Study of heat treatments and surface finishes in Ti-6Al-4V alloy produced by DMLS for use in implants

Orientador: Maria Clara Filippini IerardiDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia MecânicaResumo: No presente trabalho, a liga de titânio Ti-6Al-4V, empregada em implantes ortopédicos permanentes ou temporários devido à sua biocompatibilidade, foi produzida a partir da manufatura aditiva utilizando o processo de Sinterização Direta de Metais por Laser (DMLS). O material foi submetido a diferentes tratamentos térmicos com o intuito de modificar suas propriedades mecânicas, e a acabamentos de jateamento, ataque químico e polimento eletroquímico para analisar os efeitos dos mesmos no acabamento de superfície. As modificações resultantes após os tratamentos térmicos e acabamentos de superfície foram analisadas por microscopia óptica, microscopia eletrônica de varredura, difração de raios-X, medidas de rugosidade e massa, microdureza Vickers, e ensaios de tração e compressão. No estudo de acabamentos de superfície, o menor valor de rugosidade foi obtido após as etapas de jateamento e ataque químico combinadas. O acabamento de jateamento é responsável por deixar uma superfície com rugosidade uniforme, enquanto o ataque químico é responsável pela limpeza da superfície e redução da rugosidade. As amostras foram submetidas aos tratamentos térmicos nas temperaturas de 850 ºC, 950 ºC e 1050 ºC durante uma hora com resfriamento em forno. Foi constatado que quanto maior a temperatura empregada, maior é a ductilidade do material e, por outro lado, menor é a resistência mecânica. Tal fato ocorreu devido à maior nucleação e crescimento da fases 'alfa' e 'beta' no material, que apresentava inicialmente uma estrutura constituída por martensita hexagonal ('alfa'). A condição de tratamento térmico a 950 ºC foi a que apresentou a melhor relação de propriedades mecânicas, satisfazendo os requerimentos da norma ASTM F136 para a utilização da liga Ti-6Al-4V em implantesAbstract: In this study, the Ti-6Al-4V titanium alloy, used in permanent or temporary orthopedic implants due to its biocompatibility, was produced by additive manufacturing using the Direct Metal Laser Sintering (DMLS) process. The material was subjected to different heat treatments in order to modify their mechanical properties, and to the surface finishes of blasting, chemical etching and electropolishing to analyze their effects on surface finish. The resulting changes after the heat treatments and surface finishes were analyzed by optical microscopy, scanning electron microscopy, X-ray diffraction, roughness and mass measurements, Vickers microhardness, and tensile and compression tests. In surface finishes study, the lowest roughness value was obtained after the combined steps of blasting and chemical etching. The blasting finish is responsible for leaving a surface with uniform roughness, while the chemical etching is responsible for cleaning the surface and reducing roughness. The samples were subjected to heat treatments at temperatures of 850 °C, 950 °C and 1050 °C for one hour followed by furnace cooling. It has been found that the higher the temperature employed, the higher the ductility of the material and, on the other hand, the lower the mechanical strength. This happened due to increased nucleation and growth of 'alfa' and 'beta' phases in the material, which initially had a structure made of hexagonal martensite ('alfa'). The condition of heat treatment at 950 ° C showed the best relation of mechanical properties, meeting the requirements of ASTM F136 for the use of Ti-6Al-4V alloy in implantsMestradoMateriais e Processos de FabricaçãoMestre em Engenharia Mecânic

Wear resistance of plasma electrolytic oxidation coatings on Ti-6Al-4V ELI alloy processed by additive manufacturing

The additive manufacturing (AM) technique can produce Ti-6Al-4V ELI (extra low interstitial) alloy for personalized biomedical devices. However, the Ti-6Al-4V ELI alloy presents poor tribological behavior. Regarding this, coatings are a feasible approach to improve the wear resistance of this alloy. In the literature, the tribological behavior of TiO2 coatings incorporated with Ca and P formed by one-step plasma electrolytic oxidation (PEO) on Ti-6Al-4V ELI alloy processed by AM has not been investigated. Thus, in the present work, it was studied the influence of Ti-6Al-4V ELI alloy processed by AM on the wear resistance and morphologic of the coating obtained by PEO (plasma electrolytic oxidation). In this way, three different voltages (200, 250, and 300 V) were employed for the PEO process and the voltage effect on the properties of the coatings. The coatings were characterized by contact profilometry, scanning electron microscopy, energy-dispersive spectroscopy, the sessile drop method, grazing-incidence X-ray diffraction, and wear tests, on a ball-on-plate tribometer. The increase in applied voltage promoted an increase in roughness, pore area, and a decrease in the pore population of the coatings. In addition, the coatings, mainly composed of anatase and rutile, showed good adhesion to the metallic substrate, and the presence of bioactive elements Ca and P were detected. The thickness of the coatings obtained by PEO increases drastically for voltages higher than 250 V (from 4.50 ± 0.33 to 23.83 ± 1.5 µm). However, coatings obtained with lower voltages presented thin and dense layers, which promoted a superior wear resistance (increase in wear rate from 1.99 × 10−6 to 2.60 × 10−5 mm3/s). Finally, compared to the uncoated substrate, the PEO coatings increased the wear resistance of the titanium alloy obtained by AM, also showing a superior wear resistance compared to the commercial Ti-6Al-4V alloy previously evaluated, being such a positive and promising behavior for application in the area of metallic implants

