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Additive manufacturing from metal powders using selective laser melting technology is gaining increasing interest in various industries. The purpose of this study was to determine the effect of changes in process parameter values on the relative density, microstructure and mechanical properties of Ti-6Al-4V and Ti-6Al-7Nb alloy samples. The experiment was conducted in response to a noticeable gap in the research on the manufacturability of the Ti-6Al-7Nb alloy in SLM technology. This topic is significant given the growing interest in this alloy for biomedical applications. The results of this study indicate that by properly selecting the volumetric energy density (VED), the relative density of the material produced and the surface roughness of the components can be effectively influenced. Microstructural analyses revealed similar patterns in both alloys manufactured under similar conditions, characterized by columnar β phase grains with needle-like α' phases. Increasing the VED increased the tensile strength of the fabricated Ti-6Al-4V alloy components, while the opposite effect was observed for components fabricated from Ti-6Al-7Nb alloy. At the same time, Ti-6Al-7Nb alloy parts featured higher elongation values, which is desirable from the perspective of biomedical applications. [ABSTRACT FROM AUTHOR]

Porous titanium scaffolds fabricated by powder bed fusion additive manufacturing techniques have been widely adopted for orthopedic and bone tissue engineering applications. Despite the many advantages of this approach, topological defects inherited from the fabrication process are well understood to negatively affect mechanical properties and pose a high risk if dislodged after implantation. Consequently, there is a need for further post‐process surface cleaning. Traditional techniques such as grinding or polishing are not suited to lattice structures, due to lack of a line of sight to internal features. Chemical etching is a promising alternative; however, it remains unclear if changes to surface properties associated with such protocols will influence how cells respond to the material surface. In this study, we explored the response of bone marrow derived mesenchymal stem/stromal cells (MSCs) to Ti‐6Al‐4V whose surface was exposed to different durations of chemical etching. Cell morphology was influenced by local topological features inherited from the SLM fabrication process. On the as‐built surface, topological nonhomogeneities such as partially adhered powder drove a stretched anisotropic cellular morphology, with large areas of the cell suspended across the nonhomogeneous powder interface. As the etching process was continued, surface defects were gradually removed, and cell morphology appeared more isotropic and was suggestive of MSC differentiation along an osteoblastic‐lineage. This was accompanied by more extensive mineralization, indicative of progression along an osteogenic pathway. These findings point to the benefit of post‐process chemical etching of additively manufactured Ti‐6Al‐4V biomaterials targeting orthopedic applications. [ABSTRACT FROM AUTHOR]

The present study considers the samples of an Ti-6Al-4V alloy obtained by selective laser melting with the addition of a 10% Cu-Al powder mixture. The microstructure, elemental composition and phase composition, as well as the physico-chemical properties, have been investigated by the methods of electron microscopy, X-ray phase analysis, and bending testing. The obtained samples have a relative density of 98.5 ± 0.1%. The addition of the Cu-Al powder mixture facilitates supercooling during crystallization and solidification, which allows decreasing the size and changing the shape of the initial β-Ti grains. The constant cooling rate of the alloy typical for the SLM technology has been shown to be able to prevent martensitic transformation. The formation of a structure that consists of β-Ti grains, a dispersed eutectoid mixture of α-Ti and Ti2Cu grains, and a solid solution of Al in Cu has been revealed. In the case of doping by the 10% Cu-Al mixture, the physico-mechanical properties are improved. The hardness of the samples amounts to 390 HRC, with the bending strength being 1550 ± 20 MPa and deformation of 3.5 ± 0.2%. The developed alloy can be recommended for applications in the production of parts of jet and car engines, implants for medicine, and corrosion-resistant parts for the chemical industry. [ABSTRACT FROM AUTHOR]

In this study, post-heat treatments were applied to Ti–6Al–4V (TC4) alloy fabricated by selective laser melting (SLM) to investigate the effects of annealing temperature (750–950 °C in 50 °C intervals) on the alloy's microstructure, residual stress and mechanical properties. The initial microstructure of as-SLMed TC4 alloy was dominated by needle-like α′ martensite with a high density of dislocations and minor β phase, resulting in high strength (1190 MPa) but limited ductility (2.2% elongation). Annealing led to the transformation of α′ martensite into α phase, with the β phase content remaining relatively stable. Increasing the annealing temperature caused the acicular martensite to evolve into bundles of coarse α laths, forming a basket-weave microstructure. Annealing at 750 °C for 2 h reduced the yield strength to 1040 MPa and improved elongation to 8.3%. Interestingly, both the strength and ductility decreased with further increases in annealing temperature. This unusual phenomenon was rarely mentioned in current literature and was considered to be associated with the abnormal variations in the Schmid factor of (0001) [11-20] slip system and the reduction of mobile dislocations within the coarsened α martensite. Additionally, annealing combined with air cooling effectively alleviated residual tensile stresses in the SLM-formed TC4 alloy.

