Selective Laser Melting Technique Research Articles

Design and simulation of a bearing housing aerospace component from titanium alloy (Ti6Al4V) for additive manufacturing

In evaluating emerging technology, such as additive manufacturing, it is important to analyse the impact of the manufacturing process on efficiency in an objective and quantifiable manner. This study deals with the design and simulation of a bearing housing made from titanium alloy (Ti6Al4V) using the selective laser melting (SLM) technique. The Finite Element Analysis (FEA) method was used for assessing the suitability of Ti6Al4V for aerospace application. The choice of Ti6Al4V is due to the comparative advantage of its strength-to-weight ratio. The implicit and explicit modules of the Abaqus software were employed for the non-linear and linear analyses of the component part. The results obtained revealed that the titanium alloy (Ti6Al4V) sufficiently meets the design, functional and service requirements of the bearing housing component produced for aerospace application. The designed bearing is suitable for a high speed and temperature application beyond 1900 K, while the maximum stress induced in the component during loading was 521 kPa. It is evident that the developed stresses do not result in a distortion or deformation of the material with yield strength in the region of 820 MPa. This work provides design data for the development of a bearing housing for AM under the technique of SLM using Ti6Al4V by reflecting the knowledge of the material behaviour under the operating conditions.

The Effect of Clinical Sandblasting With Different Powders on the Surface Roughness of Cores for Metal-Ceramic Crowns and Their Fracture Resistance After the Addition of Repair Material: An In-Vitro Study.

Background One of the most frequently encountered issues with metal-ceramic restorations is the fracture of veneering porcelain. This in-vitro study aims to evaluate the effect of clinical sandblasting with 50 μm aluminum oxide and 30 μm silica-coated particles on the surface roughness of metal cores and the subsequent effect on their fracture resistance after the addition of specific adhesive and packable composite as a repair material. Methodology Metal cores (n = 21) were digitally designed and three-dimensionally printed by selective laser melting (SLM) technique. These cores were randomly divided into three groups. Group A (n = 8) was sandblasted with 50 μm aluminum oxide and veneered with light cure composite. Group B (n = 8) was sandblasted with 30 μm silica-coated particles and veneered with light cure composite. Group C control group (n = 5) was sandblasted in the laboratory with 250 μm aluminum oxide and veneered with porcelain. All specimens were tested for surface roughness by a stylus profilometer. After adding the veneering material, all specimens were subjected to a fracture resistance test through a universal testing machine. Results One-way analysis of variance test showed a significantly higher difference for the specimens sandblasted in the laboratory using 250 μm aluminum oxide. Fracture resistance values showed no significant difference between groups A and B. Conclusions Groups A and B showed no significant difference in surface roughness, but their fracture resistance values were above the acceptable clinical limit.Despite the rough nature of metal cores fabricated by the SLM technique, sandblasting with silica-coated particles may be an effective way to optimize the fracture resistance of the repair material because it provides the basis for chemical adhesion.

Biocompatibility of a Zr-Based Metallic Glass Enabled by Additive Manufacturing.

The present work explored the use of the selective laser melting (SLM) technique to develop a Zr-based bulk metallic glass (BMG) and investigate the influence of the process parameters on obtaining different levels of surface roughness. Moreover, the potential of the additively manufactured BMG Zr59.3Cu28.8Al10.4Nb1.5 (trade name AMLOY-ZR01) as an implant material was studied by evaluating the osteoblastic cell response to the alloy and its stability under simulated biological environments. The materials were characterized in terms of degree of crystallinity, surface roughness, and morphology, followed by a systematic investigation of the response of the MC3T3-E1 preosteoblastic cell line to the as-printed samples. The materials supported cell proliferation and differentiation of the preosteoblastic cells, with results comparable to the reference material Ti-6Al-4V. The surface microroughness and surface morphology (porous or groove-type laser tracks) investigated in this study did not have a significant effect on modulating the cell response. Ion release experiments showed a large increase in ion release under inflammatory conditions as compared to regular physiological conditions, which could be attributed to the increased local corrosion under inflammatory conditions. The findings in this work showed that the surface roughness of the additively manufactured BMG AMLOY-ZR01 can be tailored by controlling the laser power applied during the SLM process. The favorable cell response to the as-printed AMLOY-ZR01 represents of a significant advancement of the investigation of additively manufactured BMGs for orthopedic applications, while the results of the ion release study highlights the effect that inflammatory conditions could have on the degradation of the alloy.

