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.

Ti-5Al-5V-5Mo-3Cr or Ti-5553 is a metastable β Titanium alloy with excellent mechanical properties. Compared to the most common titanium alloy, the α and β Ti6Al4V, even at high cooling rates as present in the laser powder bed fusion process, it establishes an β dominant microstructure which is further highly tunable by heat treatment at lower temperatures than Ti6Al4V. In the scope of this contribution, the processability of T‑5553 is investigated, and the effects of stress relief heat treatment are evaluated. Its influence of achieved microstructures on hardness and impact strength is shown.

This study evaluated the manufacturing of metal–polymer hybrid parts using a 3-axis desktop Fused Filament Fabrication (FFF) printer. Two printing strategies were employed: a more trivial one, consisting of 3D-printing the polymer directly onto the metal surface, and an alternative one, consisting of encasing the metal with printed polymer. Materials used were Ti-6Al-4V (both rolled/sandblasted and 3D-printed by laser powder bed fusion) and polyamide-based polymers. Demonstrators were designed to resemble omega-shaped skin stringers commonly used in vehicular applications. Several challenges were addressed, including harvesting the heat emanating from the deposited polymer to locally increase the substrate temperature, as well as positioning the metallic parts to avoid undesired collisions during the print job. Furthermore, to better understand the behavior of the encased metal under load, pullout tests were conducted on commercially available M6 and M8 steel nuts that were enclosed in a 3D-printed composite block. Results revealed that the length of the edge shared by the enclosure and metal significantly impacted the pullout strength.

The selective laser melting process, commonly known as laser‐based powder bed fusion (LB‐PBF), enables the production of structures with unprecedented degrees of freedom that represents an excellent condition for development of metallic implants for biomedical applications. Herein, the effects of laser energy density on relative density and microstructure (presence of internal defects) of cp‐TiGd2 fabricated by LB‐PBF are studied. Additionally, the influence of printing orientation and different surface treatments on surface topography and biocompatibility are investigated. The aim of the research is to develop additive manufacturing process parameters that can achieve full density of cp‐TiGd2 with satisfactory biocompatibility, as a low‐cost alternative to biomedical materials such as Ti–6Al–4 V and Ti–6Al–7Nb. A wide range variation of process parameters leads to an optimized process with high density up to 99.97 ± 0.008%, improved surface roughness, and noncytotoxicity in horizontal and inclined as‐built condition, as well as in Al2O3 (blasting angle 0°) condition.

