Fibrous PCL/PLLA Scaffolds Obtained by Rotary Jet Spinning and Electrospinning

Rotary jet spinning (RJS) and electrospinning are techniques to obtain fibrous scaffolds. RJS is a simple method, which fabricates three-dimensional fibers by exploiting a high-speed rotating nozzle, creating a polymer jet which stretches until solidification, and does not require high voltage. In opposite, electrospinning technique needs the presence of an external electric field to create fiber from the polymeric jet solution. This article investigates both processes using two different biocompatible polymers: Poly(L-lactic acid) (PLLA) and Poly(e-caprolactone) (PCL). Samples were characterized by scanning electron microscopy, thermogravimetric analysis, differential scanning calorimeter, and Fourier-transform infrared spectroscopy. Morphological observations showed the efficiency of both techniques in obtaining nanofibers. Thermal analyses of data indicate immiscible property of different blends and the total solvent evaporation. In vitro cytocompatibility test showed that RJS and electrospinning samples exhibited good cytocompatibility. Based on these results, it may be concluded that the fibers obtained with both technologies are non-cytotoxicity and with good biocompatibility, and might be suitable for applications as scaffold for cell growth.CAPESFAPESPBiofabris-INCTBiomaterials Laboratory PUC/SP SorocabaUniv Estadual Campinas, Fac Engn Mecan, Campinas, SP, BrazilPontificia Univ Catolica, Sao Paulo, SP, BrazilUniv Fed ABC, Ctr Ciencias Nat & Humanas, Santo Andre, BrazilUniv Fed Sao Paulo, Dept Ciencias Mar, Santos, SP, BrazilUniv Fed Sao Paulo, Dept Ciencias Mar, Santos, SP, BrazilFAPESP: 2013/19372-0Web of Scienc

Unidirectional solidification of Zn-Mg alloys : microstructural evolution, mechanical properties and corrosion resistance

