Steel 316LVM Research Articles

Computational Material Analysis of Structural and Hemodynamic Model of Coronary Stent by CFD/FEA in Computer Aided Mechanical Engineering Approach

With the development of new technologies, it is very popular to use a coronary stent that is a small mesh tubeshaped medical device deployed to treat narrow or weak arteries as part of a procedure called percutaneous coronary intervention. Several aspects, such as stent design, stent wire type, mechanical and material characteristics of stent have different influences on stent intervention. It has not been reported about what impacts on stent struts by the hemodynamic behavior on stent material and very few numerical studies have considered both the mechanical and hemodynamic impact of stent implementation. Computational simulation method for realization of realistic structural and hemodynamic micro environment model in this research provided valuable results of long-term functional knowledge of stent material behavior that are time consuming and expensive to determine otherwise. Computational fluid dynamics and finite element analysis simulation models were investigated and developed to evaluate engineering properties that affect stent functional attributes. These characteristics are dependences of material properties on blood flow conditions such as structural load, shear-strain rate, radial strength, and wall shear stresses, which need to be scientifically explored. To understand the material (Fe-18Cr-14Ni-2.5Mo as stainless steel 316LVM) mechanical performance of the stent, a finite element analysis simulation model was established when exposed to pulsatile blood pressure. In this study, computational fluid dynamics model was generated to calculate the wall shear stresses and strain distribution in stented vessel carrying blood to heart. The analytical analysis of mechanical and hemodynamic conduct of a stent in this investigation may help for better designs of stent, and provide deeper comprehension to support clinical cardiovascular surgeons and guide potential therapeutic strategies.

Potentiostatic, Potentiodynamic and Impedance Study of TiO2 Layers Deposited of 316 LVM Steel Used for Coronary Stents

Abstract The objective of the study is assessment of suitability of the ALD method for application of a TiO2 layer on surface of 316LVM steel used for production of vessel stents. Selection of the appropriate process parameters for application of the layer affects its electrochemical properties, which largely determine resistance of the biomaterial to corrosion in the blood environment, thus affecting its hemocompatibility. To assess resistance of the AISI 316LVM steel with modified surface to corrosion, voltammetric and impedance measurements were conducted. The proposed variant of surface processing allows safe deformation of the TiO2 layer without its delamination.

Corrosion Resistance, EIS and Wettability of the Implants Made of 316 LVM Steel Used in Chest Deformation Treatment

Abstract The paper presents the influence of mechanical surface damage on the physicochemical properties of plates after implantation made of CrNiMo stainless steel, used in the treatment of anterior surface deformity of the chest. Analysis of the data allowed us to investigate the effect of implant design and condition of their surface on the results of chest deformation treatment. Results of electrochemical, impedance and surface wettability tests and SEM observations were compared with clinical observations. When removing the plates we found only slight inflammatory-periosteal reactions. On the basis of obtained results, it can be stated that plates, in spite of mechanical damage of the surface, were characterized by good corrosion resistance, a fact which is confirmed by the results of clinical evaluation.

Mechanical properties of atomic layer deposition (ALD) TiO2 layers on stainless steel substrates

Surface modification techniques play a major role in shaping the physicochemical properties of 316 LVM steel used for implants. The utilised methods of surface layer modification must ensure repeatability and uniformity of the physical and chemical properties. The structure and chemical composition of 316 LVM steel implants can be modified using various methods, among which anode oxidation and sol‐gel methods are dominant. One of the more important aspects related to maintaining implants (e.g. vessel stents) is ensuring the maintenance of their geometric characteristics along their entire length, which some methods cannot guarantee. For this reason, the most appropriate technique of surface modification in this context appears to involve atomic layer deposition (ALD). Improved biocompatibility is also directly related to ensuring an appropriate set of mechanical properties for the deposited layer. Thus, the study attempted to assess the mechanical properties of the TiO2 layers on a 316 LVM steel substrate, deposited using an atomic layer deposition‐based method.

