Examinando por Autor "Rams, Joaquín"

Mostrando 1 - 20 de 31

Additively Manufactured Al/SiC Cylindrical Structures by Laser Metal Deposition
(Mdpi, 2020) Riquelme, Ainhoa; Rodrigo, Pilar; Escalera-Rodríguez, María Dolores; Rams, Joaquín
Preliminary characterization of the microstructure of Al/SiCp composites prepared by Laser Metal Deposition (LMD) was analyzed, and the microhardness and wear behavior of the materials manufactured have been evaluated. It has been determined that the combined e ect of the laser speed and power is decisive for the fabrication process. The microstructure characterization shows that the presence of hygroscopic Al4C3 can be avoided by adding Ti to the composite matrix. The wear behavior of the LMD samples and their microhardness have been compared with Powder Metallurgy samples with the same composition. The LMD samples showed higher hardness and wear resistance.
Anticorrosion and Cytocompatibility Assessment of Graphene-Doped Hybrid Silica and Plasma Electrolytic Oxidation Coatings for Biomedical Applications
(ACS, 2021) Fernández-Hernán, Juan P.; López, Antonio J.; Torres, Belén; Martínez-Campos, Enrique; Matykina, Endzhe; Rams, Joaquín
Magnesium AZ31 alloy substrates were coated with different coatings, including sol−gel silica-reinforced with graphene nanoplatelets, sol−gel silica, plasma electrolytic oxidation (PEO), and combinations of them, to improve cytocompatibility and control the corrosion rate. Electrochemical corrosion tests, as well as hydrogen evolution tests, were carried out using Hanks’ solution as the electrolyte to assess the anticorrosion behavior of the different coating systems in a simulated body fluid. Preliminary cytocompatibility assessment of the different coating systems was carried out by measuring the metabolic activity, deoxyribonucleic acid quantification, and the cell growth of premyoblastic C2C12-GFP cell cultures on the surface of the different coating systems. Anticorrosion behavior and cytocompatibility were improved with the application of the different coating systems. The use of combined PEO + SG and PEO + SG/GNP coatings significantly decreased the degradation of the specimens. The monolayer sol−gel coatings, with and without GNPs, presented the best cytocompatibility improvement.
Application of DOE and ANOVA in Optimization of HVOF Spraying Parameters in the Development of New Ti Coatings
(Springer, 2020-02-03) Pulido-González, Nuria; García-Rodríguez, Sonia; Campo, Mónica; Rams, Joaquín; Torres, Belén
High velocity oxygen fuel (HVOF) thermal spray technique has been used to develop new Ti coatings on 1045 steel and 316L stainless steel for different applications. Optimization of the HVOF parameters requires numerous experiments to perform that can be reduced using the Taguchi Design of Experiment (DOE) methodology. By using DOE, it has been possible to identify the effects of the HVOF spraying parameters (spraying distance, number of layers, gun speed, powder feed rate, type of substrate and type of combustion) on the main characteristics of the coatings (porosity, thickness, hardness and adhesion). According to Taguchi method, the resulting orthogonal matrix corresponded to a L16 (44 × 22) matrix. Using this matrix, the number of experiments was reduced from 1024 to 16 and a first approximation of the best conditions for a real application was obtained. To evaluate the significant spraying variables, a statistical analysis of variance (ANOVA) was used. It has been determined that there is a relationship between coating characteristics and HVOF parameters. Also, the influence of the parameters on the characteristics and properties of the coatings (from high to low) is as follows: spraying distance, number of layers, gun speed, powder feed rate, type of substrate and mixture of gases used in the process.
