Angeliki Lekatou

• PhD
• Professor (Full) at University of Ioannina

This article presents the systematic data on the effects of carbon and boron on the microstructure and phase elemental composition of the hybrid multi-component alloys, containing (wt pct) 5W–5Mo–5V–10Cr–2.5Ti–1Mn–1Si–Fe(balance). The nominal concentrations of boron were 1.5, 2.5 and 3.5 wt pct; at each boron level, the carbon content was 0.3, 0.7...

This study examines the effect of a Ca-rich fly ash additive, a liquid migrating corrosion inhibitor (Inhibitor B), and a vapor phase inhibitor (Inhibitor C), individually and in combination, on the corrosion performance of 304L stainless steel rebars embedded in concrete cubes. This was assessed through open circuit potential (OCP) measurements ov...

The present work evaluates the effect of Co content on the microstructure and corrosion performance of Al–Co alloys of various compositions (2–32 wt% Co), fabricated by flux-assisted stir casting. A preliminary investigation on the effect of heat treatment (600 °C, up to 72 h) on the microstructure and corrosion behavior of Al–20 wt% Co and Al–32 w...

This study aims at evaluating the effect of simulating porcelain firing on the microstructure, corrosion behavior and mechanical properties of a Co-Cr-Mo alloy fabricated by Metal Soft Milling (MSM). Two groups of Co-28Cr-5Mo specimens (25 × 20 × 3 mm) were prepared by MSM: The as-sintered (AS) specimens and the post-fired (PF) specimens that were...

Salt hydrates are commonly used as buffer materials in thermal storage applications. One of the major problems usually encountered is corrosion issues related with the heat exchanger (HE) materials that are in contact with them. In this study we report results demonstrating a way for addressing this problem by means of thin film coating of the heat...

Co-28Cr-6Mo alloy (ASTM F75) is widely used in different biomedical applications (dental devices, orthopedic implants, etc.). Casting and metal forming are the two conventional technologies for the fabrication of this alloy. Recently, additive manufacturing has also been adopted. Due to the peculiarities of this technological process, 3D-printed al...

The present work compares WC-10Co-4Cr coatings fabricated by HVOF spraying of a conventional powder (1.33 ± 0.67 μm) and a nanostructured powder (0.17 ± 0.06 μm) on Al7075-T6, in terms of microstructure and phase composition, microhardness and fracture toughness, corrosion performance in 3.5 wt% NaCl (potentiodynamic polarization, chronoamperometry...

Combustion-assisted flame spraying (CAFSY) is a novel method that allows in-flight synthesis of alloys during flame spraying. The in-flight synthesis of alloys by the CAFSY method during flame spraying combines two different methods: the self-propagating high-temperature synthesis (SHS) and flame spraying (FS). The present work studies the corrosio...

Al-Co alloys is an emerging category of metallic materials with promising properties and potential application in various demanding environments. Over the years, different manufacturing techniques have been employed to fabricate Al-Co alloys, spanning from conventional casting to rapid solidification techniques, such as melt spinning, thus leading...

The present work studies the effect of fly ash content (0-25 wt.%), pH (8, 12.5), and steel type (316L, 304L) on the cyclic polarization of stainless steel rebars in electrolytes, simulating fresh concrete exposed to acid rain and corroded concrete cover that has exposed the reinforcement to direct acid rain attack. At the same time, it tries to el...

The structural features and nanoindentation/tribological properties of 316 stainless steel fabricated by conventional rolling and laser-based powder bed fusion (LPBF) were comparatively investigated regarding the effect of surface-pulsed plasma treatment (PPT). PPT was performed using an electrothermal axial plasma accelerator under a discharge vol...

The objective of this effort is to study the effect that the combination of fly ash (FA) with a liquid corrosion inhibitor has on the mechanical degradation of 316L rebars embedded in concrete specimens during salt fog testing for a period of four months, as well as the porosity of concrete. Partial replacement of Ordinary Portland Cement (OPC) by...