Synthesis and Electrochemical Characterization a Coating of β -Tricalcium Phosphate Deposited on Steel 316LVM

Synthesis and Electrochemical Characterization a Coating of β -Tricalcium Phosphate Deposited on Steel 316LVM

Evaluation of physicochemical properties of SiO2-coated stainless steel after sterilization

The study of most of the literature devoted to the use of coronary stents indicates that their efficiency is determined by the physicochemical properties of the implant surface. Therefore, the authors of this study suggested conditions for the formation of SiO2 layers obtained with the use of sol–gel methodology showing physicochemical properties adequate to the specific conditions of the cardio-vascular system. Previous experience of authors helped them much to optimize the coating of 316LVM steel surface with SiO2. The values of parameters that determine the usefulness of the coating in medical applications have been determined. In order to identify the phenomena taking place at the boundary of phases and to evaluate the usefulness of the proposed surface modification, taking into consideration the medical sterilization (steam or ethylene oxide (EO)), the potentiodynamic, impedance, adhesion, surface morphology and biological assessment characterizations were performed. Regardless of the usage of the sterilizing agent (steam, EO) the study showed the reduction of critical force causing layer's delamination. The research results of corrosion resistance study also confirmed a slight decrease of SiO2 barrier properties of the samples after sterilization in contact with the artificial plasma. SiO2 layers after the sterilization process did not show significant features of cytotoxicity and had no negative influence on blood cell counts, which confirmed the results of quantitative and qualitative studies.

Caracterización de recubrimientos DLC/Si bajo la influencia de un fluido biológico simulado

Uno de los materiales más usados como biomaterial es el acero 316LVM, sin embargo, presenta complicaciones al trabajarlo como reemplazo permanente, debido a que libera iones metálicos a los tejidos, generando aumento en el número de intervenciones que deben realizarse, ante esto, se estudia cómo mejorar el comportamiento de materiales convencionales mediante recubrimientos que elevan sus propiedades mecánicas y anticorrosivas, incrementando su vida útil. Se evaluó el comportamiento ante el fenómeno de micro-abrasión-corrosión de recubrimientos DLC/Si depositados mediante la técnica de deposición química de vapor asistida por plasma en contacto con solución de Ringer, simulando un ambiente biológico. Los resultados indican que el recubrimiento experimenta un aumento en el volumen de desgaste cuando se encuentra sometido al mecanismo de micro-abrasión-corrosión en relación con la prueba de solo microabrasión, además, la pérdida más significativa se encuentra en el sustrato sin recubrimiento, esto demuestra el efecto protector del recubrimiento.

Taguchi Approach for the Optimization of Cutting Parameters in Finish Turning of Medical Stainless Steel

Optimization of cutting parameters in finish turning of medical stainless steel 316LVM with coated carbide tools using Taguchi method is proposed in this paper. Four cutting parameters namely, insert radius, depth of cut, feed and cutting speed are optimized with considerations of surface roughness as performance characteristic. The effects of cutting parameters on the surface roughness were experimentally investigated. Experimentation was conducted as per Taguchi's orthogonal array. Four cutting parameters with three levels are arranged in L27 orthogonal array. The orthogonal array, measured values of surface roughness, signal-to-noise ratios and analysis of variance are employed to study the surface roughness. Based on the analysis, the optimal cutting parameter settings were determined. Through the confirmation test with optimal cutting parameter settings the effectiveness of the optimization approach are validated. The obtained results have shown that Taguchi method is suitable for optimizing the cutting parameter levels with the minimum number of experiments.

