Additively processed TiAl6Nb7 alloy for biomedical applications

Laser beam melting (LBM) is an advanced manufacturing technology providing special features and the possibility to produce complex individual parts directly from a CAD model. TiAl6V4 most common used titanium alloy particularly in biomedical applications. TiAl6Nb7 shows promising improvements especially regarding biocompatible properties due substitution of hazardous vanadium. This work focuses on examination laser melted TiAl6Nb7. For microstructural investigation scanning electron microscopy including energy-dispersive x-ray spectroscopy as well backscatter diffraction are utilized. The related acicular microstructure corresponding mechanical properties, which determined by hardness measurements tensile tests, investigated. meets, except breaking elongation A, demands like ultimate strength Rm, yield Rp0.2, Vickers HV international standard ISO 5832-11. Next steps contain comparison between different conditions. Further investigations aim at improving heat treatments assessment their influence corrosive behavior human body-like Das Laserstrahlschmelzen ist eine fortschrittliche Fertigungstechnologie, die besondere Merkmale und Möglichkeit bietet, komplexe individuelle Teile direkt aus einem CAD-Modell herzustellen. am häufigsten verwendete Titanlegierung, insbesondere biomedizinischen Anwendungen. zeigt vielversprechende Verbesserungen hinsichtlich der biokompatiblen Eigenschaften durch Substitution des schädlichen Vanadiums. Diese Arbeit konzentriert sich auf Untersuchung von selektiv laserstrahlgeschmolzenem Für mikrostrukturelle Untersuchungen werden Rasterelektronenmikroskopie einschließlich energiedispersiver Röntgenspektroskopie sowie Elektronenrückstreuung eingesetzt. Die dem selektiven resultierende nadelförmige Mikrostruktur entsprechenden mechanischen Eigenschaften, Härtemessungen Zugversuche bestimmt werden, untersucht. mittels selektivem laserstrahlschmelzen verarbeitete Legierung erfüllt, mit Ausnahme Bruchdehnung Anforderungen wie Zugfestigkeit Streckgrenze Rp0,2 Vickershärte internationalen Norm nächsten Schritte beinhalten einen Vergleich zwischen verschiedenen Zuständen. Weitere zielen Verbesserung Wärmebehandlungen Beurteilung ihres Einflusses korrosiven Verhaltens unter körperähnlichen Bedingungen. Additive has received increasing attention academia industry recent years progress computation systems technology. process developed with high potential for both, industrial applications university research 1. defined DIN EN ISO/ASTM 52900 where objects joined materials 3D model data, layer 2, 3. Compared conventional, e. g. subtractive technologies, additive enables fabrication very based Computer Aided Design powder bed fusion metal or is, metals, one established technique, consequence fabricate fully dense geometric comparable conventionally manufactured components 1, 4, 5. provides wide range advantages, such reduced production time, increased manufacturer flexibility material utilization. small medium batch sizes aerospace already established. now, challenges still exist, challenges, anisotropy undesired phase compositions, processing remaining defects low build-up rates 6. be free design have so called complexity-for-free, patient-specific, implants customized each patient 7. In processes fast heating rates, respectively cooling result characteristic compared conventional 8-10. These additively materials, grain refinement, strongly connected prior conditions restrictions. By local through beam, top some beneath, solidified layers metallurgical bonded. Usually scan velocity around 500 mm s−1–2000 s−1. resulting melt pool, rate 103 K s−1–106 s−1 11. interaction period approximately 4⋅10−3 s–4⋅10−4 s, much faster example casting 12. Therefore, experiences cyclic cooling, lead quenched tempered microstructure. Biomedical gained decades. According specific application, biomaterials can body. Often replacing lost diseased biological structures, increase life quality 13-15. Implants must adequate wear resistance, corrosion excellent biocompatibility, osseointegration, non-cytotoxicity avoid revision surgeries 16. Immediately after implant placed, reactions surface host tissue take place. Here, biocompatibility leads success failure implantation 17. To toxic elements avoided. Elements titanium, niobium, molybdenum, tantalum, zirconium, gold, tungsten, tin biocompatible, whereas aluminum, vanadium, chromium, nickel probably body 18, 19. mandatory alloys, usage properties. use load bearing elastic modulus, strength, elongation, fatigue important factors 20. Titanium its alloys possess addition other