Functionalization by anodizing of Ti-6Al-4V ELI scaffolds produced by additive manufacturing for use in orthopedic implants

Orientadores: Cecília Amélia de Carvalho Zavaglia, Maria Aparecida LarosaTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia MecânicaResumo: A Sinterização Direta de Metais por Laser (DMLS) é uma técnica de manufatura aditiva que, quando direcionada à Medicina, permite a construção de implantes e dispositivos personalizados com geometrias complexas, como estruturas porosas denominadas scaffolds. Este trabalho teve como objetivo a produção de scaffolds da liga Ti-6Al-4V ELI por DMLS, visando a mimetização do tecido ósseo, e a funcionalização de suas superfícies através da técnica de anodização eletroquímica. Dois tipos de anodização foram adotados: anodização em solução de 1 M de H2SO4 e 34,5 mM de HF (AN1) e em solução de 1 M de NH4H2PO4 e 0,3 M de NH4F (AN2), ambas com tensão de 20 V durante 5 min a 20 ± 2 °C. Técnicas de caracterização geométrica e estrutural (microscopia óptica, microscopia eletrônica de varredura, medidas de massa e microtomografia de raios-X), mecânica (ensaios de compressão), microestrutural (difração de raios-X e análise metalográfica), de superfície (perfilometria confocal óptica, ângulo de contato, microscopia eletrônica de varredura, ensaios de corrosão e cromatografia iônica) e biológica (ensaios de citotoxicidade) foram empregadas para análise. Foram produzidos scaffolds de distintos tipos de célula unitária (cúbica, diamante e hexagonal) com estruturas contínuas e poros interligados, que apresentaram valores de rigidez e porosidade compatíveis ao osso trabecular humano. A microestrutura do material é formada por martensita acicular com nanocristais de fase ? entre as agulhas de martensita. Como resultado das técnicas de anodização, uma camada duplex constituída por uma camada barreira e uma de nanoporos foi obtida para as duas condições. Como consequência, fluoretos foram incorporados às camadas anódicas e aumentos da hidrofilicidade e da resistência à corrosão foram obtidos. As superfícies não apresentaram citotoxicidade em teste de viabilidade celular indireto (por veículo de extração). No geral, estruturas funcionalizadas e que mimetizam o tecido ósseo foram obtidas com sucesso. A célula unitária hexagonal foi a que apresentou as melhores propriedades mecânicas e ambas as técnicas de anodização mostraram-se válidas para a funcionalização. Os resultados sugerem que o uso de distintas tecnologias na confecção de implantes ortopédicos personalizados e otimizados, apesar de envolverem um alto custo, resultam na melhoria de qualidade de vida dos pacientes e, a longo prazo, numa redução do custo envolvido na cirurgia e manutenção de implantes ortopédicosAbstract: Direct Metal Laser Sintering (DMLS) is an additive manufacturing process that, when applied to Medicine, allows the construction of implants and custom devices with complex geometries, including porous structures called scaffolds. This work produced Ti-6Al-4V ELI alloy scaffolds by DMLS, aiming bone tissue biomimetics, and the functionalization of their surfaces through electrochemical anodizing technique. Two types of anodizing were applied: anodizing in 1 M H2SO4 and 34.5 mM HF solution (AN1) and in 1 M NH4H2PO4 and 0.3 M NH4F solution (AN1), both with a voltage of 20 V for 5 min at 20 ± 2 ° C. Geometric and structural (optical microscopy, scanning electron microscopy, mass measurements and X-ray microtomography), mechanical (compression tests), microstructural (X-ray diffraction and metallographic analysis), surface (confocal optical profilometry, contact angle, scanning electron microscopy, corrosion tests and ion chromatography) and biological (cytotoxicity assays) characterization techniques were used for analysis. Scaffolds of different unit cell types were produced (cubic, diamond and hexagonal) with continuous structures and interconnected pores, which presented values of stiffness and porosity compatible with human¿s cancellous bone. The material microstructure is constituted by acicular martensite with ?-phase nanocrystals among martensite needles. As result of the anodizing techniques, a duplex layer consisting of a barrier layer and a nanoporous layer was obtained in both conditions. As consequence, fluoride ions were incorporated into the anodic layers and an increase in hydrophilicity and in corrosion resistance was obtained. The surfaces did not present cytotoxicity in cell viability assays by extraction vehicle. In general, functionalized structures, which mimic bone tissue, were successfully obtained. The hexagonal unit cell presented the best mechanical properties and both anodizing techniques were successful in functionalizing the surfaces. The results suggest the use of different technologies for manufacturing customized and optimized orthopedic implants, although involves a high cost, improve the patients¿ quality of life and, in the long term, result in a reduction of the costs involved in surgery and maintenance of orthopedic implantsDoutoradoMateriais e Processos de FabricaçãoDoutor em Engenharia Mecânica141221/2015-1CNP

