Frictional behaviour of multilayered graphene was studied in air with different relative humidity (RH) levels (10–52% RH). Pin-on-disk type sliding tests were performed and the running-in and steady state coefficient of friction (COF) values were measured against M2 tool steel counterface. On increasing the RH, multilayered graphene showed a reduction in steady state COF from 0.11 at 10% RH to 0.08 at 52% RH. The low steady state COF values observed in graphene could be attributed to the transfer layer formed on the M2 tool steel counterface. A sliding-induced structural change was observed in graphene transfer layers which could have facilitated the graphitic transfer layer formation. The multilayered graphene showed a lower steady state COF values at all RH compared to non-hydrogenated diamond-like carbon (NH-DLC) which recorded a steady state COF of 0.47 at 10% RH and 0.25 at 52% RH.

Newly discovered MAX phases are attractive due to their unique combined properties: mechanical, high temperature, erosion and corrosion resistance. These materials are considered metallic and ceramic at the same time, and they could be the perfect solution for a variety of industrial and scientific applications. In this study, detailed attention has been paid to complex compositions of several transition metals, such as Ti and Cr in TiCrSiCN, whereas Al and Si are recommended for TiAlSiCN. These materials require a combination of both C and N to form the MAX phases (in the “X” position in the formula M(n+1)AXn). The purpose of this study was to investigate the effect of these elements located at the “M”, “A” and “X” positions on the mechanical properties of the materials. The results of the thermogravimetric analysis of TiCrSiCN showed that this phase is stable at temperatures as high as 1400 °C, while the Ti3SiC2 phase is stable up to 1300 °C.

Fast-quenched alloys with amorphous and microcrystalline structures were obtained by the cooling drum spinning method during plasma-arc melting process. Thermal load measurements carried out during the melting process and the spinning of the molten material that followed, helped us to modify the existing plasma-arc equipment. Metallographic analyses of the amorphous alloys showed the influence of some quenching process parameters on the creation of their microstructure and revealed the nature of the formation of the crystal structures.

A simulation model is presented, where temperature, phases and internal stresses can be predicted as a function of time during the heating of large steel ingots for forging. Heating cycle measurements and computer simulations are compared for an A105 steel grade 34-Ton tapered ingot. A study of the heat transfer inside a natural gas-fired furnace was carried out to make an estimation of internal stresses due to thermal expansion and phase transformation from α ferrite and pearlite to γ austenite during heating. The model was validated with a second test of an AISI 4330 steel grade 35.4-Ton ingot. The simulation model described can calculate internal stresses in any ingot in order to optimize its heating cycle without compromising ingot internal quality, reducing energy consumption and increasing productivity of the furnace.

A very realistic 1:17 scale physical model of a 140-ton gas-stirred industrial steel ladle was used to evaluate flow patterns measured by Particle Image Velocimetry (PIV), considering a three-phase system (air-water-oil) to simulate the argon-steel-slag system and to quantify the effect of the slag layer on the flow patterns. The flow patterns were evaluated for a single injector located at the center of the ladle bottom with a gas flow rate of 2.85 l/min, with the presence of a slag phase with a thickness of 0.0066 m. The experimental results obtained in this work are in excellent agreement with the trends reported in the literature for these gas-stirred ladles. Additionally, a mathematical model was developed in a 2D gas-stirred ladle considering the three-phase system built in the physical model. The model was based on the Eulerian approach in which the continuity and the Navier Stokes equations are solved for each phase. Therefore, there were three continuity and six Navier-Stokes equations in the system. Additionally, turbulence in the ladle was computed by using the standard k-epsilon turbulent model. The agreement between numerical simulations and experiments was excellent with respect to velocity fields and turbulent structure, which sets the basis for future works on process analysis with the developed mathematical model, since there are only a few three-phase models reported so far in the literature to predict fluid dynamics in gas-stirred steel ladles.

