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Herein, the effects of Gd2O3 on the laser cladding NiCoCrAlYTa coatings in terms of microstructure, phase structures, high temperature oxidation behaviors were investigated. The results showed that the addition of Gd2O3 changed the composition of coating phases, promoted homogeneous phase distribution, reduced porosity and improved coating density. During oxidation at 1100 °C for 150 h, the increase in the content of added Gd2O3 (at mass fractions of 0, 0.5, 1, 2, 5 and 10%) exhibited an initial inhibitory and then increased effect on the weight-gain rate of the coatings. Overall, 1% Gd2O3 addition resulted in the greatest improvement in the oxidation resistance of the coatings, with 49.58% decreases in oxidation kinetic constants, respectively, compared with those of unmodified coatings. However, at a Gd2O3 content of 10%, the thermally grown oxide on the coating surface exhibited large flaking areas. The high-temperature oxidation kinetic parameters of the coatings exhibited an inverted parabolic form with increasing Gd2O3 content. The higher Gd2O3 content led to the formation of excessive oxygen diffusion channels along grain boundaries, which is the reason for the decrease in the anti-oxidant performance of the coating. [ABSTRACT FROM AUTHOR]

In this work, rare-earth elements Eu and Y were added to La2Zr2O7 (LZ) as doping elements, and the ceramic coating of (La0.5Eu0.25Y0.25)2Zr2O7 (LEYZ) was prepared. The evolution of the sintering resistance, thermal shock resistance, and thermal insulation properties of the multi-element rare-earth co-doped modified coatings under long-term and high-temperature conditions was studied. The results showed that the sintering resistance of the doped coating was significantly improved, and the coating still does not fall off after 200 h at 1100 °C. The thermal shock life of the coating at 1000 °C is increased by 47% compared with that of the undoped modified LZ coating. The length of the vertical cracks in LEYZ ceramic layer is obviously shorter than that in LZ coating, which will be more beneficial to preventing the coating from peeling off. Compared with LZ coating, the insulation temperature of the LEYZ ceramic coating is increased by 24, 26 and 34% in the range of 900 ~ 1100 °C, respectively. The coating has the best thermal insulation effect, which is consistent with theoretical calculation results. The results demonstrate that the modified lanthanum zirconate coatings doped with Europium and Yttrium has great potential in high-temperature performance. [ABSTRACT FROM AUTHOR]

We study the vanishing shear viscosity limit and incompressible limit of two dimensional compressible dissipative elastodynamics systems near the equilibrium. The large value of the volume viscosity forces the limit system to be incompressible, and the vanishing shear viscosity indicates that the limit system is inviscid. Due to the weak dispersive estimate in dimensions two and the lack of the null structures in nonlinear terms, the generalised energy method (Klainerman and Sideris in Commun Pure Appl Math 49(3):615–666, 1996; Sideris in Ann Math 151(2):849–874, 2000; Sideris and Thomases in Commun Pure Appl Math 58(6):750–788, 2005), combined with the "ghost weight" method in (Alinhac in Invent Math 145(3):597–618, 2001), guarantees the global-in-time convergence from compressible dissipative elastodynamics to incompressible elastodynamics with the help of vector fields. [ABSTRACT FROM AUTHOR]

Nanostructured carbon diffusion layers were produced on the 18Cr2Ni4WA low carbon steel using supersonic fine particles bombarding (SFPB) with activated carbon powders and low-temperature annealing at 500 °C. The microstructures and the formation mechanism of hard nanocrystalline carbon diffusion layers were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and molecular dynamics simulation. Additionally, the nano-hardness of the diffusion layer was measured by nanoindentation apparatus and the tribological properties were tested by wear tester. The results show that the thickness of the hard nano-carburized layer is about 20 μm. During SFPB treatment, high-speed Al2O3 particles carrying activated carbon powder impact on the surface of 18Cr2Ni4WA steel, resulting in the formation of high-density dislocations and nano-surface structure, and a large amount of carbide precipitates at grain boundaries and internal defects. The carbon content of the steel surface increased from 0.17 to 4.2% (wt.%). After annealing treatment, the nano-hardness of the carburized layer reaches 7.6 GPa and the friction coefficient decreases to 0.63. [ABSTRACT FROM AUTHOR]

