Halina Krawiec

Influence of the Chemical Dissolution of MnS Inclusions on the Electrochemical Behavior of Stainless Steels

Immersion of stainless steel containing a well-controlled density of MnS inclusions in 1 M NaCI, pH 3 leads to the chemical dissolution of these heterogeneities. This process was studied using in situ atomic force microscopy and the dissolution rate of MnS inclusions was estimated between 0.01 and 0.19 μm 3 /min. The effects of MnS dissolution on the chemical composition and the local electrochemical behavior of the specimen surface were investigated using secondary ion mass spectroscopy, X-ray photoemission spectroscopy, and the electrochemical microcell technique. It was shown that stable CrS and unstable FeSO 4 were formed. The size of the areas around MnS inclusions affected by the presence of sulfur-containing species depends on the immersion time and the composition of the native film. The local electrochemical measurements reveal that the chemical dissolution of MnS inclusions promotes pitting corrosion in the surrounding grains at moderate applied potentials for short immersion time and general corrosion of the whole specimen surface for long immersion time.

Influence of surface preparation and microstructure on the passivity and corrosion behaviour of duplex stainless steels

The influence of various surface preparation methods (mechanical polishing, electropolishing and etching) on the passivity and the corrosion behaviour of a duplex stainless steel (UNS S32202) was studied using Auger spectroscopy and the electrochemical microcell technique. From surface analyses, the thickness and chemical compositions (ratios Cr/Fe and O2−/OH−, distribution of chloride and nitrogen) were determined. The corrosion behaviour of samples was investigated from local polarization curves. The presence of oxidation peaks and stable pitting was discussed considering the specimen microstructure and the properties of the passive film.

Corrosion resistance of titanium alloys in the artificial saliva solution

Purpose: The purpose of this article was to characterize the corrosion behaviour and compare two biomedical titanium alloys (Ti-6Al-4V and Ti-10Mo-4Zr) in an artificial saliva solution (MAS) containing lactic acid and hydrogen peroxide (H2O2) used in dentistry. The addition of these two compounds simulate the situation, where the alloy is implanted in the human body and hydrogen peroxide is generated by the inflammatory reaction and lactic acid is release by bacterial in the oral cavity. Design/methodology/approach: In this studies were used following electrochemical techniques: Open Circuit Potential (OCP), Linear Sweep Voltamperometry (LSV), Chronoamperometry at constant potential and Electrochemical Impedance Spectroscopy (EIS). Electrochemical impedance spectra were carried out at the 0.5 V vs. Ag/AgCl potential. The EIS data were fitted using the ZViev software. Findings: The results presented in the work demonstrate that the titanium alloys have a good corrosion resistance. The corrosion behaviour was determined by surface condition of alloys and presence different chemical compounds in the solution. For Ti-10Mo-4Zr titanium alloy in MAS with different concentration of hydrogen peroxide in anodic domain it was seen more clearly. Research limitations/implications: In the future passive films of both titanium alloys will be investigated by: X-ray photoelectron spectroscopy (XPS) and scanning electron spectroscopy (SEM). Originality/value: The corrosion behaviour of biomedical titanium alloy contains molybdenum and zirconium selected as safe alloying elements for human body is presented and compared to commercial Ti-6Al-4V alloy. The corrosion resistance of the titanium alloys was investigated in the artificial saliva solution with addition of lactic acid and hydrogen peroxide.

Influence of the Crystallographic Orientation of Grains and Plastic Deformation on the Electrochemical Behavior of Pure Aluminum in Sodium Chloride Solution

In this paper, the influence of the crystallographic orientation of grains on the corrosion behaviour of pure aluminium is investigated combining the Electrochemical Microcell and the X-Ray Diffraction (XRD) Techniques. Crystallographic orientation has strong influence on the current density in the cathodic branch and the breakdown potential. The influence of plastic deformation (compression) on the corrosion resistance is also investigated. Compression has nearly no influence on the current density in the cathodic domain, but improves the corrosion resistance of aluminium in sodium chloride solution.

Application of the Electrochemical Microcell Technique in Solid State Surface Analysis

In the two last decades, the Electrochemical Microcell Technique (EMT) was used in various electrochemical surface investigations. The diameter of microcapillaries was in the range between few and few hundred microns. This technique was commonly used in corrosion research. Indeed, metallic alloys exhibit a complex microstructure consisting of different metallic and intermetallic phases, inclusions, precipitates... The use of microcapillaries based techniques like EMT makes possible to perform local electrochemical measurements in individual phases. Therefore, it was possible to get information about the behavior of a single grain, inclusion, precipitate... From these information, precursor sites can be identified and criteria leading to corrosion can be proposed.

