The use of stainless steel alloys in reinforced concrete structures has shown great success in mitigating corrosion in even the most severe of exposures. However, the use of high-strength stainless steels (HSSSs) for corrosion mitigation in prestressed concrete (PSC) structures has received limited attention. To address these deficiencies in knowledge, an experimental study was conducted to investigate the feasibility of using HSSSs for corrosion mitigation in PSC. The study examined mechanical behavior, corrosion resistance, and techniques for the production of HSSS prestressing strands. Stainless steel grades 304, 316, 2101, 2205, 2304, and 17-7 along with a 1080 prestressing steel control were included in the study. Tensile strengths of 1250 to 1550 MPa (181 to 225 ksi) were achieved in the cold-drawn HSSSs. 1000 hr stress relaxation of all candidate HSSSs was predicted to be between 6 and 8 % based on the results of 200 hr tests conducted at 70 % of the ultimate tensile strength. Residual stresses due to the cold drawing had a significant influence on stress vs. strain behavior and stress relaxation. Electrochemical corrosion testing found that in solutions simulating alkaline concrete, all HSSSs showed exceptional corrosion resistance at chloride (Cl-) concentrations from zero to 0.25 M. However, when exposed to solutions simulating carbonated concrete, corrosion resistance was reduced and the only HSSSs with acceptable corrosion resistance were duplex grades 2205 and 2304, with 2205 resistant to corrosion initiation at Cl- concentrations up to 1.0 M (twice that in seawater). Based on these results, duplex grades 2205 and 2304 were identified as optimal HSSSs and were included in additional studies which found that: (1) 2304 is susceptible to corrosion when tested in a stranded geometry, (2) 2205 and 2304 are not susceptible to stress corrosion cracking, and (3) 2205 and 2304 are susceptible to hydrogen embrittlement. Efforts focused on the production of 2205 and 2304 prestressing strands showed that they could be produced as strands using existing ASTM A416 prestressing strand production facilities. Due to the ferromagnetic properties of 2205 and 2304, a low-relaxation heat treatment was found to be a viable option to reduce stress relaxation and improve mechanical properties. The overall conclusion of the study was that HSSSs, especially duplex grades 2205 and 2304, show excellent promise to mitigate corrosion if utilized as prestressing reinforcement in PSC structures exposed to severe marine environments.

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The research objectives for this project were to explicitly define the anchor bolt corrosion problem in the state of Georgia and recommend action to the Georgia Department of Transportation. The bearing assembly of concern is the plate bearing assembly, in which carbon steel and/or bronze plates are anchored by either carbon steel or stainless steel anchor bolts. Inspection report data revealed that anchor bolt corrosion was ubiquitous for all environments in Georgia; the problem was reported for 27% of the steel girder bridges throughout the state. Based on a synthesis of the field investigations, bolt failure analyses, laboratory experimental testing, and review of GDOT inspection report surveys, the corrosion of carbon steel anchor bolts is caused universally by concentration cell corrosion. Other corrosion mechanisms of concern are galvanic and crevice corrosion, which are both enhanced by the current bearing design. Corrosion protection provided through zinc galvanization cannot sufficiently protect the carbon steel bolt for its entire service life. Corrosion potential and cyclic polarization data confirmed that ASTM Type 304, Type 316, Type 2101, and Type 2205 were protected from concentration cell and localized corrosion in the simulated bearing environment. Therefore, it is recommended that the stainless steel anchor bolts of these types be use in future designs and that the bolts should be electrically separated from all dissimilar metals using a Nylon or Teflon washer to prevent preferential corrosion of carbon steel. It is further recommended that the bronze lube plate should be eliminated entirely and that the bearing type should be a reinforced elastomeric bearing. Maintenance of existing sliding plate bearings should include regular cleaning by brushing away debris from the bearing surfaces, and bridges with carbon steel anchor bolts should be retrofitted to provide additional lateral restraint according to current maintenance procedures.

