Formation Of Mixed Layer Research Articles

Research on the oxidation behavior and oxidation mechanism of NiCrAl-bentonite abradable seal coatings at 650 °C

To study the oxidation behavior and microstructure transformation mechanism of NiCrAl-bentonite abradable seal coatings (ASCs), the NiCrAl-bentonite ASCs were prepared on GH4169 substrate with NiAl as the bonding layer, and the oxidation experiments were carried out at 650 °C at different time (24 h, 48 h, 72 h, 96 h, 144 h, 192 h). The evolution of surface, interior, and interface microstructure of the coating with different oxidation time was analyzed through X-ray diffractometer (XRD) and scanning electron microscope (SEM). The results indicated that the microstructure changes of the coating surface were as follows: the initiation of spot-like oxide → the growth of acicular oxide → the production of continuous oxidation film → the generation of NiO. The internal microstructure changes of the coating were as follows: the formation of Cr oxide layer → the formation of mixed oxide layer. The microstructure changes of the coating's interface were as follows: the initiation and growth thickening of the oxide layer. Element diffusion and oxygen partial pressure controlled the overall oxidation behavior of the coating. The formation of NiO and α-Al2O3 on the surface of coating after oxidation for 192 h at 650 °C had a bad effect on the service performance of the coating.

Effect of diffusion barriers on steam oxidation properties and interface evolutions of Cr coating for zirconium alloy at 1200 °C

Under the ATF design concept, Cr-based coating is the most promising zirconium alloy cladding protective coating in the case of PWR accidents. However, the primary factor affecting the oxidation resistance of Cr coatings is the interdiffusion of Cr and Zr. In this study, Cr coatings with three refractory metal interlayers of Nb, Mo, and Ta were deposited on zirconium alloy surfaces using closed-field unbalanced magnetron sputtering. The study investigated the effects of different interlayers on the microstructure, oxidation properties, and interface evolution process of Cr coatings under steam conditions at 1200 ℃, and compared them with Cr coatings without intermediate layers. The results indicate that the refractory metal interlayer influences the orientation and growth rate of Cr coating grains. The formation of a Laves phase mixed layer in the interlayer during oxidation effectively hinders the diffusion of O and Cr to the zirconium alloy matrix, enhancing its oxidation resistance. Furthermore, the diffusion rate and vacancy concentration of Mo and Ta elements to the Zr layer exceed that of diffusion to the Cr layer. During the cooling process, a precipitate phase forms in the Zr-4 matrix, while the Nb coating forms an infinite solid solution in the β-Zr.

Wear behaviour analysis of thermo-mechanically processed AA7075 and AA7075/SiC/Graphite composite

The current work focuses on investigating the tribological performance of AA7075 alloy and AA7075 hybrid composite with SiC and graphite reinforcements of 2 and 0.5 wt percentages, respectively. The alloy and hybrid composite are fabricated through stir casting and thermo-mechanically processed through hot rolling routes. Dry sliding wear characterization has been carried out using a pin-on-disc wear testing setup for alloy and composite under various processing conditions using experiments designed according to Taguchi's L9 orthogonal array. The technique for order preference by similarity to ideal solution (TOPSIS) method has been adopted to achieve a single multi-response index (MRI) considering the minimization of multiple objective functions for specific wear rate (SWR) and coefficient of friction (COF). The analysis of variance (ANOVA) results of the MRI indicated that sample processing condition and load were the most significant parameters. The wear mechanism at different experimental conditions was studied using Scanning electron microscope (SEM) micrographs, energy dispersive spectroscopy analysis and 3D surface profile of wear track. The AA7075 composites are found to be comparatively good in all experimental conditions compared to the base alloy due to load-bearing SiC particles and solid lubricant graphite as reinforcing elements. The mechanically mixed layer (MML) formation in hybrid composites helped achieve good tribological properties. The AA7075 alloy and hybrid composites cross rolled at 350 °C yielded better results than other samples. The wear mechanism was abrasive and adhesive at low temperature and low load conditions in both alloy and hybrid composites. Whereas, at higher temperatures and high loads oxidative wear mechanism with delamination was prevalent. The transition of SWR from mild to severe value occurs at 250 °C in all experimental cases. The specific wear rate was improved by 85.64 % between worst and best conditions, i.e., annealed alloy and cross rolled composite.