Surface Finishes For Ti-6al-4v Alloy Produced By Direct Metal Laser Sintering

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)The implant's surface is responsible for direct interaction with the human body. For cases where osseointegration must be favored and the risk of bacteria proliferation is lower, rough surfaces are more suitable, while for implants where the risks are higher, a reduced surface roughness is required. This study aimed to analyze and produce different surface finishes on samples of Ti-6Al-4V alloy produced by additive manufacturing technique of Direct Metal Laser Sintering (DMLS). Surfaces of the samples were analyzed in the as-built condition, after blasting, after chemical etching, after electropolishing and two different combinations of these methods. The surfaces were studied using the technique of scanning electron microscopy, and surface roughness and mass measurements. The lower roughness value was obtained after a combination of blasting and chemical etching. Blasting results in a surface with uniform roughness while chemical etching cleans the surface and reduces its roughness.184838842Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Corrosion resistance improvement of additive manufactured scaffolds by anodizing

Ti–6Al–4V ELI scaffolds produced by additive manufacturing and functionalized by anodizing technique in two different conditions have been evaluated using scanning electron microscopy, energy-dispersive X-ray spectroscopy, optical confocal microscopy, cyclic potentiodynamic polarization curves (CPP), and electrochemical impedance spectroscopy (EIS). Despite the differences in composition and morphological features between the anodic layers grown, the results revealed an improvement of the corrosion resistance in both anodized conditions regarding non-anodized samples. The non-anodized scaffolds presented pitting corrosion in phosphate-buffered saline solution at 37 °C. Conversely, the anodized samples prevented pitting corrosion and enhanced barrier properties by decreasing the passive current density in two orders of magnitude. EIS data show, anodized scaffolds presented good stability after 168 h of immersion time and better protective properties than non-anodized samples.Peer reviewe

Influence of unit cell and geometry size on scaffolds electrochemical response

Additive manufacturing is a recent tool in medicine able to fabricate scaffolds to replace or regenerate bone tissues. The process permits the user to control scaffolds parameters such as size, unit cell, porosity, wall thickness, etc. However, the use of these three-dimensional geometries might negatively affect their corrosion behaviour. This paper studies the influence of Ti-6Al-4V ELI scaffold unit cell and, geometry size on the electrochemical response. Three different types of scaffold unit cell and three different geometry sizes were fabricated by additive manufacturing technique. The porosity of the scaffolds was studied by X-ray microtomography while surface changes, by scanning electron microscopy. Electrochemical behaviour was evaluated by potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) in a phosphate buffered saline solution at 37 degrees C. Potentiodynamic polarization curves show that scaffolds showed a higher pitting susceptibility than solid samples at potentials higher than 1 V. EIS spectra show that the scaffolds geometry size promotes narrowing of the maximum phase angle at the high frequency range (10(2)-10(5)) due to a non-homogeneous distribution of current and potential853CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ141221/2015-1; 158744/2018-7National Council for Scientific and Technological Development (CNPq)National Council for Scientific and Technological Development (CNPq) [141221/2015-1, 158744/2018-7]; Spanish Ministry of Science, Innovation and Universities BaCTeria Project [MAT2017-86163-C2-R

Anodic Oxidation of 3D Printed Ti6Al4V Scaffold Surfaces: In Vitro Studies

This study focuses on the surface modification of Ti6Al4V scaffolds produced through additive manufacturing using the Powder-Bed Fusion Electron-Beam Melting (PBF-EB) technique. From our perspective, this technique has the potential to enhance implant osseointegration, involving the growth of a layer of titanium dioxide nanotubes (TiO2) on surfaces through anodic oxidation. Scaffolds with anodized surfaces were characterized, and the formation of a nanoporous and crystalline TiO2 layer was confirmed. The analysis of cell morphology revealed that cells adhered to the anodized surfaces through their filopodia, which led to proliferation during the initial hours. However, it was observed that the adhesion of Saos-2 cells was lower on anodized scaffolds compared to both built and chemically polished scaffolds throughout the cell culture period. The results obtained here suggest that while anodic oxidation is effective in achieving a nanoporous surface, cell adhesion and interaction were affected by the weak adhesion of cell filopodia to the surface. Thus, combining surface treatment techniques to create micro- and nanopores may be an effective alternative for achieving a favorable cellular response when the objective is to enhance the performance of porous titanium scaffolds in the short term