The development of commercially available niobium (Nb) base alloy powders for additive manufacturing (AM) opens completely new opportunities to produce high-temperature, high-performance components that are particularly interesting for aerospace applications. It is crucial to comprehend the entire workflow, which ranges from powder production and characterization to the determination of optimal process parameters. Insights into the preparation, characterization, and processing of Nb-base alloy powders using metal AM techniques are presented in detail. Nb-base alloys such as C-103 and FS-85 are emerging as promising candidates to improve the capabilities of additive manufacturing, particularly in aerospace applications. What sets Nb-base alloys apart from common materials are their exceptional properties-remarkably low density combined with high thermal conductivity, and outstanding mechanical strength at high temperatures. These properties make such alloys a superior alternative to traditional Ni- and Co-base materials, particularly in environments with temperatures surpassing 1,050 degrees C. While C-103 has become firmly established in conventional manufacturing, there is still no experience with conventional molding for FS-85, which is currently the focus of interest due to its extraordinary strength at elevated temperatures. The commercial availability of FS-85 alloy powders for additive manufacturing opens exciting possibilities for producing high-performance components with complex geometries.

The additive manufacturing of titanium–niobium–tantalum alloys with nominal chemical compositions Ti–xNb–6Ta (x = 20, 27, 35) by means of laser beam powder bed fusion is reported, and their potential as implant materials is elaborated by mechanical and biological characterization. The properties of dense specimens manufactured in different build orientations and of open porous Ti–20Nb–6Ta specimens are evaluated. Compression tests indicate that strength and elasticity are influenced by the chemical composition and build orientation. The minimum elasticity is always observed in the 90° orientation. It is lowest for Ti–20Nb–6Ta (43.2 ± 2.7 GPa) and can be further reduced to 8.1 ± 1.0 GPa for open porous specimens (p < 0.001). Furthermore, human osteoblasts are cultivated for 7 and 14 days on as-printed specimens and their biological response is compared to that of Ti–6Al–4V. Build orientation and cultivation time significantly affect the gene expression profile of osteogenic differentiation markers. Incomplete cell spreading is observed in specimens manufactured in 0° build orientation, whereas widely stretched cells are observed in 90° build orientation, i.e., parallel to the build direction. Compared to Ti–6Al–4V, Ti–Nb–Ta specimens promote improved osteogenesis and reduce the induction of inflammation. Accordingly, Ti–xNb–6Ta alloys have favorable mechanical and biological properties with great potential for application in orthopedic implants.

The present study reports on additive manufacturing of a Ti-30Ta (at.%) high-temperature shape memory alloy (HT-SMA) using electron beam powder bed fusion (PBF-EB/M) technique. Detailed microstructure analysis was conducted to reveal the microstructural evolution along the entire process chain, i.e. from gas-atomised powder to post-processed material. PBF-EB/M processed structures with near full density and an isotropic, β-phase stabilised microstructure, i.e. equiaxed β-grains of around 20 µm in diameter with no preferred crystallographic orientation, are reported. As revealed by differential scanning calorimetry, post-process heat-treated Ti-Ta demonstrates a reversible martensitic phase transformation well above 100°C. Although partly unmolten Ta-particles after both gas atomisation and PBF-EB/M remain a challenge towards robust processing, PBF-EB/M appears to show significant potential for fabrication of Ti-Ta HT-SMAs, especially when functional metal parts and components with complex shapes are required, which are difficult to fabricate conventionally.

Additive manufacturing of pre-alloyed Ti-27Nb-6Ta powder by laser beam powder bed fusion (PBF-LB/M) employing a wide range of processing parameters is reported. An in-depth microstructure analysis along the whole process chain from powder feedstock material to additively manufactured bulk structures was conducted employing scanning electron microscopy (SEM) as well as X-ray and high-energy synchrotron diffraction. It is shown that near-fully dense parts (>= 99.96 %) with beta+alpha"dual-phase microstructure and very homogenous element distribution are obtained in a large process window. In particular, a considerable influence of the energy input during PBF-LB/M on the solidification microstructure, i.e. phase composition and texture, is found. With increasing energy per unit area (EA) both an increase in the volume fraction of the bcc beta-phase and more pronounced texture components are seen. Furthermore, the mechanical behavior was evaluated under monotonic tensile loading. The PBF-LB/M processed Ti-27Nb-6Ta structures feature good mechanical properties with ultimate tensile strength (UTS) and strain to failure values of up to 768 MPa and 33.8 %, respectively. Due to the strong impact of the energy input during additive manufacturing on the microstructure evolution, however, an inverse strength-ductility behavior is observed. While UTS clearly decreases with increasing EA values, strain to failure increases at the same time. The underlying relationships between processing (energy input), microstructure and mechanical properties are explored and rationalized.