Carrying Gas Influence and Fabrication Parameters Impact in 3D Manufacturing of In Situ TiN-Ti Composites by Direct Laser Deposition
(Springer, 2022) Sánchez de Rojas Candela, Carmen; Riquelme, Ainhoa; Rodrigo, Pilar; Rams, Joaquín
The difculty of getting a correct distribution of the reinforcement in the metal matrix and the complexity for achieving a good-metallurgy matrix-reinforcement bonding has limited the development of additive manufacturing of metal matrix composites. This research proposes the use of a reactive atmosphere during the fabrication process to obtain titanium matrix composites reinforced with TiN. The relation between the carrying gas and the process parameters used with the presence of porous and defects, the microstructure, and microhardness has been obtained. Nitrogen was used as the carrying gas of the titanium powder. Under laser irradiation, the particles melt and react with nitrogen, resulting in the formation of a titanium matrix composite highly reinforced with TiN. The composite obtained had a microhardness increase between 50 and 100% in comparison with titanium samples fabricated in the same conditions in an argon atmosphere. Three reaction mechanisms have been proposed to take place in the microstructure, depending on the amount of nitrogen in the titanium particles, and its difusion in them during the manufacture.
Characterisation and mechanical properties of Al/SiC metal matrix composite coatings formed on ZE41 magnesium alloys by laser cladding
(Elsevier, 2019) Riquelme, Ainhoa; Rodrigo, Pilar; Escalera-Rodríguez, María Dolores; Rams, Joaquín
Metal matrix composite coatings on light alloys are in high demand in the transport industry to reduce the weight of vehicles without a reduction in mechanical properties. Composite coatings with various mixtures of Al, Si, Ti and SiC could be a good option for this application but the high reactivity between the melted aluminium and the reinforcement must be avoided. This study provides a solution for this problem for laser cladding composite coatings on ZE41 magnesium alloys. The method employed consists of the addition of different alloying elements (silicon or titanium) to the composite matrix to avoid Al4C3 formation. A dilution of magnesium from the substrate in the aluminium coating matrix takes place and it produces an important effect in the matrixreinforcement reactions. The microstructure and mechanical properties of the coatings are analysed. The reaction mechanisms are also determined. Al4C3 formation is avoided and the mechanical properties are improved. Introduction The increased awareness of the need to save energy is one of the most important reasons for the development and research of magnesium alloys. The interest in this topic has increased since the 1990s [1,2] because of the oil crisis. Environmental legislation related to polluting gas emission from transport vehicles is becoming more restrictive. For this reason, the aeronautic and automotive transport sectors have been forced to reduce the weight of their components by employing lighter materials [3–5]. Lights alloys, like magnesium, are attracting high attention due to their reduced density, which provides them with high specific values of stiffness and strength. Nevertheless, the use of these alloys is limited because of their low superficial properties. The superficial property modification in these alloys could increase the variety of applications in which they could be used. This study provides a solution for this problem by fabricating aluminium matrix composite (Al-MMC) coatings on magnesium alloys. In previous research, laser cladding with Al/SiC particles (SiCp) on aluminium alloys was successfully carried out [6]. SiC, in the shape of particles, is an excellent reinforcement
Comparison of Different Additive Manufacturing Methods for 316L Stainless Steel
(MDPI, 2021-10-29) Bedmar, Javier; Riquelme, Ainhoa; Rodrigo, Pilar; Torres, Belén; Rams, Joaquín
In additive manufacturing (AM), the technology and processing parameters are key elements that determine the characteristics of samples for a given material. To distinguish the effects of these variables, we used the same AISI 316L stainless steel powder with different AM techniques. The techniques used are the most relevant ones in the AM of metals, i.e., direct laser deposition (DLD) with a high-power diode laser and selective laser melting (SLM) using a fiber laser and a novel CO2 laser, a novel technique that has not yet been reported with this material. The microstructure of all samples showed austenitic and ferritic phases, which were coarser with the DLD technique than for the two SLM ones. The hardness of the fiber laser SLM samples was the greatest, but its bending strength was lower. In SLM with CO2 laser pieces, the porosity and lack of melting reduced the fracture strain, but the strength was greater than in the fiber laser SLM samples under certain build-up strategies. Specimens manufactured using DLD showed a higher fracture strain than the rest, while maintaining high strength values. In all the cases, crack surfaces were observed and the fracture mechanisms were determined. The processing conditions were compared using a normalized parameters methodology, which has also been used to explain the observed microstructures.
