Investigation on the corrosion resistance of laser cladding Fe-based alloy coating against molten zinc

In this paper, laser cladding technology was used to prepare a Fe-based coating on H13 steel substrate and its corrosion behavior in molten zinc was studied. The results show that laser-cladding Fe-based coating can effectively protect the substrate from the corrosion of molten zinc, which is mainly related to its microstructure. The typical microstructure of the coating is composed of α-(Fe, Cr) solid solution matrix and CrFeB eutectic phases continuously distribute around the matrix. When molten zinc contacts with the surface of the coating, it corrodes the α phase matrix preferentially and CrFeB eutectic phases with better corrosion resistance interweave with each other to form a three-dimensional skeletal structure, which can play the role of diffusion barrier and slow down the diffusion rate of liquid zinc. The corrosion by molten zinc leads to the formation of a transition layer and an outer corrosion layer above the coatings. With the prolongation of the corrosion time, a large number of micro cracks are generated inside the transition layer and fracture gradually occurs under the action of thermal stress. The partial spalling of the transition layer and the corrosion of α phase matrix occur at the same time, making the corrosion depth of the coating increase continuously. However, the dense corrosion layer above the coating and the dispersed boride fragments can still function as a barrier to the inward diffusion of molten zinc.

Phase transformation of the corrosion layers on nuclear fuel cladding. Raman spectroscopy study.

The goal of this work was the phase analysis of corrosion layers on zirconium alloys. In the environment of nuclear reactors, zirconium alloys are covered with a protective layer of zirconium oxide, which occurs in two crystalline modifications - monoclinic and tetragonal. The distribution of these phases in the corrosion layer can affect the overall corrosion rate. Raman spectroscopy was used to determine the composition of the corrosion layers. The use of this method is advantageous because the monoclinic and tetragonal phases can be easily distinguished in the spectra of the corrosion layers. In total, samples of two alloys were measured. The samples were pre-exposed at 360 °C in Li+ containing water (70 mg/l Li as LiOH) . Exposure times were between 21 d and 231 d, so the series contained both pre- and post- transition samples. The relative proportion of the tetragonal phase decreases significantly after the transient. It has also been found that the corrosion layers are highly heterogeneous in terms of the distribution of crystalline modifications.

Wetting Behavior of LBE on Corroded Candidate LFR Structural Materials of 316L, T91 and CLAM

In this work, the wetting behaviors of lead-bismuth eutectic (LBE) on corroded 316L, T91, and CLAM surfaces were studied. The wettability of LBE on virgin and corroded surfaces were tested at 450 °C by using the sessile-drop (SD) method after immersing the samples in LBE with saturated oxygen concentration for 400, 800, and 1200 h at 450°C. Additionally, the morphology, as well as element distribution of the corrosion structure, were characterized by scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS). The results showed that the virgin samples of three materials are non-wetting to LBE, and the formation of corrosion structures further reduces the wettability. Besides, the thickness of the corrosion layer formed on the 316L surface grew more slowly than the other two steel, which results in better corrosion resistance of austenitic steel 316L than that of ferritic/martensitic steels T91 and CLAM at 450 °C. Meanwhile, the morphology and distribution of corrosion products are important factors affecting the wettability of the steel surface. The formation of corrosion products with high roughness as well as disorder results in a significant reduction in surface wettability.

Study on Concrete Cracking Caused by Non-Uniform Corrosion of Steel Bar

In this paper, the cracking of concrete cover caused by steel bar corrosion was discussed and studied based on the three-period model of steel bar corrosion in concrete. In the analysis, according to the non-uniformity of steel bar in reinforced concrete under natural environment, the contour of corrosion layer is simplified into a semi-ellipse. The steel bar corrosion was divided into three different periods by two corrosion points, namely, the void to be filled was exactly filled and the concrete cover was exactly cracked. Different model assumptions are made for each corrosion period. Before the concrete cover cracks, it is developed into an elastic plate. Based on the theory of elastic mechanics, the maximum corrosion depth of steel bar when concrete cover cracks is predicted.....

Corrosion Behaviour of Titanium Alloy and Carbon Steel in a High-Temperature, Single and Mixed-Phase, Simulated Geothermal Environment Containing H2S, CO2 and HCl

The corrosion behaviour of a new titanium-based alloy, with nickel, molybdenum and zirconium as the main alloying elements, was studied in a simulated geothermal environment at various phase conditions of a corrosive fluid. Corrosion testing of carbon steel was also conducted for comparison. Both materials were tested at an elevated temperature between 180 and 350 °C and at a 10 bar gauge pressure in H2O containing HCl, H2S, and CO2 gases with an acidic condensate of pH = 3. The study found that the titanium alloy demonstrated good corrosion resistance in a single- and multiphase geothermal environment. In the testing volume, where the boiling of testing fluid occurred, the carbon steel was prone to localized damage of oxide, sulphide and chloride corrosion products. In the superheated testing volume, a homogeneous oxide corrosion layer was observed on the carbon steel. In the testing volume where condensation of the testing fluid occurred, a sulphide layer with an oxide sublayer was formed on the carbon steel.

The Archaeometallurgical Evaluation of Three Bronze Socketed Axes, Discovered in Eastern Romania

This paper presents the study of three bronze socketed axes discovered in Neamţ County, Romania. The surface structures and those from the interface of the corrosion layer with the metal core of the basic alloy were analyzed, in order to elucidate the nature of the materials used and the manufacturing processes. The analyzes by optical microscopy (OM) and electron microscopy (SEM), coupled with X-ray spectrometry (EDX), revealed the type of their degradation during the depositional period, as a result of the processes of chemical alteration and physical damage. A series of metallurgical techniques used were also established, as well as the identification of some finishing and decoration processes that led to the establishment of the objects’ functionality.

Thinning Evaluation of Steel Plates for Weathering Tests Based on Convolutional Neural Networks

Weathering tests using monitored steel plates are a widely applied method for evaluating the atmospheric corrosion rate in Japan. To calculate the regional corrosion rate, the corrosion layer on the surface of the steel plate needs to be removed to determine the thinning. However, the process of removing the corrosion layer is time and labor consuming. To tackle this issue, this study proposed an image recognition method based on convolutional neural networks (CNNs) to evaluate the thinning of weathering test samples. To this end, the existing data collected from the weathering tests were reused to generate a dataset named “Corrosion-Fukui” that consisted of 77 raw images labeled with their numerical extent of thinning. To generate more samples for training, a criteria based on thinning extent that classified the raw images into six corrosion levels were defined to implement cropping operation on the raw images with uniform corrosion morphology. Correspondingly, the raw images of the corroded samples with uniform corrosion morphology were chosen as “training” and “validation samples” to be cropped into small pieces labeled with the corrosion levels, whereas other raw images with nonuniform corrosion morphology were chosen as “test samples.” The performance of the proposed baseline model VGGGAP as well as three state-of-art CNN models was cross-validated on the augmented dataset and tested upon the test images using a sliding window method. The evaluation results of the 17 testing samples indicated that the corrosion thinning of the weathering test samples can be directly evaluated more efficiently from digital images using CNNs than using conventional corrosion removal methods.