Multifunctional materials have been described to meet the diverse requirements of implant materials for femoral components of uncemented total knee replacements. These materials aim to combine the high wear and corrosion resistance of oxide ceramics at the joint surfaces with the osteogenic potential of titanium alloys at the bone-implant interface. Our objective was to evaluate the biomechanical performance of hybrid material-based femoral components regarding mechanical stress within the implant during cementless implantation and stress shielding (evaluated by strain energy density) of the periprosthetic bone during two-legged squat motion using finite element modeling. The hybrid materials consisted of alumina-toughened zirconia (ATZ) ceramic joined with additively manufactured Ti-6Al-4V or Ti-35Nb-6Ta alloys. The titanium component was modeled with or without an open porous surface structure. Monolithic femoral components of ATZ ceramic or Co-28Cr-6Mo alloy were used as reference. The elasticity of the open porous surface structure was determined within experimental compression tests and was significantly higher for Ti-35Nb-6Ta compared to Ti-6Al-4V (5.2 ± 0.2 GPa vs. 8.8 ± 0.8 GPa, p < 0.001). During implantation, the maximum stress within the ATZ femoral component decreased from 1568.9 MPa (monolithic ATZ) to 367.6 MPa (Ti-6Al-4V/ATZ), 560.9 MPa (Ti-6Al-4V/ATZ with an open porous surface), 474.9 MPa (Ti-35Nb-6Ta/ATZ), and 648.4 MPa (Ti-35Nb-6Ta/ATZ with an open porous surface). The strain energy density increased at higher flexion angles for all models during the squat movement. At ∼90° knee flexion, the strain energy density in the anterior region of the distal femur increased by 25.7 % (Ti-6Al-4V/ATZ), 70.3 % (Ti-6Al-4V/ATZ with an open porous surface), 43.7 % (Ti-35Nb-6Ta/ATZ), and 82.5% (Ti-35Nb-6Ta/ATZ with an open porous surface) compared to monolithic ATZ. Thus, the hybrid material-based femoral component decreases the intraoperative fracture risk of the ATZ part and considerably reduces the risk of stress shielding of the periprosthetic bone.

Niobium (Nb) is a transition metal commonly used as an alloying element for increasing strength, toughness, corrosion resistance, and other properties of steel and superalloys. Pure Nb, however, is a very interesting metal for its excellent superconductivity. This makes it suitable for producing superconducting magnets and devices for particle acceleration systems and particle physics research (e.g., superconducting resonant cavities). In this work, the production of Nb by the Laser-Based Powder Bed Fusion (PBF-LB/M, also known as Laser Powder Bed Fusion or LPBF) process was examined. Manufacturing parameters were investigated to achieve additively manufactured parts with a relative density higher than 99.5% and showing a down-skin surface roughness in the range of 20–70 μm, depending on the inclination angle. Studies related to the limiting angle of self-supported Nb parts were also conducted, and innovative non-contact supporting structures were successfully developed. These allowed to creation of parts with very small overhang angles, without compromising the downward-facing surfaces; indeed at the same time, the as-built surface finish was improved.

Aseptic implant loosening after a total joint replacement is partially influenced by material-specific factors when cobalt–chromium alloys are used, including osteolysis induced by wear and corrosion products and stress shielding. Here, we aim to characterize a hybrid material consisting of alumina-toughened zirconia (ATZ) ceramics and additively manufactured Ti-35Nb-6Ta (TiNbTa) alloys, which are joined by a glass solder. The structure of the joint, the static and fatigue shear strength, the influence of accelerated aging, and the cytotoxicity with human osteoblasts are characterized. Furthermore, the biomechanical properties of the functional demonstrators of a femoral component for total knee replacements are evaluated. The TiNbTa-ATZ specimens showed a homogenous joint with statistically distributed micro-pores and a slight accumulation of Al-rich compounds at the glass solder–TiNbTa interface. Shear strengths of 26.4 ± 4.2 MPa and 38.2 ± 14.4 MPa were achieved for the TiNbTa-ATZ and Ti-ATZ specimens, respectively, and they were not significantly affected by the titanium material used, nor by accelerated aging (p = 0.07). All of the specimens survived 107 cycles of shear loading to 10 MPa. Furthermore, the TiNbTa-ATZ did not impair the proliferation and metabolic activity of the human osteoblasts. Functional demonstrators made of TiNbTa-ATZ provided a maximum bearable extension–flexion moment of 40.7 ± 2.2 Nm. The biomechanical and biological properties of TiNbTa-ATZ demonstrate potential applications for endoprosthetic implants.