Orientador: Amauri GarciaTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia MecânicaResumo: A adição de Mg para melhorar a estabilidade à corrosão de recobrimentos de Zn, é uma prática comum na produção de componentes de uso na construção civil e na indústria automotiva. O Zn é um metal biocompatível, biodegradável e bioabsorvível e essencial na nutrição humana. Apresenta ainda baixo ponto de fusão (420°C), boa resistência à corrosão e baixa reatividade no estado líquido. O Mg é um metal atóxico, biodegradável e biocompatível, no entanto, suas ligas apresentam elevada taxa de corrosão em meios fisiológicos. Sabe-se que o Zn é mais nobre que o Mg, e que a adição de Mg em ligas de Zn pode afetar positivamente tanto o comportamento mecânico quanto a resistência à corrosão. Em geral os comportamentos mecânico e eletroquímico das ligas Zn-Mg são influenciados diretamente por características microestruturais. Estudos experimentais enfatizando fatores relacionados à parâmetros da microestrutura, bem como sua correlação com propriedades mecânicas e químicas são escassos na literatura. No presente trabalho, foram realizados experimentos de solidificação unidirecional com ligas hipoeutéticas e hipereutéticas Zn-Mg ao longo de uma extensa faixa de taxas de resfriamento para a análise da evolução da microestrutura. Ligas Zn-Mg hipoeutéticas diluídas (0,3 e 0,5%Mg) apresentaram uma zona colunar curta seguida de zona equiaxial até o topo dos lingotes, enquanto as demais ligas examinadas apresentaram macroestrutura equiaxial ao longo de todo o comprimento dos lingotes. Mostra-se que a microestrutura é formada por uma matriz rica em Zn de diferentes morfologias e por misturas eutéticas competitivas (Zn-Zn11Mg2 e Zn-Zn2Mg). Para as ligas com 0,3 e 0,5%Mg, a matriz rica em Zn é caracterizada por células tipo placa de altas taxas de resfriamento (>9.5ºC/s e 24ºC/s, respectivamente), seguida de uma transição morfológica granular/dendrítica para taxas de resfriamento mais baixas. Em contrapartida, os lingotes das ligas hipoeutéticas (1,2 e 2,2%Mg) apresentaram uma matriz rica em Zn formada somente por grãos dendríticos equiaxiais, enquanto as ligas hipereutéticas (3,15 e 5,15%Mg), por grãos eutéticos equiaxiais de micromorfologia lamelar. Resultados de fluorescência de raios X mostraram a ocorrência de macrossegregação de Mg ao longo do comprimento de todos os lingotes unidirecionais, induzida por diferenças de densidade. São propostas leis experimentais de crescimento relacionando os espaçamentos entre células tipo placa, dendrítico primário e secundário e eutético com parâmetros térmicos de solidificação, ou seja, taxa de resfriamento e velocidade de solidificação. A combinação de macrossegregação de Mg e a evolução das escalas microestruturais em todos os lingotes unidirecionais das ligas Zn-Mg analisadas, conduziu a microdurezas Vickers essencialmente constantes ao longo dos comprimentos dos lingotes, entretanto, com o aumento no teor de Mg de 0,3 a 5,15 % a microdureza aumentou de 58 HV0,5 a 130 HV0,5. Ensaios de tração foram realizados apenas para as ligas Zn-0,3%, 1,2% e 3,15%Mg, sendo que a liga Zn-3,15%Mg, com morfologia microestrutural eutética, apresentou maiores valores de alongamento específico, limite de escoamento e limite de resistência à tração. A fim de se obter uma comparação direta com as propriedades mecânicas de tração, os ensaios de corrosão também foram realizados nas ligas Zn-Mg de mesmas composições, em uma solução de 0,06M de NaCl. Para a liga Zn-0,3%Mg, a amostra de micromorfologia celular tipo placa, da zona colunar, apresentou maior resistência à corrosão. As ligas Zn-1,2%Mg e Zn-3,15%Mg, de morfologia totalmente equiaxial, mostraram melhores resistências à corrosão associadas a amostras mais afastadas da base refrigerada, ou seja, de microestruturas mais grosseiras. Palavras-chave: Ligas Zn-Mg; Solidificação Transitória; Microestrutura; Propriedades Mecânicas; Resistência à CorrosãoAbstract: The addition of Mg to improve corrosion stability of Zn coatings is a technologically common practice for corrosion protection of products of use in the civil and automotive industries. These alloys show also potential application in biomedical implants. Zn is a biocompatible, biodegradable and bioabsorbable metal essential in human nutrition. It also has a low melting point (420 °C), good corrosion resistance and low reactivity in the liquid state. Mg is a non-toxic, biodegradable and biocompatible metal; however, its alloys have a high corrosion rate in physiological media. It is known that Zn is nobler than Mg, and that the addition of Mg to Zn alloys can positively affect both mechanical behavior and corrosion resistance. In general the mechanical and electrochemical behavior of Zn-Mg alloys is directly influenced by microstructural characteristics. Experimental studies emphasizing factors related to microstructure parameters as well as their correlation with mechanical and chemical properties are scarce in the literature. In the present work, transient directional solidification experiments have been carried out with Zn-Mg hypoeutectic and hypereutectic alloys under an extensive range of cooling rates with a view to analyzing the evolution of microstructure. Dilute hypoeutectic alloys Zn-Mg (0.3 and 0.5wt%Mg) alloys are shown to have a short columnar zone followed by an equiaxed zone up the top of the castings, while the other alloys examined are characterized by equiaxed macrostructures along the entire length of the castings. It is shown that the microstructure is formed by a Zn-rich matrix of different morphologies and competitive eutectic mixtures (Zn-Zn11Mg2 and Zn-Zn2Mg). For 0.3 and 0.5wt%Mg alloys, the Zn-rich matrix is shown to be characterized by high cooling rates plate-like cells (cooling rates > 9.5ºC/s and 24ºC/s, respectively), followed by a granular-dendritic morphological transition for lower cooling rates. In contrast, the hypoeutectic alloys castings (1.2 and 2.2wt%Mg) are shown to have the Zn-rich matrix formed only by dendritic equiaxed grains, while the hypereutectic alloys (3.15 and 5.15wt%Mg), by equiaxed eutectic grains of lamellar micromorphology. Results from X-ray fluorescence showed the occurrence of Mg macrosegregation along the length of all directionally solidified castings, induced by differences in density. Experimental growth laws are proposed relating the plate-like cellular interphase, the primary and secondary dendritic arm and the eutectic interphase spacings to solidification thermal parameters, i.e. cooling rate, and growth rate. The combination of Mg macrosegregation and the evolution of microstructural length scales in all the Zn-Mg alloys castings examined, has led to essentially constant Vickers microhardness along the length of the castings, however, with the increase in the alloys Mg content from 0.3 to 5.15wt%, the microhardness increased from 58 HV0.5 to 130 HV0.5. Tensile tests were carried for Zn-0.3, 1.2 and 3.15wt%Mg alloys and the Zn-3.15wt%Mg alloy, with eutectic microstructure, is shown to have higher elongation, yield strength and ultimate tensile strength. In order to obtain a direct comparison with tensile test results, the corrosion tests were also carried out in alloys of same compositions in a 0.06M NaCl solution. The Zn-0.3wt%Mg alloy showed better corrosion behavior associated with the sample of cellular plate-like micromorphology from the columnar region. The Zn-1.2 and 3.15 wt% Mg alloys, having equiaxed morphology, were shown to have better corrosion resistances associated with samples of coarser microstructures. Keywords: Zn-Mg alloys; Transient Solidification; Microstructure; Mechanical Properties; Corrosion ResistanceDoutoradoMateriais e Processos de FabricaçãoDoutor em Engenharia Mecânica155863/2013-4CNP

