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Papers by Seifallah Fetni

International Journal of Renewable Energy Research, 2019

Thermal exposure changes in the microstructure of the 9Cr-1Mo steel, largely used in thermal powe... more Thermal exposure changes in the microstructure of the 9Cr-1Mo steel, largely used in thermal power plants and petro-chemical industry, have been investigated, through long term experience at 550◦C in furnace, up to 7000 hours. Detailed analysis of the microstructural evolution and changes in secondary carbides (M23C6) were carried out through SEM, XRD and EDX analysis. Electrochemical extractions were done because of the small volume of carbides. A progressive restoration of the tempered martensite matrix was observed. Moreover, a continuous increase of M23C6 size is revealed until stabilization after about 5000 hours of exposure. The nucleation of Laves phases is here found ; two inverse contributions may be concluded. When nucleating far from secondary precipitates, these phases grow by consuming matrix elements, which can trigger creep damages. Nevertheless, by surrounding the M23C6 carbides like a shell, Laves phases can slow down their growth and so contribute in solid solution...

- In the recent years, biodiesel has become a promising solution to the rapid depletion of the fo... more - In the recent years, biodiesel has become a promising solution to the rapid depletion of the fossil fuel reserves as well as to the alarming amount of discharged pollutants. But inherent properties such as low volatility, high density and high viscosity have been pointed at for inducing most of its drawbacks. Many studies have been undertaken in order to inhibit these deficiencies. Hence, the aim of this study is to investigate the effect of varying injection pressure on performance and emission characteristics of a four-cylinder, four-stroke, compression ignition direct injection engine fuelled with mineral diesel fuel and 20%, 40% and 60% waste cooking oil biodiesel blends (B20, B40 and B60). To that end, five injection pressures were tested: the original 200 bar, 220 bar, 240 bar, 260 bar and 280 bar. Experiments were conducted in accordance with the procedure dictated by DIN 70020. This study revealed that implementing the injection pressure up to 240 bar induces significant improvement in the performance characteristics for all tested fuels to varying degrees. The B20, under this optimized injection pressure was found to offer the best performances characteristics. Increasing injection pressure has proven its worth within a restricted limit. Indeed, for 260 bar and 280 bar, for all tested fuels, performance and smoke level characteristics were found to be dwindling.

Seifallah Fetni. University of Liège, UEE Research Unit, MSM division, allée de la Découverte, 9 ... more Seifallah Fetni. University of Liège, UEE Research Unit, MSM division, allée de la Découverte, 9 B52/3, B 4000 Liège, Belgium Quy Duc Thinh Pham. Thu Dau Mot University, Vietnam University of Liège, UEE Research Unit, MSM division, allée de la Découverte, 9 B52/3, B 4000 Liège, Belgium Van Xuan Tran. Thu Dau Mot University, Vietnam Corresponding author: xuantv@tdmu.edu.vn Laurent Duchêne. University of Liège, UEE Research Unit, MSM division, allée de la Découverte, 9 B52/3, B 4000 Liège, Belgium Hoang Son Tran. University of Liège, UEE Research Unit, MSM division, allée de la Découverte, 9 B52/3, B 4000 Liège, Belgium Anne Marie Habraken. University of Liège, UEE Research Unit, MSM division, allée de la Découverte, 9 B52/3, B 4000 Liège, Belgium Fund of Scientific Research F.R.S-FNRS

The aim of this study is optimizing the creep properties of T91 weld joints at high temperature a... more The aim of this study is optimizing the creep properties of T91 weld joints at high temperature and pressure. After welding, tube portions were subjected to different cycles of post welding heat treatment, than creep tests at 650°C and a range of pressure values. Crept specimens were exterminated in order to determine the weakest zones in the joint. It was found that the rupture occurs in the base metal at high pressures and in the heat affected zone at low ones. The creep rupture time of weld joint is lower than those of the base metal.Microstructure after creep is compared to the original one, to better understand the impact of creep exposure on microstructure evolution and to evaluate the strength of weld joints.

