Cr-enriched Layer Research Articles

Oxidation behavior of a cathodic arc evaporated Cr0.69Ta0.20B0.11N coating

CrTaBN hard coatings deposited by cathodic arc evaporation are a promising new material class for use in demanding applications, due to their high hardness and good thermal stability in protective atmosphere. Up to now however, studies on the detailed oxidation mechanism of quaternary CrTaBN coatings are lacking in the literature. Thus, within this work, the oxidation behavior of a Cr0.69Ta0.20B0.11N coating grown by cathodic arc evaporation was studied in a combinatorial approach of advanced characterization techniques. In situ high-energy x-ray diffraction at a synchrotron radiation facility showed that up to ∼1100 °C, only the face-centered cubic (fcc) CrxTayB1−x−yN solid solution of powdered CrTaBN contributes to the crystalline phase composition. As the temperature is further increased, tetragonal CrTaO4 and rhombohedral Cr2O3 form. In situ high-temperature Raman spectroscopy evidenced that B2O3 contributes to the phase composition of the material in the temperature regime from ∼600 to 1000 °C. Applying high-resolution transmission electron microscopy allowed to identify the presence of four discrete zones in a partly oxidized CrTaBN coating on sapphire: intact fcc-CrTaBN at the interface to the substrate, followed by a Cr-deficient and Cr-enriched layer, respectively, and a porous layer with small grains at the surface.

Effects of alternating dissolved oxygen and dissolved hydrogen on the corrosion behavior of alloy 52 in high temperature high pressure water

The effects of alternating dissolved oxygen (DO) and dissolved hydrogen (DH) on the corrosion behavior of Alloy 52 are studied by electric/electrochemical methods measured in situ including contact electric resistance (CER) and electrochemical impedance measurements (EIS) together with multiple ex-situ surface analysis techniques including scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analysis. The film resistance changes cyclically in both DO and DH cycles. In DO cycle film resistance decreases with the increase of corrosion potential (Ecorr) while in DH cycle film resistance shows an opposite trend. The preformed oxide film in a low DO condition can suppress the oxidation rate in middle DO condition, whilst a high DO level can deteriorate the protectiveness of Cr enriched layer. In the DH cycle, the immersion in a low DH condition can increase the resistance in the following high DH condition. All the results indicate the characteristic of oxide formed in one water chemistry is highly influenced by the pre-immersion history, which should be paid much attention in the study of DO or DH effects on the properties of the oxide film and stress corrosion cracking (SCC) initiation.

INNOVATIVE METHOD FOR PREPARATION OF Fe–Al–Cr INTERMETALLIC FUNCTIONALLY GRADED MATERIAL ON 1045 STEEL WITH UNIQUE TRIBOLOGICAL PROPERTIES

By combining the plasma ion implantation (PII) technology and double glow plasma surface metallurgy (DGPSM), a Fe–Al–Cr intermetallic functionally graded material was deposited on 1045 steel. The obtained Fe–Al–Cr intermetallic functionally graded material was around 11[Formula: see text][Formula: see text]m in thickness and was composed of a Cr-enriched layer (Cr-enriched Fe–Cr compounds), a Fe–Al–Cr-enriched layer (Fe2AlCr and Al8Cr5 compounds), and a Fe-enriched layer (Fe-enriched Fe–Cr solid solution). The interfacial contact between the Fe–Al–Cr intermetallic functionally graded material and the steel substrate is excellent due to the metallurgical bonding. The wear rate of the Fe–Al–Cr intermetallic functionally graded material was only around 25% of that of the 1045 steel substrate. Due to the different compound distributions in the Cr-enriched layer, Fe–Al–Cr-enriched layer, and Fe-enriched layer, the friction coefficients were different and their tribological behaviors were abrasive wear, oxidative wear and adhesive wear, respectively.

Effects of solution composition on corrosion behavior of 13 mass% Cr martensitic stainless steel in simulated oil and gas environments

The effects of CH₃COONa and CO₂ on the corrosion behavior of 13 mass% Cr martensitic stainless steel in simulated oil and gas environments were investigated with electrochemical and surface analysis techniques. The electrochemical results showed that a plateau region and sudden increase in the current density of the anodic polarization curves. The current density of the plateau region decreased with increasing CH₃COONa concentrations. The pitting corrosion potential shifted to the positive direction with increasing CH₃COONa concentrations, and shifted to a negative value by adding CO₂. From the surface analysis, a Cr enriched layer had formed on the sample surface after immersion tests, and the thickness of this layer became thinner with increasing CH₃COONa concentration. The surface analysis results after the immersion tests suggested the presence of CH₃COO⁻ or HCO₃⁻ on the surface.