Corrosion behavior of 316L stainless steel coatings on ZE41 magnesium alloy in chloride environments
(Elsevier, 2019-11-25) García-Rodríguez, Sonia; Torres, Belén; Pulido-González, Nuria; Otero, Enrique; Rams, Joaquín
The corrosion behavior of the ZE41 magnesium alloy with a HVOF 316L stainless steel coating was electrochemically evaluated in 3.5 wt% NaCl solution and by salt spray testing. Electrochemical Impedance Spectroscopy (EIS) allowed determining the resistance of the coatings deposited, the growth of compact corrosion products on the ZE41 Mg alloy and the failure of the non-optimized coatings. The best coating resisted the chloride attack for long times in immersion and in salt spray environments, and it drastically reduced galvanic couple formation. Its behavior is associated with its reduced porosity and its higher compactness and mechanical stability.
Corrosion Resistance of Al/SiC Laser Cladding Coatings on AA6082
(Mdpi, 2020) Riquelme, Ainhoa; Rodrigo, Pilar; Escalera-Rodríguez, María Dolores; Rams, Joaquín
Aluminum matrix composites reinforced with silicon carbide particles (SiCp) were deposited by laser cladding on AA6082 aluminum alloy. Di erent compositions of the matrix of the composites coating were used and di erent amounts of Si and Ti were added to a base of Al-12Si in order to control the reactivity between molten aluminum and SiCp during laser cladding. The corrosion behavior of the coatings deposited was evaluated in 3.5 wt.% NaCl solution using gravimetric analyses and electrochemical polarization tests. The corrosion products observed were Al(OH)3 and Al2O3, and they formed a layer that limited the evolution of corrosion. However, the presence of discontinuities in it reduced the corrosion resistance of the coating. The corrosion mechanisms were di erent depending on the coating composition. The addiction of Ti to the alloy allowed for better corrosion behavior for the composite coating than that of the aluminum substrate.
Effect of Heat Treatment on the Dry Sliding Wear Behavior of the Mg-3Zn-0.4Ca Alloy for Biodegradable Implants
(Multidisciplinary Digital Publishing Institute, 2023-01-10) Pulido-González, Nuria; García-Rodríguez, Sonia; Torres, Belén; Rams, Joaquín
The wear behavior of the Mg-3wt.% Zn-0.4wt.% Ca (ZX30) alloy was tested using a pin-on-disc configuration with AZ31 alloy discs as counterparts under dry sliding conditions. The ZX30 alloy was tested in different states: as-cast, solution-treated, peak-aged, and over-aged. Wear rates and friction coefficients were measured at different loads and sliding speeds. Abrasion and oxidation were the main wear mechanisms found in all the conditions tested. Moreover, aluminum oxides were detected on the worn surfaces, which indicates the presence of an adhesive wear mechanism. The wear behavior of the studied ZX30 alloy showed a greater tendency towards oxidative wear than other Mg alloys, and the microstructure observed strongly affected the wear behavior.
Effect of the process parameters in the additive manufacturing of in situ Al/AlN samples
(Elsevier Sci Ltd, 2019) Riquelme, Ainhoa; Rodrigo, Pilar; Escalera-Rodriguez, María Dolores; Rams, Joaquín
Additive manufacturing has revolutionized the manufacturing industry. Researchers have investigated various techniques for increasing the reliability of the metal Additive Manufacturing processes. However, there are few studies about Additive Manufacturing of metal matrix composite components, so, it is necessary increase the research about this topic. In situ Al/AlN composite was synthesized using Direct Laser Deposition equipment in which aluminum powder was deposited through a laser beam using N2 as carrying and reactive gas. This composite powder has been melted and directly deposited layer by layer to form an additive structure. The effect of the laser parameters on the geometry, microstructure and properties of the fabricated structures have been analysed. This allowed the development of a process map for Al and Al/AlN pieces fabricated by Direct Laser Deposition. In situ Al/AlN samples have higher mechanical properties than Al samples.
Effects of the heat treatment on the microstructure and corrosion behavior of 316 L stainless steel manufactured by Laser Powder Bed Fusion
(Elsevier, 2022) Bedmar, Javier; García-Rodríguez, Sonia; Roldán, M.; Torres, Belén; Rams, Joaquín
Additively manufactured AISI 316 L stainless steel samples were heat treated at temperatures from 400 ◦C to 1100 ◦C, and the corrosion behavior in chloride environments was electrochemically studied. Heat treatments at 400 ◦C and 650 ◦C increased the grain size and the treatment at 1100 ◦C formed MnCr2O4 inclusions. Also, these postprocessing techniques reduce the hardness and increased the porosity. Heat treatment at 400 ◦C increased the polarization resistance and maintained the pitting corrosion mechanisms of the additively manufactured samples. Heat treatments at higher temperatures reduced the polarization resistance but changed the corrosion resistance mechanisms.