An Al-5Mg alloy (AA5083) block, deposited over an AA6061 substrate by wire-arc additive manufacturing, was electrochemically tested along two different cross-sectional planes by cyclic polarization in 3.5 wt.% NaCl. The deposited layers and the interlayer boundaries showed similar polarization behavior regardless of the cross-sectional direction. T...

The present study investigates the effect of fly ash (FA) as a corrosion inhibitor on the electrochemical performance of 316L stainless steel concrete reinforcement in a simulating concrete pore solution exposed to a coastal environment that is severely polluted by acid rain (AR). The corrosion behavior of 316L stainless steel is examined by means...

Al–Co alloys of various compositions (2–20 wt.% Co) have been fabricated by vacuum arc melting and evaluated with respect to their microstructure and dry sliding wear performance. A variety of microstructures have been attained, ranging from that of a dual fibrous and lamellar Al/Al9Co2 eutectic (Al-2 wt. % Co), to that of coarse primary Al9Co2 pla...

The effect of repeated heat-treatment (HT) cycles, as precisely applied in the regular dental practice to produce metal-ceramic restorations, on microstructure, mechanical properties, and corrosion resistance of CoCrMo dental alloys, fabricated via the advanced digital technique of selective laser melting (SLM) (with the aid of CAD technology), is...

Al–Co alloys of various Co contents (2–20 wt.% Co) were fabricated by vacuum arc melting (VAM) with the scope to investigate the influence of cobalt on the microstructure and corrosion resistance of Al in 1 M H2SO4. The obtained microstructures were directional, consisting of Al9Co2 platelets (grown to coarse acicular plates as the Co content incre...

We study the effect of introducing different carbon fillers in epoxy, i.e. milled carbon (MC) and carbon nano tubes (CNTs), either separately or combined to produce binary and ternary composites with tailored material. The waterinduced degradation was assessed in relation to the employed carbonaceous filler. All specimens were immersed in water unt...

A “Quenching and Partitioning” (Q&P)–based heat treatment has been applied to rolled grinding steel (0.75 wt pct C-Mn-Cr) balls of 104-mm diameter to prevent their cracking during heat treatment. The conventional route of ball manufacturing includes rolling, water quenching interrupted when the bulk average temperature is 220 °C to 250 °C, and self...

The corrosion behavior of 304L stainless steel rebars in an alkaline solution simulating new concrete subjected to acid rain attack and a mildly to slightly acidic solution simulating corroded cover concrete that ex¬posed the reinforcement to direct acid rain attack, was investigated by reverse polarization. Both solutions contained Ca(OH)2 and fly...

In the present effort, aluminium matrix composites (AMCs) were produced by the addition of submicron‐sized WC particles of low (up to 2.5 vol%) content into a melt of Al1050. Casting was assisted by the use of K2TiF6 as a wetting agent and mechanical stirring in order to limit particle clustering. Particle distribution was reasonably uniform compri...

The present effort compares the corrosion performance of WC-10Co-4Cr coatings prepared from near-nanostructured and conventional WC–10Co-4Cr powders by HVOF spraying on Al7075, a structural alloy of marine and aeronautical applications. The main initiatives for this work are the limited literature on the corrosion behavior of nanostructured cermet...

The electrochemical performance of 316L stainless steel rebars in a solution of pH~8 consisting of Ca(OH)2 and fly ash (0-25 wt.% of the dry mixture) in an acid rain simulating solution was investigated by reverse polarization. Concrete cubes containing 0-25 wt.% fly ash and reinforced with 316L or 304L rebars were subjected to salt spraying. The s...

In the presented research effort, cyclic polarization tests were conducted coupled with acoustic emission measurements, in order to monitor the corrosion phenomena. Previous studies have shown that epoxy composite coatings offer satisfactory corrosion protection to aluminum substrates minimizing and even eliminating some degradation phenomena. I...