Corrosion behavior of a 3 % Cr tubing steel in a CO2 saturated high-salinity brine

Abstract Corrosion behavior of 3 wt.-% Chromium (3Cr) tubing steel in CO2 saturated high-salinity brine was investigated by using an autoclave in the laboratory. The partial pressure of CO2 and the Cl− concentration were fixed at 0.2 MPa and 139552 mg × l−1, respectively. The water cut was varied from 20 to 100 vol.-%, and the temperature was varied from 50 to 110 °C. For comparison, the corrosion behaviors of N80 carbon steel and 13 wt.-% Cr (13Cr) martensitic stainless steel were tested in the same conditions. The surface morphologies and chemical composition of corrosion product layers were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectrometry (EDS) technologies. The results show that the 3Cr steel's corrosion rate increased as water cut increased, especially when the water cut exceeded 70 vol.-%. Serious general corrosion and local attack occurred on the 3Cr samples in a 0.2 MPa CO2 and 139552 mg × l−1 Cl− corrosion environment. The product layer structure of 3Cr steel in high-salinity brine is demonstrated. When the chloride ion concentration is high enough, the Cr-enriched layer no longer provides sufficient protection against the chloride ion penetration and pitting attacks may occur.

TRIBOLOGICAL BEHAVIOR OF Al–Cr COATING OBTAINED BY DGPSM AND IIP COMPOSITE TECHNOLOGY

An Al–Cr composite alloyed layer composed of an Al enriched layer, a Cr enriched layer and a transition layer from the surface to the bulk along the cross-section was deposited on a 45# steel substrate by composite technology, where Cr was deposited using double glow plasma surface metallurgy (DGPSM), and Al was then implanted by ion implantation (IIP) to achieve higher micro-hardness and excellent abrasive resistance. The composite alloyed layer is approximately 5[Formula: see text][Formula: see text]m, and as metallurgical adherence to the substrate. The phases are Al8Cr5, Fe2AlCr, Cr[Formula: see text]C6, Cr (Al) and Fe (Cr, Al) solid solution. The wear resistance tests were performed under various rotational speed (i.e. 280, 560 and 840[Formula: see text]r/min) with silicon nitride balls as the counterface material at ambient temperature. The Al–Cr composite alloyed layer exhibits excellent wear resistance when the speed is 280[Formula: see text]r/min with a friction coefficient as low as 0.3, which is attributed to Al8Cr5 in the Al implanted layer that withstands abrasive wear. Better wear resistance (friction coefficient: 0.254) at 560[Formula: see text]r/min is resulted from the formation of a high micro-hardness zone, and an oxidation layer with lubrication capacity. In addition, the composite alloyed layer suffers severe oxidative wear and adhesive wear at 840[Formula: see text]r/min due to the increment of the frictional heating. When compared to the 45# steel substrate, the enhanced wear resistance of the Al–Cr composite alloyed layer demonstrates the viable method developed in this work.

Interface Microstructure and Formation Mechanism of Diamond Abrasives Laser Brazed with Ni-Cr Solder

Abstract The laser brazing of diamond abrasives was investigated using Ni-based solder in an Ar atmosphere. The microstructure and the phase composition of the interface between diamond abrasives and Ni-based solder were analyzed using scanning electronic microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Meanwhile, the formation mechanism of carbides at the interface between solder and diamond abrasives was discussed. The results indicate that during laser brazing, the Cr-enriched layer around the diamond surface reacts with C in the diamond surface and consequently Cr 3 C 2 is formed. Based on reaction thermodynamic and kinetic analysis, it is revealed that the interface reaction products can be formed via replacement reaction, which realize the tight combination between diamond abrasives and solder.

Electrochemical analysis on the growth of oxide formed on stainless steels in molten carbonate at 650 °C