Metal powder-based additive manufacturing (AM) has increasingly gained importance in the last decades. Powder-based techniques are well-known because of their versatility, allowing high degrees of geometric complexity and a wide range of chemical compositions. It enables a myriad of alloys to be printed and, e.g., the production of parts with functional gradient given the possibility of tailoring the alloy composition by changing in situ the process parameters. Moreover, the processes have been constantly developed, leading to fast, reproducible, and ready-to-use net shape parts becoming powder-based AM economically attractive. The factors mentioned above attracted the attention of aerospace, biomedical, energy and others, being the focus of intense investigations in processing and related material processing phenomena; these led to the understanding of key phenomena and consequently to the improvement of AM as a production tool. This chapter aims to explore recent developments in the powder-based AM of elementary classes of alloys for different applications. The first section is devoted to aluminium alloys, where one discusses the general challenges of printing these alloys by laser powder bed fusion (LPBF) technique, such as crack formation, porosity and the influence of building direction on the tensile properties. Further, a general overview of essential aluminium alloys produced by laser-based techniques is given. AlSi10Mg, the most common one, is the first discussed with a focus on the heat treatment of as-produced parts and its impact on tensile behaviour. Attention is also given to AlSi12, the promising Sc, Zr-based Al alloys, the hardly processable Al-Cu, the strong AA7075, and AA6061. The following two sections clarify how LPBF and laser metal deposition (LMD) are suitable for printing tool steels. The former explores hot work tool steels, giving a complete overview of the effect of processing on microstructure, phase transformation/precipitation, and the formation of defects such as cracks; high speed and cold work tool steels are briefly explored at the end of this section. The latter section deals with printing several tool steels (hot and cold work, and high speed) by LMD, correlating, e.g., printing strategies and cooling effect on the mechanical properties (such as hardness), microstructure, phase transformation and precipitation. Ahead, a section is dedicated to the powder-based AM of shape memory alloys (SMA). A general overview of the processes currently employed for printing SMAs is given. Moreover, some highlightable results of the effects of processing parameters on the transformation temperatures and functional properties are explored. Also, the microstructure evolution based on different process parameters of directed energy deposition samples is clarified. The fabrication of NiTi-based high-temperature SMA and in situ alloying of NiTi SMA are briefly explored. Some examples of application in the biomedical and micro-electromechanical are illustrated, followed by the last section, where the AM of alloys other than NiTi (e.g., iron and copper-based SMAs) is discussed. High entropy alloys (HEA) are in the subsequent section. An explanation about this novel class of alloys comes first, followed by a short technological overview and a concise sub-section regarding the powder development of HEAs. Successfully printed HEAs may be found in two separate tables where it is possible to find the technique and related process parameters. Lastly, in this section, one compares the mechanical properties of several printed HEAs. In sequence, it is possible to find the AM of magnetic materials. An introduction about Nd-Fe-B magnets is presented, and some techniques used to print magnets are explored within this sub-section; the same applies to the sub-section on Fe-Co alloys. Lastly, the AM of soft magnetic materials is explained using some examples of the effect of process parameters on the magnetic properties and the role of in situ alloying in overcoming the difficulties of printing magnets. Still, on the topic of in situ alloying, the last section of this block on specific classes of alloys is dedicated to exploring this method, focusing on the powder quality and mixing, the melting temperature, energy input and homogeneity, i.e., feedstock properties and process features. The last section is preceded by one focused on the recyclability of Ti-64 powder, where it is possible to keep up the influence of the reuse on the powder itself, the built parts and respective mechanical properties. Then, this chapter finishes with an outlook of new powder-based AM processes based on sintering-debinding, binder jetting, metal AM based on extrusion of highly filled polymer filaments, lithography and cold spray-based AM. The basics of each process are enlightened, and some examples are given to illustrate the capability of each process.

Titanium alloy Ti6Al4V is the most used titanium alloy due to its high specific strength, ductility, corrosion resistance, and weldability. Currently, this alloy is produced with a density above 99% with laser welding-based additive manufacturing processes. However, the costs of titanium powder are high, and for critical components, the excess powder is usually not reused. In this work, we characterized the powder and additively manufactured Ti6Al4V parts by reusing the powder of a single batch to determine the impact on morphology, chemical composition, melt pool viscosity, density, microstructure, and tensile and impact strength. We aimed to deter-mine the limits of powder reuse to increase sustainability and reduce the carbon footprint of Laser Powder Bed Fusion (L-PBF). We found that the powders pick up oxygen after each cycle to form an oxide layer up to 20 nm, causing a change in the optical and thermal properties of the titanium powders. This change affected the laser absorption and, with this, the melt pool properties. The powders reused after 18 cycles were responsible for a drop in the relative density of 0.1%. However, the tensile properties remained unchanged. The reused powders also presented a small shift in particle size distribution that did not affect the sphericity and increased flow -ability. In this work, we proved that the powders of Ti6Al4V alloys could be reused up to 18 cycles without any modification to the tensile properties but with a decrement in the impact strength of 30% for vertical-and 12% for horizontal stress-relieved specimens and 19% and 16% for furnace-annealed specimens, respectively.