Electrochemical Behaviour of Co-Cr and Ni-Cr Dental Alloys

The purpose of this paper was to study the corrosion resistance of Co-Cr and Ni-Cr dental alloys in simulated artificial saliva by means of electrochemical techniques. Co and Ni based alloys are widely used in dental skeletal structures and orthopedic implants such as screws, pins and plater. And recently they have been applied for making stents. The advantages of these alloys include low cost of casting, matching thermal expansion coefficient with the ceramics of metal-ceramic restorations, and acceptable mechanical and tribological properties in vivo. The microstructure of investigated alloys were studied by using optical microscopic observation, X-ray diffraction measurements and Scanning Electron Microscope with X-ray microanalyzer. The mechanical properties were characterized by microhardness tests.

Influence of Plastic Deformation on the Corrosion Behaviour of As-Cast AlMg2 and AlCu4Mg1 Aluminium Alloys in NaCl Solution

The influence of plastic deformation on the corrosion behavior of as-cast AlMg2 and AlCu4Mg1 aluminum alloys was studied at the microscale using the Electrochemical Microcell Technique and surface microgauges. It was shown that large strain gradients develop locally. The corrosion behavior of both alloys was affected by plastic deformation. The most active sites contain large strain gradients in AlMg2 and cracks with damage in the matrix in AlCu4Mg1.

Improvement of the Corrosion Resistance of Biomedical Magnesium Alloys in the Ringer’s Solution Using Protective Coatings

The corrosion resistance of magnesium alloys depends on their microstructure, especially the presence of different intermetallic phases and precipitates. In this paper, the electrochemical behaviour of Mg1Ca and Mg1Ca1Si magnesium alloys has been investigated in the Ringer’s solution at 37 °C. In order to improve the corrosion resistance of these magnesium alloys composite coatings were fabricated by modification of a chitosan layer. The coatings were prepared by dip-coating in a chitosan solution and then modified by electrochemical deposition of a layer from a solution containing fluorine ions and water glass. The electrochemical performance of chitosan and chitosan modified coated alloys was evaluated by linear sweep voltamperometry and electrochemical impedance spectroscopy. The coated magnesium alloys possess suitable corrosion behaviour for the application as biodegradable implant material.

Corrosion Behaviour of Ti6Al4V and TiMo10Zr4 Alloys in the Ringer’s Solution: Effect of pH and Plastic Strain

The corrosion behaviour of titanium alloys is not well understood – especially the role of the microstructure and plastic strain. In this paper, the influence of the microstructure and plastic strain on the corrosion resistance of TiMo10Zr4 and Ti6Al4V alloys was studied in the Ringer’s solution at 37 °C. Measurements were performed for different pH values and in aerated and de-aerated solutions using potentiodynamic polarization techniques. Results obtained on the two alloys were compared. It was shown that in the absence of plastic strain TiMo10Zr4 shows better corrosion resistance than Ti6Al4V (especially for pH = 8). By contrast, the current density in the passive range measured after 8% plastic strain was greater on TiMo10Zr4 than on Ti6Al4V, indicating that the passive film on TiMo10Zr4 is less protective than that formed on Ti6Al4V.

Influence of the Metal/Mold Processes on the Casting Mechanical Parameters and Corrosion Resistance

This chapter presents the issue related to the morphology of graphite, namely, flake/compacted/spheroidal graphite that is the main controlling factor of the mechanical and physical properties of cast irons. It is presented that flake graphite in the surface layer can be regarded as a local source of stress concentration and thus the crack growth resistance of the cast iron with flake graphite is extremely poor. It has also been shown that the presence of flake graphite in the surface layer has a significant influence on the mechanical properties of spheroidal graphite cast iron (SGI) and compacted graphite cast iron (CGI), including firstly its plasticity, which decreases with the increasing thickness of the flake graphite layer. Moreover it was shown that the presence of flake graphite makes the surface layer brittle, non-plastic, which results in forming cracks. No flake graphite in the surface layer causes the specimen to deform uniformly, providing the most favorable combination of mechanical properties. Finally, the results of SGI iron corrosion resistance, performed in 0.1 M sodium chloride solution, are shown. It has been indicated that the presence of a thick layer of flake graphite in the surface layer of the castings significantly increases the cathode current, which stimulates the cathodic reaction and oxygen reduction.