Evaluation of the Wear Resistance and Corrosion Behavior of Laser Cladding Al/SiC Metal Matrix Composite Coatings on ZE41 Magnesium Alloy
(MDPI, 2021-05-27) Riquelme, Ainhoa; Rodrigo, Pilar; Escalera-Rodriguez, María Dolores; Rams, Joaquín
Aluminum matrix composites reinforced with SiC particles (SiCp) were deposited on ZE41 magnesium substrates by laser cladding in order to improve their tribological performance. Silicon and titanium were added to the matrix in order to avoid Al-SiC reactivity. The addition of these elements to avoid Al4C3 formation during the laser cladding fabrication was successfully explored in previous research, but the effect of these elements on the wear behavior and the corrosion resistance of these coatings has not been studied. During the fabrication process, there is dilution with the substrate that forms an Al-Mg matrix, which has an influence on the wear and corrosion behavior. Electrochemical polarization and impedance measurements in a 3.5% NaCl solution and the dry sliding conditions on a pin-on-disc tribometer were used to evaluate the different compositions of Al/SiCp coatings on the ZE41 magnesium alloy and uncoated ZE41. All of the composite coatings had lower wear rates than the substrate. However, the coatings showed worse corrosion behavior than the ZE41 substrate, although the addition of Si or Ti improves the corrosion behavior and the wear resistance.
High Power Diode Laser (HPDL) surface treatments to improve the mechanical properties and the corrosion behaviour of Mg-Zn-Ca alloys for biodegradable implants
(Elsevier, 2020-11-25) Pulido-González, Nuria; Torres, Belén; Zheludkevick, Mikhail L.; Rams, Joaquín
Biodegradability, low density and mechanical properties close to those of the bone are some of the intrinsic properties of the Mg-Zn-Ca alloys that have attracted significant attention for developing biodegradable implants. However, rapid degradation constitutes the main disadvantage of these alloys. In this work, two different alloys, Mg-1Zn-1Ca and Mg-3Zn-0.4Ca, were laser surface treated using a HPDL to increase hardness and to improve the corrosion performance. Depending on the laser parameters, a complete laser surface melting (LSM) or a selective laser surface melting (SLSM) were reached. The microstructure, mechanical properties and corrosion behaviour were established and compared. Higher laser input energies led to larger treated zones and in these cases two different regions could be distinguished: the outer zone, where the LSM took place, presented a more refined microstructure with a greater dispersion of secondary phases; the following zone suffered SLSM, in it only the secondary phases were modified by the HPDL. Hardness was 24%–27% higher than that of the untreated samples. The HPDL also reduced the corrosion rate by 21% and 37% for the Mg-1Zn-1Ca alloy and the Mg-3Zn-0.4Ca alloy, respectively, after 336 h of immersion in Hanks' solution at 37 °C.
Influence of roughness and grinding direction on the thickness and adhesion of sol-gel coatings deposited by dip-coating on AZ31 magnesium substrates. A Landau–Levich equation revision
(Elsevier, 2021-01-02) Fernández-Hernán, Juan Pablo; López, Antonio Julio; Torres, Belén; Rams, Joaquín
AZ31 magnesium alloys with four different roughness values and two different grinding directions were coated with sol-gel silica coatings to assess the influence of the initial surface conditions of the substrates on the final coating thickness. Sol-gels were prepared from two silicon alkoxide precursors and deposited on the surface of the magnesium substrates by the dip-coating method. Roughness tester and scanning electron microscopy (SEM) were used to assess the thickness of the silica coatings and the presence of defects in the coatings. Shear stress tests were developed to study the adhesion of the coatings. An analysis of variance was carried out to determine the implication of the substrate roughness and the direction of the grinding lines in the final sol-gel coating thickness and its adhesion on the substrate. The results show that the roughness has a significant influence both on the thickness and on the adhesion of the coatings. Thus, thicker coatings were obtained on substrates with higher roughness values, going from 2.18 μm to 1.42 μm for substrate roughness values of 1.47 μm and 0.27 μm respectively, in the case of horizontal grinding lines, and from 2.01 μm to 1.37 μm for substrate roughness values of 1.47 μm and 0.27 μm respectively, in the case of vertical grinding lines. However, the grinding direction has no significant influence on the thickness nor the adhesion, but it has a clear influence on the formation of defects in the coatings. Finally, the inclusion of the r parameter in the Landau-Levich equation is proposed to adjust it, taking into account the roughness of the substrates intended to be coated and the evaporation of solvent and water from the coating during the dip-coating.
