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The oxidation of 3Cr3Mo2NiW and 3CrNi3Mo steels was studied at 600 °C in air, and the test results suggest that the parabolic rate law fitted the oxidation kinetics of both steels. The microstructure, morphology, structure, and phase composition of the oxide film cross-sectional layers of the two Cr-Ni-Mo hot-work die steels were analyzed using scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), and X-ray diffraction (XRD). The influences of Cr, Ni, and Mo on the high-temperature oxidation resistance of the two Cr-Ni-Mo hot-work die steels are discussed, and the oxidation mechanism is summarized. Heat-treated samples were analyzed using electron backscattered diffraction (EBSD) to obtain inverse pole figures (IPFs) and average sample grain sizes, and the percentages of twin grain boundaries (TGBs) (θ = 60°) were also measured. After heat treatment, recrystallization was observed in both steels with a large portion of twin grain boundaries. After 10 h of oxidation, the dense chromium-rich oxide layer that formed in the inner oxide layer of 3Cr3Mo2NiW steel effectively prevented the continuation of oxidation. The inner oxide layer in 3CrNi3Mo steel formed an adhesion layer with a network structure composed mainly of Ni- and Cr-rich spinel oxide, without forming a barrier to prevent oxidation. [ABSTRACT FROM AUTHOR]

This paper reports an experimental study on the microstructure and corrosion resistance of electro-less Ni-P coatings with increasing content of the rare element cerium (Ce). Surface morphology and the composition of the electro-less Ni-P coatings were studied by scanning electron microscope (SEM), X-ray energy dispersed analysis (EDS) and X-ray diffraction analysis (XRD). Hardness and Adhesive force are researched by a HX-200 Vickers diamond indenter micro-hardness tester. Furthermore, we study the adhesive force by using the Revetest scratch tester. We get the possession of Ce amorphous Ni-P coatings which has excellent properties in anti-corrosion. The effect of the rare element cerium concentration on corrosion resistance of the coatings was evaluated in the groundwater immersion test and porosity test, respectively. The results indicated that added little the rare element cerium into the plating bath increased the phosphorus content of the coatings, decreased the corrosion rates, it also decreases the porosity of the amorphous Ni-P coatings. The lowest corrosion rates of the amorphous Ni-P coatings in groundwater immersion test is 4.1 um · h-1, at the rare element cerium concentration of 0.12g · L-1.

Ti-Ni composite sub-micron powders with different compositions were prepared by vacuum melting and atomization technology. These powders, after being mixed with a solution of phenolic resin and alcohol, were applied on the mold cavity wall, by which a casting-infiltration layer was introduced on the surface of ZG45 steel via reactions between the powders and molten steel under the heat released by solidification. The effects of the powders' composition and pouring temperature on the corrosion resistance of the casting-infiltration layer were studied. An optimal casting-infiltration layer with a thickness of ∼7 mm was obtained by infiltrating the Ti-Ni composite powders containing 35wt.% Ti to ZG45 steel pouring at 1,650 °C. The casting-infiltration layer has a good metallurgic bonding with the matrix, and is mainly composed of Fe2Ti phase and continuous γ-(Fe, Ni) solid solution. In the corrosive H2SO4 solution, the corrosion potential of the casting-infiltration layer is lower than the matrix, tending to form a passivation film, which lowers the dissolution rate especially when the potential rises to 0.50 V. After dipping in the 10wt.% NaCl solution for 480 h, a lot of corrosion holes appear in the ZG45 steel matrix, while there are no obvious traces of corrosion on the casting-infiltration layer. [ABSTRACT FROM AUTHOR]