Ultrasonic-Assisted Electrochemical Milling of SLM-Printed Hastelloy X Based on Analysis of Material Passivation Characteristics

Hastelloy X (HX) is widely used in the aerospace field for its excellent corrosion resistance and high-temperature mechanical properties that can be fabricated into complex structures directly by the selective laser melting (SLM) technique. However, SLM-printed (SLM-ed) HX with high strength and hardness is challenging to process using conventional manufacturing techniques and may result in machining flaws that don’t fulfill engineering standards. Therefore, an ultrasonic-assisted electrochemical milling (UAECM) method using a tube electrode is proposed to fabricate high aspect ratio structures on SLM-ed HX with high-quality. Firstly, the passivation characteristics of SLM-ed HX before and after solid solution treatment (SST) were investigated using polarization curves and electrochemical impedance spectroscopy (EIS). Secondly, the electrochemical milling process and the electrode gap flow field were simulated. Then, the effect of processing parameters such as ultrasonic amplitude, electrical parameters, and mechanical parameters on the groove width and stability was investigated by the orthogonal and single factor experiments. Finally, the cavity and bump structures were machined by layered milling with an average groove width of 960 ± 15 μm, a groove depth of 4.4 mm, an aspect ratio of 4.5, and surface roughness of 1.524 μm and 1.622 μm, respectively, demonstrating the adaptability and machining accuracy of the UAECM method.

Dynamic Load Mitigation of 3D-printed Triply Periodic Minimal Surface Structures

Three types of triply periodic minimal surface (TPMS) structures are chosen to investigate the quasi-static and dynamic compressive behaviors in this paper. All the TPMS lattices (Primitive, Gyroid, IWP) have the same relative density of 37.5%, and the samples are fabricated by the 3D printing of selective laser melting technique using AlSi10Mg powder. The energy absorption performance and dynamic load mitigation of the 3D printed TPMS structures under three different impact velocities are compared, and the corresponding engineering strain rates are 143 s −1, 286 s −1, and 571 s −1, respectively. The results of numerical simulation indicate that the IWP structure has the highest specific energy absorption (SEA) and plateau stress, followed by the Gyroid structure, and finally the Primitive structure. The SEA of Primitive and Gyroid structures increases with the impact velocity and decreases for IWP structure.

Effect of fabrication method and surface roughness on spray characteristics for small pressure-swirl atomizers

The paper investigates the effect of the fabrication method, precision and surface roughness on atomization nozzle performance. A comprehensive review of the available knowledge on the topic is an integral part and an indispensable prerequisite of the study. It focuses on the requirements for atomizing nozzles and their production from the point of view of surface quality, dimensional and shape accuracy. The published results on the influence of surface quality and roughness on internal flow and atomizer performance are discussed. Available atomizer manufacturing techniques are reviewed with a focus on Rapid prototyping methods, accuracy and geometrical imperfections.Classical Machining and two 3D printing techniques were applied to produce small pressure-swirl atomizers. They were fabricated in a number of versions. The machined nozzles featured several specific defects. Spray quality measurements of these atomizers, at selected operation regimes, were made on a cold test bench using PDA and mechanical patternation to evaluate discharge coefficient (CD), Sauter mean diameter, spray cone angle, nozzle efficiency (ηn), breakup length and liquid distribution in the spray.The results show the important and systematic effects of surface quality and manufacturing imperfections on the atomizer characteristics. The exit orifice imperfections harm the circumferential uniformity and other spray characteristics. The effect becomes significant when the exit orifice shifted out of the nozzle axis by >2 % of the chamber diameter, and the orifice edge is chamfered by >20 % of the orifice length. The swirl chamber surface modified by scratches has a minor effect.Replacement of machining with current commercial 3D printing techniques, namely Selective laser melting and PolyJet technique, is associated with increased surface roughness. It worsens spray quality, liquid distribution uniformity and ηn and increases the CD when relative surface roughness exceeds 0.007.The result presentation using dimensionless criteria allows for generalisation of the outcomes to other atomizer types and scales.

