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Conducting the carburizing process on the surface layer of low-carbon steel and subsequent austempering heat treatment can be implemented to obtain nanobainite microstructure on the surface of steels. In this research, steel with 0.23 wt.% carbon was carburized for 3 h at 900 degrees C in a liquid salt bath containing sodium cyanide, sodium carbonate, and sodium chloride and immediately quenched to room temperature. The samples were then heated to 900 degrees C for 30 min and isothermally transformed at three different temperatures of 200, 250 and 300 degrees C for 72, 24 and 12 h, respectively. It was found that nanostructured bainite was formed on the surface layer and the subunits of bainitic ferrite and high-carbon austenite films were almost 60-300 nm thick depending on the heat treatment temperature. It was also found that the samples austempered at these temperatures contained 18, 21 and 28% volume fractions of retained austenite on the surfaces, respectively. Due to the comparable microstructural characteristics, similar friction coefficients were obtained as for ordinary nanostructured bulk bainitic steels with high-carbon content.

It is an important challenge to reduce the carbon content in nanostructured bainitic steels for commercialization purposes while still being able to gain the desired microstructural characteristics in nanoscale and not to deteriorate the strength–ductility combinations. That is the point at which an appropriate heat treatment procedure design would be an important parameter. This article aims to investigate how to obtain nanostructured bainite in steel with 0.26 wt% carbon content by applying multi-step austempering procedures. One-, two- and three-step austempering processes have been implemented, and proper heat treatment temperatures and approaches were selected based on dilatometry tests. Results indicated that it has become possible to achieve bainitic ferrites and austenite films with overall thicknesses of 164, 145 and 132 nm and 134, 105 and 90 nm at the end of one-, two- and three-step austempering heat treatments, respectively. Meanwhile, microstructural characteristics resulted in enhanced mechanical properties with ultimate tensile strength (UTS) of 1435, 1455 and 1428 MPa in combination with elongation levels of 15.4, 13.6 and 11.4% after implementing those heat treatments. Finally, it has been shown that applying the multi-step austempering heat treatments resulted in enhanced yield strength and impact toughness values due to the microstructural characteristics and proper heat treatment procedure design.

Ausforming is being widely used to overcome the kinetics barrier in nanostructured bainitic steels and to enhance its practical industrial applications. It would also affect the microstructural cha...

The Zn-Ni-Mn/Zn Ni multi-layer coatings were electrodeposited under switching potential regime from an alkaline solution. In order to deposit Zn Ni layers, more positive potential −1560 mV was used as first electrodeposition potential in each cycle. More negative potentials −1860 mV and −1980 mV was used as the second potential in the various potential regime. The pulse-electrodeposited samples showed a smoother surface compared to coatings electrodeposited at a constant potential. Also, potentiodynamic polarization and electrochemical impedance spectroscopy were used to study the corrosion resistance of these coatings. All coatings electrodeposited at constant potential showed passivation behavior, while such behavior was only seen in pulse-electrodeposited samples from bathes with Mn2+ concentration higher than 1.17 μM. Samples electrodeposited using −1860 mV as the second potential for 30 s in each cycle had more positive corrosion potential and lower corrosion current density compared to samples deposited at a constant potential, while samples electrodeposited under potential regimes with more negative second potential had more negative corrosion potential and higher corrosion current density. The electrochemical impedance curves showed that the coatings electrodeposited at constant potential had higher polarization resistance and the passive layer formed at their surface was more compact than the pulse-electrodeposited ones.

Nanobainitic structures were produced in a low alloy carburised steel at temperatures of 200, 250 and 300°C. Scanning electron microscope micrographs indicated bainitic ferrites formed with a thickness range of 30–150 nm. Wear test results revealed that the coefficient of friction for nanobainitic samples was smaller and narrower compared to that of the martensitic sample which showed higher and larger variations indicative of better wear performance for nanobainite samples. The wear mechanism of nanobainitic samples due to their tough matrix was oxidative which resulted in small debris and smaller fluctuations in coefficient of friction. The large variation in the coefficient of friction in the martensitic sample was believed to be because of the detaching of larger fragments from the worn surface.

Outstanding mechanical properties of nanostructured carbide-free hard bainitic steels, also known as super bainite, with microstructural constituents of less than 100 nm thicknesses make them prone to be used in different engineering applications. However, besides their exceptional strength and ductility combinations during ordinary static or quasi-static deformation modes, it would be also interesting to evaluate their mechanical behavior under high strain rate deformation conditions. This article aims to investigate the mechanical performance of nanostructured super bainite isothermally obtained at 300 °C by applying both tensile and compressive high strain rate deformation modes. Hopkinson compressive and tensile tests were performed up to the maximum strain rate levels of 1.82 × 103 s−1 and 1.040 × 104 s−1, respectively. Results indicated that strength and ductility properties both significantly were dependent on the strain rate values during tension and compression even if the effect of tensile deformation mode was more considerable. The strength level enhanced to almost 3000 MPa at the highest tensile deformation rate. According to the results, the transformation-induced plasticity (TRIP) effect could not be effective in ductility promotion at higher tensile strain rate deformations since the austenite-to-martensite transformation did not take place gradually to produce a proficient transformation-induced plasticity effect. As a result, a premature TRIP effect occurred and resulted in lower energy absorption during deformation processes.