3D printing technology proves itself to be effective in the field of medical industry due to processing potential of titanium alloys. Nonetheless it also has its drawbacks, the most severe being high roughness of printed elements’ area as well as the need to remove support structures created following the printing. Mechanical processing is commonly used for said parameters being enhanced. The completion of that process, however, takes a lot of time and prevents hard-to-reach elements from being reached. The task of this article is to provide a new method of firming the print’s surface and removing load-bearing structures. To achieve this, selective laser melting (SLM) technology will be used along with bathing prints in HF/HNO3 solution, all of which are supported by ultrasound. This process will enhance the material fatigue processing while reducing the postprocessing time and complexity. [ABSTRACT FROM AUTHOR]

The parameters used in the production process in laser powder bed fusion (L-PBF) technology, one of the additive manufacturing methods, have a critical effect on the mechanical behavior and density properties of the product and can change the properties of the product. Therefore, this study examined the influence of laser power, scanning speed, hatch spacing and beam rotation angle on the tensile strength, impact energy, surface roughness, and porosity levels of Ti–6Al–4V produced through the L-PBF method. It was observed that the tensile strength changes directly proportional to the laser power. In addition, the tensile strength decreases significantly with a value of 645 MPa obtained at lowest 0.07 mm hatch spacing, 190 W laser power and 900 mm scanning speed. The lowest value of impact energy, with a value of 8.7 J, was reached at a rotation angle of 180°. It has been determined that surface roughness decreases significantly with increasing laser power, while it demonstrates an increase with higher scanning speeds. Surface roughness values of 8.9 μm parallel and 8.35 μm perpendicular to the building direction were achieved at a laser power level of 220 W. Laser power was identified as the most influential factor in determining the porosity ratio, with a high porosity rate 0.48% occurring at 160 W laser power. Furthermore, an increase in scanning speed resulted in a corresponding increase in the porosity rate.

A post-heat treatment is necessary to finely adjust the desired microstructure and mechanical properties of Ti alloys produced by additive manufacturing. This research offers a comprehensive study of how electropulsing treatment (EPT) changes the microstructure and microhardness of Ti–6Al–4V alloy fabricated by selective laser melting. It verifies the potential benefits of using EPT instead of the conventional furnace heat treatment (FHT). The microstructural evolution was interpreted based on the number and magnitude of electropulses, which were then compared with FHT samples treated at the same temperatures and durations. Notably, the harmful columnar microstructure completely disappeared though the application of multiple electropulses at a current density of 20 A mm−2. Such a result was not attained by the FHT counterpart using the same peak temperature (1319 K) and duration (23 min). Furthermore, the EPT specimen exhibited a significant β-grain refinement. The accelerated atomic diffusion flux, one of athermal effects of EPT, resulted in the fast transformation of columnar microstructure into fine and equiaxed prior-β grains. The microhardness was affected by both lath thickness and phase constituents in the as-built alloy, whereas it was only governed by the former after the post-heat treatments. Utilizing EPT as an alternative post-heat treatment can effectively alleviate the microstructural inhomogeneity of additively manufactured metals. [ABSTRACT FROM AUTHOR]

In this study, we compared the material properties of linearly and sharply graded Ti6Al4V additively manufactured samples to investigate whether the more severe discontinuities caused by sharp grading can reduce performance. We performed compression testing with digital image correlation (DIC) in two loading directions for each grading design to simulate iso-stress and iso-strain conditions. We extracted the elastic stiffness, yield strength, yield strain, and energy absorption capacity of each sample. In addition, we used micro-computed tomography (micro-CT) imaging to examine the printing quality and dimensional accuracy. We found that sharply graded struts have a 12.95% increase in strut cross-sectional areas, whereas linearly graded struts produced an average of 49.24% increase compared to design. However, sharply graded and linearly graded FGL samples do not have statistically significant differences in elastic stiffness and yield strength. For the iso-strain condition, the average DIC-corrected stiffnesses for linearly and sharply graded samples were 6.15 GPa and 5.43 GPa, respectively (p = 0.4466), and the yield stresses were 290.4 MPa and 291.2 MPa, respectively (p = 0.5734). Furthermore, we confirmed different types of printing defects using micro-CT, including defective pores and disconnected struts. These results suggest that the loss of material properties caused by manufacturing defects outweighs the adverse effects of discrete-grading-induced discontinuities. [ABSTRACT FROM AUTHOR]

In an effort to contribute to the ongoing development of ASTM standards for additively manufactured metal lattice specimens, particularly within the field of medicine, the compressive and tensile mechanical properties of biomimetic lattice structures produced by laser powder bed fusion (L-PBF) using Ti-6Al-4V feedstock powder were investigated in this research. The geometries and porosities of the lattice structures were designed to facilitate internal bone growth and prevent stress shielding. A thin strut thickness of 200 µm is utilized for these lattices to mimic human cancellous bone. In addition to a thin strut size, two different strut geometries were utilized (cubic and body-centered cubic), along with four different pore sizes (400, 500, 600, and 900 µm, representing 40–90% porosity in a 10 mm cube). A 10 mm3 cube was used for compression testing and an experimental pin-loaded design was implemented for tensile testing. The failure mode for each specimen was examined using scanning electron microscopy (SEM). Lattice structures were compared to the mechanical properties of human cancellous bone. It was found that the elastic modulus of human cancellous bone (10–900 MPa) could be matched for both the tensile (92.7–129.6 MPa) and compressive (185.2–996.1 MPa) elastic modulus of cubic and body-centered cubic lattices. Body-centered cubic lattices exhibited higher compressive properties over cubic, whereas cubic lattices exhibited superior tensile properties. The experimental tensile specimen showed reacquiring failures close to the grips, indicating that a different tensile design may be required for consistent data acquisition in the future. [ABSTRACT FROM AUTHOR]

Additive manufacturing from metal powders using selective laser melting technology is gaining increasing interest in various industries. The purpose of this study was to determine the effect of changes in process parameter values on the relative density, microstructure and mechanical properties of Ti-6Al-4V and Ti-6Al-7Nb alloy samples. The experiment was conducted in response to a noticeable gap in the research on the manufacturability of the Ti-6Al-7Nb alloy in SLM technology. This topic is significant given the growing interest in this alloy for biomedical applications. The results of this study indicate that by properly selecting the volumetric energy density (VED), the relative density of the material produced and the surface roughness of the components can be effectively influenced. Microstructural analyses revealed similar patterns in both alloys manufactured under similar conditions, characterized by columnar β phase grains with needle-like α’ phases. Increasing the VED increased the tensile strength of the fabricated Ti-6Al-4V alloy components, while the opposite effect was observed for components fabricated from Ti-6Al-7Nb alloy. At the same time, Ti-6Al-7Nb alloy parts featured higher elongation values, which is desirable from the perspective of biomedical applications.

