Papers by Keyword: Corrosion

Abstract: Anodizing process conducted in Al7xxx/SiC produced non-uniform thickness of porous anodic film with cavities, micro-pores and micro-cracks. Cerium sealing was chosen as a post treatment to remedy the poor anodic film by providing a composite layer in order to further enhance the corrosion resistance in aggressive environment. In this study, anodizing process was conducted in H₂SO₄ solution at current density values of 15, 20, and 25 mA/cm² at room temperature, 0°C and-25°C for 30 minutes. Subsequently, electroless sealing was conducted in CeCl₃.6H₂O + H₂O₂ solution at room temperature and pH 9 for 30 minutes. Integrated protection composed of anodizing at 0°C and cerium sealing process in Al7xxx/SiC produced cerium rich deposits in the diameter of 64 nm (± 3nm) on the surface of anodic oxide layer. These spherical deposits covered the entire surface of anodic oxide layer in accordance with the morphology of the oxide layer. Otherwise, almost no cerium deposit formed on the surface of the oxide layer by conducted integrated protection at room temperature and-25°C. The integrated process conducted at anodizing temperature of 0°C presented a highest protection degree. The cerium protective layer which leads to the decreasing of corrosion rate and current density up to 99,99% or four orders magnifications than that of bare composite.

Abstract: Nitriding treatment is well known as one of the corrosion protection methods for steels as well as a way to prevent wear and fatigue. Initially, salt bath nitrocarburizing was popular, but recently, gas nitriding, gas nitrocarburizing, plasma nitriding and so on have come to be used more often because of their superior nitriding ability. In the case of nitriding, only nitrogen (N) diffuses into the steel, but in the case of nitrocarburizing, both nitrogen and carbon (C) diffuse into the steel. General speaking, nitriding includes all the treatments mentioned above. The corrosion behavior of nitride carbon steels has been understood mainly by salt bath or gas nitrocarburizing treatments^1)-4).However, recently, nitriding is mainly applied to parts for things such as automobiles which need protection from wear and fatigue, and is seldom used for parts which need corrosion resistance. The present paper is to remind researchers again that nitrided steels show good corrosion resistance.Therefore, the comparison of various thicknesses of nitride layers as well as the comparison between nitride layers on steel has been carried out in this examination, using the salt spray corrosion test method. The effect of oxidation treatment after nitriding was also investigated.

Abstract: The purpose of the present study is to evaluate the effect of the electroless Ni-P/diamond/graphene composite coating on the structure and surface hardness of 2024-T6 aluminum alloy as well as their effect on the corrosion and wear resistance of the alloy in 3.5 % NaCl solution. The electroless Ni-P plating solution was prepared by adding different size diamond (6-12 μm and 0.2 μm) and nanographene into the electroless Ni-P plating solution to obtain Ni-P/diamond, Ni-P/graphene and Ni-P/daimond/graphene composite coatings for comparison. Experimental results indicated that the Ni-P/diamond, Ni-P/graphene and Ni-P/daimond/graphene composite coatings can be successfully electroless deposited on anodized 2024-T6 aluminum alloy. The anodically oxidized films, that formed on the aluminum alloy using phosphoric acid as the electrolyte, was porous with high density of pores, and thus could enhance the adhesion of the composite coatings. The Ni-P/daimond/graphene hybrid coating had a higher hardness as well as better corrosion and wear resistance of 2024-T6 alloy in 3.5 wt.% NaCl solution as compared with other composite coatings. When the combination of nanographene and smaller diamond particles added this beneficial effect was significantly raised, especially the composite coating was further vacuum annealed at 400 °C for 24 h to obtain a more smooth and defect-free coating structure.