Al-matrix composites, ex situ reinforced with WC nanoparticles and in situ reinforced with Al3(Ti,W), Al12W, Al5W and Al4W, have been fabricated by casting assisted by K2TiF6 wetting agent addition and mechanical stirring. A satisfactory particle incorporation and distribution accompanied by a high reactivity have been attained. The presence, topog...

Purpose. This study investigates the possibility of improving the quality of grinding steel balls with a diameter of 100 mm by using Q-n-P heat treatment. Methodology. Steel grinding balls with a diameter of 100 mm, obtained by transverse screw rolling, were used as a material. The heat treatment consisted of balls quenching in a drum-type device a...

Α Co1.5CrFeNi1.5Ti0.5 high-entropy alloy (HEA) of the well-known family of CoCrFeNiTi has been designed using empirical parameters. The aim of this design was the production of a HEA with fcc structure that gives ductile behavior and also high strength because of the solid solution effect. The VEC calculations (8.1) supported the fcc structure whil...

The objective of the present study is the assessment of the employment of fly ash (0 wt.% - 25 wt.%) as corrosion inhibitor of AISI 316L and AISI 304L stainless steels either directly immersed in solutions simulating concrete exposed to acid rain mimicking environment (cyclic potentiodynamic polarization) or embedded in standard concrete cubes (sal...

The main objective of this work is to produce a composite consisting of (a) a cast heat-treatable Al-Mg-Si alloy with high contents of Mg for corrosion resistance and Si to offset the Mg-due poor castability (in situ hypoeutectic Mg2Si/Al composite) and (b) TiC particles at high enough volume fractions (≤ 15%), in order to achieve a satisfactory co...

The effect of pulsed plasma deposition (by an electrothermal axial plasma accelerator) followed by post-heat treatment on the structure and microhardness of a 28 wt.% Cr white cast iron is analyzed and discussed with respect to the microstructure of the conventionally cast monolithic counterpart. The cast iron (as deposited on a 14 wt.% Cr cast iro...

In the present effort, aluminium matrix composites (AMCs) were produced by the addition of submicron‐sized WC particles of low (up to 2.5 vol%) content into a melt of Al1050. Casting was assisted by the use of K2TiF6 as a wetting agent and mechanical stirring in order to limit particle clustering. Particle distribution was reasonably uniform compri...

The accelerated corrosion performance of AISI type 316L stainless steel rebars in solutions simulating concrete exposed to various environments was studied by means of cyclic polarization, before and after a four month salt spray test. B500A structural steel rebars were also tested for comparison reasons. Although 316L showed some susceptibility to...

In the present effort, Al-AlxW composites have been prepared by vacuum arc melting (VAM), conventional casting (CAST) and free sintering (PM) with the objective to determine an effective fabrication route in terms of low cost, ease of manufacture and property boosting. The produced Aluminium Matrix Composites (AMCs) contain several types of in-situ...

The accelerated corrosion performance of AISI type 316L stainless steel in solutions simulating concrete exposed to acid rain with the use of fly ash as corrosion inhibitor was studied by means of cyclic polarization. Fly ash was added to concrete simulating solutions at proportions of 0–25 wt%. Although 316L showed susceptibility to localized corr...

The effect of plasma parameters on the case hardening of wear-resistant high-chromium cast iron in different structural condition is studied. Correlation relations were established between the initial and finite microstructure of the surface layer formed after plasma hardening at different heating rates. Microhardness profiles over the cross-sectio...

The present study deals with the accelerated corrosion performance of AISI 316L & AISI 304L stainless steel reinforcements in solutions simulating concrete exposed to acid rain by means of cyclic polarization.

Plasma transferred arc technique was used for the surface modification of 14.5 wt%-Cr cast iron. The objective of this work was to investigate the microstructural and hardness changes, caused by plasma surface melting and post heat treatment. The processing parameters were: arc current 250 A, voltage 60 V, working gas – argon, scanning speed: 0.25...