O presente trabalho apresenta um estudo do efeito do hidrogênio, a influência da temperatura e do tempo no processo de pós-oxidação por plasma pulsado na liga ferrosa AISI 1045 previamente nitretada a plasma. O estudo das fases cristalinas presentes no sistema foi realizado pela técnica de difração de raios X (DRX). O método de refinamento por Rietveld foi utilizado para quantificar o conteúdo de fases presentes. A estrutura eletrônica da superfície oxidada foi estudada por espectroscopia de fotoelétron induzidos por raios X (XPS). A morfologia e espessura da camada do óxido foram avaliadas por microscopia eletrônica de varredura (MEV) e microscopia de força atômica (AFM). As propriedades mecânicas foram estudadas mediante ensaios de nanoindentação. Ensaios de névoa salina foram executados com o intuito de estudar a resistência à corrosão acelerada do sistema tratado. O hidrogênio controla a formação das fases oxidadas (hematita (α-Fe2O3) e magnetita (Fe3O4)). Uma concentração de 25% de H2 na mistura gasosa oxidante proporciona uma camada de óxido livre de hematita. Por um lado, a espessura do óxido segue um comportamento exponencial tipo Arrhenius em função da temperatura de tratamento típico de um processo termicamente induzido, com uma energia de ativação de 68±5 kJ/mol. Por outro lado, a espessura de óxido segue um comportamento tipo-parabólico com o tempo de tratamento típico de um processo de reação-difusão. Baixas temperaturas e curtos tempos de processo proporcionam camadas de óxidos mais homogêneas, compactas e com maior dureza. Os ensaios de corrosão mostraram que superfícies sem estruturas globulares, mais compactas e com poros fechados possuem uma maior resistência à corrosão, porém ainda não atende a especificação mínima para possível substituição do cromo duro em ligas ferrosas. / Submitted by Marcelo Teixeira (mvteixeira@ucs.br) on 2014-06-03T20:03:33Z No. of bitstreams: 1 Dissertacao Ane Cheila Rovani.pdf: 4107903 bytes, checksum: b0c996d1f4f11b450359612f22128b77 (MD5) / Made available in DSpace on 2014-06-03T20:03:33Z (GMT). No. of bitstreams: 1 Dissertacao Ane Cheila Rovani.pdf: 4107903 bytes, checksum: b0c996d1f4f11b450359612f22128b77 (MD5) / This work shows the hydrogen effect and the influence of processing temperature and time in the post-oxidation treatment by pulsed plasma on nitrided AISI 1045 ferrous alloy. The crystalline structure was analyzed by X-ray diffraction (XRD). The Rietveld refinement method was used in order to quantify the present phases in the system. The electronic structure of the oxide layer was studied by X-ray photoemission electron spectroscopy (XPS). The morphology and oxide layer thickness were analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The mechanical properties were studied by nanoindentation tests. In an effort to know the corrosion resistance of our systems, salt spray tests were executed. Hydrogen controls the formation of oxide phases (hematite (α-Fe2O3) and magnetite (Fe3O4)). A 25 % H2 concentration in the oxidation gas mixture leads to obtain a hematite-free oxide layer. On one hand, the oxide layer thickness follows an exponential Arrhenius-like behavior with processing temperature which is characteristic of a thermally induced-process with activation energy of 68±5kJ/mol. On the other hand, the oxide layer thickness follows a parabolic-like behavior with processing time which is characteristic of the reaction-diffusion process. Lower temperatures and shorter times of processing render more homogenous and compacts oxide layers with higher hardness. Although, corrosion tests show that surfaces without globular structures, more compacts and with closed-pores have higher corrosion resistances, our system does not attend the minimal specification in order to substitute hard chromium in ferrous alloys.

