Dependence Of Corrosion Resistance Research Articles

Investigation on the effect of scanning strategy on the corrosion properties of gum metal produced using selective laser melting

Effect of scanning strategy (CB, R90, R67) on the microstructure and corrosion behaviors of Ti35Nb2Ta3Zr0.3O (wt%, TNTZO) prepared by selective laser melting (SLM) in 3.5 wt% NaCl solution were systematically investigated. The results of electrochemical tests indicated that the corrosion resistance of vertical planes was better than that of horizontal planes for all three scanning strategies, particularly sample R67 and R90, of which sample R67 performing the highest corrosion resistance. The dependence of corrosion resistance on the scanning strategy only exhibits for the vertical planes. The various electrochemical properties of horizontal and vertical planes are attributed to the density of crystallographic texture more than the grain boundary for the as-built TNTZO alloy.

Corrosion Resistance of MAO Coatings on Al-Si Alloys

The paper presents the results of an experimental study of the influence of micro-arc oxidation (MAO) on the parameters and the corrosion resistance of MAO-treated surfaces on a high-silicon aluminum alloy, M244 (Si ~ 25 %). The article describes the study methodology, comprising forming a coating on the surface of laboratory samples by means of MAO at different process modes and the study of their parameters, properties, and corrosion resistance. The experiments were conducted in accordance with the 23 full factorial experiment design theory. The MAO process was carried out using a silicate-alkaline electrolyte. MAO factors were as follows: the concentration of the electrolyte components (potassium hydroxide – KOH and liquid glass – Na2SiO3) and electrical parameters of the process, determined by the capacitor capacitance of the processing unit. The samples were tested to define thickness, porosity and micro-hardness of the MAO layer. Being corroded in a corrosive solution for 144 hours, their corrosion resistance was estimated by a mass corrosion rate. The data obtained made it possible to form mathematical models, based on the dependence of corrosion resistance, thickness, porosity and micro-hardness on the process factors. A verification of the obtained models was carried out to determine adequacy and their analysis. Conclusions on the extent of the MAO effect on the corrosion resistance of the samples were drawn. MAO modes were stated to have a significant impact on the corrosion resistance of the samples. MAO should be carried out using low electrolyte concentrations and a low-capacity processing unit for improved corrosion-protective properties of the coating on the M244 (Mahle) aluminum alloy. It is necessary to increase the concentration of the electrolyte components and the processing unit capacity, to obtain a thicker coating with low micro-hardness and porosity.

PECULIARITIES OF ELECTRODEPOSITION OF COBALT—WOLFRAM—RENIUM ALLOY

The methods of stationary voltammetry and chronovoltammetry have been used to study deposition processes of ternary CoWRe alloys at different rhenium content of the electrolyte and deposition current density. It has been found that the limiting currents have a diffusive nature and are proportional to the concentration of perrhenate ions in the electrolyte. The CoWRe alloys should be formed by the discharge of bimetallic citrate complexes of the following composition [(Co)(WO4)(H)(Cit)]2- and rhenium electrodeposition. Rhenium does not form complexes with citrate ions and deposits better in an alloy with iron group metals than in the form of an individual metal from a perrhenate solution. It can be assumed that the discharge of rhenium into the alloy occurs from a surface complex, the nature of which has not yet been established. The alloy current efficiency reaches 93% due to the high overpotential of hydrogen evolution on the alloy surface. According to the results of investigations of the catalytic properties of alloys in the hydrogen reduction reaction, it has been found that with increasing the rhenium content of the electrolyte and alloy, an increase in hydrogen overpotential is observed. Based on the Tafel coefficients found, it was found that in an acidic and neutral medium, the limiting stage of the cathodic and anodic reaction is the transfer of the first electron. In an alkaline medium, the anode process is complicated by the simultaneous transport of two electrons. The found values of corrosion resistance are 1-2 kOm·cm-2 in solutions of 0.01 M H2SO4; 20-110 kOm·cm-2 in 2.5% NaCl; 10-30 kOm·cm-2 in 1.0 M KOH. Based on the dependence of corrosion resistance on the refractory metals content of the alloy and the electrodeposition conditions, the optimum deposition current density of 10 mA·cm-2 has been found.

