Use Of Selective Laser Melting Research Articles

Controlling mechanical properties and energy absorption in AlSi10Mg lattice structures through solution and aging heat treatments

The use of Selective Laser Melting (SLM) has gained popularity due to its ability to produce complex-shaped parts, which includes lightweight lattice structures that are appealing to a variety of industries. AlSi10Mg alloy is a favored choice for SLM due to its excellent specific properties. The utilization of AlSi10Mg in lattice structures further reduces their mass while enhancing specific mechanical properties. However, the inherent brittle deformation behavior of as-built AlSi10Mg restricts the energy absorption potential of lattice structures. This study explores the control of mechanical properties and energy absorption in AlSi10Mg lattice structures and bulk tensile samples through solution and aging heat treatments, examining their impact on microstructural transformations. The results show that solution heat treatment decreases the mechanical properties of lattice structures and bulk tensile samples while improving their ductility and energy absorption. This change is attributed to the transformation of the alloy's fine cellular microstructure into coarser Si-precipitates. Subsequent aging treatments lead to increased mechanical properties in lattice structures solution heat treated at 500 and 550 °C, albeit with a slight reduction in energy absorption. Intriguingly, lattice structures heat treated at 460 °C exhibit unchanged mechanical properties and energy absorption, as confirmed by the t-test. Additionally, the absence of the Al5FeSi intermetallic phase suggests that aging did not occur following solution heat treatment at 460 °C. These findings offer valuable insights into manipulating the mechanical properties and energy absorption of AlSi10Mg lattice structures through controlled heat treatments. Such control can significantly enhance the performance and functionality of lattice structures in practical applications.

Influence of bio-inspired surface texture of additively manufactured 17-4 PH stainless steel adherends on the strength of adhesively bonded joints

The bonding potential of as-printed additively manufactured stainless steel is largely unknown, and the use of additional hierarchical bio-inspired surface texture has not yet been explored or characterized. In this study, it is demonstrated with the use of Selective Laser Melting (SLM) that a hierarchy of three surface features at different length scales can greatly improve the shear strength of metal-metal adhesive joints. The intrinsic stochastic texture of the SLM as-printed surface showed a high contact angle and a mixed failure with a dominance of adhesive failure. However, enhancing the as-printed surface with the Tree Frog (TF) and Fish Scale (FS) bio-inspired textures produced super-wetting surfaces, significantly improving the shear strength due to the synergistic effect of mechanical interlocking and physical adsorption adhesion mechanisms, resulting in mixed failure. The results indicated that the interfacial bonding performance was in line with the super-wetting behavior and was higher for the samples with a hierarchy of three surface features. The highest increase in bond strength was found for the tree frog hierarchical hexagonal texture (+70% compared to the as-printed texture). In contrast, abrasion of the as-printed surface with P1000-grit paper significantly reduced the surface roughness and increased the water contact angle, resulting in the lowest shear strength.

Crystallographic Texture and Substructural Phenomena in 316 Stainless Steel Printed by Selective Laser Melting.

There is a fast-growing interest in the use of selective laser melting (SLM) for metal/alloy additive manufacturing. Our current knowledge of SLM-printed 316 stainless steel (SS316) is limited and sometimes appears sporadic, presumably due to the complex interdependent effects of a large number of process variables of the SLM processing. This is reflected in the discrepant findings in the crystallographic textures and microstructures in this investigation compared to those reported in the literature, which also vary among themselves. The as-printed material is macroscopically asymmetric in terms of both structure and crystallographic texture. The <101> and <111> crystallographic directions align parallel with the SLM scanning direction (SD) and build direction (BD), respectively. Likewise, some characteristic low-angle boundary features have been reported to be crystallographic, while this investigation unequivocally proves them to be non-crystallographic, since they always maintain an identical alignment with the SLM laser scanning direction, irrespective of the matrix material's crystal orientation. There are also 500 ± 200 nm columnar or cellular features, depending on the cross-section, which are generally found all over the sample. These columnar or cellular features are formed with walls made of dense packing of dislocations entangled with Mn-, Si- and O-enriched amorphous inclusions. They remain stable after ASM solution treatments at a temperature of 1050 °C, and therefore, are capable of hindering boundary migration events of recrystallization and grain growth. Thus, the nanoscale structures can be retained at high temperatures. Large 2-4 μm inclusions form during the solution treatment, within which the chemical and phase distribution are heterogeneous.