This study reveals an unprecedented capacity of flake graphene sheets in manipulating semi-solid deformation of aluminium matrix nanocomposites by restricting the grain growth of the nanograins during the reheating process to significantly enhance (173%) the yield strength of the fabricated composites. The graphene sheets with onion shape have also shown the unique capability in alleviating the agglomeration of SiC nanoparticles, attributed to the manipulated Hamaker constant of these particles as a result of wrapping graphene sheets. A devised mathematical approach has authenticated, for the first time, the effect of wrapping graphene sheets on subtle adjusting the Hamaker constant of SiC nanoparticles to stimulate engulfment of these nanoparticles within solidifying matrix rather than agglomeration at grain boundaries. This, therefore, has resulted in diminishing the porosity and stimulating multi-scaled micro/nano grains, thereby significantly enhancing the tensile properties of the fabricated composites.

This study presents the fracture toughness improvement of the powder metallurgical high speed steel ASP2030 by replacing the martensitic matrix with a bainitic one. For this purpose, the fracture toughness of the steel is compared in both the austempered and marquenched states. The heat treatment of the samples was carried out by austenitizing in the range of 1150–1185 °C followed by either austempering at 235 °C or marquenching processes. Triple tempering at 560 °C for 2 h was also performed on all specimens. Fracture toughness measurements were performed on circumferentially notched tensile specimens. The microstructural features of the specimens were investigated using X-ray diffraction, optical and electron microscopy, and electron backscatter analysis. The results showed that the fracture toughness is sensitive to small changes in austenitizing temperature at both heat treatment conditions. By increasing the austenitizing temperature from 1150 to 1170 °C, the fracture toughness increases and then decreases with a further increase in temperature to 1185 °C. The results suggest that the changes in fracture toughness are due to the simultaneous effects of the volume fraction of undissolved carbides and the lattice microstrain values at different austenitizing temperatures. It can be concluded that the fracture toughness increases when the martensitic matrix is replaced by a bainitic structure. This improvement is related to finer bainitic laths width and also to the larger spacing between the particles of the undissolved carbides.

Objectives: The electrocardiogram (ECG) of patients with BrS in sinus rhythm might reflect intrinsic atrial electrical abnormalities independent from any previous atrial fibrillation (AF). Aim of this study is to investigate the presence of P-wave abnormalities in patients with BrS and no history of AF, and to compare them with those displayed by patients with documented paroxysmal AF and by healthy subjects. Methods: Continuous 5-min 16-lead ECG recordings in sinus rhythm were obtained from 72 participants: 32 patients with a type 1 Brugada ECG, 20 patients with a history of paroxysmal AF and 20 age-matched healthy subjects. Different ECG-based features were computed on the P-wave first principal component representing the predominant morphology across leads and containing the maximal information on atrial depolarization: duration, full width half maximum (FWHM), area under the curve and number of peaks in the wave. Results: Patients with BrS and no history of AF (mean age: 53 +/- 12 years; males: 28 pts., spontaneous type 1 ECG: 20 pts., SCN5A mutation: 10 pts) presented with longer P-wave duration, higher FWHM and wider area under the curve in comparison with the other two groups. Although P-wave features were abnormal in BrS patients, no significant difference was found between patients with spontaneous type 1 ECG and ajmaline-induced type 1 ECG, symptomatic and asymptomatic ones, and between patients with a pathogenic SCNA5 mutation and patients without a known gene mutation. Conclusions: Patients with BrS without previous occurrence of AF present with a concealed abnormal atrial phenotype. In these patients atrial electrical abnormalities can be detected even in the absence of an overt ECG ventricular phenotype, symptoms and a SCN5A mutation. (c) 2017 Elsevier B.V. All rights reserved.

