Surface Investigation of Ni81Fe19 Thin Film: Using ARXPS for Thickness Estimation of Oxidation Layers

This work demonstrates the dependence between magnetic properties and the thickness of NiFe thin films. More importantly, a quantitative study of the surface composition of NiFe thin film exposed to atmospheric conditions has been carried out employing angle-resolved X-ray photoelectron spectroscopy (ARXPS). In this study, we fabricated Ni81Fe19 (NiFe) thin films on Si (100) substrate using electron beam evaporation and investigated their surface morphologies, magnetic properties, and the thickness of the surface oxide layer. The coexistence of metallic and oxidized species on the surface are suggested by the depth profile of ARXPS spectra. The thickness of the oxidized species, including NiO, Ni(OH)2, Fe2O3, and Fe3O4, are also estimated based on the ARXPS results. This work provides an effective approach to clarify the surface composition, as well as the thickness of the oxide layer of the thin films.

Isothermal Oxidation Behavior of FGH720Li Superalloy at Service Temperatures

The oxidation behavior of FGH720Li(P/M Udimet720Li) superalloy was investigated under static atmosphere in temperature ranging from 600°C to 730°C. The oxidation kinetics, composition and morphology of the oxidation layers were characterized by means of isothermal oxidation tests, X-ray diffraction(XRD), scanning electron microscopy（SEM）and energy dispersive X-ray spectroscopy(EDS). The results showed that the oxidation kinetics curves of FGH720Li superalloy followed the parabolic law. The results of cross-sectional morphology and elemental distribution indicated that the oxidation layer could be divided into three parts：porous Cr2O3 outer layer, dense Cr2O3 medium layer and oxidation affected zone with nail-like Al2O3 inner layer. The oxidation process was primarily controlled by the diffusion of chromium and oxygen through the oxide scale.

High-temperature oxidation behavior of SiBN fibers in air

SiBN fibers are one of the most admirable microwave-transparent reinforced materials for high Mach number aircrafts. Currently, the detailed high-temperature oxidation behavior of SiBN fibers has not been studied yet. In this work, we studied the high-temperature oxidation behavior of SiBN fibers with different boron contents at the temperature range of 1000–1400 °C in air. SiBN fibers started to be oxidized at 1100 °C, with Si3N4 and BN phase oxidized to SiO2 and B2O3, respectively. Due to the gasification and the escape of molten B2O3 at high temperatures, amorphous SiO2 could be remained at the fiber surface. As the fiber further oxidized, the molten B2O3 at the inside may infiltrate into the fiber interior to react with Si3N4, causing the precipitation of hexagonal boron nitride (h-BN) nanoparticles and the formation of SiO2/BN layer. Finally, complex oxidation layers with two distinct concentric sublayers accompanied with two transition sublayers could be formed after the oxidizing treatment.

High-temperature oxidation behavior of SiBN fibers in air

SiBN fibers are one of the most admirable microwave-transparent reinforced materials for high Mach number aircrafts. Currently, the detailed high-temperature oxidation behavior of SiBN fibers have not been studied yet. In this work, we researched the high-temperature oxidation behavior of SiBN fibers with different boron contents at the temperature range of 1000 ~ 1400℃ in air. SiBN fibers started to be oxidized at 1100℃, with Si3N4 and BN phase oxidized to SiO2 and B2O3, respectively. Due to the gasification and the escape of molten B2O3 at high temperature, amorphous SiO2 could be remained at the fiber surface. As the fiber further oxidized, the molten B2O3 at the inside may infiltrate into the fiber interior to react with Si3N4, causing the precipitation of h-BN nanoparticles and the formation of SiO2/BN layer. Finally, complex oxidation layers with two distinct concentric sublayers accompanied with two transition sublayers could be formed after the oxidizing treatment.

