest samples were obtained at an energy density of 125 J/mm3 with maximum microhardness (86.8 ± 1.5 HV), and the compressive yield strength and ultimate strength reached 301.8 ± 5 MPa and 467.9 ± 5 MPa.

Selective laser melting processing of heterostructured Ti6Al4V/FeCoNiCrMo alloy with superior strength and ductility

In the selective laser melting (SLM) process, the transient nature of the molten pool and rapid cooling rate facilitates partial homogenization of components, resulting in attaining a finer scale concentration modulation and spatial heterostructure. However, the SLM-processed Ti6Al4V alloys have long suffered from the problem of both large detrimental columnar grains and poor work-hardening capacity. In this study, a high entropy alloy of FeCoNiCrMo particles was incorporated into the Ti6Al4V alloy and fabricated by the SLM technique. The resulting alloys exhibited a fine-scale modulated β + α' spatial heterostructure, delivering a notable tensile strength of 1366.4 MPa and a uniform elongation of approximately 8.7% with an excellent work-hardening capacity exceeding 300 MPa. This outstanding performance can be attributed to the progressive transformation-induced plasticity (TRIP) effect and hetero-deformation induced (HDI) strengthening within the ultra-refined α' martensite and metastable β phase regions. This work provided a compelling model of additive manufacture of heterogeneous structures while offering new insights and directions for the development of metallic materials with high strength-ductility characteristics.

Powder sheet additive manufacturing of multi-material structures: Experimental and computational characterizations

Selective laser melting (SLM) of multi-material structures (MMS) is of significance because it allows for bespoke structural innovation and high-accuracy process tailoring. However, most of the currently developed loose powder-based SLM techniques for MMS are limited by the long changeover time and potential cross-contamination between materials. To address these issues, a novel Metal Additive Manufacturing using Powder Sheets (MAPS) technique is proposed for printing MMS within a single process. It utilizes flexible powder sheets as the feedstock material, which are composed of metal powder-polymer binder composites. The printability of MMS by MAPS is assessed through the fabrication of three-phase SS304-IN718-SS304 composites with increased geometric dimensions on the SS316 baseplates. The effects of part size on the evolution of the melt-pool morphology and the formation of defects during MAPS are investigated by experimental characterizations and computational modeling. The results show that when fabricating larger MMS, the use of a longer scan-vector easily leads to defects such as lack-of-fusion porosity, balling and cracks. This is due to the longer duration of inter-hatch cooling time, the reduced amount of thermal accumulation and the higher degree of residual stresses. By adopting an island scanning strategy, a defect-free large-size MMS with variations of chemical composition, microstructure and microhardness is successfully printed by MAPS. The proposed MAPS method offers a new solution for producing high-quality MMS.

Fit Accuracy of Cobalt–Chromium and Polyether Ether Ketone Prosthetic Frameworks Produced Using Digital Techniques: In Vitro Pilot Study

This pilot study aimed to compare the fit accuracy of cobalt–chromium (Co-Cr) and polyether ether ketone (PEEK) removable partial denture frameworks, produced by digital technologies. Two study models of previously prepared Kennedy’s Class I and Class III mandibular dental arches were scanned. For each model, two frameworks were digitally designed and manufactured using a Co-Cr alloy via the selective laser melting (SLM) technique, and using PEEK via the milling technique. A qualitative assessment of the framework’s fit accuracy to the corresponding study models was carried out using calibrated endodontic instruments and image amplification. Best-fit superimpositions between the reference design and the scanned frameworks were performed using the Geomagic Control X version 2018, 3D Systems software, allowing the expression of trueness by calculating the root mean square (RMS) value. Higher fit accuracy was observed for the milled frameworks, with the Class I PEEK framework showing the best fit accuracy to the corresponding model. RMS values were Class I—148.3 μm for Co-Cr and 69.2 μm for PEEK; Class III—107.2 μm for Co-Cr and 59.7 μm for PEEK. In the experimental conditions used, the milled PEEK frameworks showed better fit accuracy and higher trueness than the SLM-printed Co-Cr ones in both Kennedy classes.

