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The poor corrosion/wear resistance of Mg alloy seriously limits its industrial application. Graphene-based anti-corrosion coatings show the excellent imperviousness, but they can provide the additional cathodic sites for Mg alloys, which accelerates the galvanic corrosion behaviors near the interfaces. A novel design of cerium-based intermediate layer (Ce(Ⅳ)) is reported in this study, which exhibits a synergistic effect of hydrogen/ionic bond on the graphene oxide (GO)/polyvinyl alcohol (PVA) biomimetic coating. It overcomes the problems of galvanic corrosion and low interfacial adhesion between Mg substrate and hybrid coating through a prominent barrier effect. Furthermore, the GO/PVA coating with “bricks and mortar” structure effectively blocks the permeation of electrolyte due to the reduced porosity and enhanced densification. The corrosion rate of Ce(Ⅳ)/GO/PVA coating is 11 and 19 times lower than bare Mg alloy and single GO/PVA film, respectively. The wear rate of GO/PVA and Ce(Ⅳ)/GO/PVA samples is decreased by 98.8% and 97.6%, which is ascribed to the high hardness and lubrication of GO sheets. Moreover, the relatively interlayer slipping between GO sheets can lubricate the sliding process. Compared with GO/PVA, the slightly decreased wear resistance of Ce(Ⅳ)/GO/PVA coating is resulted from the enhanced shear force.

The high temperature oxidation behavior of a high Al-containing ferritic heat-resistant stainless steel at temperatures of 800, 900, and 1000 °C in air were studied in isothermal oxidation tests. The results showed that the isothermal oxidation kinetic curves obtained at different temperatures followed the parabolic law, and the weight gain per unit at 1000 °C was significantly higher than that at 800 and 900 °C. The oxidation rate at 1000 °C was about three times faster than that at 800 and 900 °C. Continuous and compact multicomponent oxide films mainly composed of Cr2O3, Al2O3, spinel MnFe2O4, and MnCr2O4 were obtained at 800 and 900 °C. The oxide film started delaminating at 1000 °C; the outer layer was composed of Cr2O3, spinel MnCr2O4, and MnFe2O4, the middle layer was composed of Fe2O3 and Fe-Cr matrix, and the inner layer was composed of Al2O3 and SiO2. Oxidation resistance at 1000 °C was reduced mainly because of porous Fe2O3 and inner oxidation of Al and Si. In addition, the oxidation mechanism was discussed based on kinetic and morphological observations.

X10CrAlSi18 FHSS (ferritic heat-resistant stainless steel) has received a lot of attention due to its advantageous combination of creep resistance and oxidation resistance. The influence of Si content on the high-temperature oxidation resistance of X10CrAlSi18 FHSS after oxidation at 700 and 800 °C for up to 180 h in air was investigated in this study. According to the results, a higher Si content could coarsen the grain of ferrite and simultaneously increased the amount of (Cr, Fe)23C6 carbides, which caused cracks and reduced the adhesion between the oxide film and the matrix. After oxidation at 700 °C, the oxide film of 0.77Si FHSS and 1.35Si FHSS were found to be primarily composed of Al2O3, SiO2, Cr2O3, Fe2O3, Mn2O3 and MnCr2O4, with thickness of 5.10 μm and 5.56 μm, respectively. The oxide films formed at 800 °C were primarily composed of Al2O3, SiO2, Cr2O3, FeCr2O4, Mn2O3 and MnCr2O4 with thickness of 5.55 μm and 7.37 μm, respectively. A higher Si content was discovered to increase the amount of MnCr2O4 in the outer layer of the oxide film, which resulted in a looser spinel structure and reduced the oxidation resistance of X10CrAlSi18 FHSS.