The effects of supersonic particle bombardment (SFPB) on the microstructure, microhardness and wear property of Ti6Al4V alloy prepared by laser metal deposition (LMD) were investigated in this paper. The electrochemical corrosion behaviors of the LMDed Ti6Al4V alloy samples before and after SFPB treatment in 3.5% NaCl solution were measured. The results showed that a gradient severe deformation layer of ~ 350 μm thickness was formed with refined equiaxed grains oriented in various directions on the surface of LMDed Ti6Al4V alloy after SFPB treatment. The microhardness of the deformation layer was significantly increased due to the plastic deformation, grain refinement, dislocations and deformation twins increment. After SFPB treatment, the LMDed Ti6Al4V exhibited higher wear resistance which is about 55.6% decrease in wear loss than that of the untreated sample. Moreover, the corrosion resistance and corrosion rate of the SFPB-treated samples in 3.5% NaCl solution improved due to the finer hexagonal grains and high density of grain boundary in the severe deformation layer. [ABSTRACT FROM AUTHOR]

A grain fine surface plastic deformation layer with a thickness of about 108.6 ± 1.5 μm was fabricated on 20Cr2Ni4A steel by supersonic fine particle bombardment (SFPB). The microstructure, wettability, and tribological properties of original and SFPB-treated (including Co-SFPB samples: activated carbon was added to the bombarded powder (Al2O3) followed by SFPB; Precoat + SFPB samples: the activated carbon is precoated on the surface of the original material followed by SFPB) low carbon steel were characterized by optical microscope (OM), scanning electron microscope (SEM), static water contact angle, friction, and wear test. The results show that SFPB can refine the surface microstructure and the grain size is about 21 nm. The surface hardness is as high as 428.1 HV0.2, which is 89.3% higher than the original samples. Compared with the residual stress of the original samples (− 116.7 MPa), the residual stress on the surface of Precoat + SFPB samples (− 333.8 MPa) is significantly increased. The measurement results of static water contact angle illustrate that Precoat + SFPB samples have the best hydrophobicity (133.4°). After the treatment of SFPB, 20Cr2Ni4A steel is worn for a certain time, combined with the comprehensive analysis results of friction coefficient, mass loss, and wear morphology, Precoat + SFPB samples have the best wear resistance, which is due to its high surface hardness, large residual compressive stress, and the alloying layer formed by pre-coating activated carbon under the SFPB. [ABSTRACT FROM AUTHOR]

This work concerns the incompressible limit of compressible viscoelastic systems when the shear viscosity converges to zero. The incompressible limit is characterised by the large value of the volume viscosity. In the limit, the dispersive effect of pressure waves disappears and the global convergence to the limit system around an equilibrium is justified with the help of vector fields. [ABSTRACT FROM AUTHOR]

The welding solidification crack is a common welding defect occurring in the narrow gap laser welded high-strength steel joint, which poses a detrimental effect in reducing the weld quality. However, the relationship between the weld geometric characteristics and the metallurgical characteristics with the solidification crack of the narrow gap laser weld is still unclear. In this study, a 20-mm-thick 10Ni5CrMoV high-strength steel with a root gap of 3 mm and groove angle of 1º was used to analyze the single-pass welding process of narrow gap laser welding using high-frequency beam oscillation. The correlation between the weld form factor and the welding solidification crack was discussed, alongside with the clarification on the influence of the welding process parameter on the welding solidification crack, the aim of which was to analyze the causes for the formation of welding solidification crack and explore the effective ways to suppress it. The results showed that the influence of welding process parameters on welding solidification crack could be attributed to change in the form factor of the weld and weld metal solidification crystallization characteristics. The smaller the weld form factor, the larger the area of the opposite crystal growth in the upper part of the weld cross section, and the higher the tendency toward solidification crack formation. Furthermore, the higher welding speed was also likely to have columnar grains with a larger angle of crystallization direction with the centerline. This resulted in a higher tendency of solidification crack formation. Under the test conditions used in this study, a weld form factor φ = 0.8 was considered effective for controlling welding solidification crack. [ABSTRACT FROM AUTHOR]

The directional array TiN-reinforced AlCoCrFeNiTi high-entropy alloy (HEA) coatings were successfully synthesized by magnetic field-assisted laser cladding on Ti-6Al-4V (TC4) alloy. The effect of magnetic induction intensity of AlCoCrFeNiTi HEA coatings was investigated methodically on thermodynamic calculation, microstructure characterization and corrosion resistance. The results show HEA coatings are mainly composed of body-centered cubic (BCC) solid solution phase, (Ni, Co)Ti2 intermetallic compound and TiN ceramic phase. With 1 T magnetic induction intensity assisted laser cladding, the microstructures of in situ TiN display a "cross" shape of the directional array. In 3.5 wt.% NaCl solution, the 1 T HEA coating could significantly decrease the corrosion rate compared with TC4 alloy. [ABSTRACT FROM AUTHOR]