Diffusion of alloying elements during high temperature oxidation in a low-cost third generation Ni-based single crystal superalloy

Diffusion of alloying elements in a low-cost third generation Ni-based single crystal superalloy during oxidation at high temperature was investigated. The evolution of oxide layers depended on dominant diffusion of alloying elements at different stages of oxidation. Outward diffusion of Cr, Co and Ni was dominant at initial stage of oxidation, resulting in the formation of (Ni, Co)O and Cr2O3. Diffusion of Al and Ta was restricted in γ/γ' area, but dominant in γ'-free layer. Due to outward diffusion of other elements, passive enrichment of refractory elements, Re, W, Mo and Ta included, caused the formation of mixed oxides layer. Finally, selective oxidation of Al led to the formation of (Ni, Co)Al2O4 and Al2O3 layer.

Research on oxidation kinetics of CoNiCrAlY coatings in pure steam environment

The investigation carried out on CoNiCrAlY coatings oxidation behavior in both pure steam and atmospheric environments using cyclic oxidation experiments at 1100 °C revealed distinct variations in the oxidation kinetics. In pure steam, the early stage of exposure causes an acceleration in the growth rate of TGO, which however stabilizes after 92 h. Steam has an impact on the movement of species at TGO grain boundaries, thus aiding internal O diffusion and the creation of a homogeneous α-Al2O3 scale. However, atmospheric oxidation of TGO results in a complicated double-layer oxidation configuration and worsens mixed oxide layer formation at the peak.

Characterization of Structural Stability of Magnetron Sputtered Tungsten-boron Thin Films at Elevated Temperatures

In the divertor of the tokamak type fusion reactors tungsten and tungsten-covered plasma facing materials are currently among the selected materials. However, metallic, high-Z plasma facing materials require plasma mitigation. Recent researches show, that mitigation with boron can be used for optimizing plasma operations, while the interactions between boron containing plasma and tungsten plasma facing materials are less investigated. The formation of mixed layers and their behaviour under plasma operations as well as reactor maintenance procedures needs to be estimated. In order to estimate properties of tungsten-boron mixed layers, such layers can be produced by deposition methods, such as the magnetron sputtering technique and further characterized and analysed. Magnetron sputtered tungsten-boron films were oxidized up to 600 °C. Prior and after thermal treatment infrared spectra and electron microscopy images of the films were registered. For comparison, W films with no addition B of were deposited. Selected parts of the films were etched, to analyse temperature dependent edge effects. Mass changes at ~ 400 – 500 °C can be attributed to the corresponding oxidation processes. The structure analysis and infrared spectrometry show the formation of W-O and W=O bonds. The obtained results will be applied for recommendations for the production of W-B thin films for microelectronic devices.

Lacustrine Shale Diagenesis—A Case Study of the Second Member of the Funing Formation in the Subei Basin

Shale diagenesis differs from that of sandstone and carbonate rocks with regard to the type, evolution stage, and evolution mode. The quality of shale reservoirs is closely linked to the extent of diagenetic evolution. This study identifies the types and characteristics of shale diagenesis using thin sections and scanning electron microscopy (SEM) observations. The stages of shale diagenesis are determined by analyzing organic matter evolution and clay mineral transformation and establishing a diagenetic evolution sequence. This paper describes the comprehensive diagenetic evolution of organic matter, clay minerals, clastic particles, and carbonate minerals to determine the diagenesis types, diagenetic sequences, and pore evolution occurring during diagenetic evolution. The results show that the diagenesis types of shale in the second member of the Funing Formation include compaction, dissolution, cementation, metasomatism, dolomitization, syneresis, and transformation of clay minerals, as well as thermal evolution of organic matter. The middle diagenetic A stage is prevalent, with some areas in the early and middle diagenetic B stages. The shale underwent a diagenetic evolution sequence, including the collapse and shrinkage of montmorillonite interlayers in the early stage; the rapid formation and transformation of illite and smectite mixed layers, massive hydrocarbon generation of organic matters, and dissolution of unstable components in the middle stage; and the occurrence of fractures filled with gypsum, quartz, ferrocalcite, or other authigenic minerals in the later stage. Dissolution pores and fractures are the dominant shale reservoirs of the second member of the Funing Formation in the Subei Basin. The results provide new insights into understanding the formation and evolution of reservoir spaces during shale diagenesis and information for the exploration and development of lacustrine shale oil and gas.