The development of spherical Ti/Nb/Ta alloy powders with compositions Ti-xNb-6Ta (x = 20, 27, 35 wt%) by electrode induction melting gas atomization (EIGA) and their processing by laser beam powder bed fusion (PBF-LB/M) are reported. Microstructure investigations by X-ray diffraction and scanning electron microscopy including energy dispersive X-ray spectroscopy and electron backscatter diffraction reveal a significant impact of the composition on the structural properties, i.e., phase evolution and texture, and the possibility for a direct microstructure design. Ti-rich alloys preferably solidify in the orthorhombic α’’-phase, whereas in Nb/Ta-rich alloys the body-centered cubic (bcc) β-phase is observed. The alloys possess a very broad processing window and can be printed to full density over a wide range of printing parameters. Additively manufactured Ti-27Nb-6Ta shows a unique behavior, since strength and elongation at failure strongly depend on the printing parameters applied. The underlying microstructural mechanisms, i.e., the influence of the laser energy on texture effects and phase formation, are discussed.

Binary Ti-Ta and ternary Ti-Ta-Al alloys attracted considerable attention as new potential biomaterials and/or high-temperature shape memory alloys. However, conventional forming and manufacturing technologies of refractory based titanium alloys are difficult and cost-intensive, especially when complex shapes are required. Recently, additive manufacturing (AM) emerged as a suitable alternative and several studies exploited elemental powder mixing approaches to obtain a desired alloy and subsequently use it for complex shape manufacture. However, this approach has one major limitation associated with material inhomogeneities after fabrication. In present work, novel pre-alloyed powder material of a Ti-Ta-Al alloy was additively manufactured. Hereto, electron beam powder bed fusion (PBF-EB/M) technique was used for the first time to process such Ti-Ta based alloy system. Detailed microstructural analysis revealed that additively manufactured structures had a near full density and high chemical homogeneity. Thus, AM of pre-alloyed feedstock material offers great potential to overcome major roadblocks, even when significant differences in the melting points and densities of the constituents are present as proven in the present case study. The homogeneous microstructure allows to apply short-term thermal post treatments. The highly efficient process chain detailed will open up novel application fields for Ti-Ta based alloys.

The synthesis of spherical titanium/niobium/tantalum (TNT) alloy powders, namely Ti-20Nb-6Ta, Ti-27Nb-6Ta, Ti-35Nb-6Ta, and Ti-22Nb-19Ta (in wt-%) by electrode induction melting gas atomization is reported. The powder materials are characterized in detail using X-ray diffraction and scanning electron microscopy. Their processability via laser beam powder bed fusion (PBF-LB/M) is proven, and microstructure as well as mechanical properties of the additively manufactured specimens are assessed. All powders feature a dendrite-type microstructure with Nb/Ta-rich dendritic and Ti-rich inter-dendritic phases. Crystal structures of the powders are strongly composition-dependent. Nb- and Ta-rich Ti-35Nb-6Ta and Ti-22Nb-19Ta feature a body-centered cubic lattice, whereas Ti-rich Ti-20Nb-6Ta and Ti-27Nb-6Ta powders are characterized by multi-phase microstructures, consisting of non-equilibrium martensitic phases. Processing by PBF-LB/M causes significant changes in their microstructures: the dendrite-type morphologies vanish, and the formation of microstructures with a homogeneous element distribution can be observed in all additively manufactured parts. Ultimate tensile strength (UTS) as well as elongation at fracture are assessed by tensile testing. UTS values are found to be in a range from 651 MPa (Ti-35Nb-6Ta) to 802 MPa (Ti-20Nb-6Ta); strain-to-failure is between 21.3 % (Ti-35Nb-6Ta) and 31.7 % (Ti-22Nb-19Ta). Ductile fracture behavior is seen for all TNT alloys investigated.

This study developed a non-equiatomic Ti28.33Zr28.33Hf28.33Nb6.74Ta6.74Mo1.55 super-solid solutionized BioHEA using laser powder bed fusion (LPBF) to reach the full potential as BioHEA. We succeeded in significant suppression of elemental segregation, thus, resulting in a single crystalline-like texture by activating layer-to-layer epitaxial growth. Relatively low Young's modulus was achieved in the single crystalline-like BioHEA. Moreover, LPBF-fabricated BioHEA exhibited significantly higher yield stress (1355-1426 MPa) due to the effective solid solution hardening compared to as-cast counterpart with marked segregation (949 MPa), and good biocompatibility. This is first report achieving BioHEA with low modulus, excellent strength-ductility balance, and good biocompatibility via LPBF. IMPACT STATEMENT This study achieved super-solid-solutionized and single crystalline-like TiZrHfNbTaMo bio-high entropy alloy using laser powder bed fusion, resulting in low Young's modulus along < 001 > oriented direction, excellent strength-ductility balance, and good cytocompatibility.