The present study considers the samples of an Ti-6Al-4V alloy obtained by selective laser melting with the addition of a 10% Cu-Al powder mixture. The microstructure, elemental composition and phase composition, as well as the physico-chemical properties, have been investigated by the methods of electron microscopy, X-ray phase analysis, and bending testing. The obtained samples have a relative density of 98.5 ± 0.1%. The addition of the Cu-Al powder mixture facilitates supercooling during crystallization and solidification, which allows decreasing the size and changing the shape of the initial β-Ti grains. The constant cooling rate of the alloy typical for the SLM technology has been shown to be able to prevent martensitic transformation. The formation of a structure that consists of β-Ti grains, a dispersed eutectoid mixture of α-Ti and Ti2Cu grains, and a solid solution of Al in Cu has been revealed. In the case of doping by the 10% Cu-Al mixture, the physico-mechanical properties are improved. The hardness of the samples amounts to 390 HRC, with the bending strength being 1550 ± 20 MPa and deformation of 3.5 ± 0.2%. The developed alloy can be recommended for applications in the production of parts of jet and car engines, implants for medicine, and corrosion-resistant parts for the chemical industry.

A powder-bed-based additive manufacturing process called electron beam melting (EBM) is defined by high temperature gradients during solidification, which produces an extremely fine microstructure compared to the traditional cast material. However, porosity and segregation defects are still present on a smaller scale which may lead to a reduction in mechanical properties. It is important to have a better knowledge of the influence of post-fabrication treatments on the microstructure and mechanical characteristics before the use of additive manufacturing parts in specific applications. In this study, the effects of solution heat treatment (SHT) and hot isostatic pressing (HIP) on the microstructure and mechanical properties of Ti-6Al-4V alloy fabricated by the EBM process have been investigated. The SHT and HIP treatments can significantly improve the ductility of EBM Ti-6Al-4V due to the coarsening of α laths and the formation of β grains. [ABSTRACT FROM AUTHOR]

When manufacturing complicated products where both material and design play a role, especially thin and curved components, it is difficult to maintain accurate dimensions in Selective Laser Melting. Considering these difficulties, this article presents the dimensional errors in the fabrication of Ti-6Al-4V discs and their thermomechanics during manufacturing. Various combinations of laser processing parameters were used to fabricate the 2.00 mm thick discs with a diameter of 5.70 mm. It was found that the thickness shortened and the round shape changed to an oval shape for most of the discs. The thickness decreased along the build-up direction from the bottom to the top and formed a taper that increased with increasing energy density (ED). The horizontal diameter of the discs changed slightly, while the vertical diameters changed remarkably with increasing ED. On the other hand, reducing the laser power resulted in a reduction of the roundness error, while it caused a reduction of the thickness. The hatch spacing significantly affected the volume of the melt pool and caused a change in the vertical diameter. The central part of the curved surface of the discs became concave and the concavity increased due to the increasing ED. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) can effectively replace traditional processing methods to prepare parts with arbitrary complex shapes through layer-by-layer accumulation. However, SLM Ti-6Al-4V alloy typically exhibits low ductility and significant mechanical properties anisotropy due to the presence of acicular α′ martensite and columnar prior β grains. Post-heat treatment is frequently used to obtain superior mechanical properties by decomposing acicular α′ martensite into an equilibrium α + β phase. In this study, the microstructure and tensile properties of SLM Ti-6Al-4V alloy before and after various heat treatments were systematically investigated. The microstructure of the as-fabricated Ti-6Al-4V sample was composed of columnar prior β grains and acicular α′ martensite, which led to high strength (~1400 MPa) but low ductility (~5%) as well as significantly tensile anisotropy. The single heat treatment samples with lamellar α + β microstructure exhibited improved elongation to 6.8–13.1% with a sacrifice of strength of 100–200 MPa, while the tensile anisotropy was weakened. A trimodal microstructure was achieved through multi-step high-to-low-temperature (HLT) heat treatment, resulting in an excellent combination of strength (~1090 MPa) and ductility (~17%), while the tensile anisotropy was almost eliminated. The comprehensive mechanical properties of the HLT samples were superior to that of the conventional manufactured Ti-6Al-4V alloy. [ABSTRACT FROM AUTHOR]