The industrial applications of Mg and its alloys are restricted by their poor corrosion resistances, owing to the rapid dissolution and hydrogen evolution behaviors. In this study, a sequentially bridged reduced graphene oxide (RGO)/bistriethoxysilylethane (BTSE) coating is successfully grafted on the surface of Mg alloy substrate, to simultaneously inhibit the corrosion and wear behaviors. It exhibits well-aligned biomimetic nacre-like “bricks and mortar” structure connected by covalent bonding networks, consisting of the Si-O-C bonds between the RGO sheets and the Si-O-Si bonds derived from BTSE self-crosslinking reactions. The reduced porosity and defects lead to a high continuity and integrity of the RGO/BTSE coating, which decreases the corrosion rate by an order of magnitude compared with bare Mg substrate and RGO coated sample, owing to the enhanced barrier effect and weakened galvanic corrosion. In addition, the hybrid coating also performs well anti-wear property due to the intrinsic lubrication of RGO sheets, which can protect the substrate from friction and wear. The wear rate decreases from 3.5 × 10−3 mm3N-1 m-1 of bare Mg alloy to 5.13 × 10-5 mm3N-1 m-1 of RGO/BTSE coated sample. The interlayer slipping between the RGO sheets effectively decreases friction resistance, although the incorporation of BTSE slightly increases their shear resistance.

In order to expand the applied range of Mg alloy, a variety of coatings have been designed to improve their corrosion and wear resistance. Here, we report a 3-aminopropyl triethoxysilane (APTES) modified Mg(OH)2/reduced graphene oxide (RGO) hybrid coating with integrated anti-corrosion/wear property on Mg alloy, which is prepared by in-situ crystallization using a facile hydrothermal method. The ultra-thin Mg(OH)2/RGO layer with 250 nm exhibits a dual-structure, in which the inner layer is composed of Mg(OH)2, and then RGO sheets hybrid with Mg(OH)2 via the hydrogen bond to form the outer layer. The lubrication of RGO sheets and the high hardness of dense Mg(OH)2 give rise to the significant decrease of wear rate, which is two orders of magnitude less than that in Mg substrate. Next, the APTES layer effectively fills the pores and defects on the surface of Mg(OH)2/RGO via the Si-O-Mg and amide bond, and it forms a barrier film enriched with Si-O-Si bond via the self-crosslinking reaction. The effective combination of inorganic and organic layer contributes to the improved anti-corrosion property.

In this study, an ultra-high yield strength (~417 MPa) and moderate ductility (~12.9%) was obtained in Mg–8.2Gd–3.8Y–1.0Zn–0.4Zr (wt%) alloy through a method of decreased-temperature multi-directional forging (MDF) processing followed by aging treatment. The ultra-fine grained structure with average grain size of ~0.9 μm was prepared after 6 passes of forging progress, which was ascribed to the occurrence of dynamic recrystallization (DRX). Both the decreased MDF temperature and precipitation of fine Mg5(Gd, Y) phase particles effectively hinder the DRX grain growth, so that the grain refinement can realize their full potential in strengthening effect. The formation of some DRX grains is also accompanied with the consumption of LPSO structures. Additionally, a weak fiber texture with c-axis perpendicular to normal direction was gradually formed during the reduplicative MDF process. As compared to the hot-extruded counterpart, the significant improvement in the yield strength of MDF-processed Mg-Gd-Y-Zn-Zr alloy can be attributed to the combined strengthening effects of the grain refinement, dynamic precipitation and broken secondary phase particles. Meanwhile, the homogenous microstructure induced by decreased-temperature MDF is also responsible for a resulting moderate ductility.

The deformation behavior and microstructural evolution of as-cast 254SMO super-austenitic stainless steel (SASS) were studied by hot compressive tests in the temperature range 900–1200 °C, and in the strain rate range 0.01–10 s −1 . The results show that the single peak characteristic appears on almost all the obtained flow curves, indicating that DRX is the primary softening mechanism. Either increasing deformation temperature or decreasing strain rate makes the flow stress level reduce remarkably. The hot deformation activation energy and the stress exponent are calculated to be 577.845 kJ/mol and 4.62 by the regression analysis of sine hyperbolic function, respectively. From the deformed microstructures, it is found that the DRX nucleates mainly through grain boundary bulging but occasional through subgrain evolution only occurred at high strain rates and high temperatures. The critical stress and corresponding strain for DRX can be expressed through the dimensionless parameter, Z / A . The critical ratios of σ c / σ p and e c / e p are also identified, which are 0.98 and 0.72, respectively. Moreover, the DRX kinetics for as-cast 254SMO SASS can be represented in the form of Avrami equation, and the predicted volume fraction of new grains based on the developed model agrees well with the experimental results.

