Corrosion Resistance of a Plasma-Oxidized Ti6Al4V Alloy for Dental Applications

A Ti6Al4V alloy was plasma-oxidized at 600 °C during 1, 2, 3, 5 and 8 h and corroded in an artificial saliva solution. Electrochemical evaluation was performed by using potentiodynamic polarization curves, linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS) measurements during 100 h. Corroded specimens were characterized by using Raman spectroscopy and scanning electronic microscopy (SEM). All tests indicated that the highest corrosion resistance was obtained for specimen oxidized during 3 h since the noblest free corrosion potential, lowest passive and corrosion current density values, as well as the highest polarization resistance values were obtained under these circumstances. EIS measurements indicated that the highest impedance and phase angle values obtained for this specimen exhibited a high capacitive behavior typical of a very compact passive film.

Formation and structure of sulfide deposits on carbon steel under free corrosion potential

The corrosion of alloy materials in the H₂S nature has considerably limited the growth of oilfield manufacturing. Those sour corrosion has frequently been paid attention to Iron, and steel corrosion under the H2S scheme have been investigated. Many parameters are affecting the corrosion of carbon steel (CS) in the H₂S natural environment, including a concentration of H2S, pH, and the temperature, which has significant impacts on the electrochemical responses of the bare metal surface, the formation, and the nature of the created sulfide scale. The latter could be either protection or non-protecting, depending on the formation conditions. This work presents a full experimental investigation for the initial corrosion events of iron/steel at the free corrosion potential for different periods of time in H2S saturated solutions of different temperatures where H₂S/N₂ gas was purged into the solutions. The structure, morphology, composition, depth, and ion- concentration of the sulfide film that is established on the pipeline CS (mild carbon steel) in an acidic sour solution was examined using different bulk and surface techniques, e.g., an optical microscope, scanning electron microscopy, and Raman spectroscopic.

Tribocorrosion Mechanisms of Martensitic Stainless Steels

In the present study, the influence of the electrochemical potential on the tribocorrosion behavior of X20Cr13 in 0.15 molar NaCl-solution was investigated with the aid of a universal-tribometer under potentiostatic control. The resulting material loss was determined through laser confocal microscopy, while the morphology of the wear tracks and the deformation of the material structure near the surface were observed using light and scanning electron microscopy. The results showed a clear dependence of the material loss and the wear mechanisms from the applied potential. Within the cathodic region, a small amount of the material degradation could be attributed to a strong adhesion and resulting strain hardening as a consequence of an electrochemical weakening and mechanical destruction of the passive layer. The maximum of wear during polarization at the free corrosion potential under friction was explained by galvanic coupling between the wear track and the passive surface near the stability threshold between Fe2+-Ion and Fe2O3 development. Through increasing Polarization onto the free corrosion potential in the absence of friction and into the passive region, a decrease in material loss could be observed which is presumably attributed to the stable passive layer that inhibits electrochemical degradation and favors the formation of a grain refinement zone that slows down mechanical destruction.

Peculiarities in structure formation and corrosion of cast quasicrystalline Al63Cu25Fe12 and Al63Co24Cu13 alloys in sodium chloride aqueous solution

In this work the structure and corrosion behavior of quasicrystalline cast Al63Cu25Fe12 and Al63Co24Cu13 alloys in 5-% sodium chloride solution (рН 6.9–7.1) were investigated. The alloys were cooled at 5 К/s. The structure of the samples was studied by methods of quantitative metallography, X-ray analysis, and scanning electron microscopy. Corrosion properties were determined by the potentiodynamic method. The made investigations confirm the formation of stable quasicrystalline icosahedral (y) and decagonal (D) phases in the structure of Al63Cu25Fe12 and Al63Co24Cu13 alloys correspondingly. In 5-% sodium chloride solution, the investigated alloys corrode under electrochemical mechanisms with oxygen depolarization. Compared with Al63Cu25Fe12 alloy, Al63Co24Cu13 alloy has a less negative value of free corrosion potential (–0.43 V and–0.66 V, respectively), and its electrochemical passivity region extends due to the inhibition of anodic processes. A corrosion current density, calculated from (E,lgi)-curve, for Al63Co24Cu13 alloy amounts to 0.18 mА/сm2 and for Al63Cu25Fe12 alloy – to 0.20 mА/сm2. The lower corrosion resistance of Al63Cu25Fe12 alloy may be explained by the presence of iron-containing phases in its structure. Based on obtained results, the Al63Co24Cu13 alloy was recommended as a coating material for rocket-and-space equipment working in a marine climate.