Thermal Parameters And Microstructural Development In Directionally Solidified Zn-rich Zn-mg Alloys

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Transient directional solidification experiments have been carried out with Zn-Mg hypoeutectic alloys under an extensive range of cooling rates with a view to analyzing the evolution of microstructure. It is shown that the microstructure is formed by a Zn-rich matrix of different morphologies and competitive eutectic mixtures (Zn-Zn11Mg2 and Zn-Zn2Mg). For 0.3 wt-pct Mg and 0.5 wt-pct Mg alloys, the Zn-rich matrix is shown to be characterized by high-cooling rates plate-like cells (cooling rates > 9.5 and 24 K/s, respectively), followed by a granular-dendritic morphological transition for lower cooling rates. In contrast, a directionally solidified Zn1.2 wt-pct Mg alloy casting is shown to have the Zn-rich matrix formed only by dendritic equiaxed grains. Experimental growth laws are proposed relating the plate-like cellular interphase, the secondary dendritic arm spacing, and the eutectic interphase spacings to solidification thermal parameters, i.e., cooling rate and growth rate. The experimental law for the growth of secondary dendritic spacings under unsteady-state solidifications is also shown to encompass results of hypoeutectic Zn-Mg alloys subjected to steady-state Bridgman growth.47A630523064FAPESP-Sao Paulo Research Foundation, Brazil [2012/08494-0, 2013/15478-3, 2013/25452-1, 2013/23396-7, 2014/50502-5]CNPq-The Brazilian Research CouncilCSIC-Spanish National Research Council [i-link0944]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Cellular/dendritic arrays and intermetallic phases affecting corrosion and mechanical resistances of an Al–Mg–Si alloy