Fundamental Study on the Development of Pure Magnesium Parts by Additive Manufacturing: An Experimental and Computational Analysis

The low density and high biocompatibility of Mg-based materials make them suitable for lightweight structural and biomedical applications. In this study, we explored the use of selective laser melting (SLM)–an additive manufacturing process wherein metal powders are consolidated in a layer-by-layer manner, allowing the fabrication of complex components. SLM typically involves complex physicochemical phenomena and results in laser-processing defects, which makes it difficult to predict the densification mechanisms of the melt pool. Therefore, a full-scale model was developed to investigate the thermal behavior of the melt pool (e.g., temperature gradient distribution, melt pool dimensions, and cooling rate) and the resultant densification activity under various laser energy density (η) values. In parallel, experimental investigations of the densification behavior and microstructural evolution were undertaken with the same SLM processing parameters. The challenges associated with the SLM processability of Mg were comprehensively addressed. Both the peak temperature gradients within the molten pool and molten pool dimensions increased with increasing η, and an opposite trend was observed for the cooling rate. A low η (i.e., high scanning speed) results in a low operating temperature and short liquid lifetime, which in turn lead to poor wettability and many pore-chain and balling defects. However, high η values generated melt pool instability, which resulted in extensive evaporation, cracks, and porosity. The SLM-processed samples had fine twin-like microstructures as a result of rapid solidification. The experimental and simulation results agreed well, validating the thermal behavior of the molten pool and underlying physical mechanism.Graphic Abstract

The effect of etched 3D printed Cu-bearing titanium alloy on the polarization of macrophage

3D printed titanium alloys have been widely used as implants in orthopedic surgery and dentistry. In recent years, Cu-bearing titanium alloys have shown great advantages in tissue engineering due to their excellent antibacterial activity and biological effect. In the current study, three alloys, namely, TC4 alloy, TC4-5Cu alloy, and TC4-6Cu alloy were fabricated by the use of selective laser melting (SLM) technology. Acid etching treatment was used to remove the metal powders on the samples and modify the surface of the manufactured alloys. The effect of different etched alloys on the biological behavior of macrophages (RAW 264.7) was studied comprehensively. Results showed that acid etching had no effect on the hydrophilicity, while contributing to the adhesion and polarization of macrophages with a lower ROS level. Moreover, Cu-bearing titanium exhibited better cell adhesion, macrophage polarization potential, and a lower ROS level. In summary, acid etching treatment provided a promising strategy to improve the biological properties of the Cu-bearing titanium alloys by SLM.

High strength and ductility of titanium matrix composites by nanoscale design in selective laser melting

• SLM parameters play a major role in densification and microstructure. • Nanosized secondary particle additions promote densification. • Nanosized BN additions produce fine, high aspect ratio TiB reinforcement. • TiB morphological evolution during SLM and heat treatment impacts properties. • High tensile strength and ductility through high aspect ratio TiB nanowhiskers. The use of selective laser melting (SLM) to produce titanium matrix composites (TMCs) with high strength while retaining sufficient tensile ductility suitable for structural applications is emerging as an attractive opportunity in the field of advanced manufacturing. However, the presence of coarse ceramic reinforcements as well as difficulties in optimizing the SLM process is a barrier to the application of TMCs. In this study, we demonstrated the production of TMCs reinforced with in situ high aspect ratio TiB nanowhiskers by selective laser melting using nanosized BN powder additions. Pure Ti with 2.5 vol.% nanosized BN powder showed promise for producing high performance TMCs with retained ductility. BN acted to produce TiB nanowhiskers with diameter < 50 nm. Further, by controlling post process furnace annealing TiB retained a low diameter but exhibited a high aspect ratio, up to 400. In addition to TiB refinement, nanosized BN addition promoted grain refinement during SLM, both acting as a solute to induce nucleation events and, as TiB is formed, providing nucleation sites leading to an ultrafine grain structure in as printed samples and after annealing. The produced TMCs exhibit high tensile yield strength, up to 1392 MPa, while retaining tensile ductility up to 10%. This study has shown how nanoscale design in powder bed fusion additive manufacturing techniques can be used to produce high performance TMCs through a combination of refined grain structure and high aspect ratio TiB leading to TMCs with significant improvement in strength, isotropic properties and retained tensile ductility.

