Papers by Keyword: Pitting Corrosion

Abstract: The influence of inclusion on pitting corrosion of X80 pipeline steel was investigated by using electrochemical test and atomic force microscope. The results indicated that corrosion potential of X80 pipeline steel sample with higher grade inclusion was lower, and decreased significantly with chloride ion concentration increasing. Inclusion was not conducive to corrosion resistance of X80 pipeline steel. The way of X80 pipeline steel pitting corrosion was that pit formed at the inclusion dissolution, and grew to pitting. There were less corrosion products near the pit hole, forming a cathode ring.

Abstract: 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.

Abstract: The authors developed a new class of multilayer materials that feature high corrosion resistance in halogenide-containing media. Corrosion resistance is provided by the multilayer structure. The principle of “sacrificial pitting protection” was formulated. The corrosion resistance tests were carried out. Explosive welding technology was introduced for fabrication of multilayer materials. It is suggested to use the multilayer materials as a structural material in construction of reservoirs for liquid radioactive waste.

Abstract: In order to improve the hemocompatibility of the Ti-6Al-7Nb alloy the study authors have proposed the modification of surface by the creation of surface layer with the application of anodic oxidation as well as sol-gel method. To verify the usefulness of the two methods and properties of created layers electrochemical testing has been proposed. Those tests have been meant to determine electrical properties that influence corrosion resistance of the alloy before and after the surface modification. Tests have been conducted with the use of measuring device equipped with PGSTAT 302n potentiostat with FRA2 attachment for impedance tests. Measurements have been taken in human blood environment simulating – artificial serum at temperature of 37 degrees Centigrade. To identify phenomenon proceeding at phases border the alloy has been additionally tested in artificial serum for 28 days. It has been found that higher voltage value (90 V) in the case of anodic oxidation has a favourable influence for electrochemical properties of the modified surface. In the case of sol-gel method, thin layer of SiO₂ (some 150 nm) baked at the temperature T = 430 degrees Centigrade has the most advantageous set of electrochemical properties. Proper selection of parameters of the surface layer deposition process has a direct influence on the success of implant implantation surgery.

Abstract: The influence of bone union activation realized with the use of the low-intensity pulsed ultrasound (LIPUS) on degradation of titanium alloys was presented in the work. Ti6Al4V ELI and Ti6Al7Nb alloy samples of modified surface layer were used in the study. The preliminary surface treatments were: grinding, vibration machining, mechanical polishing, sandblasting and electrochemical polishing. The final procedures of the surface modification were anodization and steam sterilization. The scope of the work included the study of pitting corrosion resistance and concentration of metal ions released to the Ringer’s solution. The study was performed for the undeformed and deformed samples subjected to the influence of ultrasound. The reference samples were the samples kept in the solution and not having the impact of ultrasound. On the basis of the study it was found that the conditions for bone union stimulation by low intensity pulsed ultrasound do not initiate pitting corrosion of the titanium alloy samples, although they increase the mass of ions released from the surface to the solution.

Abstract: The influence of surface pretreatment prior to the anode oxidation of Ti6Al7Nb alloy samples on corrosion resistance was presented in the work. The preliminary surface treatments were: grinding, vibration machining, sandblasting and electrochemical polishing. Anodic oxidation process was carried out at different voltages. The final procedure of the surface modification was steam sterilization. The scope of the work included: corrosion resistance study (pitting and crevice) of both non-sterilized and sterilized samples, and samples after 28 days exposure to the Ringer’s solution, concentration evaluation of metal ions releasing from the sterilized surface as well as observations of surface topography. The research revealed a significant influence of surface pretreatment of Ti6Al7Nb alloy, prior to the anode oxidation and steam sterilization, on corrosion resistance.

Abstract: The aim of the paper was to compare physicochemical features of hip joint cups coated with hydroxyapatite in the initial state and after period of 36 months of implantation. The cups we produced from stainless steel Cr-Ni-Mo with increased content of azote dedicated to implants which chemical composition is compatible with recommended ISO 5832-9 standards. On the basis of obtained results it can be stated that hydroxyapatite resorption did not affect equally the entire surface of the cup. It was also stated that tested biomaterial of the cup was well wetted (hydrophilic). For all the tested samples prepared from cups in the initial state and cups after the implantation the presence of transpassivation potential E_tr was stated, which proves not only good corrosion resistance but also biocompatibility of analyzed cups.

Abstract: Corrosion fatigue is of great significance in research of submarine structure operating in marine environment for long term since the seawater corrosion effect will reduce the resistance to fatigue failure of structure components. The paper interests on the introduction of pitting corrosion and analysis method of corrosion fatigue life. Finite element method was adopted to analyze the stress concentration factor of pitting corrosion and local corrosion fatigue of spherical-headed cylindrical shell with following conclusion. In the estimation of corrosion fatigue life of spherical-headed cylindrical shell, the proposed formula has some practical value, and only the corrosion fatigue of structure surface should be considered.

Abstract: Pit morphology on sensitized 310S stainless steel has been studied using an image processing method based on reflected light microscopy (profile and surface). Salt Spray test has been used to induce the pitting corrosion. Morphological pits character do not depend on sensitization heat treatments here applied. Nucleation rates and growth may be associated with quantity and distribution of chromium carbides. This being so, condition I (heating up to 1065^o C during 1 h and air cooling) and condition II (heating up to 1065^o C during 1 h and air cooling followed by reheating up to 670°C during 5 h and again air cooling) are the most susceptible to pitting, in particular the first one. In these two conditions, pits are nucleated in grains and in grain boundaries, while in condition III (heating up to 1065^o C during 1 h and air cooling followed by reheating up to 620^o C during 24 h and again air cooling), pits are preferentially nucleated in boundaries of small grains. Thence, pits usually grow more rapidly in depth than in width, being able to occur partial or total grains separation. Pits are mainly hemispherical, near-hemispherical, near-conical and near-cylindrical without significant geometric transition associated with an increasing exposure period.

Abstract: In this paper, the polished specimens of high Zn content Al-Zn-Mg-Cu alloy after various aging treatments were immersed in 3.5 wt.% NaCl for up to 240 mins. The development of corrosion was monitored using scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX). There are two stages during the corrosion process, the first stage of attack started with localized corrosion of trenching around the Al-Zn-Mg-Cu particles. In the second stage the pitting corrosion appeared at the grain boundaries, and then developed into intergranular corrosion. This phenomenon is related to the potential difference between the matrix and the precipitates.