The directional array TiN-reinforced AlCoCrCuNiTi high-entropy alloy (HEA) coating was designed and the correlative coating was successfully synthesized by magnetic-field-assisted laser cladding on Ti-6Al-4V (TC4) alloy. The effect of the directional array TiN on the phase structure, microstructure, microhardness and wear resistance of HEA coating were investigated methodically. As a result, the HEA coatings are mainly composed of body-centered-cubic solid solution phase, (Ni, Co)Ti2 inter metallic compound and TiN ceramic phase. With 1 T magnetic induction intensity assisted laser cladding, the microstructure of in-situ TiN displays a "cross" shape of the directional array. And the coating shows excellent wear resistance with an average microhardness of 760 HV. The worn surface morphologies of HEA coatings show that the wear mechanism is adhesive wear regardless of whether a magnetic field is added. This work can provide a novel and effective method to synthesize directional array microstructures to improve the performance of HEA coating, which will promote the further application of directional array microstructures in advanced manufacturing fields. [ABSTRACT FROM AUTHOR]

Growing evidence suggested that microRNAs (miRNAs) contributed to the progression of Crohn's disease (CD), but the exact physiological functions of many miRNAs in CD patients still remain illusive. In this study, we explore the potent pathogenicity of miRNAs in CD. Expressions of miRNAs and aryl hydrocarbon receptor (AHR) protein were determined in the colitic colon of 2,4,6-trinitrobenzenesulfonic acid (TNBS)-induced colitis mice and CD patients. Colitis was induced in wild-type (WT), miR-124a overexpression (miR-124a-Nju), and AHR knockout (AHR−/−) mice. Intestinal barrier function was evaluated in colitis mice and Caco2 monolayers. There was a negative relationship between miR-124a and AHR protein in inflamed colons from CD patients. MiR-124a-Nju and AHR−/− mice treated with TNBS had more severe intestinal inflammation than WT mice. Both miR-124a-Nju mice and AHR−/− mice underwent evident intestinal barrier destruction, and anti-miR-124a administration could reverse this dysfunction in miR-124a-Nju mice but not in AHR−/− mice. In vitro studies revealed that miR-124a mimics downregulated the expression of AHR and tight junction proteins and induced hyperpermeability by increasing miR-124a expression, which was abrogated by miR-124a inhibitor and AHR antagonist FICZ. This study suggests that miR-124a can induce intestinal inflammation and cause intestinal barrier dysfunction by supressing AHR. [ABSTRACT FROM AUTHOR]

The aim of this work is to study the effect of solution treatment time on the Ti2Ni second phase morphology, phase transformations, mechanical properties and superelastic behavior of plasma arc deposited (PAD) nitinols. The results demonstrate that the Ti2Ni second phases are significantly affected by the solution treatment time. The Ti2Ni second phase is dissolved into the TiNi matrix phase gradually, and its size and volume fraction also gradually decreases with increasing solution treatment time. Additionally, the solution treatment time exhibits a visible influence on the phase transformation, mechanical properties and superelasticity of the PAD nitinol, but the degree of influence depends on the size, volume fraction and distribution of the Ti2Ni second phase. With increasing solution treatment time, the phase transformation temperatures gradually increase, and the phase transformation peaks decrease in width and become sharp with a single transformation. Besides, the compressive strength first increases and then decreases, while the plasticity increases with solution treatment time increases from 0 to 8 h. Moreover, the superelastic stability of the PAD nitinol is improves as the solution treatment time increases from 0 to 6 h and then decreases. This phenomenon is closely related to the critical stress for dislocation slip, which depends on the change in the Ti2Ni second phase. [ABSTRACT FROM AUTHOR]

A Ni-Cr-Co-Ti-V-Al high-entropy alloy (HEA) coating with a BCC phase and (Ni, Co)Ti compounds was synthesized successfully by laser surface alloying on a Ti-6Al-4V substrate. The microstructure of as-synthesized coatings is typical, namely, the microstructure from the coating to the substrate changes from equiaxed grains to columnar grains. After remaining at 900 °C for 8 h, the constituent phases remain unchanged. However, owing to the unceasing dissolution of the Ti element, the lattice parameter of the BCC HEA phase changes from 3.06 Å to 3.16 Å. The thermoanalysis results show that the oxidation film on the Ni-Cr-Co-Ti-V-Al HEA coating is mainly composed of TiO, VO, and NiO. The oxidation resistance of this HEA coating may be due to the existence of NiO and the alloying elements Al, Cr, and Co; the oxidation phenomenon should be responsible for the mass increase in the thermogravimetry process. The differential scanning calorimetry and the dynamic differential scanning calorimetry curves show that the synthesized HEA coating is stable below 1005 °C. [ABSTRACT FROM AUTHOR]