For the first time, functionally electroless nickel plated ZrO2 (NCZ) graded Ni-NCZ composite coating has been successfully co-electrodeposited from a bath with gradually increasing of stirring rate. Studies showed that co-electrodeposition in a bath with stirring rate of 250 r/min results in the maximum co-electrodeposited particle content and the best particle distribution. To produce NCZ graded Ni-NCZ composite coating, the stirring rate was continuously increased from 0 to 250 r/min. The electroplated coating had a continuous gradient increasing of co-electrodeposited NCZ content from substrate towards the surface. The results showed that with increasing the co-electrodeposited NCZ particles content in Ni matrix, microhardness increases from interface towards the surface of the coating. Little crystallite size of Ni matrix and higher co-electrodeposited hard particles content were recognized as the reasons of microhardness increasing. Bend test revealed that the functionally graded composite coating shows more excellent adhesion to the substrate compared with the ordinary distributed Ni-NCZ on the same substrate. This result is attributed to lower mechanical mismatch between coating and substrate in the functionally graded composite coating with respect to the uniformly distributed one. The results of wear resistance measurements reveal that wear resistance of functionally graded Ni-NCZ is higher than that of ordinary distributed composite coating.

Functionally graded Ni-ZrO2 (FGN-Z) and functionally graded Ni-NCZ (FGN-NCZ) composite coatings have been successfully co-electrodeposited from a bath containing variable concentrations of the particles. NCZ (electroless‑nickel coated ZrO2) particles were manufactured by dispersing of ZrO2 powder in an electroless-Ni plating bath. To produce functionally gradient composite coatings, ZrO2 and NCZ concentrations were continuously increased in the electroplating bath. With increasing of co-electrodeposited ZrO2 and NCZ particles content in Ni matrix, microhardness increases from interface towards the surface of the coating. The results showed that FGN-NCZ has higher wear resistance and corrosion resistance compared to FGN-Z. These were attributed to the higher amounts of co-electrodeposited second phase particles, stronger bonds between matrix and second phase particles and larger amounts of microhardness achieved for FGN-NCZ with respect to FGN-Z.

Normobaric hypoxia (NH) is used as a surrogate for hypobaric hypoxia (HH). Recent studies reported physiological differences between NH and HH. Baroreflex sensitivity (BRS) decreases at altitude or following intense training. However, until now no study compared the acute and chronic changes of BRS in NH vs. HH. First, BRS was assessed in 13 healthy male subjects prior and after 20 h of exposure at 3450 m (study 1), and second in 15 well-trained athletes prior and after 18 days of "live-high train-low" (LHTL) at 2250 m (study 2) in NH vs. HH. BRS decreased (p

Metallic molybdenum coating was deposited from an aqueous electrolyte containing a high concentration of acetate and molybdate ions in pH of 6.8 ± 0.2. It is complicated to deposit molybdenum from an aqueous electrolyte because of its high reactivity with oxygen. The mole ratios of water to acetate were in the range of (2.4 ± 0.2):1. It was found that the change in bath stirring rate can result in the deposition of molybdenum oxide insisted of Mo coating. Also the morphological differences of metallic Mo and molybdenum oxide layer were investigated. In the present study, a successful attempt was made metallic Mo coating with a thickness of 3–7 μm that was dependent on the DC current density. The XRD investigation indicated that the crystal structure of Mo coating was amorphous. The surface composition of deposits was ascertained by energy dispersive X-ray microanalysis (EDS) that showed the presence of high Mo content (90.7%) and low content of oxygen (9.3%). In addition, different EDS analysis was obtained from the top surface of coating and subsurface section. The surface morphology of coating was studied by scanning electron microscopy (SEM). Also, XPS analysis confirmed deposition of Mo(0) metal.

It is critical to obtain nanocrystalline materials in large chunks rather than only in thin film or rod shapes and nanostructured bainitic steels are good examples of bulk nano materials. This article aims to investigate the hardenability of nanobain steel to estimate the biggest cross section that can be successfully austempered to form nanocrystalline bainite. Isothermal heat treatments were conducted at different temperatures using salt bath furnaces, the quench severity factors of which were determined at bainitic transformation temperature ranges. It was found that, the proper chemical composition selection increased the hardenability and shifted the upper C-curve of the Time–Transformation–Temperature diagram to longer heat treatment times. Accordingly, large chunks of nanostructured bainite with almost 330, 340 and 390 mm diameters could be austempered to obtain nanobain successfully in salt bath furnaces of 300, 250 and 210 °C, respectively. The nanocrystalline bainite was composed of nanoscale bainitic subunits of 30–70 nm thicknesses depending on transformation temperature.

It is crucial to eliminate the thermally and mechanically less stable austenite blocks as much as possible if enhanced mechanical properties are demanded in high performance nanostructured bainitic steels. Step-austempering would be an efficient procedure in this regard. This article aims to investigate the strength-ductility- impact toughness combinations in nano-bainite after two-step austempering process comparing with those obtained after conventional isothermal bainite transformation. It has been shown that large austenite blocks further decomposed to bainite after step-austempering process which in turn decreased the average volume fraction of austenite, increased its mechanical stability and generally refined the final microstructure. Step-austempering increased the hardness value and enhanced the yield strength and ultimate tensile strength properties. Additionally, the higher mechanical stability of retained austenite in step-austempered samples increased the elongation level and improved the impact toughness at earlier stages of the second step of transformation. The important point is, it has been found that ductility and toughness properties were influenced by transformation time at the second stage of austempering which approved the idea that not only the mechanical stability and morphology of retained austenite but also its volume fraction must be taken into account when applying a multi-step austempering heat treatment in nanobain steels.