Effect of Conducting Polyaniline/Graphene Nanosheet Content on the Corrosion Behavior of Zinc-Rich Epoxy Primers in 3.5% NaCl Solution

The corrosion behavior of zinc-rich epoxy primers or paints (ZRPs) with different conducting polyaniline-grafted graphene (PANI/Gr) contents was investigated. Conductivity of the formed PANI/Gr nanosheets was significantly improved by employing the Gr as the inner template to synthesize the PANI. The protective properties and electrochemical behavior of coatings with artificial defects were investigated by monitoring the free corrosion potential versus time and by using localized electrochemical impedance spectroscopy (LEIS). A synergetic enhancement of the physical barrier role of the coating and the zinc sacrificial cathodic protection was achieved in the case of ZRP including PANI/Gr nanosheets. In addition, the ZRP mixed with the PANI/Gr at a content of 0.6% exhibited the best anticorrosion performance across the range of investigated PANI/Gr contents.

Detailed mechanisms of hydrogen charging and hydrogen stress cracking of steel in liquid ammonia storage

The available polarisation curves of the literature are analysed in view of the theoretical analysis of the corrosive medium in Part I (J.-L. Crolet, Matériaux & Techniques 107, 401, 2019) and the new views on passivation and hydrogen charging. The accurate electrochemical conditions of the respective cathodic and “anodic” hydrogen charging are thus defined, or more exactly the paradox of a protonic cathodic reaction only running at high potential. Similarly in the available exposure test results, the locus of the ternary redox equilibrium between ammonia and its two decisive contaminants, oxygen and water, separates contaminated ammonia into two domains, on the one hand, a safe domain where the undersaturated oxygen cannot act as an oxidiser, hence no anodic HSC at the free corrosion potential, and on the other hand, a dangerous domain where oxygen is supersaturated, hence oxidising conditions, steel passivation, high potentials, anodic charging and anodic HSC. Likewise, all the known features of this environmental cracking are also explained, with no exception nor contradiction, including the differences between the liquid and vapour phases. An experimental method is also proposed to directly check the occurrence of anodic charging, and proposals are also made for at the same time improving safety and reducing operational or capital expenditures.

Steel Reinforcement Corrosion in a Low Calcium Fly Ash Geopolymer Concrete

Geopolymer concrete (GPC) has significant potential as a more sustainable, low-embodied carbon alternative for ordinary Portland cement concrete (PCC). However; as a rather new engineering material, there are some concerns over the durability aspects of geopolymeric binders. In this study, performance of chloride contaminated reinforced GPC specimens manufactured using low calcium fly ash is investigated by long-term monitoring of corrosion parameters such as free corrosion potential and polarization resistance. It was found that low calcium fly ash GPC can perform as well as PCC during the propagation phase of corrosion; although, some conventional reference values of corrosion parameters which are indicative of severity of the steel corrosion in PCC are not suitable for GPC. Additionally, commonly used electrochemical test methods are successfully employed to assess the degree of reinforcement corrosion in geopolymeric binders within an acceptable level of accuracy.

Some Possibilities of Evaluation of Corrosive Resistance of Metal and Non-Metal Coatings

The study investigated the possibilities of determination of corrosion resistance of metal and non-metal (organic) coatings deposited to steel surface in the corrosion environment. To determine the corrosion rate of metal PVD coating based on Ti, we used the method involving measurement of polarization conductivity. Corrosion resistance of galvanic Ni or Ni-Co coatings was determined by measuring free corrosion potential ESCE (against that of saturated calomel electrode SCE), or by means of potentiodynamic polarization relationships according to Tafel. These methods provided the basic corrosion characteristics: corrosion potential Ecorr, instantaneous corrosion rate jcorr and polarization resistance Rp. Corrosion resistance of organic coating Woerodur, which was applied by pressure spray to the substrate pre-treated in various ways, was tested in a salt-fog environment. After the exposure to the respective environment we evaluated the appearance of coating. The aim of the study was to point out to the availability of methods suitable for evaluation of corrosion resistance of coatings, and to the possibilities of their application under real practical conditions.

Influence of sulfate reducing bacteria on the cupronickel corrosion

Purpose – The purpose of this study is to explore the influence of the sulfate reducing bacteria (SRB) on the corrosion of cupronickel. Design/methodology/approach – Tests monitoring the change in free corrosion potential, linear polarization resistance and electrochemical impedance spectroscopy and examination using the scanning electron microscope and energy spectrum analysis were used to investigate the corrosion behavior of cupronickel in blank medium and in media inoculated with SRB to explore the influence of the SRB on the corrosion behavior of cupronickel alloy. Findings – The results show that SRB can destroy the surface oxide film of cupronickel and significantly reduce the free corrosion potential and polarization resistance of the cupronickel, causing the cupronickel to corrode significantly. Originality/value – SRB are widely found in the water supply system and is one of the important factors inducing microbial corrosion. This paper verified that SRB promote cupronickel corrosion and explored the influence and mechanism of attack.