Ti6Al4V is the most widely used α‑β Titanium alloy for application in medicine, automotive, and aerospace, known for its high strength and corrosion resistance, but also its high maximal operating temperature of around 420 °C. Combined with its decent weldability under a shield atmosphere it has become a standard alloy for additive manufacturing processes, especially laser and electron beam powder bed fusion (L-PBF). Although this material is well studied, the influence of the L‑PBF process on its tensile properties at elevated temperatures remains almost unexplored. For that reason, this contribution focuses on the analysis of the tensile properties of Ti6Al4V up to 500 °C for different heat treatments and compares it to aerospace standards. Furnace annealed samples reach a tensile strength between 1022 to 660 MPa from room temperature to 500 °C respectively, while stress-relieved specimens reach 1205 to 756 MPa. Stress-relieved samples show a lower ductility at room temperature, but elongation at break increases at high temperature and outperforms furnace annealed samples at 500 °C.

The scope of this work is to provide an overview of the influences of process parameters, print orientation, and post-process treatments of Ti6AlV4 processed by laser powder bed fusion on its microstructure and physical and mechanical properties and their anisotropic behavior. To avoid the influence of changes in powder quality and ensure comparability, experiments were carried out using a single batch of virgin powder. First, characterization of the density and surface roughness was performed to optimize the process parameters utilizing design of experiment. Tensile, notched bar impact and compression test specimens were built in three different orientations: vertically, horizontally, and inclined at 45° to the build plate. Later, the influence of the staircase effect and the possible course of anisotropy from vertical to horizontal were investigated. Subsequently, heat treatments for stress relief, furnace annealing, and hot isostatic pressing were performed. In addition to as-built samples, mechanical machining and a two-step electrochemical polishing surface treatment were applied to investigate the influence of the surface roughness. With parameter optimization, a relative density of 99.8% was achieved, and surface roughness was improved over default parameters, reducing Ra by up to 7 µm. Electrochemical polishing is a viable way to decrease the surface roughness. An Ra value of 1 µm and an Rz value of 4 µm can be achieved for 45° downskin surfaces with as-built surface roughness values of Ra 24 µm and Rz 117 µm. As-built and stress-relieved conditions show little anisotropy in their yield and tensile strength (max 2.7%), but there is a strong influence of the build orientation on necking, and brittle fracture behavior is shown due to the martensitic microstructure (up to 70%). Heat treatment can increase the ductility and further decrease the strength anisotropy with both furnace annealing and hot isostatic pressing delivering similar results for tensile properties, while angled samples exhibit behavior that is closer to vertical than horizontal, indicating a non-linear change in break behavior. Electrochemical polishing increases fracture necking, and its isotropy drastically increases from 4% to over 30% compared with as-built parts, which is close to the level of the machined specimen.

Besides process parameters, powder properties such as grain size, morphology, and chemical composition have the highest impact on the material properties of parts produced by powder-based additive manufacturing. These properties are strongly influenced by the production process of the powder and its feedstock. In the scope of this work, the influence of three different powder producers of Ti6Al4V, on density, chemical composition, and mechanical properties of build samples, is investigated. Furthermore, the effects of the varying atomization process on morphology, particle size distribution, chemical composition, and oxide layers are studied. Particle size distribution and flowability seem to have a minor influence on the production process while density depends highly on the surface topology, sphericity, and nature of the oxide layer, which affect energy intake. Tensile properties are highly influenced by chemical composition, mainly dissolved oxygen, and polluting satellites, while notched bar impact strength is additionally influenced by the oxide layer and suspected TiO2 precipitations caused by it.

