Insights into the oxidation resistance mechanism and tribological behaviors of multilayered TiSiN/CrVxN hard coatings

In the last decades,vanadium alloyed coatings have been introduced as potential candidates for self-lubrication due to their perfect tribological properties.In this work,the influence of V incorporation on the wear performance and oxidation resistance of TiSiN/CrN film coatings deposited by direct current(DC)reactive magnetron sputtering is investigated.The results show that vanadium incorporation significantly decreases the oxidation resistance of the coatings.In general,two layers are formed during the oxidation process:i)Ti(V)O_(2) on top,followed by a protective layer,which is subdivided into two layers,Cr_(2)O_(3) and Si-O.ii)The diffusion of V controls the oxidation of V-containing coatings.The addition of vanadium improves the wear resistance of coatings,and the wear rate decreases with increasing V content in the coatings;however,the friction coefficient is independent of the chemical composition of the coatings.The wear of the V-containing coatings is driven by polishing wear.

Steam Oxidation Resistance Comparison of Several Silicon Carbide Refractories at Elevated Temperatures

The oxidation tests of different SiC refractories including Si3N4-SiC bricks,Si3N4-Si2N2O-SiC bricks from China(SNO-1),Si3N4-Si2N2O-SiC bricks from overseas(SNO-2),SiAlON-SiC bricks,oxides bonded SiC bricks,self-bonded SiC bricks as well as SiC castables were carried out in the steam atmosphere(1 000 ℃,32 kg·m-3·h-1)for different durations(100,200,300,400 and 500 h).The mass,the volume,the bulk density and the apparent porosity before and after the oxidation were tested.The XRD and SEM analyses were conducted.The results indicate that:(1)under the steam atmosphere condition(1 000 ℃,32 kg·m-3·h-1),as the oxidation time increases from 0 to 500 h,the volume and the mass of the silicon carbide refractories increase,while the bulk density decreases;in terms of the apparent porosity,oxides bonded SiC bricks and SiC castables present an increasing trend,Si3N4-SiC bricks,SiAlON-SiC bricks and self-bonded SiC bricks present an increasing trend first and then a decreasing trend,and Si3N4-Si2N2O-SiC bricks present a decreasing trend or a trend of decreasing first and then increasing;(2)as for Si3N4-Si2N2O-SiC bricks,SNO-1 and SNO-2 have basically the same chemical and phase composition,SNO-2 has the lower mass change rate than SNO-1 during oxidation from 200-500 h,which indicates that SNO-2 has the better steam oxidation resistance than SNO-1.

Preparation and oxidation resistance of mullite/SiC coating for carbon materials at 1150 ℃

To protect carbon materials from oxidation, mullite/SiC coatings were prepared on graphite by chemical vapor reaction (CVR) and slurry sintering. The XRD analyses show that the phase of the outer-layer coating is composed of SiO2 and mullite, and the inner-layer coating is mainly composed of β-SiC. The anti-oxidation behavior of the coating and the Rockwell hardness (HRB) of the coating after oxidation were investigated. The oxidation test shows that the as-prepared multi-layer coating exhibits excellent antioxidation and thermal shock resistance at high temperature. After oxidation at 1150 ℃ for 109 h and thermal shock cycling between 1150 ℃ and room temperature for 12 times, the mass gain of the coated sample is 0.085%. Meanwhile, the indentation tests also demonstrate that the as-prepared coating has good bonding ability between the layers.

High temperature oxidation resistance and microstructure change of aluminized coating on copper substrate

The outermost coating with single phase Ni2Al3 was obtained on copper surface by electrodepositing nickel followed by slurry pack aluminizing at 800 °C for 12 h. The oxidation resistance and microstructure of the coating oxidized in ambient air at 1000 °C for 25-250 h were investigated using SEM, X-ray diffraction and optical microscope methods. The results show that the copper with single phase Ni2Al3 coating possesses the best high temperature oxidation resistance, and the mass gain of the coating is 1/15 that of pure copper and 1/2 that of nickel coating, respectively. The specimen surface after being oxidized for 25 h still comprises Ni2Al3 phase. However, when the time of oxidizing treatment increases to 50 h, the Ni Al phase is formed. It is also found that the Ni2Al3 phase completely turns into Ni Al phase after oxidizing treatment for 100 h and above. The Ni Al coating shows excellent high temperature oxidation resistance when oxidation time is 250 h.