Impact of Polyamide Surface Preparation on the Formation of Mixed CdS-CdTe Layers

CdTe-CdS layers were formed on polyamide (PA) 6 films with different surface modifications using the sorption-diffusion method. Part of the samples of the PA films was boiled in distilled water for 2 h and the other ones were stored in concentrated acetic acid at 20 °C for 0.5 h. After this stage, all the PA 6 films were chalcogenized at 20 °C for 1 or 5 h using an acidified 0.1 mol/L solution of K2TeS4O6. Then, the chalcogenized samples were treated with a 0.1 mol/L solution of cadmium acetate at 70, 80 or 90 °C for 10 min. The elemental and phase composition and the morphological and optical properties of the obtained films were determined. XRD analysis showed that cadmium chalcogenide layers consist of four phases: hexagonal CdTe, orthorhombic CdS, rhombohedral Te and orthorhombic S18. The average crystallite size among the obtained layers was very similar and was in the range of 36–42 nm. The concentrations of cadmium, sulfur and tellurium in the layers on PA 6 and the optical properties of the CdTe-CdS layers were dependent on the method of preparation of the polyamide film, the duration of chalcogenization and the temperature of the Cd(CH3COO)2 solution.

Film-forming amines adsorption and corrosion kinetics on carbon steel surface in neutral solution investigated by EIS and PM-IRRAS analysis

N-oleyl-1, 3-propanediamine (OLDA) is one of the most used film-forming amines (FFAs) for the corrosion protection of carbon steel circuits of a wide range of industrial plants. The present work focused on the study of OLDA adsorption kinetics onto the carbon steel surface by electrochemical impedance spectroscopy (EIS). The diagrams were obtained in a 200 mg.kg−1 NaCl with and without OLDA for immersion times ranging from 2 min to 140 min and for two temperatures (25°C and 50°C). It was shown that, from the beginning of immersion (2 min), OLDA adsorption and corrosion occurred simultaneously on the carbon steel surface. With increasing immersion time, a dynamic and competitive process between both phenomena was established until a steady-state was reached and the corrosion was slowed down. Ex situ Raman spectroscopy analyses revealed a heterogeneous distribution of the OLDA molecules on the surface with a preferential adsorption on the corrosion products, mainly γ-FeOOH. Ex situ Polarization Modulation Infrared Reflection Absorption Spectroscopy (PM-IRRAS) analyses confirmed the formation of mixed barrier layers (OLDA molecules/corrosion products) whose thickness increased with time and temperature.

The effect of recrystallization annealing on the tungsten surface carbidization in a beam plasma discharge

<abstract> <p>Tungsten was chosen as the plasma facing material (PFM) of the ITER divertor. However, graphite and carbon-graphite materials are used as PFM in some research thermonuclear facilities, including the Kazakhstan materials science tokamak. This circumstance determines the interest in continuing the study of the formation of mixed layers under plasma irradiation. This article is devoted to the study of the effect of preliminary recrystallization annealing on the carbidization of the tungsten surface in a beam-plasma discharge (BPD), which is one of the ways to simulate the peripheral plasma of a tokamak. Experiments on preliminary isochoric and isothermal annealing of tungsten samples were carried out in the mode of direct heating of tungsten samples by an electron beam. The carbidization of tungsten samples after annealing was carried out in a methane atmosphere in the BPD at a temperature of 1000 ℃ for a duration of 3600 s. Optical microscopy (OM) and X-ray diffraction were used to analyze the structure of the tungsten surface. It has been established that differences in the structure arising during recrystallization annealing affect the transfer of carbon atoms in the near-surface area of tungsten and the formation of tungsten carbides (WC or W<sub>2</sub>C).</p> </abstract>