High-Mn Twinning-Induced Plasticity (TWIP) steels are advanced high-strength steels (AHSS) currently under development; they are fully austenitic and characterized by twinning as the predominant strengthening mechanism. TWIP steels have high strength and formability with an elongation up to 80%, which allows reduction in automotive components weight and fuel consumption. Since the targeted application field of TWIP steels is the automotive industry, steels need high mechanical performance with good weldability and excellent corrosion resistance. However, there is lack of information about the weldability behavior of these advanced steels. This research work aims to study the weldability of a new generation of high-Mn austenitic TWIP steels microalloyed with B. Weldability was examined using spot welds produced by Gas Tungsten Arc Welding. Microstructural changes were examined using light optical metallography. Segregation of elements in the weld joint was evaluated using point and elemental mapping chemical analysis by Scanning Electron Microscopy and Electron-Dispersive Spectroscopy; while the hardness properties were examined with Vickers microhardness testing (HV25). Experimental results show that the welded joint microstructure consists of austenitic dendritic grains in the fusion zone, and equiaxed grains in the heat affected zone. Notably, the boron microalloyed TWIP steel exhibited poor weldability, showing hot cracking. Additionally, the studied TWIP steels showed a high degree of segregation in the fusion zone; Mn and Si segregated into the interdendritic regions, while Al and C preferentially segregated in dendritic areas. Finally, the welded joints of the TWIP steels showed microhardness values lower than the base material. In general, the present TWIP steels have problems of weldability, which are corroborated with microstructural changes, elements segregation and microhardness loss.

When high strength and high ductility are required, the Twinning Induced Plasticity steels are an excellent choice. Their mechanical advantages are perfectly known in the automotive industry. Then, they are currently deeply studied. During the deformation at high temperature, TWIP steel experiences dynamic recrystallization. This mechanism results from dislocation interactions, and it depends of temperature, stress, strain, and strain rate. Experimental data give the maximum stress reached by the material, but the critical stress which determinates the DRX onset must be calculated from the strain hardening rate. Both stress and strain change simultaneously, and this variation gives the analytic data to determine σc, which is located at the inflection point of θ-σ plot. The main purpose of this paper was to study how the chemical composition and the experimental parameters (temperature and strain rate) affect the DRX, by the calculation and analysis of the σc values. Hot compression tests were applied to a pair of TWIP steels to compare the DRX onset and its relationship with the vanadium addition. The experimental variables were temperature and strain rate. The true stress–true strain plots were used to calculate σc by cutting data up to a previous point before the σp value, then, a polynomial fit and derivation were applied. The Zener-Hollomon parameter (Z) versus the stresses (peak and critical) plots show how the micro-alloying element vanadium improves the strain hardening in the analyzed TWIP steels.

Low-density steels, with an excellent combination of outstanding mechanical properties, ultimate tensile strength and specific weight reduction, have been attracting great attention as a new group of materials in many industrial applications, particularly in the automotive industry. The aim of this work was to characterize the microstructure of a Ti-containing low-density Fe-Mn-Al-C steel in the as-cast condition. For this purpose, Ti-containing low-density steel was melted in an induction furnace using high purity raw materials and cast into a metal ingot mold. Chemical composition of the studied steel was Fe-32Mn-7.0Al-2.2C-0.5Ti (wt%). Samples were prepared by standard metallographic technique (grinding and polishing) and chemically etched with 2% nital solution, in order to reveal the dendritic microstructure. Microstructure observations were performed by scanning electron microscopy and the chemical nature of the present phases was determined by energy-dispersive X-ray. X-ray diffraction was performed at room temperature using a diffractometer with Cu Kα radiation. Phase equilibria by thermodynamic calculations for the studied steel were performed using JMatPro® software package. In general, results revealed a finer dendritic microstructure composed of ferritic matrix and austenite islands. The presence of ferrite and austenite in the steel was also confirmed by X-ray diffraction.

In this work, the effect of three principal and independent parameters of Atmospheric Plasma Spray on the properties of coatings deposited using mixtures of commercial powders of titanium dioxide (TiO2) and chromium oxide (Cr2O3) was studied. The results of this work are used for special applications on turbomachinery components such as wear protection in sliding seals and in steam valves for turbines, chemical protection for centrifugal compressor members, and special seal applications.