The potentiostatic electrodeposition of Zn−Ni−Mn was carried out in an alkaline solution with the addition of Mn salt. The effects of electrolyte Mn2+ concentration and deposition potential on the surface morphology, phase structure and corrosion behavior of coatings were studied. The results of corrosion polarization showed that the presence of higher Mn content in Zn−Ni−Mn coatings could lead to the formation of a good passive layer with a 7-fold increase in Rp of coating and a significant decrease in the corrosion current density compared to those of Zn−Ni coating. The XRD and the XPS analyses from the surface of Zn−Ni−Mn after corrosion test showed that the passive layer was composed of zinc hydroxide chloride, zinc oxide, zinc hydroxide carbonate, and manganese oxides.

In this study, functionally NCZ (electroless nickel plated ZrO2) content graded Ni-NCZ composite coating has been successfully co-electrodeposited from a bath with gradually increasing of stirring rate. For this, different composite coatings were electroplated in the same bath with different stirring rates to find the optimum condition. SEM, XRD, EDX and electrochemical studies showed that co-electrodeposition in a bath with stirring rate of 250 rpm results in the maximum co-electrodeposited particle content and the best particle distribution and corrosion resistance. Also, this sample had the highest wear resistance with respect to the other samples. To produce NCZ content graded Ni-NCZ composite coating, the stirring rate was continuously increased from 0 to 250 rpm. The electroplated coating had a continuous gradient increasing of co-electrodeposited NCZ content from substrate toward the surface. This distribution of NCZ particles results in a gradient increasing of the microhardness in the cross section of the coating. Bend test revealed that the functionally graded composite coating shows better adhesion to the substrate compared with the uniformly distributed Ni-NCZ on the same substrate. This result has been attributed to lower mechanical mismatch between coating and substrate in the functionally graded composite coating with respect to the uniformly distributed one.

Acceleration of the bainitic transformation and modifying the microstructural characteristics are believed to be of major concerns in production of Low-Temperature Bainite. Ausforming prior to isothermal bainitic transformation seems to be an effective procedure in this regard. This article aims to study the influence of different ausforming strains on transformation kinetics and microstructural features of low temperature nano bainite obtained after austempering at 300 °C. Results indicated that bainitic transformation tended to be accelerated by plastic deformation of primary austenite depending on applied strain level. In addition, the volume fraction and morphology of the microstructural constituents have been shown to be affected by ausforming after which higher volume fraction of bainite, finer austenite micro blocks and thinner bainitic ferrites could be achieved. Finally, quantitative analysis demonstrated that ausforming favoured the distribution of bainitic sheaves in limited crystallographic directions whereas they spread randomly in different crystallographic orientations in non-ausformed specimens. This was more evident at higher ausforming strain levels at which bainitic sheaves' orientation distributions were narrower relative to the rolling direction regardless of the isothermal bainitic heat treatment time.

For the first time, functionally ZrO2 content graded Ni–ZrO2 composite coating has been successfully co-electrodeposited from a bath with gradually increasing stirring rate. For this, different composite coatings were electroplated in the same bath with different stirring rates to find the optimum stirring rate in which the maximum content with uniform distribution of ZrO2 particles in the coating can be achieved. To produce ZrO2 content graded Ni–ZrO2 composite coating, the stirring rate was continuously increased from 0 to optimum value. The results showed that functionally graded Ni–ZrO2 composite coating has been successfully electroplated with continuous gradient distribution of Zirconia content in the coating using controlling of bath stirring rate. With increasing of ZrO2 particles content, the microhardness increases from the interface towards the surface of the coating. This could provide a high wear resistance with high adhesion of the coating to the substrate.

This study reveals a promising feature of graphene encapsulating process to significantly enhance the mutually inclusive tensile strength and ductility of aluminium based composites using the semi-solid powder forming process. It was corroborated based on van der Waals–Casimir interaction free energy that graphene sheets have an unprecedented capacity to manipulate the Hamaker constant of SiC nanoparticles, prompting formation of nano/micro-sized grains. Authenticating by the strengthening model, fractographic observations have also demonstrated the unique functionality of graphene sheets in strengthening via grain refining, thermally enhanced dislocations, shear-lag, geometrically necessary dislocations, crack bridging and fibre pull out mechanisms.