The Selective Laser Melting (SLM) process based additive manufacturing has wide applications in medical, aerospace, defense, and automotive industries. To qualify the components for certain tribological applications, the characterization of surface texture is very important. But the applicability of traditional methods and parameters to characterize the surface texture were under evaluation. As the nature manufacturing the components were very different and complex, the unconventional surface characterization methods also under evaluation to reveal much more meaningful information. This study demonstrates the surface characterization of Ti-6Al-4V SLM components using fractal analysis of the surface images. The computed fractal dimension using the Fourier transform method showed a strong correlation of more than 0.8 with the measured 3D surface roughness parameters. The change in anisotropic nature of the surface images with the process parameter variation is studied and found that the surface textures showed a weaker anisotropic nature at lower laser power ranges, high scanning speed, and high hatch distance values. The lacunarity analysis is carried out using the gliding box algorithm to study the homogeneity nature of the surface texture and found that the surface texture is more homogeneous at higher surface roughness conditions. The study results can be utilized for the development of a quick, low-cost surface monitoring system in real-time for additive manufacturing industries. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) techniques, such as wire arc additive manufacturing (WAAM), offer unique advantages in producing large, complex structures with reduced lead time and material waste. However, their application in fatigue-critical applications requires a thorough understanding of the material properties and behavior. Due to the layered nature of the manufacturing process, WAAM structures have different microstructures and mechanical properties compared to their substrate counterparts. This study investigated the mechanical behavior and fatigue performance of Ti-6Al-4V fabricated using WAAM compared to the substrate material. Tensile and low-cycle fatigue (LCF) tests were conducted on both materials, and the microstructure was analyzed using optical microscopy and scanning electron microscopy (SEM). The results showed that the WAAM material has a coarser and more heterogeneous grain structure, an increased amount of defects, and lower ultimate tensile strength and smaller elongation at fracture. Furthermore, strain-controlled LCF tests revealed a lower fatigue strength of the WAAM material compared to the substrate, with crack initiation occurring at pores in the specimen rather than microstructural features. Experimental data were used to fit the Ramberg–Osgood model for cyclic deformation behavior and the Manson–Coffin–Basquin model for strain-life curves. The fitted models were subsequently used to compare the two material conditions with other AM processes. In general, the quasi-static properties of WAAM material were found to be lower than those of powder-based processes like selective laser melting or electron beam melting due to smaller cooling rates within the WAAM process. Finally, two simplified estimation models for the strain-life relationship were compared to the experimentally fitted Manson–Coffin–Basquin parameters. The results showed that the simple "universal material law" is applicable and can be used for a quick and simple estimation of the material behavior in cyclic loading conditions. Overall, this study highlights the importance of understanding the mechanical behavior and fatigue performance of WAAM structures compared to their substrate counterparts, as well as the need for further research to improve the understanding of the effects of WAAM process parameters on the mechanical properties and fatigue performance of the fabricated structures. [ABSTRACT FROM AUTHOR]

In an effort to contribute to the ongoing development of ASTM standards for additively manufactured metal lattice specimens, particularly within the field of medicine, the compressive and tensile mechanical properties of biomimetic lattice structures produced by laser powder bed fusion (L-PBF) using Ti-6Al-4V feedstock powder were investigated in this research. The geometries and porosities of the lattice structures were designed to facilitate internal bone growth and prevent stress shielding. A thin strut thickness of 200 µm is utilized for these lattices to mimic human cancellous bone. In addition to a thin strut size, two different strut geometries were utilized (cubic and body-centered cubic), along with four different pore sizes (400, 500, 600, and 900 µm, representing 40–90% porosity in a 10 mm cube). A 10 mm3 cube was used for compression testing and an experimental pin-loaded design was implemented for tensile testing. The failure mode for each specimen was examined using scanning electron microscopy (SEM). Lattice structures were compared to the mechanical properties of human cancellous bone. It was found that the elastic modulus of human cancellous bone (10–900 MPa) could be matched for both the tensile (92.7–129.6 MPa) and compressive (185.2–996.1 MPa) elastic modulus of cubic and body-centered cubic lattices. Body-centered cubic lattices exhibited higher compressive properties over cubic, whereas cubic lattices exhibited superior tensile properties. The experimental tensile specimen showed reacquiring failures close to the grips, indicating that a different tensile design may be required for consistent data acquisition in the future.

Herein, it is aimed in this study to assess a long‐standing question, "whether reliable predictive models can be developed for surface roughness of laser additively manufactured alloys, with aggregated knowledge learned but little new experimentation?" A most comprehensive dataset is obtained from mining the literature on as‐built Ti–6Al–4V alloy via selective laser melting (SLM), which includes the major SLM process parameters, average and variance of powder particle size, and resultant surface roughness. Five supervised machine‐learning models and one traditional regression model are proposed to evaluate the predictability of average surface roughness Ra of SLM‐produced Ti–6Al–4V alloy. Using tenfold cross validation on dependable literature data, the six models are trained and compared. To ultimately test the developed models, cubic Ti–6Al–4V samples are fabricated and the models are employed to predict their surface roughness. It is discovered that while all six models show overall satisfactory performance, the traditional regression model possesses the lowest prediction accuracy. Two of the best models, that is, Gaussian process regression and neural network models, exhibit root‐mean‐squared error of 0.51 and 0.58 μm, respectively, and are championed as industry ready. Herein, an alternative path for predicting SLM contingencies is proved by this research, where resources are limited but historical experience can be mined. [ABSTRACT FROM AUTHOR]

In the present study, Ti-6Al-4V alloy was fabricated by Selective Laser Manufacturing (SLM) technique and subsequently subjected to an annealing treatment at, above and below the β transition temperature. We emphasized the influence of porosity, oxygen and phase morphology on the strength, ductility and elongation of SLM-manufactured Ti-6Al-4V and compared the alloy's properties with conventionally manufactured Ti-6Al-4V from the literature. The as-built Ti-6Al-4V sample showed a very high strength due to acicular martensite, and the growth of α+β lamellae on heat treatment improved ductility. Energy Dispersive Spectroscopy (EDS), Optical and Scanning Electron Microscopy (SEM) were used to identify the chemical composition, calculate lamellar width and analyze the fracture mechanisms. The grain size and the average thickness of α lamellae, inter-granular β and prior β grain boundary increased with annealing temperature. The porosity and oxygen content of the samples were found to have a consequential effect on the strength, especially in as-built and high-temperature annealing conditions and optimum mechanical properties were observed in SLM Ti-6Al-4V annealed at 800 °C. [ABSTRACT FROM AUTHOR]