Influence of the Feed Powder Composition in Mechanical Properties of AlN-Nano-Reinforced Aluminium Composites Coatings Deposited by Reactive Direct Laser Deposition
(Mdpi, 2020) Riquelme, Ainhoa; Rodrigo, Pilar; Escalera-Rodriguez, María Dolores; García-Fogeda, Pablo; Rams, Joaquín
Aluminium matrix composite coatings reinforced with AlN nanopaticles have been manufactured by direct laser deposition on an AA6082 alloy substrate. The reinforcement of the composite has been generated by the direct nitridation reaction of the feed powder with the carrier gas (N2) heated by an HPDL beam during the fabrication of the coating. The coating obtained consists of nano-sized AlN particles in an aluminium matrix, and the crystalline structure of the obtained AlN depends on the characteristics of the powder used. In this work, the influence of the feed powder composition is studied by comparison among pure aluminium, Al12-Si alloy, and AA6061 alloy, on the formation ofAlNand its crystalline structure. Acorrelationwas established between the temperature distribution reached by the particles, their composition, and the nitridation reaction mechanisms. The effect of the reinforcement was evaluated by comparing the microstructure and mechanical properties (microhardness, nanoindentation) of the composite costing with non-reinforced Al coatings and uncoated AA6082. Al/AlN composite coatings with improved properties were achieved, reaching hardness values that were 65% higher than coatings without reinforcement.
Influence of the surface state on the corrosion behavior of the 316 L stainless steel manufactured by laser powder bed fusion
(Elsevier, 2022) Bedmar, Javier; Abu-Warda, Najib; García Rodríguez, Sonia; Torres, Belén; Rams, Joaquín
The effect of surface roughness on the corrosion behavior of 316 L stainless steel manufactured by LPBF has been evaluated. The behavior of the steel in the as-built state was compared to that ground up to 2500 grade. Three different aggressive environments were used: 3.5 wt% NaCl water solution, 3 wt% H2SO4 solution, and hightemperature oxidation at 800 ºC. The ground specimens showed higher corrosion resistance. The corrosion resistance was much smaller in the as-built samples for electrochemical tests, and the lowest mass gain after hightemperature oxidation was found in the ground specimens.
Magnesium Alloys: Fundamentals and Recent Advances
(Elsevier, 2022) Rams, Joaquín; Torres, Belén; Pulido-González, Nuria; García-Rodríguez, Sonia
Magnesium alloys are finding a relevant role in the materials sectors mainly due to its lightness but also to other properties such as high specific mechanical properties, high castability and an adequate compatibility to the human body. Due to this, Magnesium alloys can be used in different systems that include the transportation section, mainly in the automotive one, the electronics and household appliances, but also in prosthesis that can be absorbed by the human body. In this article, a revision on the general characteristics of Magnesium alloys, as well as to the applications that Magnesium is currently finding is made. Due to the combination of lightness, castability, recyclability and biocompatibility, Magnesium alloys are helping to the reduction of pollution, increase the electronics portability and even helping to solve serious health issues that would require the use of medical implants.