Dynamic nanomechanical properties of novel Si-rich intermetallic coatings growth on a medical 316 LVM steel by hot dipping in a hypereutectic Al–25Si alloy

This aim of this study is to determine the elastoplastic properties of Ni-free Al3FeSi2 intermetallic coatings grown on medical stainless steel under different experimental conditions. Elastoplastic properties are defined by the plasticity index (PI), which correlates the hardness and the Young׳s modulus. Special emphasis is devoted to correlate the PI with the wear resistance under sliding contact, determined by scratch testing, and fracture toughness, determined by using a novel method based on successive impacts with small loads. With regard to the substrate, the developed coatings are harder and exhibit a lower Young׳s reduced modulus, irrespective of the experimental conditions. It has been shown that preheating of the samples prior to hot dipping and immersion influences the type and volume fraction of precipitates, which in turn also affect the nanomechanical properties. The higher the preheating temperature is, the greater the Young׳s reduced modulus is. For a given preheating condition, an increase of the immersion time yields a decrease in hardness. Although apparent friction coefficients of coated specimens are smaller than those obtained on AISI 316 LVM, they increase when using preheating or higher immersion times during processing, which correlates with the PI. The presence of precipitates produces an increase in fracture toughness, with values greater than those presented by samples processed on melted AlSi alloys with lower Si content (12wt%). Therefore, these intermetallic coatings could be considered “hard but tough”, suitable to enhance the wear resistance, especially when using short periods of immersion.

Improvement of the blasting induced effects on medical 316 LVM stainless steel by short-term thermal treatments

Blasting of 316 LVM steel was performed by using alumina and zirconia particles that yield rough (up to Ra ~8μm) and nearly smooth (up to Ra ~1μm) surfaces, respectively. Besides roughening, the severe plastic deformation imposed during blasting yields subtle sub-surface microstructural changes such as grain size refinement, α′-martensite formation, and work hardening. In this work we investigate the thermal treatment at 700°C of the blasted steel, aimed to reverse the strain induced α′-martensite to austenite, with special emphasis in the correlation of the microstructural changes with the fatigue resistance. Blasting with rounded zirconia particles increases the fatigue resistance whereas the opposite effect is observed using alumina ones, which are more abrasive and cause a huge amount of embedded particles acting as stress raisers. It is shown that thermal treatment at 700°C is very effective in the reversion of martensite, even after 2min of annealing. Interestingly, the short thermal treatment of the alumina blasted steel increases the fatigue strength to values close to non-blasted material (400MPa). Prolonged exposures, however, contribute to a full relaxation of the beneficial compressive residual stresses, being the net effect a decrease in the fatigue limit (340MPa).

Influence of loose PMMA bone cement particles on the corrosion assisted wear of the orthopedic AISI 316LVM stainless steel during reciprocating sliding

Corrosion assisted wear behavior of orthopedic AISI 316LVM stainless steel is explored by using tribological tests and SEM/EDS analysis. Wear mechanisms were investigated in three different environments, under reciprocating sliding at micro-loads. Variation of the sliding speed was also observed. Samples were subjected to the dry sliding, sliding in Ringer's solution and in Ringer's solution containing PMMA bone cement particles. Influence of the loose PMMA particles on the corrosion and wear of the orthopedic AISI 316LVM stainless steel during reciprocating sliding was investigated.Experimental data showed that the presence of the cement particles in Ringer's solution had deleterious influence on the wear of the 316LVM steel. Cement particles were embedded into the surface of the flat steel sample and represented non-metallic inclusions highly contributing to the increase of the corrosion assisted wear process. Pitting, crevice corrosion and stress corrosion cracking (SCC) were all observed on the steel samples, especially under the lowest applied load (100mN). Governing wear mechanism was abrasive wear together with corrosion assisted wear in wet environments. Plastic deformation controlled wear was observed for the higher loads (250–1000mN). Sliding speed showed no influence on the wear level.