Preparation of TiNbTaZrMo high-entropy alloy with tunable Young's modulus by selective laser melting

Biological high-entropy alloy (Bio-HEA) is a new generation of biomedical alloys with excellent mechanical properties and good biocompatibility. However, elemental segregation often exists during conventional casting or arc melting, which dramatically degrades their mechanical performance. Here, we utilized the selective laser melting (SLM) technique to fabricate dense blocks with low Young's modulus and good compression property at room temperature. Then, we fabricated HEA with triply periodic minimal surface (TPMS) lattice, which has Young's modulus (6.71–16.21 GPa) very close to that of human trabecular bone. This structure provides the possibility of meeting the requirement of various bone implants by customizing the shape and porosity of the TPMS lattice, affirming the possibility of Bio-HEA for biomedical applications.

Comparative study on process-structure-property relationships of TiC/Ti6Al4V and Ti6Al4V by selective laser melting

Titanium matrix composites (TMCs) have gained tremendous attention due to their excellent mechanical properties by combining the advantages of Ti6Al4V matrix and ceramic reinforcement. In current study, the selective laser melting (SLM) technique is applied to manufacture TiC/Ti6Al4V and Ti6Al4V. Systematic characterization and analysis are conducted to reveal and compare their process-structure-property relationships. The results reveal that the near fully dense parts could be manufactured by process optimization upon the systematic investigation on their densification behaviors. The addition of TiC effectively refines the matrix grain and changes the microstructures. The SLM-manufactured (SLM-ed) Ti6Al4V exhibits typical coarse columnar grains with ultrafine lamellar α+β microstructures distributed inside (average α-lath thickness: 282 nm). Nevertheless, the SLM-ed TMCs possess a peculiar molten pool morphology, in which the sub-columnar grains grow upward along the direction of the steepest temperature gradient. The acicular nanoscale TiC is dispersed inside the sub-columnar grains, while the chain-like TiC is distributed along the boundary. Meanwhile, an evolution process is proposed to describe the microstructure evolution of the SLM-ed TMCs. The interrelationships between energy density and resulting microstructures are also identified, based on which, strong and ductile Ti6Al4V specimens (tensile strength: 1390 MPa, elongation: 9.66%) and ultra-strong TMCs specimens (tensile strength: 1538 MPa) are manufactured. The strengthening effects are mainly attributed to the Hall-Petch strengthening and load-bearing transformation. Fracture analysis indicates that the failure of the SLM-ed Ti6Al4V is caused by the micro-voids nucleation and coalescence at the interface of α and β phases, whereas the premature fracture of the SLM-ed TMCs is originated from the chain-like TiC.

Effect of SiC Addition on Microhardness and Relative Density during Selective Laser Melting of 316L Stainless Steel

The utilization of 316L stainless steel has been very common in marine, automotive, architectural, and biomedical applications due to its adequate corrosion resistance to cracks after the completion of welding process. However, there has been ongoing attempts to investigate the potential enhancement in the strength and durability of 316L stainless steel by reinforcing it with silicon carbide (SiC). The present work adopts the selective laser melting (SLM) technique to fabricate SiC-reinforced 316L steel to boost its microhardness and strength properties. The methodology involved the addition of 1% wt. silicon carbide with particle sizes <40 μm to reinforce the stainless steel matrix. An SLM metal printing machine equipped with a continuous wave of 300 W fiber laser is employed to form the specimens. To measure the properties of the final product, EDX, XRD, FESEM, and universal tensile test machines have been used. The maximum value of 296 HV was obtained for a 1% volume of SiC compared to the 285 HV microhardness of pure stainless steel 316L. FESEM examination showed that the SiC microparticles were dissolved completely and they were randomly distributed in the melting basin. The samples were dissolved entirely, and the best porosity was obtained at 0.4% with influential parameters of 200 W laser power, 70 µm hatching distance, 30 µm layer thickness, and 700 mm/s velocities. The results also revealed that the microhardness at these parameters is the best compared to the samples produced with different values. The volumetric energy density was also considered. The findings can be informative to the researchers and manufacturers interested in 316L steel industry.