Abstract: In this study nanoTiO₂ particles were incorporated into the electroless plating solution to prepare Ni-P-TiO₂ composite coating on anodized AA7075 aluminum alloy to improve the wear and stress corrosion cracking resistance of the coated alloy in 3.5%NaCl solution. The anodized AA7075 aluminum alloy was also performed by a boiling water sealing treatment for comparison. The wear and stress corrosion cracking (SCC) characteristics were investigated using a self-designed block-on-ring machine and slow strain rate test. The effect of corrosion was evaluated by electrochemical polarization measurements. The surface morphology, element composition and surface hardness of the coating were analyzed by scanning electron microscopy (SEM), X-ray energy dispersive spectrometry (EDS) and Vicker′s hardness tester. Experimental results indicated that after boiling water sealing treatment the resistance properties of the anodized AA7075 aluminum alloy were further improved. The anodizing treatment of AA7075 aluminum alloy gave a thick film with high porosity. The porous film efficiently improved the cohesion, adhesion and hardness of the electroless Ni-P composite coating. Therefore, the electroless Ni-P composite coating deposited on the anodized AA7075 aluminum alloy offered a superior wear, pitting corrosion and stress corrosion cracking resistance properties than both anodizing and sealing treatment. By comparison with Ni-P and Ni-P-TiO₂ coatings the incorporation of TiO₂ resulted in a more uniform and crack-free surface structure of the composite coating. This is responsible for the higher hardness, better wear, pitting corrosion and stress corrosion cracking resistance of the electroless Ni-P-TiO₂ coating.

Abstract: Corrosion is an everyday occurrence. It provokes the materials destruction, what directly translates into the durability, survivability and reliability of the equipment, specially of working in the aggressive environments one – e.g. afloat ships or boats. Corrosion is a cause of growth of the requirements of the raw materials needed for production of more and more new products and increase amount of waste come from this production.In the paper authors show the results of the experimental tests and they describe the meaning of the selection of laser bean parameters oriented for surface of chosen steel exposed to even corrosion.

Abstract: Magnesium-zinc (Mg-Zn) alloys are strong candidates as medical implant materials due to their good biocompatibility and relatively high strengths. To manipulate the degradation of Mg-Zn alloy in the human body, a plasma electrolytic oxidation (PEO) treatment was applied to Mg-10%wt. Zn in this study because it produces a coating that is non-harmful to the human body and the process is inexpensive and environmentally friendly. Potentiodynamic polarization corrosion tests, performed in a simulated body fluid (Hanks’ Balanced Salt Solution) were applied to the coated and uncoated Mg-Zn samples. The results of the testing showed that the coated Mg-Zn exhibited higher corrosion resistance than the substrate. With the PEO coating thickness of 7.2 microns, the corrosion current density was reduced by 1.00 μA/cm² from the uncoated Mg-Zn respectively, indicating a significant reduction in the degradation rate between pure Mg-Zn and coated Mg-Zn from 7.0 to 3.7 kg/year. A pin-on-disc tribometer was employed to measure the coefficient of friction (COF) for the coated and uncoated Mg-Zn samples, lubricated with and without Hanks’ solution. The measured COF of the coated sample was very low (averaging to be about 0.22 under the lubricated condition) and comparable to that of the substrate which exhibited an averaged COF of 0.13 under the lubricated condition.