Analysis of Electrochemical Impedance Spectroscopy Results and Ion Release In Vitro of Si+ Ion Implanted Medical 316 LVM Steel

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Grit blasting of medical stainless steel: implications on its corrosion behavior, ion release and biocompatibility

This study reports on the biocompatibility of 316 LVM steel blasted with small and rounded ZrO(2) particles or larger and angular shaped Al(2)O(3) particles. The effect of blasting on the in vitro corrosion behavior and the associated ion release is also considered. Surface of Al(2)O(3) blasted samples was rougher than that of ZrO(2) blasted samples, which was also manifested by a higher surface area. Compared to the polished alloy, blasted steels exhibited a lower corrosion resistance at the earlier stages of immersion, particularly when using Al(2)O(3) particles. With increasing immersion time, blasted samples experienced an improvement of the corrosion resistance, achieving impedance values typical of passive alloys. Blasting of the alloy led to an increase in Fe release and the leaching of Ni, Mn, Cr and Mo. On all surfaces, ion release is higher during the first 24 h exposure and tends to decrease during the subsequent exposure time. Despite the lower corrosion resistance and higher amount of ions released, blasted alloys exhibit a good biocompatibility, as demonstrated by culturing osteoblastic cells that attached and grew on the surfaces.

Enhancing resistance to pitting corrosion in mechanically polished stainless steel 316 LVM by water treatment

We present an extremely simple and environmentally friendly technique that appears to dramatically reduce pitting corrosion on stainless steel 316LVM. Mechanically polished SS 316LVM wire samples were treated in 90 °C high purity deionized water for different durations, then tested for pitting corrosion using potentiodynamic, potentiostatic as well as in situ imaging techniques. Wires treated for 2 or 3 h showed the greatest enhancement of pitting resistance when tested in 0.9% (by mass) NaCl solutions. To investigate the most plausible cause for the increased corrosion resistance, preliminary scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) tests were performed on SS AISI 316L disks. We identified micron sized MnS inclusions on the polished disk surfaces. After treatments in heated high purity deionized water, SEM revealed micropits and EDS did not detect sulfur where MnS previously existed.

Electrophoretically deposited nanosized hydroxyapatite coatings on 316LVM stainless steel for orthopaedic implants

Hydroxyapatite is widely used bioceramic material in implant coatings research because of its bioactive behavior when being deposited onto the metallic implant and compatibility to the human bones composition. The coating of nanosized hydroxyapatite was electrophoretically deposited on blasted surface of stainless steel 316LVM samples at constant voltage, for different deposition times and subsequently sintered in both, vacuum and argon atmosphere, at 1040?C and 1000?C, respectively. Although sintering temperatures needed to achieve highly dense coatings can cause HAp coating phase changes, the possibility to obtain a bioactive coating on 316LVM substrate, without the coatings phase changes due to the nature of the used stoichiometric nanostructured hydroxyapatite is presented in this work. The thermal stability of the used HAp powder was assessed by DTA-TG analyses over the temperature range of 23?C-1000?C, i.e. at the or nearby experimental sintering temperature. The microstructure characterization was accomplished using SEM, while phase composition was determined using XRD.

Nanomechanical properties of novel intermetallic coatings developed on austenitic stainless steels by siliconisation in liquid phase

Advanced nanomechanical testing has been used to evaluate mechanical properties of Ni-free Al 12(Fe,Cr) 3Si 2 intermetallic coatings grown on the 316 LVM steel by hot dipping in a Al-12.6 at.% Si liquid alloy for various immersion times. Despite the ultrafine-grained structure of the coating (∼200 nm), the indentation size effect is more pronounced for the intermetallic coating than for the steel, which is explained by the higher geometrical necessary dislocation (GND) density of the intermetallic coating. To determine the true hardness of the coatings, the model of Nix and Gao was used. It has been shown that the hardness of the coating decreases from 6.2 GPa for the shortest time of immersion (60 s), to 3.36 GPa for the highest immersion time (600 s), which is always much higher than that for the substrate (1.82 GPa). The decrease in both hardness and GND with increasing immersion time is related to the relaxation of residual stresses, which act as a hardening factor. The net effect is an increase of the plasticity index of the coating. Young’s modulus for the intermetallic phase (146 GPa) is lower than that for the austenitic steel 316 LVM (220 GPa), which will favour the load transfer at the bone/metal interface, weakening the so-called “stress shielding effect”. Hence, the nanomechanical properties of this novel Ni-free intermetallic coating, tightly adhered to the substrate, offer a window of opportunity for orthopaedic applications.

