Papers by Fani Stergioudi
The feasibility of a cost-efficient method to produce carbon coated Al-foams in a single-step hea... more The feasibility of a cost-efficient method to produce carbon coated Al-foams in a single-step heating process is investigated. In this context, a dissolution-sintering process for manufacturing metal foams is developed using raw cane sugar as both the space holder material and the carbon generating medium. The structural characteristics of the produced carbon coated Al-foams were evaluated by XRD, Raman and SEM analyses. Static compression tests were conducted to determine the mechanical response of the produced carbon coated Al-foams. The produced carbon coated Al-foams were fully covered with an external carbon layer having a relatively uniform thickness, despite the inherent complex 3D surface of the foam. The carbon deposition process led to a significant increase of the compression strength of the Al-foam. A strain softening behavior was observed for the carbon coated Al-foams attributed to micro-cracking of aluminum carbides. The produced carbon coated Al-foams can potentially be used as a catalyst support structure.
The aim of the present study is to introduce a cost-effective and environmentally friendly produc... more The aim of the present study is to introduce a cost-effective and environmentally friendly production process of open-cell metal foams with a view to manufacture porous materials exhibiting good morphological and structural homogeneity. The work also focuses on optimizing the production process control to produce higher quality materials and to achieve a better reproducibility and predictability of their properties. A space-holder method using crystalline raw cane sugar, as a novel leachable pattern for manufacturing open-cell metal foams is described. The mechanical behavior of the produced Al-foams as well as the deformation mechanisms developed during mechanical testing are investigated experimentally and analytically through a developed Finite Element Method simulation of compression tests using the real porous geometry, obtained via computed tomography. Additionally, the feasibility for carburized foam production in an one step-process using crystalline raw cane sugar and emplo...
Defect and Diffusion Forum, 2020
Nano-composite (NCD) and multi-layered (MLD) diamond coatings deposited on cemented carbide tools... more Nano-composite (NCD) and multi-layered (MLD) diamond coatings deposited on cemented carbide tools are often applied in machining of non-ferrous materials. A critical issue for their wear behavior, especially in cutting processes in which interrupted repetitive loads are applied such as milling, is the fatigue strength. The latter parameter is significantly affected by the level of residual stresses in their diamond film structure. For investigating such an issue, untreated as well as annealed for 8h vacuum NCD and MLD coatings of the same thicknesses were produced. Inclined impact tests supported by appropriate FEA models were conducted for calculating the level of the residual stresses and for determining the critical impact force for the fatigue damage after 106 impacts. Moreover, the wear behavior of diamond coated inserts was investigating in milling aluminum foam. According to the attained results, the reduction of the residual stresses in the diamond film structure contributes...
Defect and Diffusion Forum, 2020
TiCN coatings of the same chemical compositions were deposited on HW/K05-K20 cemented carbide ins... more TiCN coatings of the same chemical compositions were deposited on HW/K05-K20 cemented carbide inserts via physical (PVD) and medium temperature chemical vapor deposition (MTCVD) techniques. Nano-indentations coupled with appropriate FEM simulations were used for characterizing the film and substrate mechanical properties. Furthermore, uncoated cemented carbide substrates were annealed in vacuum at temperatures and durations corresponding to the related ones during the PVD and MTCVD process for recording the effect of the deposition temperature and duration on the substrate strength properties. Perpendicular and inclined impact tests at various loads were performed for checking the coating fatigue endurance and adhesion respectively. These material data were considered in FEM supported calculations for predicting the developed stress fields in the cutting edge during turning cast iron GG30 using the PVD and MTCVD TiCN coated inserts. According to the obtained result, both coatings po...
Different manufacturing and surface modification treatments distinctively affect the surface char... more Different manufacturing and surface modification treatments distinctively affect the surface characteristics and microstructure of the workpiece, having a different impact on their effective life-span. The corrosion-fatigue behavior of as-machined (wire-EDM), blasted and anodized aluminum alloy 7075-T651 was investigated using 3.5wt% NaCl aqueous solution and distilled water as corrosive media. An in-situ corrosion-fatigue device capable of producing cyclic loads in a corrosive solution was employed, coupled with FEM analysis. Blasting process offered a prolongation of the corrosion-fatigue life-span in both corrosive media, when compared to the as-machined samples under identical conditions. Anodizing had a deleterious effect in all the examined cases.