Materials & Design, 2021

This work focuses on the thermal modeling of the Directed Energy Deposition of a composite coatin... more This work focuses on the thermal modeling of the Directed Energy Deposition of a composite coating (316L stainless steel reinforced by Tungsten carbides) on a 316L substrate. The developed finite element model predicts the thermal history and the melt pool dimension evolution in the middle section of the clad during deposition. Numerical results were correlated with experimental analysis (light optical and scanning electron microscopies and thermocouple records) to validate the model and discuss the possible solidification mechanisms. It was proven that implementation of forced convection in the boundary conditions was of great importance to ensure equilibrium between input energy and heat losses. The maximum peak temperature shows a slight increase trend for the first few layers, followed by an apparent stabilization with increasing clad height. That demonstrates the high heat loss through boundaries. While in literature, most of the modeling studies are focused on single or few layer geometries, this work describes a multi-layered model able to predict the thermal field history during deposition and give consistent data about the new materiel. The model can be applied on other shapes under recalibration. The methodology of calibration is detailed as well as the sensitivity analysis to input parameters.

International Journal of Renewable Energy Research-IJRER, 2018

In the recent years, biodiesel has become a promising solution to the rapid depletion of the foss... more In the recent years, biodiesel has become a promising solution to the rapid depletion of the fossil fuel reserves as well as to the alarming amount of discharged pollutants. But inherent properties such as low volatility, high density and high viscosity have been pointed at for inducing most of its drawbacks. Many studies have been undertaken in order to inhibit these deficiencies. Hence, the aim of this study is to investigate the effect of varying injection pressure on performance and emission characteristics of a four-cylinder, four-stroke, compression ignition direct injection engine fuelled with mineral diesel fuel and 20%, 40% and 60% waste cooking oil biodiesel blends (B20, B40 and B60). To that end, five injection pressures were tested: the original 200 bar, 220 bar, 240 bar, 260 bar and 280 bar. Experiments were conducted in accordance with the procedure dictated by DIN 70020. This study revealed that implementing the injection pressure up to 240 bar induces significant imp...

Procedia Manufacturing, 2020

In this work, a 2D-thermal model of laser cladding (also called Directed Energy Deposition) of co... more In this work, a 2D-thermal model of laser cladding (also called Directed Energy Deposition) of composite coating (316L stainless steel reinforced by hard WC carbide particles) was developed. The temperature field and its time evolution were computed by the Finite Element software Lagamine and then compared to experimental measurements. Indeed, in a related work, the effects of the high temperatures on the WC particles in contact with the molten metal and the resulting microstructure at the end of the fabrication were evaluated by means of different experimental techniques. Thus, correlations between simulated thermal histories and microscopic analysis as well as thermocouple records were established. The temperature distribution in the substrate allows the prediction of the depths of the melt pool as well as the thermal histories of the different parts of the clad. Such a model is of great interest and can be applied in situ-calculations to offer quick data about the influences of the process parameters on the properties of the built part.

The use of waste cooking oil (WCO) as a reagent for biodiesel synthesis ensures their transformat... more The use of waste cooking oil (WCO) as a reagent for biodiesel synthesis ensures their transformation from harmful products into beneficial ones. The possibility of safe use as pure fuels or mixtures with diesel is a promoting and an environmental friendly alternative. This strategy is very encouraging especially for countries which have not enough space to produce vegetable oils. However, the researches in this field (WCO biodiesels) are still rare. In this work, we have synthesized biodiesel from WCO using the transesterification technique, then experimental investigations have been carried out on a four cylinder-direct injection diesel, engine equipped with a turbocharger on a test bench, according to the International norm ISO 27.020. In a first time, effects of different blends of methyl-ester/diesel in different proportions (B00, B10, B20 and B30) on engine behavior were studied and compared with petroleum diesel. In a second time, B20 blend was investigated but with variation of injection timing compared to original settings (as set by the engine manufacturer), on the same engine and following the same testing procedure. Experimental results showed that engine performances decreased with increasing amount of methyl ester in the fuel mixture. Moreover, it is found that advanced injecting B20 fuel by 2 crank angle degrees compared to that of the original injection timing, gives better performance without penalty on pollutant emissions (smoke opacity). The use of B20 accompanied with the advanced injection timing lead to a significant power increase (up to 4%) as well as an increase in torque (up to 2.8%) on conventional diesel engines compared to diesel. Emissions such as Smoke opacity remained close to the original values (without variation of injection timing).