O presente trabalho apresenta um estudo do efeito do hidrogênio, a influência da temperatura e do tempo no processo de pós-oxidação por plasma pulsado na liga ferrosa AISI 1045 previamente nitretada a plasma. O estudo das fases cristalinas presentes no sistema foi realizado pela técnica de difração de raios X (DRX). O método de refinamento por Rietveld foi utilizado para quantificar o conteúdo de fases presentes. A estrutura eletrônica da superfície oxidada foi estudada por espectroscopia de fotoelétron induzidos por raios X (XPS). A morfologia e espessura da camada do óxido foram avaliadas por microscopia eletrônica de varredura (MEV) e microscopia de força atômica (AFM). As propriedades mecânicas foram estudadas mediante ensaios de nanoindentação. Ensaios de névoa salina foram executados com o intuito de estudar a resistência à corrosão acelerada do sistema tratado. O hidrogênio controla a formação das fases oxidadas (hematita (α-Fe2O3) e magnetita (Fe3O4)). Uma concentração de 25% de H2 na mistura gasosa oxidante proporciona uma camada de óxido livre de hematita. Por um lado, a espessura do óxido segue um comportamento exponencial tipo Arrhenius em função da temperatura de tratamento típico de um processo termicamente induzido, com uma energia de ativação de 68±5 kJ/mol. Por outro lado, a espessura de óxido segue um comportamento tipo-parabólico com o tempo de tratamento típico de um processo de reação-difusão. Baixas temperaturas e curtos tempos de processo proporcionam camadas de óxidos mais homogêneas, compactas e com maior dureza. Os ensaios de corrosão mostraram que superfícies sem estruturas globulares, mais compactas e com poros fechados possuem uma maior resistência à corrosão, porém ainda não atende a especificação mínima para possível substituição do cromo duro em ligas ferrosas. / This work shows the hydrogen effect and the influence of processing temperature and time in the post-oxidation treatment by pulsed plasma on nitrided AISI 1045 ferrous alloy. The crystalline structure was analyzed by X-ray diffraction (XRD). The Rietveld refinement method was used in order to quantify the present phases in the system. The electronic structure of the oxide layer was studied by X-ray photoemission electron spectroscopy (XPS). The morphology and oxide layer thickness were analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The mechanical properties were studied by nanoindentation tests. In an effort to know the corrosion resistance of our systems, salt spray tests were executed. Hydrogen controls the formation of oxide phases (hematite (α-Fe2O3) and magnetite (Fe3O4)). A 25 % H2 concentration in the oxidation gas mixture leads to obtain a hematite-free oxide layer. On one hand, the oxide layer thickness follows an exponential Arrhenius-like behavior with processing temperature which is characteristic of a thermally induced-process with activation energy of 68±5kJ/mol. On the other hand, the oxide layer thickness follows a parabolic-like behavior with processing time which is characteristic of the reaction-diffusion process. Lower temperatures and shorter times of processing render more homogenous and compacts oxide layers with higher hardness. Although, corrosion tests show that surfaces without globular structures, more compacts and with closed-pores have higher corrosion resistances, our system does not attend the minimal specification in order to substitute hard chromium in ferrous alloys.

M.Ing. / During all manufacturing processes it is crucial to use certain design criteria and guidelines. Special care should be exercised when the final product of a manufacturing process is used in the automotive industry, because the failure of such a component may have tragic consequences. The failure of a bus chassis in the public transport sector is an example of a case where the failure of a product can have serious consequences. In recent years it has become common practice to use corrosion-resisting steel in the manufacture of these vehicles. The reason for this is the corrosion caused by a prolonged service life and adverse conditions such as salted road surfaces (The salt is used to melt the ice that forms on roads, particularly in European countries). These bus structures consist of tubes of varying size and geometry, and the manufacturing process of these tubes is considered in the present investigation. In a tube manufacturing process the design criteria may consist of such properties as the tube size and geometry, the thickness of the sheet that is used and the radius of the corners of the tube. Design criterion is also dependent upon the material that is used. The change in mechanical properties of the material during a manufacturing process is an important consideration during the establishment of design guidelines. The purpose of this investigation is to study the effects of particularly the cold forming manufacturing process on the mechanical properties of the material. The material used is 3CR12 corrosion resisting steel, a proprietary alloy also known as Type 1.4003, that was developed by Columbus joint venture as a cheaper alternative to stainless steels. 3CR12 is not a substitute for stainless steel but it is an alternative to treated mild steel, providing a cost-effective solution to corrosion. An experimental investigation is conducted into the forming of 40mm 3CR12 square tubes and normal plate bending of 3CR12. Various different wall thicknesses and bend radiuses are considered. A numerical investigation consisted of simulating the above-mentioned manufacturing processes using non-linear finite element analysis and then comparing its results to the experimental investigation. The experimental investigation showed that substantial work hardening occurred in the corner regions of the tube during forming. A loss of up to 70% of 3CR12's ductility may result in the corner regions. The work hardening at the inside of the tube was found to be higher than at the outside. A region of very little work hardening near the middle of the tube wall thickness was also identified (neutral axis). This neutral axis also seems to shift slightly more to the inside of the tube with thicker wall sections. The numerical analysis confirmed the experimental observations. An excellent correlation between the experimental and numerical results was achieved.