Manufacturing of Aluminum Matrix Composites Reinforced with Carbon Fiber Fabrics by High Pressure Die Casting
(MDPI, 2022-05-09) Bedmar, Javier; Torres, Belén; Rams, Joaquín
Aluminum matrix composites reinforced with carbon fiber have been manufactured for the first time by infiltrating an A413 aluminum alloy in carbon fiber woven using high-pressure die casting (HPDC). Composites were manufactured with unidirectional carbon fibers and with 2 2 twill carbon wovens. The HPDC allowed full wetting of the carbon fibers and the infiltration of the aluminum alloy in the fibers meshes using aluminum at 680 C. There was no discontinuity at the carbon fiber-matrix interface, and porosity was kept below 0.1%. There was no degradation of the carbon fibers by their reaction with molten aluminum, and a refinement of the microstructure in the vicinity of the carbon fibers was observed due to the heat dissipation effect of the carbon fiber during manufacturing. The mechanical properties of the composite materials showed a 10% increase in Young’s modulus, a 10% increase in yield strength, and a 25% increase in tensile strength, which are caused by the load transfer from the alloy to the carbon fibers. There was also a 70% increase in elongation for the unidirectionally reinforced samples because of the finer microstructure and the load transfer to the fibers, allowing the formation of larger voids in the matrix before breaking. The comparison with different mechanical models proves that there was an effective load transference from the matrix to the fibers.
Mg–1Zn–1Ca alloy for biomedical applications. Influence of the secondary phases on the mechanical and corrosion behaviour
(Elsevier, 2020-08-05) Pulido-González, Nuria; Torres, Belén; García-Rodríguez, Sonia; Rodrigo, Pilar; Bonache, Victoria; Hidalgo-Manrique, Paloma; Mohedano, Marta; Rams, Joaquín
An as-cast Mg–1Zn–1Ca alloy has been soundly characterized to be used as a biodegradable material in biomedical applications. Ca and Zn additions have a great influence in the microstructure, mechanical properties and corrosion behaviour of Mg alloys. SEM examinations revealed that most of the Ca and Zn atoms form Mg2Ca and Ca2Mg6Zn3 precipitates, which distribute preferentially along the grain boundaries forming a continuous network of secondary phases. The results of nanoindentation tests show differences in hardness and elastic modulus between the α-Mg matrix and the secondary phases. The results of three-point bending tests shows that cracks propagate following the network formed by the intermetallic compounds at the grain boundaries (GBs). The evolved hydrogen after immersion in Hank’s solution of the alloy has been also estimated, showing a change in the corrosion mechanism after 160 h. The intermetallic compounds act as a barrier against corrosion, so that it progresses through the α-Mg matrix phase.
Microhardness and wear behavior of nanodiamond-reinforced nanocomposites for dental applications
(Wiley, 2024-10-04) Moriche, Rocío; Artigas-Arnaudas, Joaquín; Chetwani, Bhanu; Sánchez, María; Campo, Mónica; Prolongo, Margarita G.; Rams, Joaquín; Prolongo, Silvia G.; Ureña, Alejandro
In polymer-based dental composites, wear is a three-body wear system mainly abrasive, because of the food particles and wear products suspended in the oral cavity, which are transferred to the microcavities of the surface of the replacements. Due to this fact, the incorporation of nanodiamond as reinforcement in these polymer–matrix composites, which promotes the creation of a solid lubricant tribofilm surface could be advantageous. With the reinforcement of nanodiamonds, BisGMA/TEGDMA-based composites increase their microhardness by 95%–420%. A maximum hardness exceeding 65 HV is achieved with a reinforcement of 3.2 wt%. The specific wear rate of neat BisGMA/TEGDMA is near 10−4 mm3/Nm and the Archard's coefficient is 2.6 × 105. The incorporation of a content of 1.6 wt% ND is enough to cause a diminution of ~78% in the friction coefficient and a reduction of the specific wear rate and Archard's coefficient of ~50%. Nevertheless, the addition of relatively high contents reduces the effectiveness of photoinitiation and photocuring, which is related to the scattering and absorption of light radiation by ND. This causes a significant decline in elastic properties starting at 50 μm from the surface. Highlights Photocuring polymer resin was successfully reinforced with nanodiamonds. Microhardness increases from 95% up to 420%, close to commercial composites. Friction coefficient and wear rate are reduced with 1.6 wt% nanodiamonds. High levels of reinforcement reduce the effectiveness of photocuring.