The influences of thermal annealing on the microstructural and tribological properties of amorphous carbon nitride films were investigated. X-ray photoelectron spectroscopy, Raman spectroscopy, and Fourier transform infrared spectrometer were utilized to characterize bond configuration and chemical state of the films. The results indicated that at low annealing temperatures (200 and 300 °C), the volatile species and surface contamination are easily dissociated without obvious bulk modification; while at high annealing temperatures (400 and 500 °C), the microstructure of carbon nitride films changed and favored a graphitization process, which indicated the growth of more graphitic film structures. The faint Raman signal of C≡N decreased with annealing temperature (TA) and completely disappeared at TA of 500 °C, indicating that nitrile bonds were thermal unstable under high temperature. Surprisingly, the tribological properties of the films showed a remarkably decreasing in friction coefficient as the TA increased; it is attributed to the graphitization of carbon nitride films during thermal annealing, which favored transfer film formation between the carbon nitride films and counterface materials. The transfer films benefit the decrease in coefficient of friction. [ABSTRACT FROM AUTHOR]

The structure, mechanical properties, and friction properties of hydrogenated graphitelike carbon film and typical hydrogenated diamondlike carbon film were investigated comparatively that the hydrogenated graphitelike carbon film has relatively high sp2 content and low bonded hydrogen content and possessed high hardness and elasticity. It was attributed to the curved graphene microstructure, which is able to form three-dimensional covalently bonded network. Furthermore, in comparison with the hydrogenated diamondlike carbon film, the hydrogenated graphitelike carbon film demonstrated excellent friction behavior probably due to the extraordinary structure of hydrogenated graphitelike carbon film. [ABSTRACT FROM AUTHOR]

The spot continual induction hardening (SCIH) process, which is a modified induction hardening, can be assembled to a five-axis cooperating computer numerical control machine tool to strengthen more than one small area or relatively large area on complicated component surface. In this study, a response surface method was presented to optimize phase transformation region after the SCIH process. The effects of five process parameters including feed velocity, input power, gap, curvature and flow rate on temperature, microstructure, microhardness and phase transformation geometry were investigated. Central composition design, a second-order response surface design, was employed to systematically estimate the empirical models of temperature and phase transformation geometry. The analysis results indicated that feed velocity has a dominant effect on the uniformity of microstructure and microhardness, domain size, oxidized track width, phase transformation width and height in the SCIH process while curvature has the largest effect on center temperature in the design space. The optimum operating conditions with 0.817, 0.845 and 0.773 of desirability values are expected to be able to minimize ratio (tempering region) and maximize phase transformation width for concave, flat and convex surface workpieces, respectively. The verification result indicated that the process parameters obtained by the model were reliable. [ABSTRACT FROM AUTHOR]

Spot continual induction hardening (SCIH) is a surface heat treatment process, which can strengthen more than one small area or relative large area on complicated component surface. In order to investigate the microstructure and mechanical properties of gray cast iron with curved surface after SCIH, the microstructure, microhardness and residual stresses were analyzed under different process conditions. The results showed that the martensite grain in hardened region of concave surface was larger than that of convex surface. The domain sizes of concave and convex surfaces were smaller than that of matrix region due to the high heating rate in SCIH process. The phase transformation depth increased with the increasing of convex surface radius but decreased with the increasing of concave surface radius. The maximum values of residual tensile and compressive stresses increased with the increasing of feed velocity for convex and concave surfaces, respectively. The appearance positions of maximum tensile and compressive stresses were closer to center for convex and concave surfaces, respectively, when feed velocity increased from 1 to 5 mm/s. The achieved results indicated that the SCIH with relatively low feed velocity was more suitable for improving the mechanical properties of gray cast iron. Compared with convex surface, the concave surface of workpiece can obtain better mechanical properties under the same feed velocity of inductor. [ABSTRACT FROM AUTHOR]

An numerical and experimental study of spot continual induction hardening (SCIH) for AISI 1045 steel was carried out to gain a better understanding of this non-stationary and transverse flux induction hardening treatment. The SCIH device was set up by assembling the single-turn coil inductor to a five-axis cooperating computer numerical control system. The influence of inductor velocity, input current, and quenching medium on temperature field was estimated via the SCIH model, and the simulated micro-hardness and microstructure were validated by experimental verification. The heating delay phenomenon appearing in the SCIH process had been analyzed. [ABSTRACT FROM AUTHOR]