This paper presents an in-depth study of the variable reference process to improve the organization and properties of selective laser melting TC4 specimens. A relationship equation between body energy density and stratification is proposed. This study aimed to look into how layer and volume energy density affect the surface, tensile characteristics, and microstructure of specimens. The test findings demonstrated that specimen densities rise as the power index falls, with the most excellent density reaching 99.42%. The number of secondary α' phases declined as the energy density of the laminae slowed down. The tensile strength of these specimens reached 1190.84 MPa, and the yield strength came at 1103.87 MPa with the same interval of variable laser power. This offers a fresh avenue for research into SLM to enhance the specimens' overall performance. [ABSTRACT FROM AUTHOR]

The reliability of a prosthetic implant needs durability, biocompatibility, and osseointegration capability. Accomplishing these characteristics, Ti-6Al-4V alloy is the main used material for implant fabrication. Moreover, it can be processed by additive manufacturing technique, permitting to meet the needs of patience-tailored, often complex shaped, prosthesis topologies. Once an implant is realized, it is finished by machining operations and its osseointegration capability is heavily influenced by the resulting surface roughness. Consequently, the assessment of this latter is mandatory to evaluate the prosthesis durability. This paper presents the analysis of surface roughness of Ti-6Al-4V micro-milled specimens produced by plastic deformation, selective laser melting, and electron beam melting processes. A central composite design was employed for planning the cutting tests. The comparison between surface roughness results and its values for enhancing osseointegration, firstly permitted to individuate the range of micro-milling suitable applications, which have been individuated as ball joints, bone plates, and screws. Next, the statistical analysis of the experimental measurements allowed the identification of the most influential micro-milling parameters together with the determination of the mathematical models of surface roughness by response surface methodology. The good comparison among calculated and experimental results revealed the reliability of the model, allowing the prediction of achievable surface roughness once micro-machining parameters are selected, or their optimization as a function of a desired surface roughness value. [ABSTRACT FROM AUTHOR]

Ti-6Al-4V titanium alloy products formed by selective laser melting (SLM) are characterized by high strength and low plasticity. In addition, there may be pores inside the material, which may become a fracture sprouting point and accelerate the failure of the parts. Using an optical microscope (OM), scanning electron microscope (SEM), and electronic universal testing machine, the effects of hot isostatic pressing (HIP) parameters on the microstructure and tensile property of SLM-formed Ti-6Al-4V titanium alloy were investigated. The results show that HIP performed below the β-phase transition temperature, and the structure of the Ti-6Al-4V titanium alloy is composed of an α phase and β phase. With the increase in the HIP temperature, the α lath coarsens into a short rod, the content of the β phase increases and coarsens, and the tensile strength and yield strength of Ti-6Al-4V show a decreasing trend. With an HIP process performed at a temperature of 910 °C and pressure of 130 MPa for 2 h, the Ti-6Al-4V titanium alloy obtains the best matching of strength and plasticity. [ABSTRACT FROM AUTHOR]

Metal additive manufacturing technologies such as laser powder bed fusion (so-called selective laser melting) have been widely applied in the field of aerospace or medical device. Moreover, porous materials have been extensively studied due to the maturity of metal additive manufacturing technology. The stress shielding effects can be reduced and the bone integration between the human bones and medical devices can be improved by introducing porous materials. Thus, the medical device would be more stable after implantation. However, in our previous study, the mechanical properties of porous materials are not only affected by the porous structure and porosity but also affected by the surface roughness and the ratio between surface roughness and strut diameter. In this study, to investigate and explore such issues, two major topics will be researched, which are (1) the formulation development of the electrolyte with a surfactant to increase the surface finish effectiveness during the electropolishing process of 3D printed Ti-6Al-4V porous materials; (2) the exploration of the relationship between the mechanical properties and the surface roughness/other factors. Also, the effect of surface roughness on mechanical properties was evaluated in terms of work of fracture and specific energy absorption.

Titanium is a most common and best biocompatible material. The demand and application of Ti alloy is increasing rapidly in orthopedics for clinical operations. The porous structures have been designed for bone tissue engineering or orthopedic applications due to its moderate Young's modulus, excellent compressive strength, biocompatibility and sufficient space for cell accommodation. The porous scaffolds with individual complex internal and external shape can be manufactured by additive manufacturing (AM) processes especially selective laser melting (SLM), both of these have great importance for repairing of large sectional bone defects. This advantage makes the SLM process one of the most competitive AM processes used in the biomedical fields. Seven different Ti–6Al–4V porous scaffolds (Diamond, Grid, Cross, Vinties, Tesseract, Star and Octet) of 15 mm cube with 65% porosity were designed using Rhino 6 software and fabricated through SLM using Ti–6Al–4V powders. This work mainly focused on porous scaffolds design and manufacturing by AM particularly SLM, can able to produce scaffolds of nanoscale grains because of its higher heating rate and lower holding time. But this process generally results insufficient compaction where desired function is not achieved. The scaffolds manufactured by SLM have relatively high accuracy of pore structure and low mechanical strength. Grid type structure exhibits lower surface roughness value and better manufacturing ability where error percentage of porosity is lower than the other scaffolds.The process parameters employed in the study like laser power, scanning speed, hatch distancing and layer thickness are the most significant factors that influence the defect behaviour and morphology of the SLM-fabricated samples. Porosity percentage and surface roughness of the scaffold palys a vital role on its desired functions. While the porosity percentage are also effected by input process parameters resulting the variation on effective elastic modulus. The increase in scanning speed leads to elevation of the cooling rate, which results in a finer microstructure. On the other hand, with lower scanning speeds, coarse microstructure is observed.