Al-7 (wt. %) Co alloys have been prepared by conventional casting (Cast), vacuum arc melting (VAM) and free sintering (FS), with the objectives to: a) determine an effective fabrication route (in terms of low cost, ease of manufacture and property boosting) and b) exploit the benefits that the combination of a complex metallic alloy (Al9Co2) with A...

Aluminum matrix composites were prepared by adding submicron sized WC particles into a melt of Al 1050 under mechanical stirring, with the scope to determine: (a) the most appropriate salt flux amongst KBF4, K2TiF6, K3AlF6 and Na3AlF6 for optimum particle wetting and distribution and (b) the maximum carbide volume fraction (CVF) for optimum respons...

The economic and effective operation of machinery and plant involved in fluids handling is increasingly dependent on the utilization of materials that combine high corrosion resistance and good wear resistance. The present study was undertaken in order to investigate the effect of solid particle erosion on the surface characteristics, the microstru...

The economic and effective operation of machinery and plant involved in fluids handling is increasingly dependent on the utilization of materials that combine high corrosion resistance and good wear resistance. The present study was undertaken in order to investigate the effect of solid particle erosion on the surface characteristics, the microstru...

The present effort was undertaken in order to investigate the manufacturing of aluminum based composites, reinforced by a dual intermetallic phase, Al 9 Co 2-Al 13 Co 4 , using a powder metallurgy route. The metal matrix was reinforced with compositions 2, 5 and 10% vol. The manufacturing of the dual Al 9 Co 2-Al 13 Co 4 powders was carried out by...

Acoustic Emission (AE) technique was employed in potentiodynamic cyclic polarization measurements so as to explore the applicability of AE in Aluminum corrosion monitoring

In the present effort, aluminum 2024-T6 substrates were used as potentiodynamic measurement specimens in cyclic polarization tests. Acoustic emission (AE) was employed in order to correlate the corrosion phenomena taking place with characteristic AE signal descriptors. AE detected signals due to hydrogen bubble related processes during cathodic pol...

Adhesive bonding repair is potentially a cost effective for repairing off shore and underwater marine structures such as underwater pipelines. In such applications steel and Nickel alloys are the most widely used choices. The main use of Invar, a Nickel based alloy, is in cryogenic environments because of it is approximately zero thermalexpansion c...

The accelerated corrosion performance of AISI type 316L stainless steel reinforcement in solutions simulating concrete exposed to various environments was examined in this paper by means of cyclic polarization before and after salt spraying for 4 m.

In this work, the tribological performance of Mo20Ta20W20Nb20V20 Refractory High Entropy Alloy was examined. The alloy's wear response was tested under different experimental conditions. With the use of a metallic ball as a counter body partner, the morphology of the wear track and the presence of Fe oxides controlled the wear rate. When using a ce...

Pulsed plasma treatment was applied for surface modification and laminated coating deposition on 14.5wt%-Cr cast iron. The scopes of the research were: (a) to obtain a microstructure gradient, (b) to study the relationship between cathode material and coating layer microstructure/hardness, and (c) to improve coating quality by applying post-deposit...

TiC crystals were developed and grown through a melt dissolution and reprecipitation mechanism, in different alloy matrices (pure Fe, 316L, Fe-22 at.%Al, Ni-25at.%Al, and pure Co) through the use of Vacuum Arc Melting (VAM) process. The TiC surfaces exhibit a characteristic faceted mode of growth which is explained in terms of classic nucleation an...

The aim of this work is the study of the electrochemical and mechanical behaviour of stainless steel (SS304) adhesively bonded with carbon nanotube (CNT)-reinforced epoxies to either SS304 or carbon-reinforced composites substrates. For metal to metal (MtM) joints, the shear strength of nano-reinforced adhesives was studied using single lap shear s...