Brush plating provides an effective method for creating a coating on substrates of various shapes. A corroded zirconium-based conversion coating was removed from the surface of a magnesium alloy and then replaced with new coatings prepared via brush plating. The structure and composition of the remanufactured coating were determined via x-ray photoelectron spectroscopy, x-ray diffraction, and Fourier transform infrared spectroscopy. The results revealed that the coatings consist of oxide, fluoride, and tannin-related organics. The composition of the coatings varied with the voltage. Furthermore, as revealed via potentiodynamic polarization spectroscopy, these coatings yielded a significant increase in the corrosion resistance of the magnesium alloy. The friction coefficient remained constant for almost 300s during wear resistance measurements performed under a 1-N load and dry sliding conditions, indicating that the remanufactured coatings provide effective inhibition to corrosion. [ABSTRACT FROM AUTHOR]

A Ni/Ti composite coating enhanced by an in situ synthesized TiN phase was fabricated on FV520B steel by plasma cladding technology. The in situ formation of the TiN phase was confirmed by XRD, SEM, and TEM. The cladding layer consisted of three regions on going from the top to the bottom, namely, columnar grain regions, columnar dendritic regions, and fine grain regions. The cladding layer was composed of NiTi, TiN, (Fe, Ni), and Ti phases. The dendritic and columnar regions were mainly composed of the NiTi and (Fe, Ni) phases. The Ti phase was observed at the branches of dendrite crystals and columnar grains. The volume fraction of the TiN phase in the cladding layer was about 3.2%. The maximum micro-hardness value of the in situ formed coating (760 HV) was higher than that of the pure coating (537 HV). The cladding layer had a small amount of scratch and wear debris when a load of 20 N was used. As the test load increased, the wear debris in the cladding layer also increased and the massive furrows were not observed. [ABSTRACT FROM AUTHOR]

The new carboxylic acid-neodymium anhydrous conversion films were successfully prepared and applied on the AZ91D magnesium alloy surface by taking absolute ethyl alcohol as solvent and four kinds of soluble carboxylic acid as activators. The corrosion resistance of the coating was measured by potentiodynamic polarization test in 3.5 wt.% NaCl solution in pH 7.0. The morphology, structure, and constituents of the coating were observed by scanning electron microscope, energy dispersivespectrum, x-ray photoelectron spectrum, and Fourier infrared spectrometer. Results show that corrosion resistance properties of samples coated with four different anhydrous conversion films were improved obviously. The corrosion potential increased, corrosion current density decreased, and polarization resistance increased. Among these four kinds of conversion films the one added with phytic exhibits the best corrosion resistant property. The mechanism of anhydrous-neodymium conversion film formation is also analyzed in this paper. It reveals that the gadolinium conversion coating is mainly composed of stable NdO, MgO, Mg(OH), and carboxylate of Nd. And that the sample surface is rich in organic functional groups. [ABSTRACT FROM AUTHOR]

The service condition determines the Rolling Contact Fatigue(RCF) failure mechanism and lifetime under ascertain material structure integrity parameter of thermal spray coating. The available literature on the RCF testing of thermal spray coatings under various condition services is considerable; it is generally difficult to synthesize all of the result to obtain a comprehensive understanding of the parameters which has a great effect on a thermal spray coating's resistance of RCF. The effects of service conditions(lubrication states, contact stresses, revolve speed, and slip ratio) on the changing of thermal spray coatings' contact fatigue lifetime is introduced systematically. The effects of different service condition on RCF failure mechanism of thermal spray coating from the change of material structure integrity are also summarized. Moreover, In order to enhance the RCF performance, the parameter optimal design formula of service condition and material structure integrity is proposed based on the effect of service condition on thermal spray coatings' contact fatigue lifetime and RCF failure mechanism. The shortage of available literature and the forecast focus in future researches are discussed based on available research. The explicit result of RCF lifetime law and parameter optimal design formula in term of lubrication states, contact stresses, revolve speed, and slip ratio, is significant to improve the RCF performance on the engineering application. [ABSTRACT FROM AUTHOR]