Loading hydrogels with ozone for antibacterial activity is an important research topic for expanding clinical applications. In particular, hydrogel network constructs and storage and controlled release of massive ozone amounts are research emphases. In this paper, a nanoclay crosslinked nanocomposite hydrogel with a bionic three-dimensional porous network structure formed by two-dimensional lamellar montmorillonite was incorporated into polyacrylamide through a crosslinking reaction, which provided enhanced mechanical properties and abundant ozone adsorption sites. The clay-based nanocomposite hydrogel had the enlarged pore structure (11.7 µm) and a stable Young's modulus (75.82 GPa), which also provided a guarantee for the highly ozone adsorption capacity. The nanocomposite exhibited timely bactericidal and long-term antibacterial effects on Staphylococcus aureus , which provides ideas for the development and application of inexpensive clay minerals in the biomedical antibacterial field. [Display omitted] • Clay-based nanocomposite hydrogel formed by 2D lamellar MMT incorporate into PAM. • Clay-based hydrogel has clear pore structure, enhanced mechanical properties. • Bionic Clay-based nanocomposite can achieve stable ozone storage and release. • Hydrogel has instant bactericidal action and long-term wound protecting. [ABSTRACT FROM AUTHOR]

Abstract: The influence of shot peening on microstructure of laser hardened 17-4PH was investigated by using X-ray diffraction profiles. The domain size, microstrain and dislocation in different depths were calculated via Voigt method and dislocation density calculation method according to Williamson''s work. Two typical materials in laser hardened 17-4PH (matrix material and laser hardened material) and three families of crystalline planes ({110}, {200}, {211}) were chosen as research objects. Microstructural results from XRD investigation quantified the shot peening influence on microstrain, domain size and dislocation density in microstructure changed layer in these three plane diffraction directions. Results showed that shot peening was an efficient cold working method to alter microstructure in near surface region and microstructure strengthening mechanism of shot peening played an important role on improving the surface mechanical properties. In microstructure changed layer, the domain size increased and microstrain as well as dislocation density decreased with depth increasing, which led to the mechanical properties decrease with depth increasing. With increasing peening intensity from 0.2mmA+0.1mmA to 0.5mmA+0.1mmA, the depth of microstructure changed layer increased but the surface microstructure did not change, no matter in matrix material or laser hardened material. As laser hardened material had a stronger resistance against shot peening influence on microstructure, the depth of microstructure changed layer in matrix material was larger than that in laser hardened material when same peening intensity was carried out on these two materials. The variation of domain size, microstrain and dislocation density in depth in {110}, {200} and {211} diffraction directions represented shot peening could alter material microstructure in all plane diffraction directions in microstructure changed layer. [Copyright &y& Elsevier]

Abstract: The aim of the present research was to investigate the influence of different substrate roughness on structure and mechanical properties of Titanium Aluminium Nitride (TiAlN) coatings. Tungsten carbide rectangular block was used as substrate. Different surface roughness was achieved by using grinding discs with different grain sizes and diamond polishing powder, and TiAlN coatings were deposited on these substrates under the same preparation technique and parameters. Morphologies of substrates and coatings, crystal structure, thickness and mechanical properties of coatings were investigated using optical microscope, AFM, XRD, CSM scratch tester and tribometer. It was shown that surface morphology of cathodic arc TiAlN coating was mainly affected by the morphology of the substrate surface and the coating growth process. The influence of substrate roughness on crystal structure and thickness of the coatings could be ignored. With the decreasing of the substrate roughness, the adhesion force between coating and substrate increased. Three stresses model was applied to interpret this result. The wear resistance of the coating was also improved with decreasing the substrate roughness. [Copyright &y& Elsevier]