Outdoor applications of Al–Mg–Si alloys have been specified due to their very good corrosion resistance when compared with those of other aluminum alloys. Nevertheless, these alloys still have corrosion problems. One of the interests consists in characterizing the microstructure evolution, which is supposed to have important role on the final properties. In many aluminum alloys, the effects of intermetallics on both the corrosion and mechanical behavior is of industrial interest. Particularly concerning Al–Mg–Si alloys, hardly anything is known about the influence of the Mg2Si phase. This work aims to encompass such analyses on an Al-3.0 wt% Mg-1.0 wt% Si alloy directionally solidified under a wide range of cooling rates. Experimental results include primary dendritic and cellular spacings, nature and distribution of intermetallics associated with corrosion potential, pitting potential, current density, ultimate tensile strength and elongation. A high-cooling rate cellular region has been identified, followed by a dendritic region that occurred for cooling rates lower than 0.8 K/s. The cellular spacing varied from about 16 μm to 38 μm whereas the primary dendritic arm spacing varied from 120 μm to 270 μm. The α-Al cellular region is shown to be characterized by finely dispersed Mg2Si and Fe-bearing particles, which allowed better mechanical properties (strength and elongation) and better corrosion resistance to be attained. Both mechanical strength and corrosion resistance (for 0.15 M and 0.5 M NaCl electrolytes) is shown to be unaffected by the scale of λ1 within the dendritic region673220230CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPNão tem857/152012/08494-0; 2013/23396-7; 2013/15478-3; 2014/50502-5; 2014/25809-0Al–Mg–Si alloySolidificationMicrostructureThe authors acknowledge the financial support provided by FAPESP- São Paulo Research Foundation, Brazil (grants 2012/08494-0, 2013/23396-7, 2013/15478-3, 2014/50502-5 and 2014/25809-0), CNPq (The Brazilian Research Council) and CAPES-COFECUB (grant 857/15

Electrochemical corrosion behavior of as-cast zn-rich zn-mg alloys in a 0.06m nacl solution

The electrochemical corrosion behavior of as-cast samples of Zn- 1.2 wt.% and Zn- 2.0 wt.% Mg alloys, solidified under similar cooling rates, is investigated in the present study. A stagnant and naturally aerated 0.06 M NaCl solution at 25 oC was used in the corrosion tests. In order to evaluate the corrosion resistance, electrochemical impedance spectroscopy (EIS) plots, potentiodynamic polarization curves and an equivalent circuit are used. It is found that the increase in the alloy Mg content (from 1.2wt.% to 2.0wt.%) refines both the Zn-rich dendritic matrix and the eutectic mixture and decreases the volume fraction of the Zn-rich phase. Consequently, this is shown to affect the cathode-to-anode area ratio, which decreases affecting the corrosion behavior. The experimental corrosion parameters demonstrated that the Mg content is associated with susceptibility to pitting corrosion1252645283CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPNão tem2013/23396-7; 2014/50502-5The authors acknowledge the financial support provided by FAEPEX-UNICAMP, CNPq - The Brazilian Research Council, FAPESP- São Paulo Research Foundation (grants 2013/23396-7 and 2014/50502-5), CNPEM and LNNano for the use of the X-Ray Diffaction (XRD) equipmen

Interrelationship of thermal parameters, microstructure and microhardness of directionally solidified Bi–Zn solder alloys

Due to the health and environmental concerns associated with lead usage, the research on alternative lead-free alloys for replacing lead-based solders is a global demand. Despite numerous studies on Sn-based lead-free solders in recent years, there is not yet a standard solder alloy able to cover the spectrum of properties furnished by the classic Sn-Pb alloy. In this sense, particular lead-free alloys compositions have been suited for specific needs and the options have been broadening when elements other than tin are used as the base component, such as indium, gold and bismuth. The later element is well known in the hall of lead-free alloys as an alloying option rather than as a base component. This study aims to establish interrelations of solidification thermal parameters (growth and cooling rates), microstructure features (primary and secondary dendrite arm spacings – λ1 and λ2; eutectic spacing – λE and interphase spacing – λint) and hardness of Bi-Zn alloys (1.5 wt% Zn-hypoeutectic, 2.7 wt% Zn-eutectic, and 5 wt% Zn-hypereutectic alloys) samples, which were directionally solidified in unsteady-state conditions under cooling rates similar to those of found in industrial soldering practice. Examination of the resulting microstructures by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) permitted the different phases morphologies to be characterized: Bi-rich trigonal dendrites and long Zn fibers, as primary phases of, hypoeutectic and hypereutectic alloys, respectively, immersed in a fiber-like eutectic mixture. The combined effects of macrosegregation, Zn alloying and representative scales of the phases forming the microstructure (λint, λ2 and λE) on hardness of the Bi-Zn alloys are evaluated and Hall–Petch type equations relating λint, λ2 and λE to hardness are proposed78100110CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPNão temNão tem2017/15158-0The authors acknowledge the financial support provided by CAPES - Coordination for the Improvement of Higher Education Personnel, CNPq - The Brazilian Research Council and FAPESP - São Paulo Research Foundation, Brazil (grant 2017/15158-0). The authors would like to thank the Brazilian Nanotechnology National Laboratory – LNNano for the use of its facilitie