The design of experiments (DoE) technique has proved to be very useful to study the influence factors and optimization. Pierlot et al. [1] demonstrated that the application of the Hadamard and two factorial design techniques are useful for the optimization of thermal spray processes. An example of the application of the DoE is the one mentioned by Murugan et al. [2]. In their work, a factorial design was used to study the interactions between gas flow, oxygen flow, powder rate and spray distance on the percentage of porosity and hardness of TiO2 - Cr2O3 composite coatings generated by High Velocity Oxy-Fuel.

The ½ fractional two-level factorial DoE technique was used to analyze and optimize the Atmospheric Plasma Spray process parameters. In the current research, experiments were conducted varying the deposition velocity, gas flow and stand-off distance. The effect of these process variables were evaluated by thickness, hardness and microstructure analysis. In this study, an empirical relationship between process variables and response parameters was developed. The entire relationship was made using the results of the DoE.

The aerospace and automotive industries demand the development of new manufacturing processes. The productivity during machining of very flexible aerospace and automotive aluminum components is limited for self-excited vibrations. New solutions are needed to suppress vibrations that affect the accuracy and quality of the machined surfaces. Rejection of one piece implies an increase in the manufacturing cost and time. This paper is focused on the design, manufacturing and characterization of a magnetorheological damper. The damper was attached to a thin-floored component and a magnetic field was controlled in order to modify the damping behavior of the system. The dynamics of the machining process was developed by considering a three-degree-of-freedom model. This study was experimentally validated with a bull-nose end milling tool to manufacture monolithic parts with thin wall and thin floor. Experimental tests and characterization of the magnetorheological damper permitted to improve the surface finish and productivity during the machining of thin-floored components. A further aim of this paper was to develop a rheological damper by using magnetorheological fluids (MR) to change the thin floor rigidity with voltage. The stability of the milling process was also analytically described considering one, two or three degrees of freedom, using a mathematical integration model based on the Enhanced Multistage Homotopy Perturbation Method (EMHPM).

Lately, the investigations of binders from ternary system Portland cement (PC), calcium aluminate cement (CAC) and calcium sulfate ($C\overline S$), have gone through a larger stage of development due to their special properties such as fast setting and rapid hardening, early strength, non-efflorescence, etc. These special properties are ensured by the binder’s microstructure, developed through hydration processes and reactions between hydrate components, which allows us to use them in special environments (aggressive environments with very low or very high level of pH, environments with high temperature, etc.). The binders from this system were simply named “dry mortars”, and provide the final user with an easy processing. In order to explain the mechanical behavior of the specimens exposed in normal curing conditions (T = 20 ± 2 °C and R.H. ≈ 95%), and with different percentages of calcium sulfate (added as hemihydrate or anhydrite), research on the microstructure of the hardened system was performed using SEM and XRD investigation techniques. The analyses have been performed on the binder pastes, hydrated for 1 and 28 days. The tests results showed that the specimen with anhydrous $C\overline S$ content had the best mechanical behavior.

Porous silicon (PSi) combines the potential of miniaturization with a very large surface area. The PSi surface can be chemically modified resulting in a high sensitivity (low detection threshold) device for chemical and biomolecular sensing. In previous work, we have shown that redox proteins and fluorescent ligands can be infiltrated into PSi (PSiMc) structures. The hybrid devices have shown interesting new properties produced by the coupling of the individual properties of PSi nanostructures and the modifiers. In this work, we have obtained a PSiMc/redox protein bioelectrode, which presents a quasi-reversible electrochemical response. This effect was attributed to the semiconducting nature of the PSi substrate and to the functional groups of the crosslinking molecules (MPTS), which together produce a capacitive effect on the device. On the other hand, the chemical modification of PSiMc with fluorescent ligands allowed us to fabricate fluorescent PSi hybrid nanostructures, which were tested for the detection of environmental pollutants such as heavy metals (specifically Hg2+). We found that the selectivity of this optical device depends on the selected recognizing molecule. The captured metal induces the formation of a metallic complex that shows higher fluorescence compared with the sensor device. These results demonstrate the viability of using porous silicon as optical sensors and electrochemical biosensors. The infiltration of fluorescent recognizing molecules and proteins into the PSi matrix were evaluated by specular reflectance, FTIR spectroscopy, fluorescence spectroscopy and cyclic voltammetry.