The deformation characteristics of as-cast S31254 superaustenitic stainless steel (SASS) have been investigated by the isothermal compression testing at temperature of 1173–1473 K and strain rate of 0.01–10 s−1 on a Gleeble-1500D thermo-mechanical simulator. The approach of processing map (PM) was used to reveal the hot workability affected by the process parameters (such as e , T and e) and microstructural evolution during the hot deformation. It is found that the process parameters have obvious effects on the power dissipation efficiency, instability factor and softening characteristic. The safe deformation domain can be identified from the PM, and the variation of peak efficiency with strain is obtained in the safe domain. The optimal hot working condition at large strains (⩾0.7) corresponds to the temperature range of 1376–1473 K and the intermediate strain rate range of 0.07–1.38 s−1, with a peak efficiency of 35% at ∼1473 K and 0.4 s−1. In this field, the original coarse grains can be substituted by the fine recrystallized grains, indicating that the high power is dissipated by the dynamic recrystallization. Meanwhile, three instable regions, which should be avoided in hot processing, are detected from the PM and the related instability mechanisms are also discussed.

Designability and adaptability are of paramount importance in the production and use of photonic crystal fiber (PCF) sensors. It is still challenging to distinguish different gases in fabricating opto-devices and gas sensors for the detection of toxic gases at low concentrations. Here, we explore a tailor-made PCF sensor based on Bragg diffraction. The silicon fiber array acts as the optical fiber cladding, and the air hole serves as the core. The coating materials are carbon nanotubes (CNT) and CdO-CNT composites, which can respectively serve as the selective “turn-on” detectors for perceiving the benzene and formaldehyde by the preferential adsorption. The CNT has a more pronounced response to benzene (0.8 nm/10 ppm) than other gases, while CdO-CNT has strong selectivity to formaldehyde (1.2 nm/10 ppm). The two sensors show strong selectivity, linear sensitivity, and good response recovery capability. The CNT and CdO-CNT coating PCF sensors can play the part of a sensor array to identify benzene and formaldehyde, which have the advantages of easily assembly and excellent selectivity, showing potential for the detection of harmful gases at low concentrations.

Hot compression tests in the temperature range from 1273 to 1423 K and strain rate range from 0.01 to 10 s–1 were carried out on a Gleeble 1500D thermo-mechanical simulator for as-cast 21Cr economical duplex stainless steel (EDSS). The deformation behavior and microstructural evolution were investigated. It is found that the flow behavior strongly depends on the strain rate and deformation temperature, and the flow stress increases with the increase of strain rate and the decrease of temperature. The softening degree of ferrite becomes larger with decreasing strain rate and increasing deformation temperature, and the austenite is gradually spheroidizing. The flow localization band easily happens at high strain rate and low temperature because of the uneven deformation in the microstructure. Moreover, the constitutive model with the compensation of strain was developed on the basis of hyperbolic sine equation to predict the flow stress of as-cast 21Cr EDSS. The material constant in the model such as α, n, Q and ln A was functioned with the strain by sixth order polynomial. The results show that the developed constitutive model has excellent predictability of flow stress under the experimental deformation conditions for as-cast 21Cr EDSS.

Hot compression tests of as-cast 904L austenitic stainless steel were carried out at deformation temperatures of 1000–1150 °C and strain rates of 0.01–10 s−1 with different strains. The hot working behavior was investigated by the analyses of flow curves, deformed microstructures and kinetics. The results show that the flow stress depends strongly on the deformation temperature and the strain rate, and it increases with the deformation temperature decreasing and the strain rate increasing. Also, the flow curves combined with microstructural evidence indicate that the dynamic recrystallization process of this material is very sluggish with the increase of strain. High temperature and low strain rate together with large deformation can provide the right changes for obtaining more equiaxed dynamically recrystallized grains. The deformation energy (Q) in the whole range of conditions is calculated to be 459.12 kJ/mol by regression analysis and the constitutive equation embraced the Zener–Hollomon parameter is developed. Furthermore, the processing maps (PMs) are generated to reveal the correlation between microstructural evolution and process parameters based on the flow stress data. It is observed from the PM that two regions of deformation stability and instability are characterized. An optimal processing window available for the hot deformation can be obtained to achieve the desired microstructure with dynamic recrystallization. In addition, the predicted instability regions are verified and the reasons of these instabilities are revealed.