Simulation of X‐ray diffractograms obtained by grazing incidence X‐ray diffraction of implanted stainless steel

AbstractA method to interpret grazing incidence X‐ray diffractograms observed for expanded phases occurring after Mo implantation in an austenitic steel was extended to Ag and N ion implantation in austenitic or ferritic stainless steels.Theoretical X‐ray diffractograms were built taking into account the information depth profile, the implanted element concentration depth profile and a linear relationship between implanted element concentration and lattice parameter through an expansion coefficient (k). Experimental X‐ray diffractograms were adjusted to the theoretical ones. The adjustment led to the determination of k and/or ion‐implanted concentration profile as a function of depth.For Ag implantation in AISI 316 LVM and 430 stainless steels, the concentration depth profile was predicted using SRIM‐2003 computer program and confirmed by experimental measurement using RBS. The built austenite or ferrite X‐ray diffraction peaks were in good accordance with the experimental ones. k was shown to be independent on the incident angle and on the fluence but dependant on the type of initial lattice.For nitrided austenitic stainless steels, the k value was determined with N‐implanted AISI 316 LVM steel. The element concentration depth profiles and k value were determined for low‐energy high‐flux nitrogen implantation‐diffusion of AISI 304 steels. The predicted profiles were confirmed by NRA measurements. Copyright © 2008 John Wiley & Sons, Ltd.

Adsorption of fibrinogen on a biomedical-grade stainless steel 316LVM surface: a PM-IRRAS study of the adsorption thermodynamics, kinetics and secondary structure changes

Polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS) was employed to investigate the interaction of serum protein fibrinogen with a biomedical-grade 316LVM stainless steel surface, in terms of the adsorption thermodynamics, kinetics and secondary structure changes of the protein. Apparent Gibbs energy of adsorption values indicated a highly spontaneous and strong adsorption of fibrinogen onto the surface. The kinetics of fibrinogen adsorption were successfully modeled using a pseudo first-order kinetic model. Deconvolution of the amide I bands indicated that the adsorption of fibrinogen on 316LVM results in significant changes in the protein's secondary structure that occur predominantly within the first minute of adsorption. Among the investigated structures, the alpha-helix structure undergoes the smallest changes, while the beta-sheet and beta-turns structures undergo significant changes. It was shown that lateral interactions between the adsorbed molecules do not play a role in controlling the secondary structure changes. An increase in temperature induced changes in the secondary structure of the protein, characterized by a loss of the alpha-helical content and its transformation into the beta-turns structure.

Structural and mechanical properties of nanocrystalline titanium and 316LVM steel processed by hydrostatic extrusion

The aim of the present study was to examine the potential of hydrostatic extrusion for the fabrication of high-strength materials for medical applications. The materials examined were 316LVM steel and technically pure titanium. The microstructures and mechanical properties of the materials before and after hydrostatic extrusion were analysed. It was found that the hydrostatic extrusion process resulted in a substantial refinement of the material microstructures. The refinement of the microstructure was accompanied by an improvement of the mechanical properties, such as the microhardness and yield stress.

The Role of Inclusions in the Corrosion Resistance of Hydrostatically Extruded Steel Products

The corrosion behaviour of 316LVM in NaCl solution steel has been investigated. Large scale polarization measurements and etching tests in V2A solution showed that the hydrostatically extruded (HE) 316LVM steel had a lower corrosion resistance than specimens in the as received condition. Small area measurements were carried out in order to determine the sites that were responsible for the decreased corrosion resistance of the HE 316LVM steel. Tests on cross sections parallel to the HE direction, showed better corrosion resistance than on cross sections perpendicular to the HE direction. These observations indicate, in combination with SEM and AFM measurements, that the inclusions which were deformed during HE, can trigger the onset of corrosion on HE 316LVM steel.