biomaterials, stainless steels cobalt chrome characteristics resistance 21-25. biocompatibilities, Young's ductility, life, etc., adjusted structural organism application hard tissues 23. Adjusting structure, building porous adjustments allotropic could 24. There two forms titanium. α temperature, hexagonal close-packed crystal structure. Above 882 °C body-centered cubic β. transformation known β-transus pure either increases decreases alloying elements, stabilizers (e. oxygen, nitrogen) β iron, chromium). largest among (α+β) metastable 26-31. commonly Typically they annealed condition 14, 26, 27, 30. Both belong group depends quenching parameters, field higher temperatures following treatment 32, 33. flow during caused predominantly downwards, previously substrate material, heated above below transus temperature. build strategy number 34. consists fine α’ martensite within β-grains. columnar β-grains transformed lattice new (α+β)-type more specifically TiAl6Nb7, being conducted. similar favorable quite microstructure, advantageous vanadium niobium 35-37. this study, examined overall objective substitute containing specimens characterization were fabricated using LT30 SLM machine (DMG MORI AG, Germany) equipped continuous wavelength fiber spot size 70 μm, maximum power 600 W. data preparation software Magics 21 (Materialise GmbH Leuven, Belgium) RDesigner used. obtain possible density melting, parameters employed, Table All constant strategy, 5 stripes layer-wise rotation vectors 67°. takes place inert argon atmosphere prevent oxidation oxygen content 0.08 %–0.13 %. Alloy W speed Hatch distance Layer thickness μm 250 880 0.11 50 supplied TLS Technik & Co. Spezialpulver KG (Germany). Powder particles concerning particle distribution, morphology chemical composition. distribution inspected Mastersizer 2000 (Malvern Instruments Ltd, United Kingdom) measure particles. determination 0.02 μm. Furthermore, compositions was measured means inductively coupled plasma optical emission spectrometry Q4 TASMAN (Bruker AXS GmbH, Germany). addition, revierlabor (Germany) investigated fluorescence analysis, combustion analysis IR-detection carrier gas hot extraction technique. accordance 5832-11, 2 38. Condition Al Nb Fe O Ti Method 5832-11 5.5–6.5 6.5–7.5 <0.25 <0.2 Bal. 6.03 6.75 0.09 0.10 external as-built 5.50 6.81 0.12 0.18 OES Relative analyzed digital confocal microscope Keyence VHX5000 (KEYENCE basis metallographic cross-sections. Grayscale differentiation identify count pores device-specific software. roughness macroscope VR-3100 arithmetical mean Ra root square Rq surfaces electrical discharge machined (EDM) specimens. Five per five line (length ≈6.8 mm) side. macroscopic observations classification fractured secondary imaging (SEM) Zeiss Ultra Plus (Carl Microstructural x-z-plane, parallel direction alloy, unit detect phases textures characterization. grinded sandpaper (grain 2500) subsequently vibration polished 12 h VibroMet (Buehler, ITW Test Measurement perpendicular Indentation automated tester KB 30 FA (KB Prüftechnik according HV5. tested nine indentations sample. tests conducted room unidirectional, quasi-static loading examinations mini built, while wire-cut cuboids, Figure 1a, b. both samples loaded z-axes Otherwise orientation solidification molten would types. Tensile performed servo-hydraulic test-rig MTS 858 Top System 20 kN cell extensometer 632.29F-20 (both Systems Corporation, USA) gage length 3 mm. test procedure 6892-71 displacement controlled crosshead 1.5 min−1 ambient determine modulus E break A. Geometry specimens; (a) as-built, (b) cuboids; BD indicating direction. powder, agreement 5832–711. nominal comprises 26.9 (D10) 52.1 (D90) Gaussian centered 37.6 (D50), 2b. mainly spherical only few agglomerations bigger particles, 2a. (scanning electrons image) characterized primary grains, oriented along nearly 30, 32-34, Long plates created inside grains. Primary boundaries indicated white lines. therefore time single passes, large effect columnar, grains 34, 39. With layers, decreasing vectors, same spot, get longer. Reheating layer, epitaxial growth results remelting previous temperature If unidirectional considered anisotropy, coarser, affect 40. emerging random twelve variants possibly Burger's relationship there no preferred variant selection, coarse, negligible 41. crystallographic 45° inclined (z-axis), Cross-section image direction; β-grain (white lines) primarily lamellas. fine, acicular, lamella 4a, Regarding inverse pole figure fine-lamellar structure width 1 μm–2 ranging 60 these needles 11, 42, 43. lines indicate boundaries, 4b. During begin