MATEC Web of Conferences, 2020
Hydrophobic films were produced on a copper surface by chemical methods. The whole process consis... more Hydrophobic films were produced on a copper surface by chemical methods. The whole process consisted of three stages. Initially the hierarchical structure of the surface was achieved by in situ reduction of Ag+ ions to Ag using silver nitrate solution, thereby creating a nanostructured surface. The copper surface was then coated with polydopamine by a simple immersion procedure. Finally, it was decorated with thiols, to achieve a hydrophobic surface. The wetting angle was used to evaluate the hydrophobicity of the produced surfaces. The anti-corrosion behavior of the produced hydrophobic films, were evaluated on the specimens that showed higher hydrophobicity by electrochemical methods. Electrochemical techniques (potentiodynamic polarization and resistance spectroscopy tests) were performed in 3.5% NaCl solution. Morphology was investigated by scanning electron microscopy (SEM). All experimental results showed a clear improvement in the corrosion behavior of the hydrophobic copper ...
MATEC Web of Conferences, 2020
Nano-composite (NCD) and multi-layered (MLD) diamond coatings were deposited on cemented carbide ... more Nano-composite (NCD) and multi-layered (MLD) diamond coatings were deposited on cemented carbide tools using hot filament chemical vapour deposition (HFCVD) techniques. Appropriate annealings were conducted on the examined diamond coatings in order to be characterized by the same level of residual stresses. The crystalline structure of the employed diamond coatings was investigated by conducting Raman spectra. Inclined impact tests at ambient and elevated temperatures were carried out for assessing their temperature-dependent fatigue strength. Moreover, the wear behaviour of diamond coated inserts was investigating in milling aluminum foam. Raman spectra were also conducted on the treated diamond coatings for capturing potential crystalline changes developed due to the exercised thermal and dynamic mechanical loads during cutting. According to the attained results, the coexistence of sp2– and sp3-bonded phases in the cases of MLD diamond coatings results in an accelerated wear devel...
Coatings, 2020
This article deals with the potential to reduce the amount of the residual stresses in the diamon... more This article deals with the potential to reduce the amount of the residual stresses in the diamond films on cemented carbide inserts for improving their effective interfacial fatigue strength and thus their wear resistance. In this context, nano-crystalline diamond coatings (NCD) were deposited on cemented carbide inserts. A portion of these coated tools were annealed in vacuum for decreasing the amount of residual stresses in the film structure. The annealing temperature was appropriately selected for keeping the substrate strength properties invariable after the coating annealing. Inclined impact tests at ambient temperature on the untreated and heat-treated diamond coated tools were conducted for evaluating their effective interfacial fatigue strength. Depending upon the impact load, after a certain number of impacts, damages in the film-substrate interface develop, resulting in coating detachment and lifting. Via appropriate FEM (Finite Element Method)-evaluation of the impact i...
MATEC Web of Conferences, 2018
Material removal processes like milling, leave only a small process window to minimally distort t... more Material removal processes like milling, leave only a small process window to minimally distort the surface of Aluminum foams. Wire-EDM arises as a suitable alternative. Closed-cell aluminum foams were produced and processed at various conditions through wire-EDM to investigate their effect on the foams' surface integrity. Microstructural analysis, porosity assessment and mechanical testing were employed to evaluate the footprint of the manufacturing process. Depending on the process parameters and especially on the working fluid, severe surface and pores damage may occur, affecting the mechanical response under quasistatic and high-velocity impact loads. A process optimization loop offered a distortion-free surface.
CIRP Journal of Manufacturing Science and Technology, 2016
Many applications are envisaged for metal foams, particularly in equipment of passive safety, bec... more Many applications are envisaged for metal foams, particularly in equipment of passive safety, because of their high capacity of energy absorption under static deformation or impact. The damage analysis in metallic foams is a complex problem and must be performed in a finite strain context. A finite element method simulation of a metal foam under static and impact loads is presented in this work. A comparison with experimental results is also addressed. Metal foams were produced to experimentally investigate their crush behavior and compare their mechanical response with the computational results. The representation of the complex geometry of metal foams, employing Non Uniform Rational B-Splines (NURBS), is a necessary step for a successful and fail-free volume discretization using finite elements. In the present study, the foams geometry has been approximated combining a parametric 3D Voronoi cell volume partitioning with sophisticated CAD algorithms. The applicability of this metho...
