Papers by Keyword: Corrosion

Abstract: The aim of this paper is to investigate the effects of elastic stress for a C-ring specimen with an18.974-mm outer diameter and a 1.244-mm wall thickness. Tests are conducted on Type 304L SS material. Half-cell potential measurement specimens are used as methods of exposure and inspection The C-ring specimen for quantitatively determining the stress corrosion. Applying ASTM G38, which is a standard practice for making and using C-Ring Stress-Corrosion, was performed for elastic stress analysis. The results show that the effects of stress on the polarization curve are due to the magnitude of stress level in the specific corrosive environment.

Abstract: Steel corrosion is one of the main problems of concrete structure durability. Compared with the steel, GFRP rebar has the advantages of high strength, low density and good corrosion resistance. Therefore, GFRP becomes a good choice to replace steel bar in concrete structure. Since GFRP material is susceptible to the alkaline conditions, it is necessary to clarify the mechanical properties and corrosion mechanism of GFRP rebar in such an alkaline environment of interior concrete. In this study, the artificial accelerated corrosion tests of two kinds of GFRP rebar (epoxy and unsaturated polyester resin matrix) were conducted at 60 °C in alkaline solution up to 90 days. Then the tensile strength tests of GFRP rebar were carried out. The solution PH values, the tensile strength and mass loss of GFRP rebar were measured. The testing results show that the mass of GFRP rebar had rarely changed, but the tensile strength reduced about 30% after 90-day immersion test in alkaline solution. During the test, the PH value of the alkaline solution decreased from 13.62 to around 12.85, which indicated that the hydroxyl ions of the alkaline solution had been consumed. The ester bonds in resin matrix may hydrolyze in alkaline solution and the bonding interface between fiber and resin can be damaged progressively. It can cause the performance degradation of GFRP rebar. In addition, the relationship between the loss of tensile strength and the reduction of PH can be determined. That means the durability of GFRP rebar in concrete can be enhanced by controlling or limiting the alkalinity when producing concrete. Finally, the GFRP rebar of epoxy resin matrix shows higher retention values of tensile strength and better alkali resistance than those of UPR matrix rebar after 90d immersion in the alkaline solution. The obtained results in this paper can provide application reference of GFRP materials in civil engineering.

Abstract: High strength-to-mass ratio light alloys, such as 7075-T6 aluminium alloys and Ti-6Al-4V titanium alloys, are commonly adopted for high performance structural components in the aeronautic, automotive and maritime sectors. For this reason, it is crucial to investigate the effects of the external environment on their mechanical properties, to avoid dramatic component failure. In the present work, experimental tests were performed on Ti-6Al-4V and 7075-T6 light alloys. Ti-6Al-4V notched flat dogbone specimens, with K_t = 1.18, were tested for quasi-static and SCC effects in a methanol-water aggressive environment at different concentrations. Rotating bending R = -1 fatigue tests were performed on 7075-T6 in air and methanol environment, to evaluate the effects of an aggressive environment on the fatigue strength at 200’000 cycles. The influence of DLC and WC/C PVD coatings on fatigue limit at 200’000 cycles has been evaluated in air and aggressive environment, to assess their mechanical and protective effects on the 7075-T6 substrate

Abstract: Electroless nickel coating is one of the versatile methods to improve the physical properties of aluminium alloys. The increasing demand for high corrosion resistant surface with improved performance leads to the development of poly-alloy and composite coatings with the aid of ultrasonication. In the present study Ni-B alloy and Ni-B-CeO₂ composite coatings were made on 356 aluminium alloy surfaces. The variation in structural and mechanical properties of coatings formed under both ultrasonication and magnetic stirring were investigated. Surface analysis by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) has shown the formation of more uniform coating under ultrasonication. The electrochemical polarization tests show enhanced corrosion resistance in ultrasonic assisted coatings.

Abstract: Rolling contact bearings often referred as antifriction bearings are found in many applications where rotating components are involved. Extreme operating conditions, counterfeit or inferior quality bearings, inadequate lubrication, etc often lead to bearing failures. Each rolling contact bearing failure leaves traces of evidences on what caused its failure. Failure analysis of one such bearing is the subject of this paper.One of the engine ground tests was aborted due to the failure of a self-aligning deep groove ball bearing used in turbo-pump of a liquid rocket engine. Series of engine ground tests are conducted as a part of injector acceptance for a liquid rocket engine. The bearing failure occurred in the seventh engine test of one of such series of ground tests. The bearing mentioned here is made of SAE 52100 steel. Post-test hardware inspection revealed that the bearing and the dynamic seals on either side of the bearing are in failed condition. Inner race of bearing was found blackish in appearance with indentation and corrosion marks. Localized black spots were observed in outer race. Bearing balls were found in deformed condition. The paper highlights the failure analysis of the bearing, root cause of the bearing failure and recommendations to avoid such failures.

