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  • 1.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Sin, Jorge Rituerto
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Bryant, Micheal
    University of Leeds, 2Institute of Functional Surfaces, School of Mechanical Engineering,, United Kingdom.
    Neville, Anne
    University of Leeds, 2Institute of Functional Surfaces, School of Mechanical Engineering,, United KingdomLeeds University, UK.
    Modelling the repassivation kinetics of CoCrMo alloys in simulated body fluids2016In: 10th World Biomaterials Congress, Montréal, Canada, 17 May - 22 May, 2016, Frontiers Media S.A., 2016Conference paper (Refereed)
    Abstract [en]

    CoCrMo alloys used for biomedical applications are often exposed to the combined effect of mechanical wear and electrochemical corrosion. Tribocorrosion tests have been performed in this work to investigate the repassivation kinetics of a HC CoCrMo alloy in four different solutions commonly used to simulate body fluids. The repassivation kinetics are analysed by fitting two different exponential equations. The comparison of the different equations reveals that that a second order exponential equation models the repassivation currents more closely than a first order exponential equation. A repassivation model based on a second order exponential equation is suggested. The repassivation currents are divided in two main phases, a ’coverage’ phase and a ’film thickening’ phase. At the initial stage, when part of the surface is exposed to the corrosive media, higher potentials lead to faster repassivation rates. By contrast, potential does not have a clear effect at the thickening phase, when the material is protected by the oxide film formed on top of the surface.Conclusions The repassivation kinetics of a CoCrMo alloy have been investigated.

  • 2.
    León Zapata, Daniel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    An Investigation of Bent-Beam Stress-Corrosion Test for Titanium Alloys2019Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Titanium alloys are highly resistant to all types of corrosion due to their excellent ability to form an oxide film on the surface. However, under certain circumstances, these alloys may experience an environmental degradation which could potentially, under the application of mechanical stress, lead to a complete failure of the material. One of these cracking processes is stress-corrosion cracking (SCC). SCC has an embrittling effect on otherwise ductile materials under tensile stress. Since titanium alloys are frequently used in the aerospace industry and it is therefore of interest to test these alloys in different environment in order to prevent any future accidents. SCC testing is frequently tested at GKN Aerospace and a new testing method is of interest. The main objective with this work was to gain knowledge of the testing method. Bent-beam testing method has been used to investigate stress-corrosion cracking (SCC) of titanium alloys in a laboratory based experiment. The bent-beam testing method was of type 2-point bent beam test, where a saline solution was applied at the apex of the specimen. The specimens were loaded to a range of stresses from 40%, to 95% of the materials yield strength and the salt concentration in the saline solution was 1wt% and 3wt%. By doing so, a relative susceptibility of the different alloys could be established. Three different titanium alloys were tested: Ti-6Al-4V, Ti-8Al-1Mo-1V, and Ti-6Al-2Sn-4Zr-2Mo. The testing method was able to cause cracking on all titanium alloys, where Ti-6Al-4V was found to be the least susceptible to SCC. Ti-8Al-1Mo-1V, and Ti-6Al-2Sn-4Zr-2Mo showed an overall high susceptibility to SCC as cracking occurred in all testing configurations. Cracking was observed on both the surface of the specimen as well as in the cross sections, where the cracks grew perpendicular to the surface. SEM was also used to evaluate the crack propagation in Ti-8Al-1Mo-1V, and Ti-6Al-2Sn-4Zr-2Mo, and it was found that the cracks grew mostly along the grain boundaries.

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  • 3.
    Linder, Clara
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Investigation of new materials and methods to reduce corrosion of stainless steel in contact with molten chloride salts.2017Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this study, the corrosion resistance of three different stainless steels (304, 316 and 309) towards eutectic chloride salts is investigated. The performances of two materials to reduce the corrosion of the steels are examined: zirconium as sacrificial anode and an Al2O3 coating deposited by flame spraying. Samples are submitted to a 24 hours corrosion test at 700°C in air. The samples are characterised by weight analysis, SEM observations and EDX analysis of their surface and cross-section. The corrosion resistance of the stainless steels is not improved by adding Zr rods in direct contact with the steel, rather decreased in the areas where the rod laid. However, in these conditions, stainless steel 316 has the best resistance to highly corrosive chloride salts. The Al2O3 coating is too porous and penetrated by the salt, the steel underneath is corroded. Nevertheless, some alumina remains intact after the corrosion test, because of the high inertness of the ceramic. The presence of O2 most certainly accelerated the corrosion mechanism studied here.

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  • 4.
    Nilsson, Erik A. A.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Degradation Mechanisms of Heat Resistant Steel at Elevated Temperatures: In an Iron Ore Pelletizing Industry2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis focuses on the different degradation mechanisms of the stainless steel in a travelling grate in a Grate-Kiln iron ore pellet indurator. The travelling grate is a conveyor belt that transports green-body pellets to a rotary kiln while the pellets are being dried and pre-heated to a temperature of 900-1100 °C by recycled hot air. After unloading of the pellets to the rotary-kiln for further sintering, the travelling grate is cooled in room temperature while returning to the loading zone of the wet pellets.

    The steel was tested during thermal cycling in a test-rig, in order to simulate the influence of thermo mechanical fatigue and oxide spallation. The influence of erosion-deposition was investigated in a modified horizontal industrial combustion kiln at 800 °C, with slag and coal from production used as erosive media and combustion fuel, respectively. The influence of minor alloying additions of Mn, Si and Ti on the microstructure was explored by eight different casted alloy compositions. Isothermal heat treatments were performed at 800 °C during 200 hours on steel immersed in deposits recovered from a travelling grate in production.