Microstructure and high temperature oxidation resistance of Si-Y co-deposition coatings prepared on TiAl alloy by pack cementation process

In order to improve the high temperature oxidation resistance of TiAl alloy, Y modified silicide coatings were prepared by pack cementation process at 1030, 1080 and 1130 °C, respectively, for 5 h. The microstructures, phase constitutions and oxidation behavior of these coatings were studied. The results show that the coating prepared by co-depositing Si?Y at 1080 °C for 5 h has a multiple layer structure: a superficial zone consisting of Al-rich (Ti,Nb)5Si4 and (Ti,Nb)5Si3, an out layer consisting of (Ti,Nb)Si2, a middle layer consisting of (Ti,Nb)5Si4 and (Ti,Nb)5Si3, and aγ-TiAl inner layer. Co-deposition temperature imposes strong influences on the coating structure. The coating prepared by Si?Y co-depositing at 1080 °C for 5 h shows relatively good oxidation resistance at 1000 °C in air, and the oxidation rate constant of the coating is about two orders of magnitude lower than that of the bare TiAl alloy.

Oxidation Resistance of Flavonoids in Chinese Jujube Stone

[Objective] The aim was to study on the oxidation resistance of flavonoids in Chinese jujube stone. [Method] The extract of flavonoids from Chinese jujube stone was added to fresh rapeseed oil and lard to explore the oxidation resistance of flavonoids; the removal rates of it to O2-·,DPPH· and ·OH were also studied. [Result] The flavonoids from Chinese jujube stone had good oxidation resistance on rapeseed oil and lard,and the effects showed dose-dependent; citric acid and vitamin C appeared synergistic effects to the flavonoids; in free-radical reaction experiment,the flavonoids from Chinese Jujube stone also showed strong scavenging ability on O2-·,DPPH· and ·OH,in addition,the scavenging ability increased with concentration increasing. [Conclusion] The result of this study had provided theoretical basis for the further development and utilization of Chinese jujube resource.

Preparation of CIP@TiO_(2) composite with broadband electromagnetic wave absorption properties

Scholars aim for the improved impedance matching (Z) of materials while maintaining their excellent wave absorption properties. Based on the hydrolysis characteristics of isopropyl titanate, a simple preparation process for the coating of carbonyl iron powder(CIP) with TiO_(2) was designed. Given the TiO2coating, the Z of the CIP@TiO_(2) composite was adjusted well by decreasing the dielectric constant. Moreover, the interfacial polarization of CIP@TiO_(2) was enhanced. Ultimately, the electromagnetic-wave (EMW) absorption property of the CIP@TiO_(2)composite was improved substantially, the minimum reflection loss reached-46.07 dB, and the effective absorption bandwidth can reach 8 GHz at the composite thickness of 1.5 mm. Moreover, compared with CIP, the oxidation resistance of CIP@TiO_(2)showed remarkable improvement. The results revealed that the oxidation starting temperature of CIP@TiO_(2) as about 400℃,whereas the uncoated CIP had an oxidation starting temperature of approximately 250℃. Moreover, the largest oxidation rate temperature of CIP@TiO_(2) increased to around 550℃. This work opens up a novel strategy for the production of high-performance EMW absorbers via structural design.