Control of texture and microstructure in additive manufacturing of stainless steel 316 L

This investigation deals with exploring the effect of rotation scan strategy on microstructural evolution and hence mechanical behaviour of 316 L stainless steel prepared by additive manufacturing using selective laser melting technique. Higher anisotropy has been observed for samples where no hatch rotation was employed compared to the samples where a hatch rotation was involved during printing. The morphology of grains gets perturbed for samples prepared by hatch rotation 60˚ and hatch rot 74˚ when compared to the samples prepared using no hatch rotation or a hatch rotation of 90˚. The crystallographic texture component of the sample consists of a combination of < 100 > and < 110 > orientation (// building direction) except for the hatch rot 60˚ sample where the texture comprises of only < 110 > . It has been noticed that texture control is possible through giving a rotation such as 60˚ or 90˚. The samples prepared without any hatch rotation exhibited higher strain hardening due to combined action of slip and twin activity when compared to hatch rot 60˚ sample where < 110 > texture reduces the deformation mechanism to slip only. This study paves a new pathway to control the mechanical properties by tuning the appropriate texture along the BD.

Comparison of tensile properties and porcelain bond strength in metal frameworks fabricated by selective laser melting using three different Co-Cr alloy powders

Statement of problemThe selective laser melting (SLM) manufacturing technique has been widely employed to produce Co-Cr dental metal frameworks. The selection of Co-Cr alloy powders has the potential to influence the microstructure and tensile properties, consequently impacting the bond strength of the metal-porcelain. However, limited information is available regarding the effect of Co-Cr alloy powder on these properties when all other factors remain consistent. PurposeThe purpose of this in vitro study was to assess how the choice of Co-Cr alloys during SLM manufacturing influences the microstructure, tensile properties, and bond strength of metal-ceramic combinations. Material and methodsThree different Co-Cr alloy powders, Co-Cr-Mo, Co-Cr-Mo-W, and Co-Cr-W were selected in this study. The powder characteristics and chemical compositions were analyzed using a scanning electron microscope (SEM) and energy dispersive X-ray (EDX) analysis, respectively. Subsequently, 12×12×15-mm cube specimens, cylindrical tensile test specimens, and 25×3×0.5-mm metal strips were fabricated using the SLM technique. Microstructural investigations of the cube specimens were conducted after metallographic preparation using SEM. The cylindrical tensile specimens (n=8) from each composition were subjected to tensile tests at a deformation rate of 0.5 mm/min. Following the application of ceramic to the metal specimens (n=10) in each group, the strength of the metal-ceramic bond was evaluated through a 3-point bend test conducted at a crosshead speed of 1 mm/min. Mechanical properties obtained from the tensile tests and bond strength values were statistically analyzed using a one-way ANOVA and Tukey post hoc comparison tests (α=.05). ResultsMelt pool boundaries, columnar and equiaxed grains, and precipitates were observed in the microstructures of 3 different alloys produced by SLM. The Co-Cr-Mo-W alloy had more uniformly dispersed and finely distributed precipitates compared with other alloy compositions. The Co-Cr-Mo-W alloy had exhibited the highest yield strength (1068.0 ±41.2 MPa) and ultimate tensile strength (1263.4 ±10.7 MPa) while showing the lowest ductility under the tensile tests (6.1 ±0.9%) among all 3 alloys. Significant differences in the tensile mechanical properties were observed in the alloys except between the yield strength of the Co-Cr-Mo and Co-Cr-W alloys. The highest elongation (8.9 ±1.2%) was seen in the Co-Cr-Mo alloy. However, no significant differences were detected regarding the bond strength of all 3 groups (P>.05). The mean bond strength values were approximately 42 MPa for all the alloys. ConclusionsThe results indicate that the selection of different Co-Cr alloy powders used in SLM production may influence both microstructure and tensile properties. However, the strength of the metal-ceramic bond of Co-Cr alloys remained unaffected by this selection.

Microstructural Characteristics and Material Failure Mechanism of SLM Ti-6Al-4V-Zn Alloy

This study focuses on the additive manufacturing technique of selective laser melting (SLM) to produce Ti-6Al-4V-Zn titanium alloy. The addition of zinc at 0.3 wt.% was investigated to improve the strength and ductility of SLM Ti-6Al-4V alloys. The microstructure and mechanical properties were analyzed using different vacuum heat treatment processes, with the 800-4-FC specimen exhibiting the most favorable overall mechanical properties. Additionally, zinc serves as a stabilizing element for the β phase, enhancing the resistance to particle erosion and corrosion impedance of Ti-6Al-4V-Zn alloy. Furthermore, the incorporation of trace amounts of Zn imparts improved impact toughness and stabilized high-temperature tensile mechanical properties to SLM Ti-6Al-4V-Zn alloy. The data obtained serve as valuable references for the application of SLM-64Ti.