BioHEAs, specifically designed high entropy alloy (HEA) systems for biomedical applications, represent a new era for biometals. However, recent challenges are (1) the poor shape customizability, and (2) the inevitable severe segregation due to the intrinsic fact that HEA is an ultra-multicomponent alloy system. To achieve shape customization and suppression of elemental segregation simultaneously, we used an extremely high cooling rate (similar to 10(7) K/s) of the selective laser melting (SLM) process. We, for the first time, developed pre-alloyed Ti1.4Nb0.6Ta0.6Zr1.4Mo0.6 BioHEA powders and SLM-built parts with low porosity, customizable shape, excellent yield stress, and good biocompatibility. The SLM-built specimens showed drastically suppressed elemental segregation compared to the cast counterpart, representing realization of a super-solid solution. As a result, the 0.2% proof stress reached 1690 +/- 78 MPa, which is significantly higher than that of cast Ti1.4Nb0.6Ta0.6Zr1.4Mo0.6 (1140 MPa). The SLM-built Ti1.4Nb0.6Ta0.6Zr1.4Mo0.6 BioHEA is promising as a next-generation metallic material for biomedical applications. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd.

Niobium is an important material for high temperature applications, in space, in superconductors or in chemical process constructions. Laser-based powder bed fusion of niobium (PBF-LB/M/Nb) offers new opportunities in design, though it is still an expensive technique. The build-up rate is an important factor for economical manufacturing using PBF-LB/M/Nb. It is largely influenced by variation of process parameters, affecting the heat flow during the manufacturing process. In this work, an empirical model for PBF-LB/M/Nb is developed. Based on this model, manufacturing parameter sets using different volume build-up rates are predicted and confirmed. They enable the manufacture of parts with homogeneous and crack-free microstructure with more than 99.9% relative density. Tensile and hardness tests of specimens, which were manufactured using different parameter sets, are performed to determine the effects of the build-up rate—and thus the heat flow during manufacturing—on different mechanical properties. The ultimate tensile strength and yield strength of as-manufactured specimens reach values up to 525 MPa and 324 MPa, respectively, while the elongation at break ranges between approximately 8 and 16%. The Vickers hardness of all specimens was in the range of 149 ± 8 HV0.1. In addition, the microstructure of the manufactured samples is investigated by means of light as well as scanning electron microscopy.

INTRODUCTION Additive manufacturing (AM) processes such as laser or electron beam powder-bed-fusion (PBF-LB or PBF-EB), and directed energy deposition (DED), enable production of parts with a high degree in freedom of design allowing e.g., topology optimization, or complex structures that open new opportunities in wide range of applications.1,2 In addition to the fact that the AM process allows the creation of new designs that are not realizable by subtractive manufacturing, the materials applied can contribute further with their intrinsic properties to optimize mechanical, biological, or chemical parameters of AM parts.3,4 While the metal AM material landscape is still mainly dominated by steel or titanium alloys with applications being limited by their intrinsic material properties, new material candidates can further expand the scope of AM technology.5,6 Tantalum and niobium are characterized by high melting points, superior corrosion resistance,7 superconductivity,8 and a high level of biocompatibility.9 Moreover, they are β-phase stabilizers in Ti alloys. These properties make them interesting candidates for applications such as biomedical implants, superconductors, high temperature components (e.g., engine parts), or parts for the chemical processing industry.10–12 While Ta/Nb and their alloys are already applied in many of these industries, the combination of their properties with the freedom of design offered by AM processing technologies is of vital importance for the realization of new and optimized solutions. Moreover, applying AM processes for Ta/Nb materials is also beneficial for cost aspects as, for example, the number of parts for assembly can be reduced by AM, or the performance of parts can be optimized due to the realization of more complex structures and geometries. Accordingly, a major field of research activity to push existing performance beyond current boundaries has been developed