While static mechanical properties of Laser Powder Bed Fusion (L-PBF) processed titanium alloy Ti6Al4V Grade 5 are sufficient and comparable to classic production processes (DebRoy et al. in Prog Mater Sci 92:112–224 [1]; Vrancken et al. in J Alloys Compd 541:177–185 [2]) the fatigue properties of L-PBF lack behind (Leuders et al. in Int J Fatigue 48:300–307 [3]; Nicoletto in Int J Fatigue [4]). However, the reason for this issue are not completely clear and uniquely assignable as combination of (sub surface) porosity, microstructure and surface roughness. This work aims to investigate the influence of several factors on the fatigue properties of controlled, single powder patch of Ti6Al4V. The use of a single patch eliminates the influences of mechanical and chemical powder properties. The investigated factors comprise mechanical and electrochemical polishing (EP) surface treatment, heat treatment (stress relief SR, furnace annealing FA, hot isostatic pressing HIP), print orientation (vertical and horizontal) and load cases (R = −1, R = 0.1). Additionally, a set of tests is performed at 80 °C. For both load cases HIP and machining show a positive impact with a higher influence of machining. For load case R = 0.1 HCF (σaD, 50%) for HIP and machined is around 400 MPa while the same surface treatment but FA reach 218 MPa and SR/EP samples at just 111 MPa. Elevated environmental temperature and horizontal orientation have a minor positive impact. For R = −1 the overall gap narrows to 300 for HIP/machined and 175 MPa for SR/EP respectively.

Complex porous 316 L stainless steel, Ti-6Al-4V, Ti-6Al-7Nb, ULTEMTM 1010 and MED610TM polymer structures were produced with additive manufacturing methods. The structures were surface functionalized by atomic layer deposition of titanium, zinc and zirconium oxide coatings with a thickness between 14 and 43 nm. Deep and narrow structures with aspect ratios >10 could be coated. Titanium oxide films are mostly amorphous when plasma-assisted deposition is used and contain nanocrystalline anatase when deposited by thermal atomic layer deposition. The deposited titanium oxide grains ranged in size from similar to 20 to 60 nm. In interior parts of the fractured porous polymer model structures with pore sizes of 1-2 mm, both thermal and plasma-assisted titanium oxide thin films and partly delamination were detected. X-ray photoelectron spectroscopy analysis revealed almost stoichiometric composition and dominance of the Ti (IV) oxidation state at a 250 degrees C deposition tem-perature. Zinc oxide coatings in porous polymer model structures partly delaminate as well, while adhesion and homogeneity is higher for printed Ti-6Al-7Nb lattice structures with a 0.5-mm mesh size. Zirconium oxide coatings on Ti-6Al-4V lattice structures with a 0.8-mm mesh size are comparable to zinc oxide coatings but are mostly crystalline. This is attributed to the relatively high, 300 degrees C deposition temperature. The findings demonstrate potential but also limitations of combined additive manufacturing and atomic layer deposition for medicine and energy production applications. In addition, the results confirm previous studies that metallic and polymeric substrate materials and process conditions strongly influence the coating structure and composition, and individual development of each intended application is required.

This paper presents the exploitation of the additive manufacturing (AM) technique laser powder bed fusion (L-PBF), for the fabrication of a K-band meta-substrate filter. The decisions made through each round of prototyping are discussed. It also presents the crucial parameters that can lead to a higher quality end product of AM. The filter response and out-of-band performance are also discussed in short.

The quality and characteristics of a powder in powder bed fusion processes play a vital role in the quality of additively manufactured components. Its characteristics may influence the process in various ways. This paper presents an investigation highlighting the influence of powder deterioration on the stability of a molten pool in a laser beam powder bed fusion (LB-PBF, selective laser melting) process and its consequences to the physical properties of the alloy, porosity of 3D-printed components and their mechanical properties. The intention in this was to understand powder reuse as a factor playing a role in the formation of porosity in 3D-printed components. Ti6Al4V (15 μm–45 μm) was used as a base material in the form of a fresh powder and a degraded one (reused 12 times). Alloy degradation is described by possible changes in the shape of particles, particle size distribution, chemical composition, surface tension, density and viscosity of the melt. An approach of 3D printing singular lines was applied in order to study the behavior of a molten pool at varying powder bed depths. Single-track cross-sections (STCSs) were described with shape parameters and compared. Furthermore, the influence of the molten pool stability on the final density and mechanical properties of a material was discussed. Electromagnetic levitation (EML) was used to measure surface tension and the density of the melt using pieces of printed samples. It was found that the powder degradation influences the mechanical properties of a printed material by destabilizing the pool of molten metal during printing operation by facilitating the axial flow on the melt along the melt track axis. Additionally, the observed axial flow was found to facilitate a localized lack of fusion between concurrent layers. It was also found that the surface tension and density of the melt are only impacted marginally or not at all by increased oxygen content, yet a difference in the temperature dependence of the surface tension was observed.

