Mechanical–Chemical Coupling Effects on an Environmental Barrier Coating System under High-Temperature Water Vapour Conditions

The degradation mechanisms for environmental barrier coatings (EBCs) under high-temperature water vapour conditions are vital for the service of aero-engine blades. This study proposes a theoretical model of high-temperature water vapour corrosion coupled with deformation, mass diffusion and chemical reaction based on the continuum thermodynamics and the actual water vapour corrosion mechanisms of an EBC system. The theoretical model is suitable for solving the stress and strain fields, water vapour concentration distribution and coating corrosion degree of an EBC system during the water vapour corrosion process. The results show that the thickness of the corrosion zone on the top of the EBC system depended on water vapour diffusion, which had the greatest influence on the corrosion process. The top corroded area of the rare-earth silicate EBC system was significantly evident, and there was a clear dividing line between the un-corroded and corroded regions.

Improved Oxidation and Hot Corrosion Resistance of 1Cr11Ni2W2MoV Stainless Steel at 650 °C by a Novel Glass-Ceramic Coating

A novel glass-ceramic coating was applied onto the 1Cr11Ni2W2MoV stainless steel. The oxidation and corrosion behaviors of coated and uncoated steels were comparatively investigated in air and in the presence of NaCl + Na2SO4 eutectic deposits at 650 °C, respectively. Protective scales formed on the surface of stainless steel prevented the severe oxidation of the alloy. Catastrophic hot corrosion occurred on the steel when a salt film was attached, producing loose iron oxide layers and internal corrosion zone. The glass-ceramic coating acted as a barrier that effectively hindered the invasion of corrosive species during the oxidation and hot corrosion tests.

Rubric Assessment and Spatial Zonal Mapping of Atmospheric Corrosion of Steel in India

Steel is an imperative engineering material due to its endurance accounts for a significant part of the world economy. It has enormous demand all over the world for its extensive use in construction and other industries. These industries are experiencing inevitable atmospheric exposure and are rapidly deteriorating due to induced atmospheric corrosion. The study assessed and interpreted trends in atmospheric corrosion rates in India for the last 39 years, and spatially mapped seasonal decade-by-decade trends. North-east India has been identified as the most corrosive region in the country, with the rainy season being the most corrosive season. Corrosion maps for India are prepared on the basis of 39 years of atmospheric data. A corrosion zone map is prepared to classify the country into five different zones based on the rate of atmospheric corrosion. Long-term atmospheric corrosion rates are projected for the next 50 years in all major cities across the country. Long-term corrosion is estimated to reduce the rate of atmospheric corrosion by 81% after 10 years of exposure and 91% after 50 years of exposure.

Protection of fuel filter with alkaline and acid zinc coatings

Galvanic coatings are applied so that the surface of the base material obtains appropriate properties, corrosion resistance, durability, aesthetic appearance, and long-term application in the appropriate industry. In this paper, the aim was to protect steel fuel filters with alkaline and acid zinc coatings of different thicknesses. The coating of zinc, which is applied from the alkaline electrolyte, provides good corrosion protection with excellent coating flexibility. The thickness of the coating by the X-ray fluorescence method was tested, followed by coating tests, corrosion resistance, and electrochemical tests. The results of adhesion showed a high quality coating, as no corrosion occurred during the test. The corrosion resistance tested by the salt chamber method speaks of the appearance of white and red corrosion. On alkaline electrolyte coatings, white corrosion occurred after 168 hours of exposure to the salt test, while on white zinc samples there was a white corrosion after 240 hours of exposure. Tafel polarization diagrams have been determined: corrosion potentials, current intensities, anode and cathode Tafel coefficients and calculated corrosion rates. The active and passive corrosion zone is determined by the cyclic voltammetry.

Propagation of reinforcement corrosion: principles, testing and modelling

Reinforcement corrosion is the risk most frequently cited to justify concrete durability research. The number of studies specifically devoted to corrosion propagation, once the object of most specialised papers, has declined substantially in recent years, whilst the number addressing initiation, particularly where induced by chlorides, has risen sharply. This article briefly describes the characteristics of steel corrosion in concrete that need to be stressed to dispel certain misconceptions, such as the belief that the corrosion zone is a pure anode. That is in fact seldom the case and as the zone is also affected by microcells, galvanic corrosion accounts for only a fraction of the corrosion rate. The role of oxygen in initiating corrosion, the scant amount required and why corrosion can progress in its absence are also discussed. Another feature addressed is the dependence of the chloride threshold on medium pH and the buffering capacity of the cement, since corrosion begins with acidification. Those general notions are followed by a review of the techniques for measuring corrosion, in particular polarisation resistance, which has proved to be imperative for establishing the processes involved. The inability to ascertain the area affected when an electrical signal is applied to large-scale elements is described, along with the concomitant need to use a guard ring to confine the current or deploy the potential attenuation method. The reason that measurement with contactless inductive techniques is not yet possible (because the area affected cannot be determined) is discussed. The method for integrating corrosion rate over time to find cumulative corrosion, P corr, is explained, together with its use to formulate the mathematical expressions for the propagation period. The article concludes with three examples of how to use corrosion rate to assess cathodic protection, new low-clinker cements or determine the chloride threshold with an integral accelerated service life method.

Electrochemical Research of the Multilayer Corrosion Resistant Material

The aim of the article is to research of the multilayer corrosion resistant material with «sacrificial pitting protection». The original chemical and electrochemical methods were developed for investigation of multilayer corrosion resistant material. It has been found that the size of free pitting corrosion zone is depending on the square of internal protection. The 12X18H10T steel’s potential change on the distance from the protector was measured. Results of research confirmed principle of “sacrificial pitting protection” and determined the direction of further tests.

Research on Salt Fog Corrosion Behavior of Welded Joint of 7N01-T4 Aluminum Alloy for High-Speed Train

Salt fog corrosion test was employed to observe the corrosion behavior of welded joint of 7N01-T4 aluminum alloy of high-speed train. Tensile strength and hardness change after corrosion were tested and micro morphology was observed by metalloscope and LCSM. The results indicated that HAZ was the most sensitive corrosion zone in welded joint of 7N01-T4 in chlorinated moisture environment. Influenced by the heat-input of welding, the grains of HAZ were coarsening and inhomogeneous. A corrosion cell between welding seam with high Mg content and HAZ with high Zn content formed. HAZ corroded preferentially as anode, and the dissolving of zinc-rich phase in grain boundary resulted in the extending of corrosion crack along grain boundaries.

Corrosion Resistance of β-SiAlON-Based Ceramics Against Molten Steel

The corrosion resistance of sialons made from commercial powders (AlN, Al2O3 and Si3N4) and from powder precursor produced by carbothermal reduction and nitridation of raw aluminosilicate (pyrophyllite) in molten steel were investigated. The corroded zone in sialon made from raw pyrophyllite (P1) is more then two times deeper compared to the corroded zone of sialon made from commercial powders (C1). The corrosion zone of sample P1 is on the average 610 μm deep, while in sample C1 it is only 260 μm. The main corrosion products are γ-Al2O3 and iron silicides. The phase compositions were estimated by neutron Rietveld refinement.