Bentonite clays of the Central Kyzylkum and their material composition and engineering and geological properties, Uzbekistan

The authors consider the conditions of occurrence, composition, and properties of the Eocene clays of the Paleogene, common in the northern part of Tamdytau, which were the foundation of the structures. The present study of the authors is aimed at studying the problem of the long-term interaction of Eocene clays with water and identifying the features of changes in their material composition and properties; the variability of the composition, properties of clays, and the reasons for these changes are analyzed. The main factors determining the differences in the composition and properties of Paleogene clays are: genetic - different salinity of the sea basin or less saline at which the reservoirs were connected with the open sea; zonal-climatic - different humidity and other physical properties. So far, no unified methodology has been developed for predicting the composition and properties of clays at the base of structures when interacting with water. The results of granulometric analysis established that Paleogene clays are classified as highly dispersed soils containing more than 55% of clay particles. Analysis of the diffraction pattern showed that the clay fraction of the studied samples contain montmorillonite (M), hydromica (H), kaolinite (K), mixed-layer formations of the montmorillonite-hydromica series.

Wear behavior and wear mechanism of iron foam reinforced SiCp/A359 interpenetrating phases composites at high temperature

The A359-SiCp/Fe interpenetrating phase composites reinforced with three-dimensional network structure iron foam and 20 wt. % SiC particles were fabricated after the infiltration technique by using the newly developed vacuum assisted infiltration procedures. The dry-sliding tribological behavior of A359-SiCp/Fe composites was investigated using the HT-1000 ball-on-disc type high temperature tribometer. The samples were subjected to a variety of temperatures and applied loads to investigate the influence on the wear rate and friction coefficient. In this study, SEM was used to analyses the wear microscopic morphology of A359-SiCp/Fe composites reinforced by iron foam. The wear longitudinal section and the morphology of the wear debris were analyzed by EDS and determined to explore the high-temperature wear mechanism under different temperatures and loads. Hardness analysis from the outer periphery to the core revealed an improvement in hardness. The hardness distribution of the wear longitudinal section is different at different temperatures. The formation of a high-hardness mechanical mixed layer with a different thickness on the wear surface can effectively reduce the wear rate. Microstructural investigations demonstrated that the change in wear debris shape with increasing temperature is mostly related to the change in wear mechanism. Abrasive wear and oxidation wear are the main wear mechanisms. With an increase in temperature and plastic deformation, delamination and adhesion are the predominant wear mechanisms, accompanied by the additional oxidative wear.

Effects of aluminosilicate particles on tribological performance and friction mechanism of Cu-matrix pads for high-speed trains

The effects and mechanism of mullite and kyanite on the friction and wear of copper-based brake pads for high-speed trains were studied. The braking performance was tested at different speeds using a pin-disc tester. The physical properties, element distribution and tribo-film formation were investigated using the hardness tester, density meter, SEM, EDS and XRD. The results showed that the braking performance of materials with 1% kyanite was optimal. The friction coefficient was the most stable and the wear rate reduces over 30%. Kyanite can promote the formation of primary platform and mechanical mixing layer, thus accelerating the tribo-film generation to protect the surface. Moreover, the wear mechanism was elucidated by characterizing the changes of worn surface, wear debris and tribo-film.