Abstract The oxide growth on stainless steel (SS) 310S and 316L, used as a cathode current collector material of molten carbonate fuel cell (MCFC), were examined in the mixture of 62 mol% Li2CO3–38 mol% K2CO3 at 650 °C by measuring the change in corrosion potential and potentiodynamic response of the alloys and also in terms of impedance analysis on the alloy|oxide layer|electrolyte system. The corrosion potential of SS 316L was in an active region for 12 h-immersion, whereas that of SS 310S drastically increased after 6 h-immersion due to an active to passive transition. The corrosion rate of the two SSs decreased with immersion due to the growth of protective oxide. However, the decrease in the corrosion rate of SS 310S is much greater than that of SS 316L. The oxide formed on the two SSs was found to be duplex layer, composed of inner Cr enriched oxide and outer Fe enriched oxide. However, the inner Cr enriched layer of 310S is more clearly separated from the outer Fe enriched layer than that of SS 316L due primarily to the higher Cr content in SS 310S. The drastic increase in the corrosion potential of SS 310S after 6 h-immersion is closely associated with the growth of the inner Cr enriched oxide layer. The corrosion resistance of SS depends dominantly on the resistance of the inner Cr enriched oxide that is determined form the impedance analysis on the alloy|oxide layer|electrolyte system. The higher corrosion resistance of SS 310S compared with SS 316L results from the more protective inner Cr enriched oxide layer, as confirmed by its higher resistance associated with the higher Cr content in SS 310S.

Formation of hard surface layer on austenitic stainless steels via simultaneous chromising and nitriding by pack cementation process

This study aims to increase surface hardness of austenitic stainless steels via simultaneous chromising and nitriding by the pack cementation process. The pack powder mixtures used for the process consisted of Cr2N as a source of both N and Cr for the simultaneous process, NH4Cl as activator and Al2O3 as inert filler; in some cases, Cr powder was added as an additional source for depositing Cr. The AISI204 austenitic stainless steel is studied as a substrate. It is demonstrated that a top Cr2N layer with a Cr enriched layer underneath can be formed on the steel surface at 1100°C. Hardness values of more than 1800HV are obtained at the outermost surface of the treated specimen. It has been shown that the hardness profile at the cross-section of the surface depends on the pack chemistry.

Corrosion behavior of novel 3%Cr pipeline steel in CO2 Top-of-Line Corrosion environment

CO2 Top-of-Line Corrosion (TLC) of carbon steel pipelines is a serious problem for wet gas transportation. We have studied the corrosion behavior of novel 3%Cr (3Cr) pipeline steel and conventional carbon steel (X70) in the simulated CO2 TLC environment. The composition and morphology of the corrosion scale are characterized by X-ray diffraction, energy dispersive X-ray spectroscopy and scanning electron microscopy analyses. The results indicate that 3Cr pipeline steel shows superior resistance to CO2 TLC, exhibiting uniform corrosion with duplex corrosion layer, while X70 suffers severe localized corrosion. It was suggested that the inner Cr enriched layer enhanced the protective ability of the scale to steel substrate and improved the resistance to localized corrosion in CO2 TLC environment.

Ni–Cr Co-implanted 316L stainless steel as bipolar plate in polymer electrolyte membrane fuel cells

A Ni–Cr enriched layer about 60 nm thick with improved conductivity is formed on the surface of austenitic stainless steel 316L (SS316L) by ion implantation. The electrochemistry results reveal that a proper Ni–Cr implant fluence can greatly improve the corrosion resistance of SS316L in the simulated PEMFC environment. The samples after the potentiostatic test are also analyzed by XPS and the ICR values are measured. The XPS results indicate that the composition of the passive film change from a mixture of Fe oxides and Cr oxide to a Cr oxide dominated passive film after the potentiostatic test. Hence, the ICR increases after polarization due to depletion of iron in the passive film. Nickel is enriched in the passive film formed in the simulated PEMFC cathode environment after ion implantation thereby providing better conductivity than that formed in the anode one.

Compositional microstructures of CoCr-alloy perpendicular magnetic recording media

Compositional microstructures of CoCrTa and CoCrPt perpendicular magnetic recording media are investigated using a high resolution transmission electron microscope equipped with an imaging filter. In the CoCrTa film, clear Cr segregation at grain boundaries is recognizable. The Cr-enriched layer is analyzed to be paramagnetic phase of which Cr concentration is greater than 30 at%. In the case of CoCrPt film, Cr segregation is observed within the grains, and the Cr contents at grain boundaries are far lower than those measured for the CoCrTa film. The difference in the compositional microstructure is related to the difference in noise characteristics of CoCrTa and CoCrPt media.

The mechanism of surface segregation by the method of mechanical polishing

Mechanical polishing and subsequent thermal oxidation are the indispensable condition for rapid formation of a continuous and highly Cr-enriched layer on the surface of a Ni-Cr alloy. Direct observations of the Cr distribution on the surface by Auger map show a possible process for Cr segregation. The huge amount of grain boundaries created by mechanical polishing promote the upward diffusion of Cr. Selective oxidation and Cr-holding effect also speed up the formation of Cr2O3.