3D-printed MoS2/Ni electrodes with excellent electro-catalytic performance and long-term stability for dechlorination of florfenicol

Here, we report the production of 3D-printed MoS2/Ni electrodes (3D-MoS2/Ni) with long-term stability and excellent performance by the selective laser melting (SLM) technique. As a cathode, the obtained 3D-MoS2/Ni could maintain a degradation rate above 94.0% for florfenicol (FLO) when repeatedly used 50 times in water. We also found that the removal rate of FLO by 3D-MoS2/Ni was about 12 times higher than that of 3D-printed pure Ni (3D-Ni), attributed to the improved accessibility of H*. In addition, the electrochemical characterization results showed that the electrochemically active surface area of the 3D-MoS2/Ni electrode is about 3-fold higher than that of the 3D-Ni electrode while the electrical resistance is 4 times lower. Based on tert-butanol suppression, electron paramagnetic resonance and triple quadrupole mass spectrometer experiments, a “dual path” mechanism and possible degradation pathway for the dechlorination of FLO by 3D-MoS2/Ni were proposed. Furthermore, we also investigated the impacts of the cathode potential and the initial pH of the solution on the degradation of FLO. Overall, this study reveals that the SLM 3D printing technique is a promising approach for the rapid fabrication of high-stability metal electrodes, which could have broad application in the control of water contaminants in the environmental field.

Evaluation of Root-Analog Implants and Standardized Specimens Fabricated by Selective Laser Melting.

To evaluate root-analog implants (RAIs) fabricated by selective laser melting (SLM). Two types of implants (a maxillary right first molar RAI and a screw-cylinder-type molar implant) were designed using CAD software. Both implant types were fabricated with the SLM technique using Ti-6Al-4V powder. The stress distribution and micromotion of the implants were evaluated using finite element analysis, and the mechanical properties of the printed implants (relative density and compression test), surface properties of an SLM-fabricated specimen (morphology, roughness, and contact angle test), and biocompatibility of an SLM-fabricated specimen (osteoblast attachment, metal ion precipitation analysis, cell viability, and osteogenic gene expression) were evaluated. The RAI model exhibited better stress distribution and less micromotion than the screw-cylinder implant model. The screw-cylinder implant was better than the RAI at withstanding pressure, but both implant types could withstand masticatory forces. The densities of both implant types were similar to those of the bulk materials. Block samples made using the same SLM technique as the RAI exhibited good surface properties and excellent biocompatibility. The properties of the molar RAI fabricated with the SLM technique suggest that it may have potential for future clinical use, but this will need to be verified by in vivo studies.

Effect of laser scanning angle on shear slip behavior along melt track of selective laser melted 316L stainless steel during tensile failure

The improved mechanical properties have been recently realized in 316 L stainless steel (SS) materials processed by additive manufacturing (AM) techniques, owing to its cross-scale structure, especially the formation of cell-structure. However, their heterogeneous structure also inevitably leads to significant mechanical anisotropy which may impede their further applications. For revealing the impact of microstructural heterogeneity on anisotropic properties of AM processed parts, this work prepared 316 L SS components using selective laser melting (SLM) techniques under different laser scanning angles. Their tensile performances are examined, and the relationship between the origin points of deformation failure and molten pool boundary is established. The results show that when the laser scanning angle is parallel with the tensile loading direction, the elongation of 316 L stainless steel fabricated by SLM is the highest, reaching 52.5%. Meanwhile, the maximum yield strength of 687.5 MPa was obtained when the laser scanning angle was 30–45°. The main reason is that the mechanical properties of the SLM parts change with the adjustment of scanning angle due to the effect of short edge grain size and poor orientation of the low grain. So, this study will provide new insights into the microscopic fracture mechanism in SLM parts.

Quasilinear pseudoelasticity and small hysteresis in SLM-fabricated NiTi

NiTi shape memory alloys with quasilinear and slim pseudoelasticity are desirable for high fatigue life and easy controllability. This paper reports that the selective laser melting (SLM) technique can encourage formation of quasilinear pseudoplasticity with small hysteresis of NiTi. The NiTi parts are found to present a high density of dislocations in the as-fabricated state. Deformation cycling of the defect-containing SLM NiTi parts promotes the formation of a unique microstructure consisting of nanocrystalline and amorphous-like phases. Such microstructure leads to a continuous and quasilinear type pseudoelasticity with small hysteresis. It is found that the scanning speed of laser affects the dislocation density and transformation behaviour, thus influencing the pseudoelastic behaviour of the SLM-fabricated NiTi. The transformation temperatures are shown to decrease while the transformation intervals to increase with increasing the scanning speed due to the increased dislocation density. The mechanically cycled SLM fabricated NiTi with a scanning speed of 850 mm/s exhibits a stable quasilinear pseudoelasticity of 5.8% and a small energy dissipation of 1.4 MJ/m3.