Effect of annealing temperature on the corrosion resistance of MgO coatings on Mg alloy

MgO coatings were electrodeposited on Mg alloy substrates via cathodic electrolytic technique and annealed at different temperatures. The protective performance of these annealed coatings was investigated, and a correlation drawn between annealing temperature of coatings and their corrosion resistances as well as mechanical hardness. At optimum temperature (250 °C), the thermal treatment relieved internal tensile stress leading to crystallization of oxide coating layers with compact and continuous multilayered microstructures. At higher temperatures (around 500 °C), phase transformations within the coating microstructure broadened inherent inter-diffusion pathways/microdefects. Surface and bulk evidences of pores and cracks are observed at 500 °C as clear evidences of the consequence of over-calcination using scanning electron microscopy. Enhanced corrosion resistance for coatings are achieved at optimum curing temperature judging from electrochemical corrosion results after chloride-induced corrosion tests. The dependence of corrosion resistance on annealing temperature of coatings has also been investigated by potentiodynamic polarization and electrochemical impedance spectroscopic techniques. A modelled curing mechanism, as it relates to barrier performance at low and high thermal conditions, has been illustrated from experimental evidences.

Dependence of corrosion resistance on grain boundary characteristics in a high nitrogen CrMn austenitic stainless steel

Processing schedules for grain boundary engineering involving different types of cold deformation (tension, compression, and rolling) and annealing were designed and carried out for 18Mn18Cr0.6N high nitrogen austenitic stainless steel. The grain boundary characteristic distribution was obtained and characterized by electron backscatter diffraction (EBSD) analysis. The corrosion resistance of the specimens with different grain boundary characteristic distribution was examined by using potentiodynamic polarization test. The corrosion behavior of different types of boundaries after sensitization was also studied. The fraction of low-Σ boundaries decreased with increasing strain, and it was insensitive to the type of cold deformation when the engineering strain was lower than 20%. At the strain of 30%, the largest and smallest fractions of low-Σ boundaries were achieved in cold-tensioned and rolled specimens, respectively. The fraction of low-Σ boundaries increased exponentially with the increase of grain size. The proportion of low-angle grain boundaries increased with decreasing grain size. Increasing the fraction of low-Σ boundaries could improve the pitting corrosion resistance for the steels with the same grain size. After sensitization, the relative corrosion resistances of low-angle grain boundaries, Σ3 boundaries, and Σ9 boundaries were 100%, 95%, and 25%, respectively, while Σ27 boundaries, other low-Σ boundaries and random high-angle grain boundaries had no resistance to corrosion.

Effect of Remelting of the Ni-22Cr-9Mo Alloy on its Microstructural and Electrochemical Properties

AbstractThe Ni-Cr-Mo alloys are used as the alternative for the cobalt alloys in the manufacture of metal prosthetic elements, i.e. crowns, bridges and frame prostheses. The article attempts at a materials science characterization of the nickel-based alloy of the commercial name Argeloy N.P Be-Free by Argen. Within the study, examinations were made on the commercial alloy as well as the alloy which was remelted and cast by the los mould (lost wax) method. Observations of the microstructure were performed with the use of optical and electron scanning microscopy. Also, X-ray structural tests were conducted as well as corrosion resistance tests in an artificial saliva solution (pH = 6,7). It was demonstrated that the examined Ni-22Cr-9Mo alloy characterized in a dendritic structure typical of the cast materials. The X-ray qualitative phase analysis revealed the phase γ'(Ni) in both examined materials, as well as the presence of Cr23C6type carbides and Nb2C, Ta2C (commercial alloy) and NbC, Ta4C0,04(cast alloy) phases. The effect of the alloy’s remelting and the morphology of the passive layer on the corrosion resistance of the Ni-Cr-Mo alloy was examined.The results of the electrochemical tests show that the process of re-casting only slightly affects the corrosion resistance and the microstructure of the considered alloy.The roles of recasting process and the passive film homogeneity on the corrosion resistance of Ni-Cr-Mo dental alloy were reviewed. The results the electrochemical study show that the dependence of corrosion resistance on the microstructure associated with the recasting process is marginal.