Preparation of Al_2O_3/Au nano-laminated composite coatings and their oxidation resistance on stainless steel

Al2O3/Au nano-laminated composite coatings were prepared by means of magnetron sputtering. The coating was compact and comprised of nano-laminated Al2O3 and Au layers. High temperature cyclic oxidation test was employed to investigate the oxidation resistance of the composite coatings. The results revealed that the applied Al2O3/Au nano-laminated composite coatings improved the oxidation and spallation resistance of the stainless steel substrate significantly. The mechanism accounting for oxidation resistance was related with the suppression of inward oxygen diffusion and selective oxidation of Cr in the substrate. The mechanism accounting for spallation resistance was attributed to the relaxation of thermal stress by the nano-laminated structure.

Preparation and oxidation resistance of B_2O_3-coated boron-modified carbon foams

To improve the oxidation resistance of boron-modified carbon foams, the B2O3 coating was prepared on boron-modified carbon foams by low-cost slurry method. The microstructures and phase compositions of the coated carbon foams were characterized by scanning electron microscopy and X-ray diffraction, respectively. Oxidation resistances of uncoated and coated boron-modified carbon foams were investigated at 873 K in air. The results showed that as-received B2O3 coating could protect boron-modified carbon foams from oxidation at 873 K. B2O3-coated carbon foam doped with 7% B2O3 （mass fraction） （BO-7） had better oxidation resistance, exhibiting mass loss of 17.40% after oxidation at 873 K for 120 min. The melting glass layer formed on the surface of BO-7 could prevent oxygen from diffusing into boron-modified carbon foams substrate during oxidation to some extent.

PREPARATION AND PROPERTIES OF BULK CERAMICS VIA PYROLYSIS OF POLYCARBOSILANE WITH ACTIVE FILLERS II.FLEXURAL STRENGTH AND ANTI-OXIDATIVE PROPERTIES OF ACTIVE FILLER/PCS DERIVED BULK CERAMICS

The flexural strengths and oxidative resistant properties of the ceramics derived from polycarbosilane and active fillers (Ti, TiH 2, TiB 2, Cr, and CrSi 2) were measured and characterized. The introduction of active fillers enhances slightly the flexural strengths, and further densification is required to obtain higher strengths. The oxidative resistant behaviors of the specimens with active fillers are, by means of weight gain in air, poorer compared with those without active fillers.

Effect of antioxidants on the efficiency of jet milling and the powder characteristics of Sm2Co17 permanent magnets

This study investigated the effect of antioxidants on the grinding efficiency,magnetic powder characteristics,microstructure,and magnetic properties of 2:17 type SmCo permanent magnet materials.The results show that adding antioxidants helps improve the dispersion among magnetic powders,leading to a 33.3%decrease in jet milling time and a 15.8%increase in magnet powder production yield.Additionally,adding antioxidants enhances the oxidation resistance of the magnetic powders.After being stored in a constant temperature air environment at 25C for 48 h,the O content in the powder decreased by 33%compared to samples without antioxidants.While in the magnet body,the O content decreased from 0.21 wt.%to 0.14 wt.%,which helps increase the effective Sm content and domain wall pinning uniformity in the magnet.Excellent magnetic properties were obtained in the magnet with added antioxidants:B_(r)=11.6 kGs,SF=79.6%,H_(cj)=16.8 kOe,and(BH)_(max)=32.5 MGOe.

Improving mechanical properties and high-temperature oxidation of press hardened steel by adding Cr and Si

This work investigated the effect of Cr and Si on the mechanical properties and oxidation resistance of press hardened steel.Results indicated that the microstructure of the Cr-Si micro-alloyed press hardened steel consisted of lath martensite,M_(23)C_(6)carbides,and retained austenite.The retained austenite and carbides are responsible for the increase in elongation of the micro-alloyed steel.In addition,after oxidation at 930℃for 5 min,the thickness of the oxide scales on the Cr-Si micro-alloyed press hardened steel is less than 5μm,much thinner than 45.50μm-thick oxide scales on 22MnB5.The oxide scales of the Cr-Si micro-alloyed steel are composed of Fe_(2)O_(3),Fe_(3)O_(4),mixed spinel oxide(FeCr_(2)O_(4)and Fe_(2)SiO_(4)),and amorphous SiO_(2).Adding Cr and Si significantly reduces the thickness of the oxide scales and prevents the generation of the FeO phase.Due to the increase of spinel FeCr_(2)O_(4)and Fe_(2)SiO_(4)phase in the inner oxide scale and the amorphous SiO_(2)close to the substrate,the oxidation resistance of the Cr-Si micro-alloyed press hardened steel is improved.