Experimental study on additive manufactured 304L stainless steel tubular sections: Material properties and cross-sectional behavior

This paper presents an experimental investigation on the material properties and cross-sectional behavior of 304L stainless steel tubular sections additively manufactured using selective laser melting (SLM). A total of 76 tensile coupons, 76 hardness test specimens, and 25 stub columns were fabricated from 304L stainless steel powders by the SLM technique. Tension coupon tests and hardness tests were conducted to determine the mechanical properties. Residual stresses and local geometric imperfections of the stub columns were measured. The effects of coupon specimen orientations, thicknesses, and annealing conditions on the measured material properties were explored. In addition, the failure modes, ultimate load-carrying capacities and structural responses of the stub columns with four different cross-sections under axial compression were obtained and analyzed to evaluate the cross-sectional behavior. The test results of ultimate strengths were compared with the predictions calculated from the current design methods. The test results showed that the tensile strength of the coupon perpendicular to the building direction was higher than that of the coupon parallel to the building direction. Moreover, the tensile strength of the coupon increased with the increase of the coupon thickness. Considering the cross-sectional behavior, the square hollow section (SHS) and circular hollow section (CHS) had greater cross-sectional axial capacities than the rectangular hollow section (RHS) and elliptical hollow section (EHS), respectively. The introduction of a single stiffener in SHS and CHS reduced the load-carrying capacities to a certain extent.

A Comparative Study of Protective Film Formation of Additively Manufactured 316L SS and Conventional Wrought 316L SS in Aqueous, Gaseous and Steam Environments

Additively prepared 316L SS using selective laser melting technique has been found to possess better passivation behavior in relation to its wrought counterpart in aqueous media such as chloride solutions, despite having cast structure. This has been attributed to the absence of manganese sulfide inclusions and higher chromium content of the passive film formed on the former. Not much work has been published on the behavior of this alloy in high temperature gaseous and steam environments though it is expected to be employed in such environments. Our studies show that the nature of the oxides formed on oxidation on the additively formed alloy has been found to be notably different from that formed on its wrought alloy counterpart. A talk will bring out the salient differences shown by these two types of alloys and their implication on the protection behavior.

Crack Formation and Control in an AlCoCrFeNi High Entropy Alloy Fabricated by Selective Laser Melting.

The equiatomic AlCoCrFeNi high entropy alloy (HEA) is prone to cracking during the additive manufacturing process due to the high cooling rates observed, which limits its application to a large extent. In this study, the selective laser melting (SLM) technique was adopted to fabricate the alloy and the mechanism of crack formation was revealed. Most importantly, a new design strategy was proposed to suppress the generation of cracks, and the optimization of the preparation process was also studied in detail. It is found that the interlaminar crack is related to the heat input at the edge of the specimen, and the internal cracks are formed by solidification cracks. Alloys without interlaminar crack can be prepared by means of combination of the side inclination angle and the process parameters. Side inclination angle optimization provides a possibility for the preparation of crack-free AlCoCrFeNi HEA by SLM.

Microstructure, texture, and anisotropic mechanical behavior of selective laser melted maraging stainless steels

In present research, the effect of building orientation on microstructure, texture and mechanical properties of a low carbon maraging steel processed by selective laser melting (SLM) technique is studied. The microstructural characterization and grain structure observations of the fabricated samples are conducted using electron microscopies and electron backscatter diffraction. It is observed that by altering the building orientation from vertical to horizontal, the morphology of the grains changes from columnar-dendritic to equiaxed. In addition, a higher volume fraction of austenite is retained in the horizontal sample compared with the vertically printed sample due to a faster cooling rate, higher degree of micro-segregation, and smaller prior austenite grains. Consequently, a higher strength and better ductility are achieved in the horizontally printed sample. The Taylor factorshows that different obtained tensile properties are not related to the crystallographic texture but are affected by grain size, retained austenite, and stress concentration conditions.