The following work presents the results of an investigation of the cause–effect relationship between the stability of a melt pool and the roughness of an inclined, unsupported steel surface that was 3D-printed using the laser powder bed fusion (PBF-L/M) process. In order to observe the balling effect and decrease in surface quality, the samples were printed with no supporting structures placed on the downskin. The stability of the melt pool was investigated as a function of both the inclination angle and along the length of the melt pool. Single-track cross-sections were described by shape parameters and were compared and used to calculate the forces acting on the melt pool as the downskin was printed. The single-melt track tests were printed to produce a series of samples with increasing inclination angles with respect to the baseplate. The increasing angles enabled us to physically simulate specific solidification conditions during the sample printing process. As the inclination angle of the unsupported surface increased, the melt-pool altered in terms of its size, geometry, contact angles, and maximum length of stability. The balling phenomenon was observed, quantified, and compared using roughness tests; it was influenced by the melt track stability according to its geometry. The research results show that a higher linear energy input may decrease the roughness of unsupported surfaces with low inclination angles, while a lower linear energy input may be more effective with higher inclination angles.

The aim of this study is to observe the effect of process parameters on residual stresses and relative density of Ti6Al4V samples produced by Selective Laser Melting. The investigated parameters were hatch laser power, hatch laser velocity, border laser velocity, high-temperature preheating and time delay. Residual stresses were evaluated by the bridge curvature method and relative density by the optical method. The effect of the observed process parameters was estimated by the design of experiment and surface response methods. It was found that for an effective residual stress reduction, the high preheating temperature was the most significant parameter. High preheating temperature also increased the relative density but caused changes in the chemical composition of Ti6Al4V unmelted powder. Chemical analysis proved that after one build job with high preheating temperature, oxygen and hydrogen content exceeded the ASTM B348 limits for Grade 5 titanium.

The repeated reuse of excess powder is an essential part of the economics of powder-bed additive manufacturing processes. Although many studies on selective laser melting cover the topics of material properties at the micro- and macroscale, little is known about the influence of the multiple reuse cycles of powder. Titanium alloys, in particular, are sensitive to chemical contamination, especially in the presence of oxygen and hydrogen which can lead to inferior material properties. Furthermore, grain size distribution and form change over time which can have an influence on build quality. In this study, the influence of the chosen powder on the quality and material properties of the widely used titanium alloy Ti6Al4V is investigated with focus on porosity, surface quality, microstructure and tensile strength.

The current work presents the results of an investigation focused on the influence of process parameters on the melt-track stability and its consequence to the sample density printed out of NdFeB powder. Commercially available powder of Nd7.5Pr0.7Fe75.4Co2.5B8.8Zr2.6Ti2.5 alloy was investigated at the angle of application in selective laser melting of permanent magnets. Using single track printing the stability of the melt pool was investigated under changing process parameters. The influence of changing laser power, scanning speed, and powder layer thickness on density, porosity structure, microstructure, phase composition, and magnetic properties were investigated. The results showed that energy density coupled with powder layer thickness plays a crucial role in melt-track stability. It was possible to manufacture magnets of both high relative density and high magnetic properties. Magnetization tests showed a significant correlation between the shape of the demagnetization curve and the layer height. While small layer heights are beneficial for sufficient magnetic properties, the remaining main parameters tend to affect the magnetic properties less. A quasi-linear correlation between the layer height and the magnetic properties remanence (Jr), coercivity (HcJ) and maximum energy product ((BH)max) was found.