Nowadays, biomaterials can be used to maintain or replace several functions of the human body if necessary. Titanium and its alloys, i.e. Ti6Al4V are the most common materials (70 to 80%) used for structural orthopedic implants due to their unique combination of good mechanical properties, corrosion resistance and biocompatibility. Addition of β-stabilizers, e.g. niobium, can improve the mechanical properties of such titanium alloys further, simultaneously offering excellent biocompatibility. In this in vitro study, human osteoblasts and fibroblasts were cultured on different niobium specimens (Nb Amperit, Nb Ampertec), Nb sheets and Ti-42Nb (sintered and 3D-printed by selective laser melting, SLM) and compared with forged Ti6Al4V specimens. Furthermore, human osteoblasts were incubated with particulates of the Nb and Ti-42Nb specimens in three concentrations over four and seven days to imitate influence of wear debris. Thereby, the specimens with the roughest surfaces, i.e. Ti-42Nb and Nb Ampertec, revealed excellent and similar results for both cell types concerning cell viability and collagen synthesis superior to forged Ti6Al4V. Examinations with particulate debris disclosed a dose-dependent influence of all powders with Nb Ampertec showing the highest decrease of cell viability and collagen synthesis. Furthermore, interleukin synthesis was only slightly increased for all powders. In summary, Nb Ampertec (sintered Nb) and Ti-42Nb materials seem to be promising alternatives for medical applications compared to common materials like forged or melted Ti6Al4V.

Long term stability of ceramics at high temperatures is one of the great challenges of the contemporary technology developments. Multi‐component ceramics such as Si–B–C–N systems gain a lot of interest for high temperature applications due to the stability of their amorphous inorganic network arising from strong covalent bonding. The polymer derived ceramics (PDC) route enables the synthesis of such materials from preceramic polymers as well as their manufacturing as specific ceramic geometries, which are difficult to obtain otherwise. This review proposes an overview of the works related to the development of Si–B–C–N ceramics through the PDC route in the last 30 years. A particular focus is made on the relation between the chemical structure of the precursors and the properties of the resulting ceramics. The main topics reviewed are related to the synthesis of tailor‐made polymeric precursors, to their processing to ceramic components, and to the characterization of the material properties and functionalities. The various strategies adopted for the development of shaped Si–B–C–N ceramics as functional materials are presented and the trend of nowadays research for future evolution of Si–B–C–N materials is discussed.

The application of Ti-6Al-4V alloy or commercially pure titanium for additive manufacturing enables the fabrication of complex structural implants and patient-specific implant geometries. However, the difference in Young’s modulus of α + β-phase Ti alloys compared to the human bone promotes stress-shielding effects in the implant–bone interphase. The aim of the present study is the mechanical characterization of a new pre-alloyed β-phase Ti-42Nb alloy for application in additive manufacturing. The present investigation focuses on the mechanical properties of SLM-printed Ti-42Nb alloy in tensile and compression tests. In addition, the raw Ti-42Nb powder, the microstructure of the specimens prior to and after compression tests, as well as the fracture occurring in tensile tests are characterized by means of the SEM/EDX analysis. The Ti-42Nb raw powder exhibits a dendrite-like Ti-structure, which is melted layer-by-layer into a microstructure with a very homogeneous distribution of Nb and Ti during the SLM process. Tensile tests display Young’s modulus of 60.51 ± 3.92 GPa and an ultimate tensile strength of 683.17 ± 16.67 MPa, whereas, under a compressive load, a compressive strength of 1330.74 ± 53.45 MPa is observed. The combination of high mechanical strength and low elastic modulus makes Ti-42Nb an interesting material for orthopedic and dental implants. The spherical shape of the pre-alloyed material additionally allows for application in metal 3D printing, enabling the fabrication of patient-specific structural implants.

Orthopaedic implant materials are exposed to high mechanical loading. Conventional materials based on stainless steel or cobalt-chromium alloys display adequate mechanical strength, but also toxicological concerns due to release of toxic or allergenic elements (particles or ions) resulting in inflammatory reactions in the adjacent tissues. Metal alloys based on titanium, tantalum and niobium represent higher biocompatibility with appropriate mechanical properties for avoiding stress-shielding and consecutive implant loosening. Application of specifically designed spherical Ti/Nb(/Ta) alloy powders in additive manufacturing, i.e. 3D metal printing processes such as selective laser melting (SLM) or electron beam melting (EBM), enable the production of components with a high degree in freedom of design. Accordingly, SLM or EBM of Ti/Nb(/Ta) alloys offer the possibility to fabricate patient-specific orthopaedic implants. The present paper gives an overview on the development of bio-compatible Ti/Nb(/Ta) alloys especially designed for application in 3D metal printing. Furthermore, the additively manufactured 3D structures are mechanically tested and the influence of differently grained alloy powders and bulk parts on the viability and proliferation of human cells (fibroblasts, osteoblasts) are examined.