Research of Oxidation Resistance of PVDF Hollow Fiber Membrane Used in Water Treatment

[Objective] The aim was to research the influences of different formulations on oxidation resistance of PVDF hollow fiber membrane.[Method]The immersion precipitation phase inversion method was employed to make casting solution with different formulations into hollow fiber membrane.The membrane was immersed in 1% NaClO solution for testing its performance changes.[Result]The membrane made by materials with bigger molecular weight had better oxidation resistance performance;the surfactant tween-80 could increase water flux,but lead to lower rupture intension;Pore-forming agent PEG400 do better than PVP in the oxidation resistance of membrane.[Conclusion]This study will provide a good idea for the development of the PVDF membrane with high oxidation resistance.

Microwave-assisted Synthesis of Al_(4)SiC_(4) and Its Effect on Properties of MgO-C Refractories

Al_(4)SiC_(4) was synthesized from Al powder, silicon carbide, and graphite by microwave sintering, and characterized by XRD and SEM. Then the synthesized material was added to the magnesia carbon refractory brick to study its effect on the oxidation resistance, apparent porosity, bulk density, elastic modulus, and modulus of rupture. It is found that Al_(4)SiC_(4) can be synthesized by microwave sintering at 1 300 ℃ and the addition of Al_(4)SiC_(4)-containing material as an antioxidant can enhance the oxidation resistance of the magnesia carbon refractory brick.

Effects of Al and N plasma immersion ion implantation on surface microhardness,oxidation resistance and antibacterial characteristics of Cu

A1 and N were introduced into copper substrate using plasma immersion ion implantation （PIII） in order to enhance its hardness and oxidation resistance. The dosage of N ion is 5 × 1016 cm-2, and range of dosage of A1 ion is 5× 1016-2× 1017 cm-2. The oxidation tests indicate that the copper samples after undergoing PIII possess higher oxidation resistance. The degree of oxidation resistance is found to vary with implantation dosage of AI ion. The antibacterial tests also reveal that the plasma implanted copper specimens have excellent antibacterial resistance against Staphylococcus aureus, which are similar to pure copper.

Layer Dependence of Graphene for Oxidation Resistance of Cu Surface

We studied the oxidation resistance of graphene-coated Cu surface and its layer dependence by directly growing monolayer graphene with different multilayer structures coexisted, di- minishing the influence induced by residue and transfer technology. It is found that the Cu surface coated with the monolayer graphene demonstrate tremendous difference in oxidation pattern and oxidation rate, compared to that coated with the bilayer graphene, which is considered to be originated from the strain-induced linear oxidation channel in monolayer graphene and the intersection of easily-oxidized directions in each layer of bilayer graphene, respectively. We reveal that the defects on the graphene basal plane but not the boundaries are the main oxidation channel for Cu surface under graphene protection. Our finding indicates that compared to putting forth efforts to improve the quality of monolayer graphene by reducing defects, depositing multilayer graphene directly on metal is a simple and effective way to enhance the oxidation resistance of graphene-coated metals.