Magnesium and its alloys are considered as the potential biomaterials due to their biocompatibility and biodegradable characteristics but suffer from poor corrosion performance. Various surface modification techniques are employed to improve their corrosion resistance. In present case, laser surface melting was carried out on AZ31B Mg alloy with various laser energy densities using a continuous wave ytterbium laser. Effect of laser treatment on phase and microstructure evolution was evaluated by X ray diffraction and scanning electron microscopy. Multi-physics thermal model predicted time temperature evolution along the depth of the laser treatment zone. Additionally, electrochemical method and bio-immersion test were employed to evaluate the corrosion behavior in simulated body fluid medium. Microstructure revealed grain refinement and even distribution of Mg17Al12 phase along the grain boundary for laser treated samples leading to substantial enhancement in the corrosion resistance of the laser treated samples compared to the untreated alloy. The laser processed samples also possessed a superior wettability in SBF solution than the untreated sample. This was further reflected in enhanced bio-integration behavior of laser processed samples. By changing the parameters of laser processing such as power, scanning speed, and fill spacing, a controllable corrosion resistance and bioactivity/biocompatibility of the implant material was achieved.

Hierarchical arrangement of biological composites such as nacre and bone containing high filler (ceramic) content results in high strength and toughness of the natural material. In this study we mimic the design of layered bone microstructure and fabricate an optimal multifunctional bio-nanocomposite having strength, toughness and corrosion resistance. Poly (butylene adipate-co-terephthalate) (PBAT), a biodegradable polymer was used as a substrate material with the reinforcement of LDH (Layered double hydroxide) as a nanofiller in different concentrations to achieve enhancement in mechanical properties as well as processing related thermostability. Corrosion resistance was increased by mimicking a layered structured which incorporated a tortuous diffusion path.

Through a series of carefully designed experiments, characterization and some modeling tools, this work is aimed at studying the role of thermal profiles on different microstructural zones and associated properties like strength and corrosion through a variation of weld parameters, thermal boundary conditions and material temper. Two different alloys belonging to the Al-Cu and Al-Cu-Li system in different temper conditions- peak aged (T8) and annealed (O) were used. A 3D-thermal pseudo mechanical (TPM) model is developed for the FSW process using heat transfer module in COMSOL Multiphysics and is based on a heat source wherein the temperature dependent yield shear stress is used for the heat generation. The precipitation and coarsening model is based on the Kampmann and Wagner theoretical framework and accounts for the competition between the various nucleation sites for both metastable and equilibrium precipitates. The model predicts different precipitate mean radius and volume fraction for the various zones in the friction stir welded material. A model for the yield strength is developed which considers contributions from different strengthening mechanisms. The predictions of the each models have been verified against experimental data and literature. At constant advance per rotation, the peak temperature decreases with a decrease in traverse speed and increases with an increase in tool rotation. Weld properties were significantly affected by choice of thermal boundary conditions in terms of backing plate diffusivity. Weld conditions with a higher peak temperature and high strain rate results in more dissolution of precipitates and fragmentation of constituent particles resulting in a better corrosion behavior for the weld nugget. For a peak aged temper of 2XXX alloys, the weld nugget experiences dissolution of strengthening precipitates resulting in a lower strength and the Heat affected zone (HAZ) experiences coarsening of precipitates. For an annealed material, both the weld nugget and HAZ experiences dissolution of precipitates with an increase in strength in the weld nugget.

Zn-Mo coatings are very promising environment friendly anticorrosive coatings as replacement materials for cadmium and chromium (VI) based conversion layers. Electrodeposition has become a favorable technique in fabricating coatings due to its low cost, ease of use, and overall experimental control of coating quality. Very little research so far has been done for the electrodeposition of Zn-Mo coatings under alkaline conditions. In this work, Zn and Zn-Mo coatings were electrochemically deposited on stainless steel from an aqueous alkaline citrate solution. An organic compound, vanillin, was added to the electrolyte as a leveling agent for improving interlayer adherence and corrosion resistance of Zn-Mo coatings. Ni-Mo alloys have been known to possess high tensile strength and excellent corrosion protection of steels, and MoTe2 layers have a potential for the application in anticorrosive coatings due to their hydrophobic properties. In this study, MoTe2-Ni-Mo coatings were deposited on stainless steel using both sputtering and electrodeposition methods. These coatings with high corrosion resistance and other desirable properties are in demand in the oil and gas industry since they can protect and thus extend the lifetime of the underlying materials when exposed to aggressive environments. The Zn-Mo and MoTe2-Ni-Mo coatings were evaluated for chemical composition and corrosion behavior using different types of instrumental and electrochemical techniques. The addition of vanillin to the electrolyte did not change the crystalline structure or composition of the Zn-Mo coating, however, the corrosion resistance of the coating was significantly improved by the leveling effect of vanillin during the electrodeposition. The corrosion resistance of the Ni-Mo coating was also enhanced by applying the hydrophobic MoTe2 monolayer on the top surface.