Deuterium Retention in Mixed Layers with Application in Fusion Technology

Formation of Be-W mixed layers in thermonuclear fusion reactors can potentially alter the retention of hydrogen isotopes and affect the retention and release properties of these isotopes. This paper reports on the retention and release characteristics of D from reference Be, W layers as well as three Be-W mixed layers with well-defined atomic concentrations (2:1, 1:1, 1:2). The layers resulted from the sputtering of Be and W materials in Ar:D (1:1) mixture at 2 Pa using DC magnetron sputtering. The mixed layers’ deposition parameters were varied to adjust accordingly the deposition rate for each material in order to obtain the desired concentrations. Scanning electron microscope images showed that morphology is independent of composition for samples deposited on silicon substrates. In contrast, layers deposited on tungsten revealed a textured surface and morphological changes with W concentration variation. X-ray diffraction patterns of mixed layers evidenced the presence of a polycrystalline tungsten phase. Additionally, the degree of crystallinity is highly influenced by the plasma parameters and enhanced amorphization is evidenced by a decrease of crystalline size by a factor of 10 for mixed layers compared to the W reference layer. The release behavior of D from the layers is affected by the trapping contribution of both Be and W. Compared with implanted layers, presented in literature studies, the co-deposited layers show a high D occupancy of low energy trapping states, the majority of the D retained in the samples being released at temperatures below 623 K. High energy trapping becomes more pronounced for layers with a high Be concentration. The oxygen contamination observed for Be layers points to a mitigation of D retention in low energy trapping states and shifts the desorption chart towards a higher temperature due to enhanced retention in BeO associated traps. The D retention presents a linear decrease of W concentration in the sample.

Investigation on mechanical and tribological properties of AA6061/Gr composites for solar header pipes

Solar header pipes desire light weight material with extensive mechanical and tribological property at high temperature. In this research work, an attempt was made to reinforce AA6061 aluminium alloy with Graphite particles through Stir Casting (SC) and Compo Casting (CC) technique for solar header pipes. The uniform dispersion of reinforcing particles over the matrix was confirmed through Scanning Electron Microscope (SEM). The tensile, hardness and wear experiments were performed on composites at elevated temperature. The wear experimental runs were designed using Taguchi mixed orthogonal array by varying temperature, applied load, sliding velocity, sliding distance and reinforcing weight percentage. The composites produced through CC method exhibit 3.8% and 2.7% higher hardness and tensile strength in comparison with SC. At elevated temperature of 300 C, the composites exhibit better wear resistance owing to the formation of Mechanical Mixed Layer (MML). The wear rate of composites at elevated temperature was three times higher than the room temperature owing to reduction in density and deformation of material. ANOVA table reveals that the most influencing process parameters was temperature followed by the load and percentage reinforcement. The worn surface morphology was analyzed using SEM. Because of the improved dispersion of reinforced particles, the composites generated by CC have higher mechanical and tribological qualities at elevated temperatures, and are considered as an alternative material for solar header pipes.

Surface modification of Hastelloy processed by the Cu mixed electric discharge alloying technique

ABSTRACT An attempt was made in this study to coat Hastelloy with copper carbide utilizing an electric discharge alloying process. Experiments were carried out in such a way that materials were initially removed from the surface, but after a prescribed time in the absence of flushing, it was coated on the surface. Experiments were conducted by varying copper powder concentration, current, pulse on time, and gap distance and experimental runs were designed using the Taguchi mixed orthogonal array. Pure dielectric medium materials were removed from the surface, at 5 g l−1 PMEDM material removal followed by deposition occurred, beyond 10 g l−1 PMEDM condition, only material deposition was observed. Surface topography revealed that the cracks formed on the coated surface with an increase in Cu concentration get intensified and penetrated the base material. The hardness and wear resistance of coated samples are enhanced owing to the presence of harder carbide particles and mechanically mixed layer formation. The mode of wear was adhesive and abrasive for the uncoated and coated samples.

Investigation of mechanical and tribological behavior of SiC and B4C reinforced Al-Zn-Mg-Si-Cu alloy matrix surface composites fabricated via friction stir processing

In this study, SiC and B4C reinforced Al-Zn-Mg-Si-Cu alloy matrix surface composites (SCs) were produced by friction stir processing (FSP) technique. Microstructural, mechanical, and tribological properties of produced SCs, and those of non-reinforced samples were examined. In B4C and SiC reinforced SCs fabricated by friction stir processing, approximately a 20% increase in hardness was achieved as compared to the base metal. The maximum microhardness values of B4C and SiC reinforced surface composites were determined as 88.1 and 89.7 HV, respectively. The tensile strengths of these samples were measured as 166.42 and 174.74 N·mm−2, respectively. As a result of the tests performed under 3, 5, and 10 N applied loads, it was observed that the friction coefficient decreased in general with the applied load. A higher coefficient of friction was obtained in SiC reinforced SCs than those of B4C reinforced SCs and non-reinforced samples. It was determined that the wear rate of B4C reinforced SCs decreased by ~30–40% and SiC reinforced SCs by ~50–55% compared to non-reinforced samples. In the examinations, it was revealed that mechanically mixed layer formation effectively reduced wear rate in these samples compared to non-reinforced samples.