Additive manufacturing (AM) is a promising technology for the personalized medicine industry, especially in the orthopedic field. It allows the production of prostheses that can fit complex anatomical sites and mimic bone morphology, featuring an external solid shell and an inner trabecular core. The new medical device regulation has recently outlined the need for safety assessment of these particular implants: to the best of the authors' knowledge, there are no defined methodologies to assess the quality of a custom product since each device is intended for single-time use. The goal of the current work is to propose a well-structured pipeline for designing and verifying an AM custom prosthesis: the exemplified case is that for the ankle joint treatment (i.e. talus resurfacing), whose standard solutions are affected by significant failure rates. A comprehensive characterization of the unique features of AM orthopedic implants will be presented, integrating finite element analyses and experiments. [ABSTRACT FROM AUTHOR]

In this study, thin tubes are mimicked based on the architecture of Euplectella aspergillum and studied for fatigue performance under variable amplitude loading. The thin tubes are fabricated with Ti‐6Al‐4V material using the selective laser melting (SLM) process. SLM printed components are always subjected to residual stresses, which can reduce fatigue performance of the components. Heat treatment effect on the fatigue performance, microstructure, and residual stress is studied. Complex geometry and sharp corners in the bioinspired tubes result in stress concentration, which further reduces the fatigue performance. The value of residual stresses at the sharp corners is dependent on the height of the tube, thickness of struts, and intersection of different struts. Heat treatment significantly reduces the residual stresses and increases the fatigue life of the thin tubes; however, strength decreases after heat treatment. Heat‐treated thin tubes showed a higher concentration of (α + β) phase, which results in decreased residual stress and improved ductility of the thin tubes. Advanced bionic thin tubes can be used for lightweight crash boxes, sandwich panels, bio‐implants, grid stiffened structures, etc. Highlights: Thin tubes are derived from Euplectella aspergillum.Thin tubes are fabricated using selective laser melting process with Ti‐6Al‐4V alloy.Heat treatment reduces fatigue strength and improves fatigue life.Residual stress decreases with heat treatment, and it is dependent on the topology. [ABSTRACT FROM AUTHOR]

In the present study, a dry sliding wear test has been conducted to analyse the wear rate of Ti-6Al-4V alloy specimens which were fabricated using selective laser melting and conventional methods. Microstructure, micro- and nanohardness, and wear behaviour of selective laser melting specimens were investigated and compared with commercially available conventionally fabricated Ti-6Al-4V specimens. The mechanism correlating microstructure and wear behaviour of conventional and selective laser melting based Ti-6Al-4V specimens have been explained. The microhardness of the selective laser melting specimen was improved by around 22.4% over the specimen from the conventional method. The selective laser melting specimen showed broadened peaks and an increase in intensity height greater than that of the conventional specimen due to the presence of the martensite phase. The selective laser melting specimen possessed 41.4% higher nanohardness than that of the conventional specimen. The selective laser melting specimen had a 62.1% lower wear rate when compared to that of the conventional specimen. The selective laser melting specimen exhibited 62.7% less coefficient of friction than that of the conventional specimen at a 50 N load with 1.2 m/s sliding velocities. The finer needle-like microstructures of the specimen produced using the selective laser melting process had higher wear resistance, as it had higher hardness than the conventional specimen. [ABSTRACT FROM AUTHOR]

Medical grade Ti–6Al–4V implants fabricated using selective laser melting (SLM) are recognized as a commercial biomaterial used for bone repairs and fracture fixation. However, there have been cases of failed bone remodeling and implant infections caused by deficient osteointegration. To improve osteogenesis, the Ti implants are treated by acid-etching. This study focused on the effect of surface treatment by using different percentages of sulfuric acid (H2SO4), hydrochloric acid (HCL), and hydrofluoric acid (HF) on the SLM Ti–6Al–4V. The microstructure and surface topography before and after treatment were evaluated. Then, the presence of a thicker anatase layer that was detectable on the surface was also observed by X-ray diffraction (XRD). The apatite-forming capabilities which indicated a sample bioactivity were assessed in simulated body fluid (SBF) for periods of 3 days and 7 days. The apatite formed on the surface of sample and XRD scanning revealed the deposition of Ca/P, suggesting successful bone-like apatite. The study discovered that these surface improvements were appropriate for the SLM Ti–6Al–4V prior to clinical applications and were likely to yield higher levels of osseointegration.

As-built, SLM-printed Ti-6Al-4V parts suffer from non-equilibrium, brittle microstructures due to the formation of metastable α’-phase martensite as a result of the printing process. Post-processing heat treatments are required to alleviate residual stress and decompose the martensite into equilibrium phases. Using unconventional ‘cyclical’ heat treatment profiles, it is possible to achieve a bimodal microstructure as opposed to a more typical lamellar microstructure achieved using conventional heat treatment profiles. In the present research, the effect of cyclical heat treatment parameters (maximum temperature, minimum temperature, number of cycles and cooling regime) on the grain morphology, phase composition and mechanical performance (static and dynamic) has been evaluated. Furthermore, a comparison to a typical lamellar microstructure has been completed as a reference.