Effect of Cerium on Microstructures and High Temperature Oxidation Resistance of An Nb-Si System In-Situ Composite

Nb-16Si-24Ti-6Cr-6A1-2Hf-xCe （x =0, 0.05, 0.1,02.5, 0.5, 1 （%, atom fraction）） in situ composites were prepared by arc melting The microstmcture and the effect of rare earth element cerium on 1250℃ oxidation resistance of the composites were investigated with scanning electron microscopy （SEM） and X-ray energy disperse spectrum （EDS）, as well as X-ray diffraction （XRD）. The experimental results showed that the high temperature oxidation resistance of the alloy was improved by adding a proper amount of cerium （Ce）. The effect of Ce was considered as the concurrent of the following three factors： first, the oxide of Ce formed in the interface reduced the internal oxidation rate; second, the lath shaped oxide containing Ce increased the cracking resistance and reduced the expansion of the oxide scale; and third, the decrease of the sificide volume fraction on account of Ce addition reduces the power of the sample resisting oxygen penetration.

MoSi_2 oxidation resistance coatings for Mo_5Si_3/MoSi_2 composites

In order to improve the oxidation resistance properties of 30 at.% Mo5Si3/MoSi2 composite at high temperature in air, a molybdenum disilicide coating was prepared on its surface by a molten salt technology. XRD and SEM analysis showed that only tetragonal MoSi2 phase existed in the coating after being siliconized for 5 h at 900℃. The oxidation film formed on the uncoated sample was not dense, so that oxygen diffused easily through it. The volatilization of MoO3 resulted in the oxidation film separating from the substrate. The MoSi2 coating was proved to be an effective method to prevent 30 at.% Mo5Si3/MoSi2 composites from being oxidized at 1200℃. A dense glassy SiO2 film was formed on the MoSi2 coating surface, which acted as a barrier layer for the diffusion of oxygen atoms to the substrate. The 30at.% MosSi3/MoSi2 composites with a MoSi2 coating showed much better oxidation resistance at high temperature.

Effects of composite scale on high temperature oxidation resistance of Fe-Cr-Ni heat resistant alloy

Fe-Cr-Ni heat resistant alloys with aluminum and silicon addition, alone and in combination, were melted using an intermediate frequency induction furnace with a non-oxidation method. By the oxidation weight gain method, the oxidation resistances of the test alloys were determined at 1,200 ℃ for 500 hours. According to the oxidation weight gains, the oxidation kinetic curves were plotted and the functions were regressed by the least squares method. The results show that the oxidation kinetic curves follow the power function of y = ax^b （a〉0, 0〈b〈1）. The effects of scale compositions on oxidation resistance were studied further by analyses using X-ray diffraction （XRD） and scanning electron microscope （SEM）. It is found that the composite scale compounds of Cr203, a-Al2O3, SiO2 and FeCr2O4, with compact structure and tiny grains, shows complete oxidation resistance at 1,200℃. When the composite scale lacks a-Al2O3 or SiO2, it becomes weak in oxidation resistance with a loose structure. By the criterion of standard Gibbs formation free energy, the model of the nucleation and growth of the composite scale is established. The forming of the composite scale is the result of the competition of being oxidized and reduced between aluminum, silicon and the matrix metal elements of iron, chromium and nickel. The protection of the composite scale is analyzed essentially by electrical conductivity and strength properties.

Effect of nano-size nickel particles on wear resistance and high temperature oxidation resistance of ultrafine ceramic coating

In order to improve the wear resistance and high temperature oxidation resistance of titanium and titanium alloy, the high temperature ultra fine ceramic coating containing nano-size nickel particles was prepared by flow coat method on the surface of industrially pure titanium TB1-0. The effects of nano-size nickel particles on the wear resistance and high temperature oxidation resistance of coating substrate system were investigated through oxidation kinetics experiment and wear resistance test. The morphologies of the specimens were examined by means of optical microscopy, scanning electron microscopy and X-ray diffraction. The results show that the high temperature ultra fine ceramic coating has notable protection effect on industrially pure titanium TB1-0 from oxidation. The oxidation and wear resistance properties of the coating can be effectively improved by adding nano-size nickel particles. The oxidative mass gain of the specimen decreases from 11.33 mg·cm-2 to 5.25 mg·cm-2 and the friction coefficient decreases from 1.1 to 0.6 by adding nano-size nickel particles, and the coating containing 10% （mass fraction） nano-size nickel shows the optimum properties.