Corrosion and wear resistance analysis of ASTM F 138 austenitic stainless steel treated by laser

Orientador: Maria Clara Filippini IerardiTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia MecânicaResumo: No presente trabalho, o aço inoxidável austenítico ASTM F 138, empregado na fabricação de implantes ortopédicos temporários e permanentes, foi submetido a tratamento de superfície por laser, com o intuito de analisar as modificações microestruturais resultantes deste tratamento e seus efeitos na resistência à corrosão e ao desgaste microabrasivo. A caracterização microestrutural foi feita por microscopia óptica, microscopia eletrônica de varredura, microdureza Vickers e difração de raios-X. Para analisar o comportamento em corrosão do aço, antes e após o tratamento, foram realizados três tipos diferentes de ensaios eletroquímicos usando solução de Ringer como eletrólito. O comportamento em desgaste foi avaliado a partir de ensaios por microabrasão do tipo esfera-sobre-placa, utilizando como abrasivos uma suspensão de partículas de carboneto de silício (SiC) em água destilada e uma suspensão de SiC em solução de Ringer. Após o tratamento por laser, o aço apresentou uma microestrutura refinada constituída por dendritas de austenita, com um aumento de aproximadamente 23% na dureza e com melhoria frente à corrosão e ao desgaste.Abstract: In this work, ASTM F 138 austenitic stainless steel, used in temporary and permanent orthopaedic implants manufacture, was subjected to laser surface treatment. The purpose is analyze the microstructural changes resulting from this treatment and their effects on the microabrasive wear and corrosion resistance. The microstructural characterization was performed by optical microscopy, scanning electron microscopy, Vickers microhardness and X-ray diffraction. In order to analyze the corrosion behavior, three different types of electrochemical tests were carried out before and after treatment, using Ringer's solution as electrolyte. The wear behavior was evaluated using ball-cratering microabrasive wear tests, using slurry of silicon carbide particles (SiC) in distilled water and slurry of SiC in Ringer's solution. After laser treatment, the steel presented a refined microstructure consisted of austenite dendrites, with a 23% hardness increase and improved corrosion and wear resistance.DoutoradoMateriais e Processos de FabricaçãoDoutor em Engenharia Mecânic

Influence of laser surface treatments on stainless steels for surgical instruments

Orientador: Maria Clara Filippini IerardiDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia MecanicaResumo: No presente trabalho, os aços inoxidáveis austenítico AISI 304 e martensítico AISI 420, empregados na fabricação de instrumentais cirúrgicos, foram submetidos a tratamentos superficiais a laser sem e com fusão, com o intuito de analisar as modificações microestruturais resultantes destes tratamentos e, conseqüentemente, seus efeitos na resistência à corrosão destes aços. A caracterização microestrutural foi feita por' microscopia óptica, microscopia eletrônica de varredura, microdureza Vickers, difração de raios-X e espectroscopia de energia dispersiva. Para analisar o comportamento à corrosão dos aços, antes e após os tratamentos, foram realizados ensaios eletroquímicos usando como eletrólitos água e detergentes enzimáticos, sendo estes utilizados na limpeza de instrumentais cirúrgicos. Após os tratamentos a laser, o aço austenítico refundido apresentou uma microestrutura refinada constituída por dendritas de austenita, porém sem um aumento significativo de dureza, mas com melhoria frente à corrosão. A estrutura do aço martensítico tratado a laser é formada por martensita, austenita residual e carbonetos dos tipos Cr7C3e Cr23C6. A dureza do aço AISI 420 aumentou significativamente mas houve uma perda na resistência à corrosão devido à precipitação de carbonetosAbstract: In this work, the austenitic AISI 304 and martensitic AISI 420 stainless steels, used in surgical instruments fabrication were submitted to laser surface treatments with and without melting. The purpose is analyse the microstructural changes resulting from laser treatments and, consequently, their effects on the corrosion resistance. The microstructural characterization was performed by optical microscopy, scanning electronic microscopy, Vickers microhardness, X-ray diffraction and energy dispersive spectroscopy. In order to analyze the corrosion behavior electrochemical tests were carried out before and afier treatments. The electrolytes consisted of water and enzymatic detergents that are used in the c1eaning procedures of the surgical instruments. After laser treatments, the remelted austenitic steel presented a refined microstructure composed of austenite dendrites. No significant hardness increase was observed. Further, corrosion resistance was improved. The structure of the treated martensitic steel consisted of martensite, residual austenite and carbides type Cr7C3 and Cr23C6. The AISI 420 steel hardness increased significantly but the corrosion resistance was decreased by carbides precipitationMestradoMateriais e Processos de FabricaçãoMestre em Engenharia Mecânic

Microstructural and mechanical characterization of a custom-built implant manufactured in titanium alloy by direct metal laser sintering

Custom-built implants manufacture has always presented difficulties which result in high cost and complex fabrication, mainly due to patients' anatomical differences. The solution has been to produce prostheses with different sizes and use the one that best suits each patient. Additive manufacturing technology, incorporated into the medical field in the late 80's, has made it possible to obtain solid biomodels facilitating surgical procedures and reducing risks. Furthermore, this technology has been used to produce implants especially designed for a particular patient, with sizes, shapes, and mechanical properties optimized, for different areas of medicine such as craniomaxillofacial surgery. In this work, the microstructural and mechanical properties of Ti6Al4V samples produced by direct metal laser sintering (DMLS) are studied. The microstructural and mechanical characterizations have been made by optical and scanning electron microscopy, X-ray diffraction, and microhardness and tensile tests. Samples produced by DMLS have a microstructure constituted by hexagonal alpha ' martensite with acicular morphology. An average microhardness of 370 HV was obtained and the tensile tests showed ultimate strength of 1172 MPa, yield strength of 957 MPa, and elongation at rupture of 11%CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP573661/2008-12008/57860-3; 2010/05321-

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