The Effects of Heat Treatment on Microstructure and Mechanical Properties of Selective Laser Melting 6061 Aluminum Alloy.

Selective laser melting technology can be used for forming curved panels of 6061 aluminum alloy thermal shield devices for the International Thermonuclear Experimental Reactor (ITER), in order to make the formed parts with better performance. This study proposes different heat treatment processes, including annealed treatment at 300 °C for 2 h, solution treatment at 535 °C and then aging at 175 °C over 2 h, to control the mechanical behavior of the 6061 aluminum alloy samples prepared by selective laser melting (SLM). The mechanical properties such as ductility, tensile strength, and hardness of SLM 6061 aluminum alloy were investigated, and the microstructure of the samples was analyzed. The eutectic silicon skeleton shape disappeared after annealing treatment at 300 °C for 2 h. The tensile strength decreased by 22.86% (from 315 MPa to 243 MPa of the deposited state samples), and the elongation increased from 2.01% to 6.89%. Moreover, the hardness reduced from 120.07 HV0.2 to 89.6 HV0.2. After solution aging, the unique microstructure of SLM disappeared. Furthermore, the precipitation of massive Si particles on the α-Al matrix increased, and a trace amount of the Mg2Si(β) phase was generated. Compared with the deposited samples, the tensile strength decreased by 12.06%, while the hardness of specimens was 118.8 HV0.2. However, the elongation showed a remarkable increase of 297% (from 2.01% to 7.97%). Therefore, solution aging can critically improve the plasticity without losing significant tensile stress in the SLM 6061 aluminum alloy. This study proposes the use of SLM 6061 aluminum alloy for the thermal shields on the ITER and provides a reference for choosing a reasonable heat-treatment method for the optimal performance of the SLM 6061 aluminum alloy.

Investigation of the Interface between Laser-Melted CoCr and a Stainless Steel Substrate

Recent advances in laser technologies offer significant flexibility in the additive manufacturing domain. Extensive work was focused on material processing using laser-directed energy deposition for repairing parts. This pilot study investigated the use of selective laser melting (SLM) for depositing a superior material such as CoCr on an existing stainless steel base. The interface between these dissimilar materials was analyzed. During fabrication, both metals were gradually mixed in the liquid state as the first CoCr powder layer was melded on the steel base without obvious defects. According to SEM and EDAX, the heat-affected zone has a limited depth (&lt;20 µm). XRD patterns recorded across the CoCr–304 interface show a homogenous mixture of γ(Fe) and α(Co) solid solutions. The microporosity calculated by CT was under 0.5%. Microhardness was measured at and near the interface region, showing that the intermixing zone has high hardness (470–480 HV1), which may be related to the fine-grained microstructure. Mechanical testing reveals that the adhesion strength at rupture is 35% higher compared with the ultimate tensile strength of 304 steel. This adhesion strength can be attributed to the complete melting of CoCr particles after laser irradiation and to the reduced thickness of the HAZ and the IZ.

Additive Manufacturing: A Brief Study on Selecting Laser Melting Technology

In today’s day and age of technological advancement, manufacturing plays a vital role in safeguarding our present and building our future. The different ways of machining materials has evolved gradually from the Stone Age to the Iron Age and so on and has reached a point where human civilization has achieved creation of unimaginable technologies to build this world in a better and more efficient way. Additive manufacturing is such an aspect of this technological milestone which is developing vastly. This is a work on additive manufacturing technologies, specifically the use of Selective Laser Melting methods and a discussion of different aspects related to it, such as the processing parameters and the material properties and characteristics of the fabricated part. In simple words, Selective Laser Melting is an Additive Manufacturing method where a high power laser beam is used to melt powdered form of material and put this molten material layer by layer to fabricate the desired part. This review work enlightens the use of Selective Laser Melting in today’s world. This review work provides vital information with regards to the parameters, material properties, material selection and an overview of additive manufacturing specifically the selective laser melting method.