Abstract: Total hip prosthese are widely used in total hip arthroplasty, offering many benefit to patients with different articular diseases like osteoarthritis or after different accidents. Many total hip prosthesis are now available to the orthopaedic surgeons to replace the hip articulation, with different design and with components made by different type of biomaterials: metallic (cobalt-chrome and titanium alloys, zirconium-niobium alloy named oxinium), ceramic (alumina, zirconia), polymers (ultra high weight molecular polyethylene-UHMWPE). Even total hip arthroplasty has a high success rate, implant loosening may occur, with different symptoms that could be attributed to metal allergy. Because the stem components of the total hip prosthesis are made by metallic biomaterials, many papers describe the adverse effects related to the release of metal ions (like cytotoxicity, carcinogenicity and metal allergy). There are different types of metal corrosion: intergranular, pitting, crevice, fatigue, stress, fretting, and galvanic. On the other hand, in many cases (like metal-on-metal prosthesis) appear corrosion and wear between two metallic components. This processes are favourable for the aparition of hypersensitivity-related tissue reactions. Especially some metallic ions (nickel, cobalt, and chromium) presents in stainless steels and cobalt-chromium alloys are most known to be released from prostheses components and give metal allergy. Of course, during the time was developped some solutions in order to improve the performance of the hip prostheses components made by metallic components like coating with thin layers using different biomaterials like porous titanium or hydroxiapatite. The aims of this review article were to explore mainly the relationship between corrosion products and implant-related hypersensitivity, the importance of surface treatment for metallic components, try define the effect of metal ion concentrations, and differentiate between allergy and infection in total hip replacement. The long-term performance of the coated components will be also analyzed and synthetic described based on clinical results. Also, some relevant aspects from our clinical experience and retrieved prosthesis analysis using stereomicroscopy and scanning electron microscopy will be shown in order to support the conclusions.

Abstract: Typical applications of metallic dental materials include metal-ceramic restorations, dental implants or orthodontic systems. Due to their contact with human tissues, corrosion resistance is one of the main requirements for dental materials. In the present paper, the corrosion behaviour in Fusayama Meyer artificial saliva solution (pH=5.2) on a selection of four different metallic dental materials (316 L steel, Au based alloy, cp-Ti, Ti6Al4V alloy) currently used in dentistry were investigated. The metallic dental materials have been investigated in terms of electrochemical analysis, chemical composition, morphology before and after corrosion, wettability and roughness. The results showed a hydrophilic behaviour in the case of Au based alloy, cp-Ti and Ti6Al4V alloy, and hydrophobic for 316L stainless steel. Considering the main electrochemical parameters, the cp-Ti alloy exhibited better corrosion resistance in artificial saliva with pH=5.2, followed by Au based alloy, Ti6Al4V alloy and 316L stainless steel. The main objective of the present paper was to evaluate the corrosion behaviour, as in important factor in the selection of metallic materials used in dentistry.

Abstract: Reinforcing bar corrosion is a major cause of the degradation of reinforced concrete structures, because the high quantities of chloride de-icing salts used. In addition the increase in construction near coastal marine environments may increase the potential for corrosion deterioration in these areas. As a result, some structures of ordinary Portland cement concrete with carbon steel reinforcement are requiring repair and remediation long before their current specified service lives (typically 40-50 years) are reached [1]. Therefore, easier, faster and more reliable condition analysis techniques are required than those currently available to allow corrosion detection at an earlier stage and, thus, permit remedial action to be take before major repairs are required.

Abstract: For ensuring fuel consumption and pollution reduction, the researches made in the past decades considerable efforts to replacing steel with aluminum alloys in manufacturing auto bodies, or in naval transportation, because the promising weight saving. The researches consisted in general corrosion (the gravimetric index and the corrosion rate, Vcorr) and tensile tests (Rm, Rp_0.2 and A5) in correlation with microstructure analysis of heat treated Al-Mg-(Si) system samples alloy, in order to obtain the best corrosion resistance and high mechanical characteristics. The Al alloys in extrusion state were solution treated at 510 – 545oC for 10-60 minutes, quenched in water 30-50o C and artificial aging at 150, 180 and 210°C at different time of aging (1, respectively 3, 7 and 11 hours). After heat treatment the obtained alloys were corroded in solution of 53g NaCl + 1000 ml distilled water and boiled in these solutions for 8, 16 respectively 24 hours. The gravimetric index was determinate by mass loss measurements for all types of heat treatment conditions. After corrosion test, samples were prepared for optical microstructural analyzing and mechanical tested. We have compared the obtained results on Al-Mg and Al-Mg-Si alloys. Were established (i) the optimum heat conditions parameters for obtaining of highest values of mechanical characteristics and corrosion resistance and also (ii) was explained the structural evolution during age (precipitation) hardening for both systems.