Glass-ceramics of eutectic composition in the wollastonite [W, CaO⋅SiO2]- tricalcium phosphate [TCP, β-Ca3(PO4)2] binary system were synthesized by using the glass-crystallization method. The parent glass was crystalized at 800-1300 °C for 0.5-5 h. The in vitro bioactivity of the synthesized glass-ceramics was tested in Kokubo’s Simulated Body Fluid (SBF) for 7-21 days, at pH = 7.4 and 37 °C. All materials were characterized by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM/EDS). The results showed that metastable Apatite phase [Ap, Ca10(PO4)6O], plus W and TCP phases expected according to the binary phase diagram, were formed. Ap was the first phase formed at 900 °C/0.5 h, which was followed by formation of W phase at 900 °C/2 h and of TCP phase at 1200 °C/0.5 h. The relative proportion of the formed crystalline phases was a function of heat treatment temperature and time. A eutectic microstructure was obtained for the materials heat-treated at 1300 °C for 2 or 5 h. All glass-ceramics showed the formation of a hydroxyapatite (HAp)-like layer during the in vitro bioactivity tests. After 21 days of soaking in SBF, the samples treated at 1300 °C/5 h showed a behavior similar to that typically shown by Bioeutectic® material, while the materials heat-treated at lower temperatures tended to form denser HAp-like layers, with similar thicknesses but with higher Ca/P molar ratios.

BaAl2Si2O8 and SrAl2Si2O8 were synthesized by solid-state reaction of stoichiometric mixtures of either BaCO3 or SrCO3 with coal fly ash and Al2O3. The mixtures were mechanically activated in an attrition mill for up to 12 h and then reaction-sintered at 900-1300 °C, aiming to promote the formation of BaAl2Si2O8 and SrAl2Si2O8 as well as the conversion from their hexagonal (Hexacelsian) into their monoclinic (Celsian) forms, which is associated with improved mechanical properties in the sintered materials. Especially in the case of SrAl2Si2O8, the formation of Celsian was favored at relatively low sintering temperatures by increasing milling time. Although only the SrAl2Si2O8 composition was fully converted into Celsian, the Hexacelsian to Celsian conversions obtained for the mechanically-activated BaAl2Si2O8 composition were significantly higher than those previously reported in the literature for this compound. This could be attributed to the use of coal fly ash as raw material, which contains mineralizers that promote the mentioned conversion.

In this work, we studied the synthesis of biodegradable copolymers of the type poly(isobutyl vinyl ether)-co-(ε-caprolactone) (PIBVE-co-PCL) using a homogeneous mono-cyclopentadienyltitanium catalyst and methylaluminoxane (MAO) as co-catalyst. These copolymers can also be used as plasticizers for flexible poly(vinyl chloride) (PVC), improving its thermal properties. The copolymer PIBVE-co-PCL could be synthesized with a high conversion (>90%). The use of 39 wt.% of the copolymer in the formulation of PVC decreases its glass transition temperature (Tg) by -6.51 °C. By varying the copolymer composition it is possible to obtain PVC with different Tg values that could be used for different applications. A particular application where one could use this type of copolymer is in PVC formulations for the fabrication of blood bags. The toxicity of dioctyl phthalate (DOP), which is the more commonly used plasticizer for PVC, limits the use of these formulations for the mentioned purpose. The PVC plasticized with the biodegradable copolymer showed an increase in the degradation temperature, improving the thermal stability of the PVC formulation in comparison with the phthalates usually used as plasticizers.

Nowadays the aeronautical industry keeps strict quality standards in its dimensional specifications, mechanical properties and microstructural characteristics. Therefore, the involved manufacturing processes require keeping high standards. The nickel based superalloys are present in many components of the jet engines, being the Inconel 718MR superalloy the most common, making up to 50% of the jet engine. This is designed to resist high temperatures, corrosion and creep. The process of rotary forging is a manufacturing process that is currently under scientific and technological development in the aeronautical industry. An Avrami model coupled with a commercial FEM platform (DEFORMTM 3D) was developed to evaluate the average grain size, as a function of the working conditions at 980 °C and 1000 °C. The results provide a better understanding of the influence of temperature in the grain size evolution during the rotary forging process, compared with previous reports.