Abstract: In this study, two Mg-Zn-Gd alloys (Mg-5Zn-5Gd and Mg-5Zn-3Gd) are fabricated using high purity raw materials and by a clean melting process and subjected to immersion testing. The results indicate an increase in corrosion rate for increase in Gd content and the results are correlated using SEM, XRD and EDS analyses. It is seen that RE addition provides a protective oxide coating over the sample surface thereby assisting the corrosion resistance.

Abstract: PVD hard coating is a well-known surface treatment technology for steels to improve wear resistance and, to some extent, corrosion resistance. In principle, hard coating can be carried out for Al alloys, but due to the natural oxide layer and the insufficient load-bearing capacity of the soft base material, the application of this technology for wear protection of components is not regarded as being particularly promising. The research activities described in this paper focused on electron beam (EB) surface alloying with a Co-based additive, and the influence of two different hardness levels (270HV0.1 and 390HV0.1) on the improvement of the local load-bearing capacity of Al alloys with thin PVD hard coatings. A further focus of this research was on the material-specific aspects of the coating deposition. Compared to steels, the hard coated surface of Al alloys is rougher and the measured adhesion of the coating is significantly lower. For this purpose, different technological PVD parameters (e.g. Ti interlayer, deposition temperature, and time) were adapted to optimize the coating properties – especially adhesion. The paper deals with comparative studies of single (PVD hard coating of Al base material) and duplex treatment (EB alloying of Al base material and subsequent PVD hard coating) by means of improvement of the coating and compound hardness, friction and wear behavior (pin-on-disc test), as well as the corrosion resistance (potentiodynamic measurements in 0.05M H₂SO₄). While the level of improvement in wear resistance as a result of the duplex treatments strongly depended on the adhesion of the thin coatings, the corrosion behavior was strongly influenced by the PVD deposition process and coating thickness.

Abstract: The aim of this work is to investigate the effect of sandblasting and electropolishing on roughness and corrosion rate of AISI 316L stainless steel. The equipment used was sandblasting machine with a working pressure of 5-7 kg/cm2 with a duration of 10 minutes. The silica sand was used with size of 500-800 μm. The equipment used in the electropolishing process is the DC power supply with a maximum output of 2x100A. Anode and cathode material were AISI 316L stainless steel. Electrolyte solution consisted of 96% mass fraction of sulfuric acid and 85% mass fraction of phosphoric acid with a ratio of 1. The parameters used in the electropolish process were voltage, electrodes distance and electropolishing duration process. The combination of sandblasting and electropolishing cause the decrease in surface roughness by more than 28 times, from 3.17 to 0.11 μm. The decrease in the rate of corrosion on specimens that have been treated sandblasting and electropolishing by 37%. The optimum parameters for testing surface roughness and corrosion rate contained in the sandblasting process electropolishing for 10 minutes with a distance of 1 cm, duration 20 minutes and voltage 8V.

Abstract: The paper present aspects about the structural modification of CuZn alloy obtained by casting and used to manufacture the housing which works in corrosive liquid mediums. The analyzed alloy has a chemical composition determine by spectral quantitative analysis, with an optic spectrometer type Foundry Masters, using cooper analysis base. The structural modifications, both in cast state, also after corrosion studies, have highlighted by SEM, at 500x and 2000x magnitude. The experiments were made on samples, with specific dimensions for each analysis.

Abstract: The occurrence of corrosion on glass surfaces results from the reaction between sodium in glass surfaces and water in the atmosphere under a certain condition. This reaction is promoted at high difference of humidity and temperature between a daytime and a nighttime especially in a rainy season. Glass surface treatments, for example by solutions, can improve the hydrolytic resistance. In the previous study, it was found that using 5wt% of alum gave the best effect to increase this property. The aim of this study was to examine the effect of closed and unclosed glass bottles during storage in a warehouse to the hydrolytic resistance. After treatment by 5wt% of alum, the amount of Na leached from the inner surfaces of glass bottles under simulated condition was determined. The weathering chamber was used to simulate the condition of a rainy season in Thailand with conditions set up and run in cycle. At first, the condition under the relative humidity (RH) value of 60 at 32°C was run for 12 hours, and then followed by RH of 80 at 25°C for 12 hours. The cycle was continued in the period of 8, 14, 21, 28, 53 days. After that the quantity of leached Na which is the conversion of hydrolytic property was analyzed by Flame-Atomic Absorption Spectrometry (FAAS). The results showed that the amount of Na leached from the untreated bottles was higher than the treated bottles around 5 times. It was also found that the quantity of leached Na from the untreated and closed bottles was raised with increasing time after 30 days while the untreated and opened bottles gave a rather constant result.