Abstract: In order to investigate the influence of shot peening on microstructure of laser hardened steel and clarify how much influence of initial microstructure induced by laser hardening treatment on final microstructure of laser hardened steel after shot peening treatment, measurements of retained austenite, measurements of microhardness and microstructural analysis were carried out on three typical areas including laser hardened area, transitional area and matrix area of laser hardened 17-4PH steel. The results showed that shot peening was an efficient cold working method to eliminate the retained austenite on the surface of laser hardened samples. The surface hardness increased dramatically when shot peening treatments were carried out. The analyses of microstructure of laser hardened 17-4PH after shot peening treatment were carried out in matrix area and laser hardened area via Voigt method. With the increasing peening intensity, the influence depth of shot peening on hardness and microstructure increased but the surface hardness and microstructure did not change when certain peening intensity was reached. Influence depth of shot peening on hardness was larger than influence depth of shot peening on microstructure due to the kinetic energy loss along the depth during shot peening treatment. From the microstructural result, it can be shown that the shot peening treatment can influence the domain size and microstrain of treated samples but laser hardening treatment can only influence the microstrain of treated samples. [ABSTRACT FROM AUTHOR]

ZnO-based varistor ceramics were prepared at sintering temperatures ranging from 900 °C to 1,300 °C, by subjecting the mixed oxide powders to high-energy ball milling (HEBM) for 0, 5, 10 and 20 h, respectively. Varistor ceramics prepared by HEBM featured denser body, better electrical properties sintered at low-temperature than at traditional high-temperature. The high density is due to the refinement of the crystalline grains, the enhanced stored energy in the powders coming from lattice distortion and defects as well as the promotion of liquid-phase sintering. Good electrical properties is attributed to proper microstructure formed at low-temperature and improved grain boundary characteristics resulting from HEBM. With increasing sintering temperatures, the electrical properties and density became worse due to the decrease in amount of Bi-rich phase. Temperature increased up to 1,200 °C or above, the Bi-rich phase vanished and the ceramics exhibited very low nonlinear coefficient. [ABSTRACT FROM AUTHOR]

Abstract: Single-crystalline α-Fe2O3 with a micro-snowflake-like morphology has been synthesized though a hydrothermal reaction in a K3[Fe(CN)6] solution without the assistance of any template or surfactant. The morphology and structure of the synthesized hematite were characterized in detail by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. A possible growth process of α-Fe2O3 crystals has been proposed, and NaOH plays a crucial role in the formation of the snowflake-like structure. Additionally, magnetic investigations show that the α-Fe2O3 crystals exhibit a weakly ferromagnetic property at room temperature with a coercive force of 134Oe and remnant magnetization of 0.67emu g−1. [Copyright &y& Elsevier]

Selective laser sintering (SLS) combined with reaction melt infiltration was used to fabricate Si–SiC ceramic matrix composites, and the effects of different concentrations of phenolic resin (PF) on the properties of the SLS green body and carbonized and final Si–SiC samples were investigated. The results showed that the impregnation with PF can increase the bulk density, reduce the porosity of the samples at all stages, and improve the mechanical properties of the reactive bonded samples. The degree of densification and mechanical properties of the sample gradually enhanced with an increase in PF concentration. The main phases of the Si–SiC composites were free Si, α-SiC, β-SiC, plus an extremely small amount of Al–Si alloy, and the SiC and the Si phase contents increased and decreased, respectively, as the concentration of PF increased when measured using Rietveld refinement and image analysis software. The macroscopic properties of the samples improved greatly after precursor infiltration pyrolysis (PIP) treatment with 66.7%vol PF-ethanol solution twice. According to the crystal nucleation-growth theory, it was inferred that the infiltrated PF could provide a certain amount of pyrolytic carbon in the carbonized specimen. During the reaction bonded process, the carbon formed by carbonization pyrolysis first dissolves into the molten Si and reaches saturation. With the further dissolution of carbon, [C] and [Si] in the liquid phase contact each other to form β-SiC nuclei, the nuclei that precipitate at the pore wall position and gradually form a continuous interfacial layer of β-SiC. The β-SiC layer prevents the liquid Si from direct contact with C inside the prefabricated body, therefore, further reactants diffuse through the layer. Finally, the fine crystalline β-SiC grains were fabricated inside the specimen. [ABSTRACT FROM AUTHOR]