Microstructure and tensile/corrosion properties relationships of directionally solidified al–cu–ni alloys

Al–Cu–Ni alloys are of scientific and technological interest due to high strength/high temperature applications, based on the reinforcement originated from the interaction between the Al-rich phase and intermetallic composites. The nature, morphology, size, volume fraction and dispersion of IMCs particles throughout the Al-rich matrix are important factors determining the resulting mechanical and chemical properties. The present work aims to evaluate the effect of the addition of 1wt%Ni into Al–5wt%Cu and Al–15wt%Cu alloys on the solidification rate, macrosegregation, microstructure features and the interrelations of such characteristics on tensile and corrosion properties. A directional solidification technique is used permitting a wide range of microstructural scales to be examined. Experimental growth laws relating the primary and secondary dendritic spacings to growth rate and solidification cooling rate are proposed, and Hall–Petch type equations are derived relating the ultimate tensile strength and elongation to the primary dendritic spacing. Considering a compromise between ultimate tensile strength and corrosion resistance of the examined alloys samples from both alloys castings it is shown that the samples having more refined microstructures are associated with the highest values of such properties24510581076CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DO AMAZONAS - FAPEAMNão temNão temThe authors acknowledge the financial support provided by CNPq—The Brazilian Research Council and FAPEAM–Amazonas State Research Support Foundation. The authors would like to thank the Brazilian Nanotechnology National Laboratory—LNNano for the use of its facilitie

Assessing Microstructure Tensile Properties Relationships in Al-7Si-Mg Alloys via Multiple Regression

The development of Al-based alloys presumes a detailed understanding of the microstructure evolution during solidification since the as-solidified microstructure also has effects on the subsequent thermo-mechanical processing. In the present investigation Al-7wt.%Si-xMg (x = 0.5 and 1 wt.%) alloys are subjected to transient directional solidification with a view to characterizing the microstructure evolution, with special focus on both dendritic evolution and the inherent features of the Mg2Si and π-AlSiFeMg intermetallics. Experimental power-type functions relating the primary, secondary and tertiary interdendritic spacings to the solidification cooling rate and growth rate are developed. It is observed that the Mg content added to the Al-7wt.%Si alloy and the consequent increase in the Mg2Si fraction tends to increase the values of the primary dendritic spacing. However, this same behavior is not verified for the growth evolution of dendritic side branches. A multiple linear regression (MLR) analysis is developed permitting quantitative correlations for the prediction of tensile properties and hardness from microstructural parameters to be established. The increase in the Mg alloy content from 0.5 to 1 was shown to promote an increase in both the ultimate tensile strength (σu) and elongation

Assessing Microstructure Tensile Properties Relationships in Al-7Si-Mg Alloys via Multiple Regression

The development of Al-based alloys presumes a detailed understanding of the microstructure evolution during solidification since the as-solidified microstructure also has effects on the subsequent thermo-mechanical processing. In the present investigation Al-7wt.%Si-xMg (x = 0.5 and 1 wt.%) alloys are subjected to transient directional solidification with a view to characterizing the microstructure evolution, with special focus on both dendritic evolution and the inherent features of the Mg2Si and π-AlSiFeMg intermetallics. Experimental power-type functions relating the primary, secondary and tertiary interdendritic spacings to the solidification cooling rate and growth rate are developed. It is observed that the Mg content added to the Al-7wt.%Si alloy and the consequent increase in the Mg2Si fraction tends to increase the values of the primary dendritic spacing. However, this same behavior is not verified for the growth evolution of dendritic side branches. A multiple linear regression (MLR) analysis is developed permitting quantitative correlations for the prediction of tensile properties and hardness from microstructural parameters to be established. The increase in the Mg alloy content from 0.5 to 1 was shown to promote an increase in both the ultimate tensile strength (σu) and elongation