Hypereutectic Al-Co alloys of various Co contents (7–20 weight % (wt.%) Co) were prepared by vacuum arc melting, aiming at investigating the influence of the cobalt content on the microstructure and corrosion behavior. Quite uniform and directional microstructures were attained. The obtained microstructures depended on the Co content, ranging from...

In this effort, AMCs reinforced with new intermetallic phases, were produced through casting and compared as far as their microstructure, sliding wear, solid particle erosion, and aqueous corrosion response. Casting was selected as a production method based on the concept: (a) ease-to-handle and low cost production route and (b) optimum homogeneity...

The oxidation and decarburization behavior of 14.55 wt pct Cr-cast iron at 1273 K to 1423 K (1000 °C to 1150 °C) in a dry air atmosphere was studied. A gravimetric investigation showed that intensive oxidation of cast iron takes place at temperatures above 1273 K (1000 °C). It is found that oxidizing heating is accompanied by decarburization, which...

Synthesis and heat treatments of NiAl-Ni3Al high-temperature sprayed coatings by in-flight combustion synthesis (CAFSY) Amalia Marinou1,2, Galina Xanthopoulou1, George Vekinis1, Angeliki Lekatou2, Michail Vardavoulias3 1 Institute of Nanoscience and Nanotechnology, NCSR “Demokritos”, 15310, Athens, Greece 2 Department of Materials Science and Eng...

4th International Conference of Engineering Against Failure (ICEAF IV) 24-26 June 2015, Skiathos, Greece. Adhesive bonding repair is potentially a cost effective for repairing off shore and underwater marine structures such as underwater pipelines. Moreover, when composite materials are employed as bonded patches, the tailoring of the composite to...

4th International Conference of Engineering Against Failure (ICEAF IV) 24-26 June 2015, Skiathos, Greece. The addition of multi wall carbon nanotubes (MWCNTs) in epoxy resins, results in nano-modified composites with enhanced properties like shear strength and stiffness. In addition, the modified epoxy resin, when used as a protective layer, can mi...

Conventional and nanostructured WC-12 %wt Co powders were HVOF sprayed on Al 7075-T6. The nanocoatings presented slightly less microporosity, higher microhardness, higher fracture toughness but higher decarburization, than the conventional ones. The nanocoatings exhibited greater resistance to general corrosion and localized corrosion in 3.5% NaCl...

The scope of the research work is the production and characterization of Al matrix composites reinforced with WC ceramic nanoparticles. The synthesis process was powder metallurgy. The produced composites were examined as far as their microstructure and mechanical properties (resistance to wear, micro/macrohardness). Intermetallic phases (Al12W and...

In the present effort, Aluminium Matrix Composites (AMCs) were produced by the addition of submicron sized TiC and WC particles of low (up to 1.0 vol%) content into a melt of Al1050. Casting was assisted by the use of K2TiF6 as a wetting agent and mechanical stirring to limit particle clustering. An extensive presence of intermetallic phases was ob...

The aim of this work is to study the lap shear strength as well as the response to galvanic corrosion and environmental degradation of Multi Wall Carbon Nanotube (MWCNT) enhanced adhesive bonding on metallic substrates so as to establish whether the response of MWCNT enhanced adhesive patches to environmental degradation is percolation or material...

Abstract: A new, cost-efficient and on-site-applicable thermal spraying process for depositing NiAl metallic overlay or bond-coat coatings for high temperature applications by synthesizing the desired intermetallic phases in-flight during oxy-acetylene flame spraying is presented. Base-metal powders were used for spraying and, by adjusting the spra...

Monolithic Co and Co based composites reinforced by TiC precipitates were fabricated by vacuum arc melting process. The ratio of hexagonal to cubic phase cobalt was affected by the presence of the TiC precipitates. The microstructure of the produced materials was also associated with the presence of TiC crystals. The TiC primary precipitates are ch...