Design and Molding of Thyroid Cartilage Prosthesis Based on 3D Printing Technology

The modeling efficiency, matching, and biocompatibility are key factors affecting the surgical success of a personalized thyroid cartilage prosthesis. We performed three-dimensional reconstruction of a thyroid cartilage prosthesis by combining reverse and forward methods, and then completed the prosthesis design with total or partial resection using a parametric modeling method. Direct manufacturing was performed using selective laser melting (SLM) molding equipment and TC4 material. The structure of the completed implant unit was optimized. The results show good modeling effects for the thyroid cartilage prosthesis with either total or partial resection by the parametric modeling method. Good matching performance was achieved, with overlap suspension between the pillars that meets the requirements of SLM manufacturing. Additionally, the use of SLM molding to produce the thyroid cartilage prosthesis resulted in less powder adhesion on the surface and no obvious nodulation between the porous pillars, allowing the direct use of the prothesis after simple post-treatment. Overall, these results should facilitate the direct application of personalized implants.

Energy performance evaluation of selective laser melting

Selective Laser Melting (SLM) is an additive manufacturing (AM) process in which a laser beam scans a selective area of a powder bed to create layers and generate components. SLM is considered to have sustainable benefits against conventional manufacturing, while current studies also point out that these benefits are only case-specific. Therefore, understanding the mechanism behind the material and energy-consuming behavior of SLM is an emerging research issue. This study focuses on three questions related to the energy performance of SLM. First, this research has compared the energy demand for processing approximately one cm³ of steel and examined the energy use of different system components. Second, considering that lightweight is the most common design approach to improve the sustainable benefits of SLM, this research has analyzed the relationship between the different levels of volume reduction during topology optimization and the energy use of SLM. Third, this research has investigated the impact of different process parameters on the energy use of SLM, which enables the energy efficiency-oriented build process design of SLM.

Structure of VT6 – SiC composite material

To date, the methods of additive technologies for manufacturing goods are applying more and more widely in the real sector of production and are rapidly developing. The development of various composite materials by these methods is of increased interest, since it has become possible to obtain composite materials with a different number of initial components of the matrix and reinforcer. It became possible to integrate ceramics into a metal matrix and vice versa by growing products from raw powder materials variously composed. The resultant materials may be used as a replacement for existing ones, since they have a cumulative unique set of properties that are necessary for technological and scientific expansion. Combination of well-known technologies, such as classical hot isostatic pressing, selective laser melting and ceramic fiber reinforcement, will make it possible to obtain unique composite materials. Thin-walled products from titanium alloys, including thin sections, may be obtained by the use of selective laser melting. The main problems in manufacturing of fiber-reinforced materials are setting the fibers in a given position, minimizing their displacement during consolidation, as well as limiting the matrix and fiber interaction during consolidation to prevent a reaction with the formation of an interaction zone. In order to create a new material, a silicon carbide reinforcing fiber was loaded into the shaped manufactured article, followed by encapsulated hot isostatic pressing. As a result, effective diffusion connections of individual matrix elements took place, as well as complete enveloping the fibers with the matrix material. A low-porosity structure without large defects visible on X-ray tomography was obtained.The work was carried out with the financial support of the Ministry of Science and Higher Education of the Russian Federation under the Grant agreement No. 075-11-2019-058 dated 25.11.2019 &ldquo;Organization of production of locally reinforced parts made of titanium alloys operating under conditions of increased loads and temperatures for advanced aviation gas turbine engines&rdquo;, approved by the Decree No. 218 of the Government of the Russian Federation.

Microstructural characterization and wear resistance of boride-reinforced steel coatings produced by Selective Laser Melting (SLM)