Mechanisms of the texture influence on the corrosion behavior of Zr-alloy cladding tubes

Different mechanisms of how the crystallographic texture affects the corrosion behavior of the cladding tubes made of commercial Zr-based alloys are considered under service conditions. It is shown that the dependence of corrosion resistance of the tubes on the degree of recrystallization correlates with the distribution of prismatic axes in the tube texture, which can be regarded as an indicator of the propensity of the tube to intergranular oxygen diffusion. The effect of the layerwise inhomogeneity of a texture on tensile stresses is studied in the surface layers of the tube. It is shown that tensile stresses enhance oxygen diffusion into internal layers of the tube. It is established that, under the action of tensile stresses arising during oxide formation in the surface layer, twinning of the α-Zr matrix takes place near the front of oxidation. The texture of the monoclinic phase of the oxide layer is stable under tube surface treatment owing to existence of the orientation relationship with the substrate.

Electrochemical behavior of Co-Cr and Ni-Cr dental cast alloys

The cast structures influencing the electrochemical corrosion behavior of Co-Cr and Ni-Cr dental alloys were studied using potentiodynamic polarization and AC impedance in 0.9% (mass fraction) NaCl solution at (37±1) °C. The phase and microstructure of the alloys that were fabricated using two different casting methods viz. centrifugal casting and high frequency induction casting, were examined using X-ray diffraction analysis, scanning electron microscopy and energy dispersive spectroscopy. The roles of alloying elements and the passive film homogeneity on the corrosion resistance of Co-Cr-Mo and Ni-Cr-Mo dental cast alloys were reviewed. The results of electrochemical study show that the dependence of corrosion resistance on the microstructure associated with the casting methods is marginal. The Co-Cr alloy exhibits more desirable corrosion resistance properties than the Ni-Cr alloy. There is severe preferential dissolution of Ni-rich, Cr and Mo depleted zones in the Ni-Cr alloy.

High Temperature Corrosion of Boiler Steels Under Chlorine-Containing Surface Deposits

The high-temperature corrosion resistance of several boiler steels was tested experimentally in laboratory and industrial conditions in the presence of chlorine-containing external deposits. The empirical kinetic equations for the calculation of corrosion depth, depending on operational time and temperature, were established and the dependence of corrosion resistance of the austenitic steels on the alloying elements ratio Ni–Cr was analyzed.

High-Temperature Corrosion of Martensite Alloy Under Oil Shale Fly Ash

Superheater surfaces in oil shale steam boilers, constructed from pearlitic or austenitic alloys, are subject to intensive corrosion, primarily from the presence of chlorine in external deposits. The applicability of martensitic alloys X10CrMoVNb91 and X20CrMoV121 for superheaters has been examined and empirical equations to predict alloy corrosion resistance have been developed for the operational temperature range. Alloy 10CrMoVNb91 is found highly suitable for superheaters in boilers firing fossil fuels that contain alkaline metals and chlorine. An abnormal dependence of corrosion resistance of martensitic alloys on temperature is revealed, namely that corrosion in presence of oil shale fly ash is more severe at 580°C than at 620°C.

Aluminum Etch and After-Corrosion Characteristics in a m=0 Helicon Wave Plasma Etcher

The etch and corrosion characteristics of stacked aluminum were investigated in a m=0 helicon plasma etcher. Wide process margin was achieved in the aspects of Al etch profile and selectivity of Al to photoresist. The dependence of corrosion resistance on etch parameters was remarkably improved under the conditions of high source power, low pressure, and no N2 addition. The sidewalls of etched Al analyzed by tunneling electron microscopy (TEM) were composed of three different layers: an outermost layer, a middle layer, an innermost layer. When N2 was added, the serious corrosion was caused by the high concentration of residual chlorine captured in the dense sidewall film which mainly consists of Al–O, Al–N, Si–O, and Si–N. It was observed that lowering the source power induced the big increase of both Cl and Cu concentrations.

マグネシウム特集号 塩水噴霧環境におけるＭｇ‐ＡｌおよびＭｇ‐Ａｌ‐Ｚｎ砂型鋳造合金の腐食挙動

Corrosion behavior of sand-casted Mg-(0-5.3%)Al and Mg-5.3%Al-(0-2.7%) Zn alloys have been investigated by salt spraying test (SST). The corrosion resistance increased with an increase of Al content in Mg-Al alloys, and more than 1% content of Zn in Mg-5.3%Al-Zn alloys. These behavior were seemed to depend on the volume fraction of nodule structure. Cross-sectional microstructure after corrosion test showed that the matrix was preferentially attacked and the nodule structure was more resistant to corrosion. These dependence of corrosion resistance on the nodule content was discussed from the view point of galvanic effect between the nodule structure and the matrix, and barrier effect of the nodule structure.