Amorphous silicon (α-Si) was deposited on glass substrates by PECVD at different deposition conditions in order to characterize the residual stress on the film. Subsequently, a thermal-annealing was applied for different times at 400 °C in a N2 atmosphere, aiming to reduce the stress in the films. The deposition power was between 15 and 30 W at 13.56 MHz, the pressure in the chamber was adjusted in a range from 600 to 900 mTorr, and the temperature was varied from 140 to 200 °C. The stress was determined by using the Stoney equation, measuring the curvature and thickness of the α-Si films with a stylus profilometer. A deposition rate between 7-24 nm/min was obtained, and the time for thermal-annealing needed to reduce the stress was reduced from 10 to 2-4 h, obtaining a minimum compressive stress of 17 MPa. With this value of stress, it was possible to use the α-Si as masking material for wet etching of glass during the manufacturing of microfluidic devices, in order to obtain microstructures in the glass with 150 μm in depth.

Hydrogenated amorphous silicon carbide (a-SiC:H) was deposited by radiofrequency-plasma enhanced chemical vapor deposition (RF-PECVD) on monocrystalline silicon substrates with different process parameters in order to analyze the residual stress, and the roughness and uniformity of the films, which are the most important characteristics in the production of membranes for cell culture. The residual stress was calculated using Stoney's equation by measuring the thicknesses of the substrate and the deposited film, in addition to the radius of curvature of the substrate with and without deposited material. From the results it was observed that as power increases from 15 to 30 W, the residual stress increases from -180 to -400 MPa. Even at low power, the residual stress is high. However, an annealing process at 450 °C in N2 atmosphere significantly reduces the residual stress to 7 MPa. It was found that the film uniformity increases when the pressure rises in the process chamber from 450 to 900 mTorr. Finally, the RMS roughness (0.7 to 5.1 nm) can be controlled by the power and pressure, allowing us to obtain a material with excellent morphological characteristics for the adherence and growth of specific cells.

It is well-known that metal and alloys develop internal cavities when subjected to uniaxial or multiaxial tensile strains at elevated temperature. In most cases, cavitation may lead to premature failure during forming. Therefore, damage and fracture behavior imposes significant limitations in hot metal-forming processes. Although high-Mn austenitic TWIP steels exhibit a unique combination of strength and ductility, cavitation during hot working is one issue that must be tackled. The aim of this research work is to determine the effect of Ti microaddition on cavity mechanisms of Fe-22Mn-1.5Al-1.3Si-0.5C TWIP steel under uniaxial hot-tensile condition at 800 °C and constant true strain rate of 10-3 s-1. For this purpose, light optical (LOM) and scanning electron (SEM) microscopies and image analysis were applied to quantify cavities formation along longitudinal section of deformed samples near to the fracture surface. The number of cavities greater than 10 µm (critical length) in non-microalloyed and Ti microalloyed TWIP steels were 2.75 and 3.75 cavities/mm2, respectively. On the other hand, average cavity area was 125 and 152 µm2, respectively. Both TWIP steels showed cavities type “r”, “l” and “A”. Finally, Ti microaddition to TWIP steel resulted in a predominant brittle fracture behavior due to finer grain-boundary precipitation, which weakens grains cohesion and accelerates crack growth by grain-boundary sliding. In this case, crack growth behavior is explained in terms of a void interconnection mechanism.

This article outlines the use of quenching dilatometry in phase transformation kinetics research in steels under continuous cooling conditions. For this purpose, the phase transformation behavior of a hot-rolled heat treatable steel was investigated over the cooling rate range of 0.1 to 200 °C/s. The start and finish points of the austenite transformation were identified from the dilatometric curves and then the continuous cooling transformation (CCT) diagrams were constructed. The experimental CCT diagrams were verified by microstructural characterization using scanning electron microscopy (SEM) and Vickers micro-hardness. In general, results revealed that the quenching dilatometry technique is a powerful tool for the characterization and study of solid-solid phase transformations in steels. For cooling rates between 200 and 25 °C/s the final microstructure consists on plate-like martensite with the highest hardness values. By contrast, a mixture of phases of ferrite, bainite and pearlite predominated for slower cooling rates (10-0.1 °C/s).