CIRP Journal of Manufacturing Science and Technology, 2015
Please cite this article in press as: Bouzakis, K.-D., et al., Repetitive impact test near uncoat... more Please cite this article in press as: Bouzakis, K.-D., et al., Repetitive impact test near uncoated and coated cutting edges for assessing their fatigue behavior.
Ceramics International, 2015
Porous calcium phosphate materials have found enormous use in biomedical applications including h... more Porous calcium phosphate materials have found enormous use in biomedical applications including hard tissue regeneration. In this study, tailored made open-cell porous calcium phosphate samples were produced by employing a novel dissolution sintering process, using crystalline raw cane sugar as a leachable pore former material. The process parameters of the production stages were properly adjusted to optimise the quality and structure of open-cell porous calcium phosphatesamples. The influence of sintering conditions on the macro and micro-structure of the resultant porous product is investigated with a view to produce high-quality and strong porous calcium phosphate samples. Preliminary in-vitro biodegradation results indicate formation of a bone-like apatite on the porous samples surface. Mechanical performance of the produced porous calcium phosphate samples is interesting and dictates their potential use as low load-bearing implants for hard tissue replacement or as filling materials and scaffolds for cancellous bone defects repairs.
Surface and Coatings Technology, 2014
This paper introduces a systematic methodology providing insights to the corrosion fatigue behavi... more This paper introduces a systematic methodology providing insights to the corrosion fatigue behaviour of highstrength steel C-ring specimens, through the development of an appropriate, fully automated, corrosion fatigue device. The apparatus is capable of adjusting the cyclic load and frequency applied on the specimens, whilst being submerged in a corrosive solution. A 3.5% NaCl solution was used as the corrosive medium for the purpose of this investigation, for both galvanized and uncoated specimens, as to quantify the effect of the coating on their fatigue response. The experimental process was simulated through Finite Element Modelling (FEM) to determine in-situ stress fields and elucidate crack propagation. The applied galvanizing process facilitated a prolongation of the corrosion fatigue endurance of the tested high-strength steel, allowing it to withstand a fourfold increased number of cycles to failure, when compared to the uncoated samples under identical conditions. The fractured surfaces of the specimens indicate a different failure mechanism for galvanized and uncoated high-strength steel.
Conventional anodizing and carbon deposition coating treatment is applied to open-cell Al foams a... more Conventional anodizing and carbon deposition coating treatment is applied to open-cell Al foams aiming to enhance the corrosion performance of the material. The Al foams used were fabricated utilizing a dissolution-sintering technique based on powder metallurgy route. X-ray computed tomography and SEM were utilized to assess the structural characteristics of the produced foams. The corrosion properties of all samples produced were assessed experimentally, employing both polarization curves and EIS measurements utilizing a 0.6 M NaCl aqueous solution. Corrosion mechanisms along with appropriate modeling circuits were deduced. Both anodizing and carbon coatings resulted in an augment of the corrosion properties of the Al foams.
The evolution of the Fe-Si phase’s formation during siliconising of ferrous material was studied.... more The evolution of the Fe-Si phase’s formation during siliconising of ferrous material was studied. The examined coatings were formed at 990 oC, via chemical deposition of Si in fluidized bed reactor (FBR). The substrate used for this purpose was carbon steel, ST37. Coatings of 10-50 μm thickness were obtained. Optical micrograph (OM) SEM analysis, as well as XRD measurements were used for coatings characterization. During an annealing process of the as formed coatings an ordering of the solid solution of α-FeSi was observed. The ordering process was found to be continuous and the phase gradually becomes super saturated. A narrow portion of the X-ray diagrams including the 110 and the 220 reflections of the α -Fe and α-Fe3Si was chosen for data elaboration.
A novel slurry-based process for aluminizing nickel foams while improving the mechanical properti... more A novel slurry-based process for aluminizing nickel foams while improving the mechanical properties and conserving the excellent ductility is reported. Cellular unalloyed nickel foams with 92% porosity and uniform pore size and distribution were used as a starting material. Several slurries of different compositions were examined to investigate the possibility of developing an aluminide-nickel intermetallic coating on a Ni foam
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Papers by Fani Stergioudi