Marginal Misfit of 3D-Printed (Selective Laser Sintered), CAD-CAM and Lost Wax Technique Cobalt Chromium Copings with Shoulder and Chamfer Finish Lines: An In-Vitro Study.

Background and Objectives: The aim was to compare the Misfit of 3D-Printed, Selective laser melting (SLM), milled (Computer aided design-Computer aided manufacture CAD-CAM) and Lost wax technique (LWT) fabricated Cobalt chromium (CoCr) alloy copings on shoulder (SH), radial shoulder (R-SH) and chamfer (CH) finish line configuration. Materials and Methods: Ninety resin, second maxillary premolar teeth were prepared for metal-ceramic crowns, equally divided into (n = 30) SH, R-SH and CH margin preparations. For each preparation design (SH, R-SH and CH), CoCr copings were prepared using SLM, CAD-CAM and LWT. This resulted in nine study groups with 10 CoCr copings each. The marginal misfit of specimens was assessed with a high-resolution digital microscope. Misfit was evaluated in vertical and horizontal dimensions in μm. Data were analyzed using ANOVA and a post hoc multiple comparisons test. Results: For vertical misfit, the highest was observed in SLM samples with chamfer margin (167.96 ± 24.1), and the least was shown by CAD-CAM samples with radial shoulder (58.8 ± 12.53). CAD-CAM and shoulder margins showed the least vertical misfit. For horizontal misfit, the maximum was observed in SLM samples with shoulder margin (137.94 ± 37.85) and the least by LWT samples with chamfer (89.38 ± 14.81). Chamfer margins and LWT samples showed the least horizontal misfit among the group samples. Fabrication technique and finish line design play a critical role in reducing the marginal misfit of CoCr copings. Conclusions: For vertical misfit, SLM copings showed poor outcomes compared to CAD-CAM specimens, however comparable outcomes to Cast specimens. SLM copings showed comparable horizontal misfit outcomes to CAD-CAM specimens and low misfit compared to Cast copings, respectively. Vertical misfit was low with shoulder margins, and horizontal misfit was better with chamfer marginal configuration.

Representative volume element homogenisation approach to characterise additively manufactured porous metals

Additive manufacturing represents a great candidate to boost smart materials expansion in the Industry 4.0 era through 4 D printing technologies. However, to fully exploit the benefits of these technologies, increasing knowledge is needed on how internal defects condition the overall behavior of the component. In this work, the Representative Volume Element approach is presented to investigate, through Finite Element Analyses, how micro-voids influence the stress-strain behavior of an AlSi10Mg additively manufactured through the Selective Laser Melting technique. An in-house code on the commercial software ANSYS Parametric Design Language APDL was developed to model a random pore distribution inside the RVE and to apply the boundary conditions necessary for the RVE periodicity; comparison with reference case studies from the literature are reported.

Effect of full arch two scanning techniques on the accuracy of overdenture conventional and CAD/CAM Co-Cr bars

PurposeThis work evaluates the internal and marginal adaptation of implant-assisted overdenture cobalt–chromium (Co–Cr) bars manufactured using conventional as well as CAD/CAM subtractive and selective laser melting (SLM) utilizing two scanning techniques. Methods: An edentulous study model containing four dental implants placed at teeth sites 36, 33, 43, and 46 was used. The study cast was scanned and compared to the virtual casts developed from two scanning techniques, straight and zigzag motion, using the in silico superimposition process. Then, conventional techniques were used to produce full-arch bars that were compared to the bars fabricated using the two scanning techniques and CAD/CAM subtractive and additive techniques. Results: The conventional impression and casting techniques had the smallest marginal gap among the groups (P-value < 0.05). The CAD/CAM subtractive milling techniques in groups II and III had significantly smaller marginal gaps than SLM technique used in groups IV and V (P-value < 0.05). The analysis of the internal gap within each group showed statistically significant differences between different implant sites in all groups (P-value < 0.001), except when using the conventional impression and casting techniques in group I (P-value = 0.20). Conclusion: The conventional impression and fabrication techniques were better than the digital impression and CAD/CAM subtractive and additive techniques for the fabrication of full-arch bars. However, both straight and zigzag scanning techniques and the CAD/CAM subtractive technique had marginal and internal gaps that were within clinically accepted ranges, and the SLM was found to be unsuitable for long-span framework fabrication with either scanning technique used.