High energy braking behaviors and tribo-map constructions of Cu metal matrix composites with different Cr volume contents

Cr, a promising abrasion component, has been introduced into Cu metal matrix composites (Cu-MMCs) to improve their high-energy braking performance. The Cu–Cr interfacial characteristics, worn surface/subsurface morphologies, and effect of Cr on the high energy braking behaviors of Cu-MMCs were measured in this study. The results indicate that an increase in Cr content prevented severe surface plastic deformation (0–5 vol. % Cr) and promoted the formation of mechanical mixed layer (MML) (15–20 vol % Cr), facilitated the improvement of wear resistance and the coefficient of friction, and reduced the thermal fade of composites. The main wear mechanism of the Cu-MMCs changed from adhesion (0–10 vol % Cr) or abrasion (10–20 vol % Cr) to delamination or mechanical mixing with an increase in braking energy density (BED). A series of corresponding friction, wear, and wear mechanism maps were established, which revealed the variation in the wear mechanism with the Cr content and BED.

Paleoenvironmental Implications of Authigenic Magnesian Clay Formation Sequences in the Barra Velha Formation (Santos Basin, Brazil)

The characterization of Mg-clays in rock samples (well P1) from the Barra Velha Formation (Early Cretaceous) allowed the establishment of mineral assemblages on the basis of their kerolite and Mg-smectite (stevensite and saponite) content. Kerolite-rich assemblages (A and B) rarely contain saponite. Assemblage B is composed of kerolite-stevensite mixed layers, while assemblage A consists of more than 95% kerolite. Mg-smectite-rich assemblages (C and CB) are made up of both Mg-smectites. The predominance of stevensite in the lower interval of the stratigraphic succession suggests evaporative conditions, higher salinity and pH, which would favor its authigenesis by neoformation. In the upper portion, the occurrence of thick kerolite-rich intervals suggests regular water inputs, contributing with a decreasing in salinity and pH, favoring the neoformation of kerolite and later kerolite-stevensite mixed layering. The saponite would be the result of the transformation from Al-smectite into Mg-smectite in a Mg2+ rich medium. The results indicate that lake hydrochemical processes would have allowed the establishment of a basic depositional sequence, from base to top, as follows: (i) initial lake expansion stage marked by the occurrence of saponite, (ii) later kerolite neoformation, (iii) formation of kerolite-stevensite mixed layer with increasing salinity, and (iv) neoformation of stevensite, marking a final stage of maximum salinity (evaporation) and alkalinity of the lake.

Microstructure, mechanical properties and reciprocal dry sliding wear behaviour of as-cast and heat-treated TiN/Al-7Si functionally graded composite

This work explores the effect of T6 heat-treatment on the microstructure, mechanical properties and dry sliding linear reciprocating wear behaviour of Al-7Si/Titanium Nitride (TiN) centrifugally cast functionally graded composite. The 10 wt% TiN particle addition and subsequent eutectic Si spheroidisation due to heat treatment revealed an improvement in microhardness, tensile strength and wear resistance of heat-treated composite when compared to as-cast composite. Reciprocating wear analysis at varying applied loads and sliding distances revealed a combination of specimen micro-ploughing and abrasive particle action at low load and sliding distances, which was in stark contrast to the combination of abrasive and adhesive wear at higher loads and sliding distances. The surface was characterised by mechanically mixed layer formation due to tribo-oxidation, adhesive and delamination wear mechanisms. This composite can be utilised to replace traditional materials employed in reciprocating pump and compressor applications.