Combining the intermetallic compound with the ductile metal at the eutectic composition is one promising method to improve the ductility of the intermetallic compound. This paper reports the microstructure and the micro-hardness of the Ni–Ni 3 Si eutectic in situ composites prepared by electron beam floating zone melting technique. Ni–Ni 3 Si eutectic in situ composites display regular lamellar eutectic structure at the solidification rate R =0.3–4.0 mm/min. The lamellar spacing is decreased with the increase of the solidification rate. The phase composition of the Ni–Ni 3 Si eutectic in situ composites is also determined by X-ray diffraction. Ni–Ni 3 Si eutectic in situ composites present lower micro-hardness than pure Ni 3 Si, although a small quantity of metastable Ni 31 Si 12 phase is formed during the directional solidification process.

Constitutive relationship of as-cast 904L austenitic stainless steel is comparatively investigated by the Arrhenius-type constitutive model incorporating the strain effect and back-propagation (BP) neural network. The experimental true stress–true strain data were obtained from hot compression tests on the Gleeble-1500D thermo-mechanical simulator in the temperature range of 1000–1150 °C and strain rate range of 0.01–10 s−1. The corrected data with the friction and the temperature compensations were employed to develop the Arrhenius-type model and BP neural network respectively. The accuracy and reliability of the models were quantified by employing statistical parameters such as the correlation coefficient and absolute average error. The results show that the proposed models have excellent predictabilities of flow stresses for the present steel in the specified deformation conditions. Compared with the Arrhenius-type model, the optimized BP neural network model has more accuracy and capability in describing the compressive deformation behavior at elevated temperature for as-cast 904L austenitic stainless steel.

Isothermal compression tests at temperatures of 1273–1473 K and strain rates ranging from 0.01 to 10 s −1 were preformed on Cr 20 Ni 25 Mo 4 Cu superaustenitic stainless steel to reveal the hot deformation characteristics. In order to give a precise prediction of flow behavior, the obtained experimental data was employed to derive the constitutive relationship incorporating the effect of strain. It is found that the effect of temperature and strain rate on flow stress is significant and their relationship can be represented by the Zener–Hollomon parameter including Arrheuins term. The material constant in the model, such as α , n , Q and ln A functioned by the strain is identified using sixth order polynomial. The flow stresses calculated by the developed model are reasonable agreement with the experimental ones, which indicates that the constitutive relationship can effectively describe the high temperature flow behavior of Cr 20 Ni 25 Mo 4 Cu superaustenitic stainless steel and can be used to numerically analyze the hot deformation process of the present material.

The hot workability of 00Cr13Ni5Mo2 supermartensitic stainless steel was investigated by hot compression and hot tension tests conducted over the temperature range of 950–1200 °C and strain rates varying between 0.1 and 50 s −1 . The processing map technique was applied on the basis of dynamic materials model and Prasad instability criterion. Microstructure evolutions, Zener–Hollomon parameter as well as hot tensile ductility were examined. The results show that, as for the hot working of 00Cr13Ni5Mo2 supermartensitic stainless steel in the industrial production, the large strain deformation should be carried out in the temperature range 1140–1200 °C and strain rate range 0.1–50 s −1 , where the corresponding Zener–Hollomon parameters exhibit low values. Moreover, when deformed under high strain rate range (above 15 s −1 ), the deformation temperature can be reduced reasonably.

The hot deformation behavior of 00Cr23Ni4N duplex stainless steel under medium–high strain rates (5–50 s − 1 ) has been analyzed using the Zener–Hollomon parameter and processing maps, which is based on compression tests made at temperatures ranging from 900 to 1150 °C. The results display the significant influence of high strain rate and high temperature on hot deformation behavior of 00Cr23Ni4N duplex stainless steel. A classical hyperbolic sine equation is applied to reveal the relations between the peak stress, strain rate and deformation temperature, in which the activation energy, Q and stress exponent, n are 263.4 kJ/mol and 2.6, respectively. The Zener–Hollomon parameters at low and high temperatures are calculated respectively to reflect the microstructural evolutions. Based on the processing map obtained, an ideal hot working condition for commercial processing is in the temperature range between 1075 and 1150 °C with a strain rate of 10 to 30 s − 1 . Under such condition, both ferrite and austenite dynamic re-crystallizations can be obtained and the corresponding Zener–Hollomon parameter is relatively low. Furthermore, the unstable domains are indicated by the processing map.