Spot continual induction hardening (SCIH) is a surface heat treatment process, which can strengthen more than one small area or relative large area on complicated component surface. In order to investigate the difference between AISI 1045 and 5140 steels on the microstructure and mechanical properties after SCIH, the microstructure, microhardness and residual stresses with different process parameters were analyzed. The results showed that there was only martensite in hardened area of AISI 5140 steel specimens while a mixture of martensite and pearlite was found in hardened area of AISI 1045. The domain size of both materials in {110} diffraction direction in hardened area was smaller than matrix area and decreased with the increasing of inductor feed velocity. The hardness distributions on the surface and in depth of AISI 5140 were more uniform than that of AISI 1045 due to the alloy element chromium, which can delay the transformation from austenite to pearlite. The surface compressive stress in hardened area decreased and tensile stress in transitional area increased with the increasing of feed velocity in both material conditions. The achieved results indicate that the SCIH with relatively low feed velocity is more suitable for improving the mechanical properties of both materials. [ABSTRACT FROM AUTHOR]

This work systematically studied the effects of stress shot peening (SSP) on the microstructure, residual stress and hardness of the ultrafine-grained Al 18 B 4 O 33 whisker reinforced Al-Mg-Si matrix composite (Al 18 B 4 O 33 w/Al-Mg-Si) by the modified Warren-Averbach method, X-ray diffraction stress equipment, transmission electron microscopy and hardness tester. The results showed that conventional shot peening generated a gradient deformation layer of the Al 18 B 4 O 33 w/Al-Mg-Si with ultrafine grains (200–400 nm) near the surface layer. By contrast with conventional SP, SSP effectively induced superior microstructures at the deformed zone with finer crystalline size and more dislocations. In parallel, SSP effectively enhanced the compressive residual stress (CRS) distribution with a higher magnitude of surface CRS (−83 MPa) and maximum CRS (−152 MPa) value and deeper affected depth along the loading direction. The fragmentized whisker during SSP acted as the pinning role on the dislocation movements, which was beneficial for grain refinement and CRS improvement. It is concluded that SSP technique can be regarded as an effective process of improving the surface properties of ultrafine-grained Al 18 B 4 O 33 w/Al composite. • A gradient ultrafine grained layer was developed by shot peening. • Stress shot peening induced smaller crystalline size, more dislocations and weaker texture. • Stress shot peening produced higher-level compressive residual stress and stiffer surface layer. • The fractured Al 18 B 4 O 33 whiskers during shot peening contribute to the improvement of surface characteristics. [ABSTRACT FROM AUTHOR]

Abstract: The major difficulty in fabricating hydroxyapatite (HA) coating on titanium substrate using the electrophoretic deposition (EPD) process is the full densification and crack prevention of the coating under the restricted sintering temperature. In this work, a combination of electrophoretic deposition and reaction bonding process was developed for the fabrication of HA/alumina (Al2O3) composite coating and HA functionally gradient coating (FGC) on titanium substrates at a relatively low sintering temperature of 850°C. The results showed that the reaction bonding process enhances the coating''s densification. The HA FGC with a thickness of about 40μm was crack-free and exhibited obvious gradient variation in chemical composition and microstructure. The HA FGC also exhibited much higher bonding strength than HA coating with the same thickness. [Copyright &y& Elsevier]

In this paper, we report a new method for synthesizing carbon nanotubes (CNTs) and other carbon nanostructures such as carbon nanoparticles (CNPs) through catalytic thermolysis of natural cotton fibers. Using the new method, long CNTs (L-CNTs), which could reach to 20 μm or longer, can be readily synthesized from natural cotton fibers under hydrogen environment at a thermolysis temperature around 1200 °C. The analysis of the microstructure of synthesized L-CNTs showed that the CNT growth from the catalytic thermolysis of cotton fibers may not undergo a carbon-containing gas generation step that is different from most of other growth methods. We further studied the dielectric and electromagnetic wave (EMW) absorption properties of synthesized CNTs by embedding them in a epoxy matrix. The measurement results show that complex dielectric permittivity ɛ and EMW absorption ratio of the composites strongly depend on CNT loading in the frequency range from 8 to 26 GHz. [ABSTRACT FROM AUTHOR]