Surface engineering is an effective method to extend the lifespan of carbon steels submitted to severe wear degradation. In this work, the surface of a low carbon steel (AISI 1020) was protected by a boron-modified stainless steel coating produced by selective laser melting (SLM). Commercial precursors such as 2205 duplex stainless steel and ferrous-alloy (Fe-B) were used to produce boron-modified steel powders by two different routes: i) gas atomization, and ii) gas atomization followed by mechanical milling of large particles (to reduce the particles’ size and to add a solid lubricant – hexagonal boron nitride, h-BN). Thick coatings (200 – 600 μm) metallurgically bonded to the substrate were produced with reduced dilution, characterized by refined, hard and rigid borides homogeneously distributed within the predominant ferritic matrix. The boron-modified steel coatings were hard (~800 HV0.5) and wear-resistant, since the specific wear rate was ~4.5 × 10−5 mm3·N−1·m−1, much inferior to that of the soft (~120 HV0.5) AISI 1020 substrate (~1.8 × 10−3 mm3·N−1·m−1). Although recognized as solid-lubrificant, the coating produced by powder containing h-BN additions did not exhibit reduced coefficient of friction. Given the high temperatures achieved during SLM process, the h-BN may decompose, being the remaining content insufficient to enable the formation of an effective lubrificating layer. The present work contributes to widespread the use of SLM to produce wear-resistant protective coatings using boride-reinforced stainless steels.

High-performance nickel coating on SLM 316L stainless steel processed by jet electrochemical machining and jet electrodeposition

Selective laser melting (SLM) is an important method in additive manufacturing. SLM has obvious advantages for the fabrication of metal parts with complex structure that cannot be processed directly and are manufactured in relatively low amounts. However, the surfaces of the SLM-formed parts contain more adhesive particles and pores than those manufactured by traditional methods, leading to the poor corrosion resistance of the parts and preventing the widespread use of SLM. To solve these problems, jet electrochemical machining and jet electrodeposition combined processing techniques were investigated for the treatment of the substrate surface in this work. Jet electrochemical machining was used to remove the surface defects of the SLM-formed parts, and the results were compared with the traditional sandblasting and sandpaper grinding surface treatment methods. Then, the nickel coating was deposited on the surface of the SLM-formed parts using jet electrodeposition to protect the surface and extend the service life of the parts. The mechanisms of the different processing techniques were analyzed, and properties such as the substrate morphology, coating morphology, corrosion resistance of the coating, and adhesion of the coating were compared. The results show that holes, adhesive particles and other defects are still present on the substrate surface after sandpaper grinding and sandblasting and affect the quality of the nickel coating. After electrochemical machining, the SLM surface defects were almost completely removed, forming a uniform microporous structure that interlocked with the nickel coating. The coating was smooth and dense and showed the best corrosion resistance and binding force. In 3.5 wt% NaCl solution, the corrosion potential reached −0.196 V, and the maximum binding force reached 35 N.

Influence of laser beam scanning strategy in the selective laser melting of 316L steel powder on macrostress

The use of selective laser melting (SLM) leads to the formation of a complex material structure with high residual elastic stresses. The work investigates the distribution of macrostresses in SLM samples using five different scanning strategies. The stresses were measured by X-ray method and by recording the change in the shape of the specimens as a result of their separation from the platform using digital correlation image method. The combined use of the two methods provides more reliable results for SLM samples. It is shown that depending on the scanning strategy, the nature and magnitude of macrostresses change which are distributed more isotropically and have a smaller value when using scanning strategies with different directions of the laser beam movement.

Formation of equiaxed grains in selective laser melted pure titanium during annealing

Commercially pure titanium (CP-Ti) has seen major applications in biomedical equipment. The use of selective laser melting (SLM) has become more common concerning the fabrication of CP-Ti components with a complicated shape in biomedical implants, where high strength and ductility are required. However, SLM manufactured CP-Ti often exhibits high strength and low ductility, as well as mechanical anisotropy because SLM process typically results in the formation of long columnar grains comprising of fine acicular α′ martensite. Heat treatment must be preceded to transform the acicular α′ to equiaxed α grain. This study demonstrated that annealing at 650 °C of SLM CP-Ti can create an equiaxed structure, resulting in a weakened texture. The formation of equiaxed grains occurred at two types of microstructural features, acicular α′ and irregular massive (α′m) martensite, which exhibited different sizes, morphologies, and contained different types of substructures under SLM as-fabricated condition. The formation mechanism of equiaxed grains in the α′ region is dominated by the coalescence of acicular α′ of the same variant and the dissolution of α′ into the matrix, whereas the formation mechanism in the α′m region is primarily dominated by the growth of the preexisting subgrains. A small number of equiaxed grains with new orientations were formed in the α′m region. The majority of equiaxed grains were formed in the acicular α′ region and inherited the grain orientations of the preexisting α′ or matrix. Therefore, a similar but weakened texture was inherited from the microstructure of the SLM CP-Ti after annealing.