Al7Mg5Si-based TiC reinforced composites have been produced by casting methods. The microstructures of the monolithic alloy and the composite materials are explained in terms of solidification phenomena. The TiC presence significantly alters the matrix microstructure both by causing extensive grain refinement and by altering the extent and morpholo...

In the present effort, AMCs reinforced by submicron TiC and WC particles of low (up to 1 vol%) content were produced by casting and compared as far as their microstructure, wear and corrosion response are concerned. Casting was selected as a production method based on the concept: (a) ease-to-handle and low cost production route and (b) optimum hom...

Al-7 (wt %) Co alloys have been prepared by casting, arc melting (AM) under argon and free sintering, with the scopes to investigate an effective fabrication method (in terms of low cost, ease of manufacture and property boosting) and exploit the corrosion-wise benefits of a single intermetallic phase and the ductility-wise benefits of the Al-rich...

Al7Mg5Si (wt%)-TiC reinforced composites have been produced by flux assisted casting followed by solution and aging heat treatments. The TiC particle addition resulted in a refinement of primary Al grains and Mg2Si Chinese-script morphology, as well as reduction of the Mg2Si phase extent. Both, heat treatment and TiC addition have a positive effect...

Purpose – Bonded composite patches are ideal for aircraft structural repair as they offer enhanced specific properties, case-tailored performance and excellent corrosion resistance. Bonding minimizes induced stress concentrations unlike mechanical fastening, whilst it seals the interface between the substrate and the patch and reduces the risk of f...

The application of bonded joints to repair or reinforce defective metallic aircraft structures is ideal as offers enhanced specific properties, case tailored performance and excellent corrosion resistance. The stress concentration is minimized because of the bonding, whilst it seals the interface between the substrate and the patch and reduces the...

Al-7 (wt %) Co alloys have been prepared by casting, arc melting (AM) under argon and free sintering, with the scopes to investigate an effective fabrication method (in terms of low cost, ease of manufacture and property boosting) and exploit the corrosion-wise benefits of a single intermetallic phase and the ductility-wise benefits of the Al-rich...

The scope of the present work is to investigate whether the introduction of a small amount of multi wall carbon nanotubes (MWCNT) into a polymer adhesive film can: (a) act as an effective corrosion barrier that inhibits access of the electrolyte to the surface of the aluminum substrate, thereby preventing or notably delaying destructive localized a...

An Al-11Mg 2 Si-Si in situ composite was prepared by a modified investment casting technique that employs sub-pressure for castability improvement and immersion of ceramic shell molds in fluidized beds of silica sand and iron particles for heat extraction improvement. The microstructure of the as-cast composite is explained according to the pseudoe...

a b s t r a c t Al-32 (wt%)Co alloys have been prepared by casting, arc melting under argon and free sintering. The received microstructures have been explained in terms of solidification sequences and solid state diffu-sion processes. Corrosion experiments in 3.5% NaCl at 25 °C showed that the alloys exhibit high resistance to localized corrosion...

In this study, Cr white iron of 18.23wt.% was subjected to a series of subcritical heat treatments. At both temperatures of 350 and 450°C, no precipitation of secondary carbides was observed, and the overall microstructure resembles to that of the as-cast condition. At 550°C, hardness values increased slightly compared to the as-cast values. No evi...

This work introduces thermal spraying of an agglomerated high energy ball milled powder produced by a commercial, martensitic steel. The nanostructure of the powder feedstock was examined by means of Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD). Varying levels of HVOF process spraying parameters were employed to deposit the nanost...

Monolithic Ni 3 Al and Ni–25 at.%Al intermetallic matrix TiC-reinforced composites were successfully produced by vacuum arc melting. TiC crystals were formed through a dissolution–reprecipitation mechanism and their final morphology is explained by means of a) Jackson's classical nucleation and growth phenomena and b) solidification rate considerat...