Effect of Temperature on Tribological Properties of Cu/Ti3AlC2 Composites

In aerospace and power generation, components will serve in high-temperature environments. In this work, the influence of temperature on the tribological performances of Cu/Ti3AlC2 composites was investigated from 25 °C to 700 °C. Cu/Ti3AlC2 composites were fabricated by hot-pressing at 800 °C. The friction coefficients of the composites were in the range of 0.19–0.28. From 25 °C to 300 °C, the wear-rates increased with temperature from 9.05 × 10−5 mm3/Nm to 110 × 10−5 mm3/Nm, and the wear-rate reached the highest value at 300 °C. Interestingly, the wear-rates plummeted to 30.8 × 10−5 mm3/Nm at 500 °C, and 31.2 × 10−5 mm3/Nm at 700 °C. It was found that tribofilms consisting of Ti3AlC2 and Cu2O covered on the wear surfaces at 25 °C and 100 °C. Plastic flow and material transfer occurred at 300 °C. From 500 °C to 700 °C, oxidation layers formed on the wear surfaces of the composites. For simplicity, a schematic of the tribological mechanisms is proposed.

ANNEALING BEHAVIOR OF Ni-TiO2 NANOCOMPOSITES

Ni-TiO2 nanocomposite have been prepared by electrodeposition. The microstructure and tribological behavior of Ni-TiO2 nanocomposite before and after annealing have been investigated compared with as-deposited Ni-TiO2 composite. The results demonstrated that TiO2 nanoparticles usually collected along the grain boundaries and nickel grains changed from columnar grains into equiaxed grains after annealing. HRTEM photographs indicated that the diffusion between crystalline nickel and TiO2 nanoparticles did happen after annealing. Wear results indicated that the main wear mechanism of as-deposited Ni-TiO2 nanocomposite was adhesion wear. The wear resistance of Ni-TiO2 nanocomposite heat-treated is better than as-deposited Ni-TiO2 nanocomposite because the oxidation layers on the worn surface of Ni-TiO2 nanocomposite masked the strengthening effect of small grain size. The corrosion behavior also has been studied and it is found that annealing reduces the corrosion resistance of composite coatings.

Internal Material Flow Layers in AA6082-T6 Butt-Joints during Bobbin Friction Stir Welding

Bobbin friction stir welding with a double-sided tool configuration produces a symmetrical solid-state joint. However, control of the process parameters to achieve defect-free welds is difficult. The internal flow features of the AA6082-T6 butt-joints in bobbin friction stir welding were evaluated using a set of developed reagents and optical microscopy. The key findings are that the dark curved patterns (conventionally called 'flow-arms'), are actually oxidation layers at the advancing side, and at the retreating side are elongated grains with a high-density of accumulation of sub-grain boundaries due to dynamic recrystallization. A model of discontinuous flow within the weld is proposed, based on the microscopic observations. It is inferred that the internal flow is characterized by packets of material ('flow patches') being transported around the pin. At the retreating side they experience high localized shearing at their mutual boundaries, as evidenced in high density of sub-grain boundaries. Flow patches at the advancing side are stacked on each other and exposed to oxidization.

Effect of Hydrogen on the Wear Resistance of Steels upon Contact with Plasma Electrolytic Oxidation Layers Synthesized on Aluminum Alloys

The different nature of the effect of hydrogen on the tribological behavior of two carbon steels (st. 45 and st. U8) upon their contact with super solid plasma electrolytic oxidation (PEO) layers synthesized on two light alloys (AMg-6 and D16T alloys as the analogists of the A 95556 UNS USA and AA2024 ANSI USA alloys correspondently) was investigated in the medium of mineral oil of the I-20 type. To compare the effect of hydrogenation on the tribological properties of the analyzed contact pairs, similar tests were also performed on the same mineral oil with clear water or an aqueous solution of glycerine added to its content. A spinel-type film (hercynite) was formed upon friction of two contacting surfaces—the iron-carbon steels and PEO layers synthesized on the AMg-6 alloy. This film was a reliable protection against wear of the surface subjected to the effect of hydrogen. When steels came into contact with the PEO layers synthesized on the D16T alloy, surface protection against wear was ensured by another mechanism. The phenomenon of selective metal transfer in the friction zone (from one to another friction surfaces) was revealed.