In this paper, five grading functional gradient lattice structures with a different density perpendicular to the loading direction were proposed, and the surface morphology, deformation behavior, and compression properties of the functional gradient lattice structures prepared by selective laser melting (SLM) with Ti-6Al-4V as the building material were investigated. The results show that the characteristics of the laser energy distribution of the SLM molding process make the spherical metal powder adhere to the surface of the lattice structure struts, resulting in the actual relative density of the lattice structure being higher than the designed theoretical relative density, but the maximum error does not exceed 3.33%. With the same relative density, all lattice structures with density gradients perpendicular to the loading direction have better mechanical properties than the uniform lattice structure, in particular, the elastic modulus of LF, the yield strength of LINEAR, and the first maximum compression strength of INDEX are 28.99%, 16.77%, and 14.46% higher than that of the UNIFORM. In addition, the energy absorption per unit volume of the INDEX and LINEAR is 38.38% and 48.29% higher, respectively, than that of the UNIFORM. Fracture morphology analysis shows that the fracture morphology of these lattice structures shows dimples and smooth planes, indicating that the lattice structure exhibits a mixed brittle and ductile failure mechanism under compressive loading. Finite element analysis results show that when the loading direction is perpendicular to the density gradient-forming direction, the higher density part of the lattice structure is the main bearing part, and the greater the density difference between the two ends of the lattice structure, the greater the elastic modulus. [ABSTRACT FROM AUTHOR]

A study has been made of the physicomechanical properties of a heterogeneous material based on TiB, TiB2, TiC, and B4C ceramics and a Ti–6Al–4V metal alloy formed by the method of selective laser melting. Consideration has been given to the influence of TiB, TiB2, TiC, and B4C ceramic particles produced by in situ synthesis in the process of laser action on the microstructure and hardness of the formed metal-matrix composite. Basic mechanisms of variation in the microstructure to form secondary ceramic inclusions were discussed and microhardness measurements at a macro- and nanolevel were carried out. It has been established that ceramic particles formed as a result of the in-situ synthesis improve sharply the hardness of the metal-matrix composite depending on the composition of the ceramics. [ABSTRACT FROM AUTHOR]

Metal additive manufacturing technologies such as laser powder bed fusion (so-called selective laser melting) have been widely applied in the field of aerospace or medical device. Moreover, porous materials have been extensively studied due to the maturity of metal additive manufacturing technology. The stress shielding effects can be reduced and the bone integration between the human bones and medical devices can be improved by introducing porous materials. Thus, the medical device would be more stable after implantation. However, in our previous study, the mechanical properties of porous materials are not only affected by the porous structure and porosity but also affected by the surface roughness and the ratio between surface roughness and strut diameter. In this study, to investigate and explore such issues, two major topics will be researched, which are (1) the formulation development of the electrolyte with a surfactant to increase the surface finish effectiveness during the electropolishing process of 3D printed Ti-6Al-4V porous materials; (2) the exploration of the relationship between the mechanical properties and the surface roughness/other factors. Also, the effect of surface roughness on mechanical properties was evaluated in terms of work of fracture and specific energy absorption. [ABSTRACT FROM AUTHOR]

Ti-6Al-4V is suitable for powder bed fusion additive manufacturing processes; however, until now, limited studies are conducted to investigate the high temperature tribological performance of Ti-6Al-4V samples made by selective laser melting (SLM) and electron beam melting (EBM) techniques. This paper investigated dry sliding wear resistance of Ti-6Al-4V alloy manufactured by SLM, EBM and conventional processes at elevated temperatures up to 600 °C in contact with WC-Co. Linear reciprocating sliding wear tests were carried out under different applied loads and temperatures, and different wear mechanisms were identified and related to the manufacturing technique. Deviations of wear track width measurements indicated shape irregularly, which has been presented and discussed by SEM images of the wear tracks. Energy-dispersive x-ray analysis of surface layer showed how increasing temperature affects the surface oxide layer and debris. The results showed that for all three types of samples, the oxygen richer oxide debris layer at higher temperatures provided a protective layer with higher wear resistance, although strength and hardness of Ti-6Al-4V are lower at a higher temperatures. So, the combination of these two effects results in no significant effect of temperature on wear rate. [ABSTRACT FROM AUTHOR]

The present study investigates the sparsely documented tribological performance of selective laser-melted Ti-6Al-4V over a wide range of temperatures (room temperature to 450 °C). The evolution of wear mechanism was traced by examining the phase changes, chemical composition, and morphology of wear tracks in the material. The native oxide layer developed on the surface of the material was found to mitigate adhesive wear during dry sliding at room temperature. At elevated temperatures, this oxide layer contributed to oxidative wear, as evidenced by the formation of a tribo-oxide layer with increased oxygen penetration. Further, abrasive wear was found to increase with increasing temperatures, which could be attributed to the presence of entrapped oxidized wear particles (third-body wear) and material softening. [Display omitted] [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) can effectively replace traditional processing methods to prepare parts with arbitrary complex shapes through layer-by-layer accumulation. However, SLM Ti-6Al-4V alloy typically exhibits low ductility and significant mechanical properties anisotropy due to the presence of acicular α′ martensite and columnar prior β grains. Post-heat treatment is frequently used to obtain superior mechanical properties by decomposing acicular α′ martensite into an equilibrium α + β phase. In this study, the microstructure and tensile properties of SLM Ti-6Al-4V alloy before and after various heat treatments were systematically investigated. The microstructure of the as-fabricated Ti-6Al-4V sample was composed of columnar prior β grains and acicular α′ martensite, which led to high strength (~1400 MPa) but low ductility (~5%) as well as significantly tensile anisotropy. The single heat treatment samples with lamellar α + β microstructure exhibited improved elongation to 6.8–13.1% with a sacrifice of strength of 100–200 MPa, while the tensile anisotropy was weakened. A trimodal microstructure was achieved through multi-step high-to-low-temperature (HLT) heat treatment, resulting in an excellent combination of strength (~1090 MPa) and ductility (~17%), while the tensile anisotropy was almost eliminated. The comprehensive mechanical properties of the HLT samples were superior to that of the conventional manufactured Ti-6Al-4V alloy.