evolve. solidification, preferentially grows <100> direction, elongated, evolve 44-46. accordingly random, fibre-like texture 46. Due passing transform Burgers relation orientations (transformation variants) [41, 47–49]. analyses grid (α α’) structures (β). difference martensitic minimal distortion, not detectable 50. probability formation 43, 51, 52. map colored red, α’, green, 4c. amounts detected arrows). should additional surround lamellas form thin film 46, 50, 53. aluminum 4e, f. evenly distributed areas. No depletion enrichment any element observable. rapid therefore, limitation diffusional 54. able diffuse evolving homogeneous concentration Electron mapping signal, figure, (c) α-Ti (red) β-Ti (green, tips arrows), (d) color legend coloring (e) homogenous (f) niobium. summarized specimen shown built values 5.1 μm±0.4 6.6 μm±0.6 unmelted layerwise than 3.0 μm±0.9 4.1 μm±1.3 smoother machining 55. Rp0.2 MPa Rm GPa A % HV5 5.1±0.4 6.6±0.6 868±48 967±34 105±17 9.9±2.4 337±23 EDM 3.0±3.9 4.1±1.3 1118±37 1223±5 109±4 7.6±1.3 401±8 Surface red measurements; measurements. 337 HV5±23 401 HV5±8 casted 257 HV0.05±29 HV0.05 22. sheet Solutions Group AG (376 HV10±6 HV10) slightly lower 56. larger into longer thicker laths smaller, finer, hardening refinement Hall-Petch relation, lamellar equiaxed microstructures 57-61, enhanced improved densification, residual stresses, instead strengthening mechanism 62. show almost values, may increased. Metallurgical changes hydrogen embrittlement diffusion stress states favour enhancement [55, 63–69]. deviations E, plastic surgery (ISO 5832-11), claiming minimum Exemplary presentations stress-strain curves 6a. Stress-strain melted, (Ti67_ab, black (Ti67_EDM, TiAl6Nb7; Properties states, out cuboid (ISO) [38]; (filled bars), (striped (checkered bars) (black line). 967 MPa±34 868 MPa±48 1223 MPa±5 1118 MPa±37 MPa, respectively. wrought products (Rm = 984 MPa–1024 MPa; 933 MPa–952 MPa), 817 dominant 7, 20, Nevertheless, lacked significantly ductility elongations 24, 25. explained microstructures, strong impact alloys. Typically, colony rather control Plastic deformation tends movement dislocations. less dislocation pile ups, smaller ups 70. As demonstrated equation, brittle occurs 71, 72. α, castings, exceed 22, least 900 (Rm), 800 (Rp0.2) 10 (A) meet requirements points. but elongation. required summarized, 6b. showed, that moduli vary certain 105 GPa–116 GPa. Comparative given literature ASM International Handbook 38, 73. differences stiffness influenced levels tend stresses flow. better area, specimen. dependency 74, 75. affected exposure area edge contiguous, non-melted surrounding less. subsequent region, taking account, rough micro notches nuclei crack initiation 76, 77. reasons also transformation, 55, 63-69. correlation TiAl6V4, empirical relationships, good agreement, obtained 78, 79. experimental exp (≈967 MPa) calculated cal, HV→Rm (≈1024 respectively, (≈1223 (≈1127 large, approximation. Probably occur. impacted underlying do fulfil demanded chirurgical possibilities 80. reduce internal 81. Heat homogeneous, decreased whole specimens, partially decomposition equilibrium laminar relaxation tensed state 82-84. Another thermomechanical isostatic pressing, minimizing porosity fuses described 85. average increases. Sliding effects will 86. reason presence An amount improves ductile 83, After performing characterize surfaces. conditions, machined, results, fracture shown. Additively processed often exhibits transformation. demonstrates behavior, propensity cleavage size, facets dimples 87. Fractured small, shallow quasi-cleavage surfaces, transgranular facets, confirming minor material. Concentric features, pores, occur 7a, b, d. typically pulled apart load. Scanning microscope-secondary images view; enlarged view boxed region (a); (b); concentric defect (gas pore). Different aspects been addressed. composition, conclusions made investigations: laths, growed elongated wise process. energy input Only noticeable. indentation hardness, microstructures. finer grain-boundary strengthening. Decreasing Small, alloy. next ascertainment behaviour performances Grain fraction adapted, Corrosion further investigations. applying physical vapour deposition coatings Institute Materials Engineering (TU Dortmund, performance features. evaluated determining viability proliferation Department Pharmacology, Toxicology Pharmacy (TiHo Hanover, equipment base LWK DMRC infrastructure. authors grateful staff members DMRC. gratefully thank German Research Foundation (DFG) financial support (SCHA 1484/45-1, ME 4991/2-1, TI 343/167-1). Open Access funding enabled organized Projekt DEAL.