    The three main degradation mechanisms found in this work are thermal spallation, erosion-deposition and deposit induced accelerated corrosion (DIAC). Thermal spallation of the oxide layer is caused by the thermal expansion difference between the oxide and the metal during heating and cooling. It has been found that Ti improves the spallation resistance while Si reduces it. Spallation of deposits is another cause believed to increase the degradation. Erosion-deposition appears due to simultaneous erosion and deposition of particles on the travelling grate that causes erosion or deposition depending on the amount of alkali metals in the environment. The velocity of the particles also influences erosion and deposition in the way that higher velocities increase erosion. DIAC is proposed to form on the travelling grate due to the concentration of chloride- and sulphate containing alkali metals in the deposits.

     Other than these major degrading mechanisms, minor degradation mechanisms such as internal oxidation, sigma formation, carburization and sensitization towards inter-granular attack have been found inside the steel during heating. Thermo mechanical fatigue (TMF) causes intergranular cracks in the material of the travelling grate. Casting issues such as micro-segregation have also been addressed in this thesis.

    A few different ways to improve degradation resistance have been proposed, such as homogenization heat treatments, optimization of process parameters and inhibitor solutions. 

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  • 5.
    Wang, Di
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Zhao, Jun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Claesson, Per
    Division of Surface and Corrosion Science, Department of Chemistry, KTH Royal Institute of Technology, Stockholm, SE-100 44, Sweden.
    Christakopoulos, Paul
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Rova, Ulrika
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Matsakas, Leonidas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Ytreberg, Erik
    Department of Mechanics and Maritime Sciences, Chalmers University of Technology, SE 412 96, Gothenburg, Sweden.
    Granhag, Lena
    Department of Mechanics and Maritime Sciences, Chalmers University of Technology, SE 412 96, Gothenburg, Sweden.
    Zhang, Fan
    Department of Engineering and Design, School of Engineering and Information, University of Sussex, Brighton, BN1 9RH, United Kingdom.
    Pan, Jinshan
    Division of Surface and Corrosion Science, Department of Chemistry, KTH Royal Institute of Technology, Stockholm, SE-100 44, Sweden.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    A strong enhancement of corrosion and wear resistance of polyurethane-based coating by chemically grafting of organosolv lignin2024In: Materials Today Chemistry, E-ISSN 2468-5194, Vol. 35, article id 101833Article in journal (Refereed)
    Abstract [en]

    Corrosion and wear pose significant challenges to equipment operating in harsh environments. Thus, protective coatings are needed. Anti-corrosion and anti-wear coatings are traditionally fossil-based and often contain environmentally harmful additives. Achieving anti-corrosion and anti-wear coatings based on environmentally benign and sustainable materials is important and a significant challenge. This work focused on the development of organosolv lignin-based polyurethane (OS_lignin-PU) coatings. The coatings were synthesised and evaluated for corrosion protection using electrochemical impedance spectroscopy (EIS) and for wear properties using nanoindentation and nano scratch measurements. EIS revealed that the optimal lignin content for corrosion protection purposes in the OS_lignin-PU coatings was 15 wt%. Moreover, addition of 15 wt% lignin to the OS_lignin-PU coatings also enhanced their wear resistance, as evidenced by reduced thickness loss during tribometer tests. The nano scratch measurements revealed that OS_lignin-PU coatings containing 15 wt% lignin exhibited the lowest scratch depth and friction coefficient. It is found that the developed lignin-containing coating exhibits remarkable corrosion and wear resistance, making it a promising sustainable material in various applications for pursuing sustainable development.

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  • 6.
    Wang, Di
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Zhao, Jun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Claesson, Per
    Division of Surface and Corrosion Science, Department of Chemistry, KTH Royal Institute of Technology, Stockholm, SE-100 44, Sweden.
    Zhang, Fan
    Department of Engineering and Design, School of Engineering and Information, University of Sussex, Brighton, BN1 9RH, United Kingdom.
    Pan, Jinshan
    Division of Surface and Corrosion Science, Department of Chemistry, KTH Royal Institute of Technology, Stockholm, SE-100 44, Sweden.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Green synergy: Eco-friendly, high-performance anti-corrosion and wear-resistant coatings utilizing organosolv lignin and polydimethylsiloxane2024In: Progress in organic coatings, ISSN 0300-9440, E-ISSN 1873-331X, Vol. 190, article id 108365Article in journal (Refereed)
    Abstract [en]

    Anti-corrosion and anti-wear coatings provide an effective solution. However, traditional coatings are often fossil-based and contain heavy metals, posing environmental concerns. The drive for eco-friendly coatings has led to the exploration of green materials. This study combined lignin, an abundant organic material, and polydimethylsiloxane (PDMS), a known hydrophobic material, to address the challenges. Organosolv lignin was functionalised with (3-Aminopropyl)triethoxysilane (APTES), then chemically grafted on PDMS for the final coating synthesis. The optimised coating achieved through an eco-friendly process, exhibiting enhanced hydrophobicity and barrier properties, showing excellent long-term corrosion resistance in NaCl solution. The optimal coating formulation contained 15 wt% lignin and 40 wt% PDMS, demonstrating a high corrosion resistance (measured impedance of 1010 Ω·cm2), which remains effective even after 3 weeks of immersion in 1 M NaCl solution. This coating also showed good wear resistance, with a low friction coefficient evident from nano scratch tests.

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1 - 6 of 6
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