Use of Selective Laser Melting (SLM) as a Replacement for Pressure Die Casting Technology for the Production of Automotive Casting

Use of Selective Laser Melting (SLM) as a Replacement for Pressure Die Casting Technology for the Production of Automotive Casting

Realizing superior ductility of selective laser melted Ti-6Al-4V through a multi-step heat treatment

The use of selective laser melting (SLM) has become more common with regard to the fabrication of high-strength Ti-6Al-4V components. However, the as-SLMed Ti-6Al-4V alloy parts typically exhibit low ductility because of the formation of acicular and brittle α′ martensites. It is essential to use post-heat treatment to change their microstructures to achieve superior mechanical properties. In this study, a particular multi-step heat treatment (MSHT) was applied to the Ti-6Al-4V alloy samples fabricated via SLM. Conventional post-heat treatments were conducted for comparison. The microstructures and tensile properties of the as-SLMed and heat-treated samples were investigated. The as-SLMed Ti-6Al-4V sample is dominated by plate and acicular α′ martensites, which exhibit high strength (1280 MPa) and low ductility (9.0%). The conventional solution plus aging or stress-relieving treatment cannot result in a good combination of strength and ductility. A single step annealing process at 700 °C for 2 h changes the martensitic structure to a fine lamellar α+β structure, which provides a strong and ductile Ti-6Al-4V with an ultimate tensile strength of 1108 MPa and a total elongation of 17.6%. In contrast, the MSHT process facilitates the globularization of α and, thereby generates a nearly equiaxed structure, resulting in superior ductility (21.8% of total elongation), while maintaining a moderate ultimate tensile strength of 953 MPa.

Creation of Textured Surfaces by Electrical Discharge Machining

The applicability of electrical discharge machining (EDM) in creating textured surfaces is investigated. Recommendations are made regarding the use of selective laser melting to create complex tool electrodes. The theoretical basis is established for the creation of textured working surfaces, so as to produce a hydrophobic material capable of oil storage, with consequent decrease in friction and increase in wear and corrosion resistance. In that case, the properties of the material are retained or improved on account of decrease in grain size. The textured material produced may also be used to obstruct the motion of structural elements.

Challenges and Opportunities in the Selective Laser Melting of Biodegradable Metals for Load-Bearing Bone Scaffold Applications

The aim of this paper is to assess the current status of processing biodegradable metals (BDM) via selective laser melting (SLM), with particular emphasis on bone scaffold applications, and provide a meta-analysis on the effect of processing parameters on relative density to better direct recommendations for the future of this growing field. Synthetic bone scaffolds are becoming a popular alternative for the treatment of critical bone defects that cannot heal without surgical intervention. These scaffolds act as a bridge allowing bone to grow across the gap. Selective laser melting can achieve bone scaffolds with complex hierarchical architecture tailored specifically to the patient. SLM-manufactured titanium scaffolds have already been clinically tested with some success. Permanent titanium alloys have a higher chance of implant rejection from the innate immune reaction, coupled with complications linked to the high mismatch in stiffness between the implant and the bone. Biodegradable metals can overcome these problems by maintaining sufficient mechanical properties for load-bearing applications during healing and eventually degrade away completely. Currently, however, the use of SLM for the manufacturing of BDM scaffolds is still in its infancy as only a few peer-reviewed studies are published, with the majority of these published in the last couple of years. Literature was systematically reviewed to critically analyze and synthesize the data in the form of a meta-analysis. Only studies that included the processing parameters used for volumetric energy density (namely the laser power, scan speed, hatch spacing, and energy density) and provided as built relative densities were used. SLM of biodegradable metals is an exciting research area that requires further exploration. Apart from overcoming the problems unique to each major biodegradable metal family, the meta-analysis showed that the vast majority of studies regard the optimization of SLM processing parameters. However, these studies are specific to the powder and machine used. Rather, broader guidelines need to be developed for modern SLM machines to allow for quicker optimization for future SLM-manufactured BDM.