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Cellular structures of metallic alloys are often made for various industrial applications by additive manufacturing. The permeability for fluid flow in these cellular structures is important. The current investigated the gas fluidity of cellular structures made by selective laser melting (SLM). The porosity and permeability of the SLM cellular structures were measured for 17-4 PH stainless steel, Inconel 718, and Ti-6Al-4V alloys. The relations between porosity and energy density are expressed using the power law. The characteristic molar energies were 1.07 × 105, 9.02 × 104, and 7.11 × 104 J/mole for 17-4 PH steel, Ti-6Al-4V, and Inconel 718 alloys, respectively. 17-4 PH steel gave rise to higher porosity at the same energy density when compared with Ti-6Al-4V and Inconel 718 alloy. The values of these molar energy density are related to the heat needed to melt the alloys, viscosity, and thermal conductivity. It was further shown that air permeability is not only concerned with the percentage of porosity in the cellular materials, but it also relates to the tortuosity of pore pathways formed in the cellular materials. At the same porosity, Inconel 718 demonstrates higher air permeability in comparison with that of Ti-6Al-4V and 17-4 PH alloys due to its smoother pore pathways. Ti-6Al-4V, on the other hand, demonstrates the highest specific surface areas due to powder sticking along the pore pathways and led to the lowest permeability among the three alloys. [ABSTRACT FROM AUTHOR]

Determining the quality of Ti-6Al-4V parts fabricated by selective laser melting (SLM) remains a challenge due to the high cost of SLM and the need for expertise in processes and materials. In order to understand the correspondence of the relative density of SLMed Ti-6Al-4V parts with process parameters, an optimized extreme gradient boosting (XGBoost) decision tree model was developed in the present paper using hyperparameter optimization with the GridsearchCV method. In particular, the effect of the size of the dataset for model training and testing on model prediction accuracy was examined. The results show that with the reduction in dataset size, the prediction accuracy of the proposed model decreases, but the overall accuracy can be maintained within a relatively high accuracy range, showing good agreement with the experimental results. Based on a small dataset, the prediction accuracy of the optimized XGBoost model was also compared with that of artificial neural network (ANN) and support vector regression (SVR) models, and it was found that the optimized XGBoost model has better evaluation indicators such as mean absolute error, root mean square error, and the coefficient of determination. In addition, the optimized XGBoost model can be easily extended to the prediction of mechanical properties of more metal materials manufactured by SLM processes. [ABSTRACT FROM AUTHOR]

This paper presents an in-depth study of the variable reference process to improve the organization and properties of selective laser melting TC4 specimens. A relationship equation between body energy density and stratification is proposed. This study aimed to look into how layer and volume energy density affect the surface, tensile characteristics, and microstructure of specimens. The test findings demonstrated that specimen densities rise as the power index falls, with the most excellent density reaching 99.42%. The number of secondary α’ phases declined as the energy density of the laminae slowed down. The tensile strength of these specimens reached 1190.84 MPa, and the yield strength came at 1103.87 MPa with the same interval of variable laser power. This offers a fresh avenue for research into SLM to enhance the specimens’ overall performance.

Ti-6Al-4V titanium alloy products formed by selective laser melting (SLM) are characterized by high strength and low plasticity. In addition, there may be pores inside the material, which may become a fracture sprouting point and accelerate the failure of the parts. Using an optical microscope (OM), scanning electron microscope (SEM), and electronic universal testing machine, the effects of hot isostatic pressing (HIP) parameters on the microstructure and tensile property of SLM-formed Ti-6Al-4V titanium alloy were investigated. The results show that HIP performed below the β-phase transition temperature, and the structure of the Ti-6Al-4V titanium alloy is composed of an α phase and β phase. With the increase in the HIP temperature, the α lath coarsens into a short rod, the content of the β phase increases and coarsens, and the tensile strength and yield strength of Ti-6Al-4V show a decreasing trend. With an HIP process performed at a temperature of 910 °C and pressure of 130 MPa for 2 h, the Ti-6Al-4V titanium alloy obtains the best matching of strength and plasticity.

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In this study, we systematically investigated the effects of short-time heat treatment on the mechanical properties and fatigue strength of Ti6Al4V alloy produced by selective laser melting (hereafter SLM material). The short-time heat treatment was composed of the following two heat treatments: the first treatment was short-time solution treatment (ST treatment) in which the SLM material was heated at 11731298K for 60 s and water-quenched; the second treatment was short-time aging treatment (AG treatment) in which the ST-treated materials were reheated at 823K for 40 s and air-cooled. Before the heat treatments, the microstructure of the SLM material was composed of the acicular ¡A martensite phase and the metastable ¢ phase. When the ST treatment was conducted at 1173K and 1223K lower than the ¢ transformation temperature of Ti6Al4V alloy (1271 K), the ¡A phase was transformed to the stable ¡ phase during heating and the new fine ¡A phase was generated in the metastable ¢ phase by water quenching. These microstructural changes reduced the static strength but increased the ductility. When the ST treatment was carried out at 1298K higher than the ¢ transformation temperature, the microstructure was almost the same as that of the SLM material and the mechanical properties were not greatly altered. AG treatment of the ST-treated materials induced the precipitation of the small ¡ phase and reduced the volume fraction of the metastable ¢ phase. This treatment improved the static strength but reduced the ductility. The fatigue strength of the SLM material was much lower than that of the wrought material (63%) because the molding defects formed inside caused stress concentration and accelerated the initiation of fatigue cracks. However, the ST treatment at 1298K and its combination with AG treatment effectively suppressed the initiation of fatigue cracks and markedly improved the fatigue strength to the same level as that of the wrought material. To improve the fatigue strength, the ST treatment at 1298K was more effective than its combination with AG treatment because the volume fraction of the metastable ¢ phase was higher and the compressive residual stress near the surface was higher. [ABSTRACT FROM AUTHOR]