Engineering Failure Analysis Volume 97, March 2019, Pages 43-52, 2019

Microstructural changes in the T91 steel (also known as the modified 9Cr1Mo steel), largely used ... more Microstructural changes in the T91 steel (also known as the modified 9Cr1Mo steel), largely used in thermal and nuclear power plants as well as petrochemical factories, have been studied, after isothermal ageing (at 550 °C) in laboratory, for different durations up to 7000 h (about 10 months of exposure).

In-depth analysis about chemical and structural changes in the metallic substrate and secondary carbides (M23C6) were conducted using SEM, EDX and X-ray diffraction instrumentations. Results reveal a progressive restoration of the tempered martensitic matrix with holding time. Then, a continuous increase in size of secondary carbides was noticed until stabilization after >5000 h of ageing. Kinetic parameters of matrix lattice were determined using Johnson-Mehl-Avrami (JMA) model. Natural logarithm of the relative lattice parameter of the matrix varies linearly with that of ageing time. Thus, the Avrami exponent n and activation energy E were established. Diffusion of chromium and molybdenum from matrix into carbides lattice was proved which explains their continuous coarsening. That has a harmful effect on the long term stability of the microstructure. The time-temperature dependence of this transformation could be then a good indicator to assess the resistance of T91 steel to heat exposure.

The objective of this work is to characterize the evolution of the microstructure of the ASTM A21... more The objective of this work is to characterize the evolution of the microstructure of the ASTM A213 T91 steel, used in power plants of electricity generation, for high temperatures up to 650° C, to optimize the performances of the installations and to reduce the pollutant emissions. The high temperature and pressure inside the boilers promote the microstructural evolution of the martensitic matrix of the T91 by increasing the size of the precipitates by the time exposure. The growth of these precipitates is explained by the absorption of the matrix elements, which will constitue in long term a favorable site for the nucleation of the microcavities; that triggers the creep phenomenon. An experience has been conducted in the aim of understanding the evolution of the microstructure ofthe steel at a temperature of 550° C. So far, four samples were removed from the furnance for time intervals of: 0, 260, 760 and 1260 hours. Examination by scanning electron microscopy of the martensitic matrix shows a slight increase of the sizes of precipitated M23C6 and stability for MX precipitates.

Corrosion of a T91 steel tube, used in subcritical conditions in an oil power plant for 157,000 h... more Corrosion of a T91 steel tube, used in subcritical conditions in an oil power plant for 157,000 hours was characterized 7 mainly through SEM, TEM, EDX and DRX analyses. Severe oxidation and carburization took place in both the outer (boiler) 8 and inner (steam) wall sides. The nature and morphology of the oxide scale multi-layer structure (hematite, magnetite and spinel) 9 depended on the environment exposure. Specific attention was given to the internal oxidation zone (IOZ) at the oxide/metal 10 interface. Diffusion of chromium during the oxidation process was determined, and was proposed to be responsible for the 11 continuous advancement of oxidation to the core of material, which eventually gave rise to the spinel. Finally, in the bulk 12 material, coarsening of the secondary carbides (M 23 C 6) was the main form of microstructural evolution. 13

Thermal exposure changes in the microstructure of the 9Cr-1Mo steel, largely used in thermal powe... more Thermal exposure changes in the microstructure of the 9Cr-1Mo steel, largely used in thermal power plants and petrochemical industry, have been investigated, through long term experience at 550 • C in furnace, up to 7000 hours. Detailed analysis of the microstructural evolution and changes in secondary carbides (M 23 C 6) were carried out through SEM, XRD and EDX analysis. Electrochemical extractions were done because of the small volume of carbides. A progressive restoration of the tempered martensite matrix was observed. Moreover, a continuous increase of M 23 C 6 size is revealed until stabilization after about 5000 hours of exposure. The nucleation of Laves phases is here found ; two inverse contributions may be concluded. When nucleating far from secondary precipitates, these phases grow by consuming matrix elements, which can trigger creep damages. Nevertheless, by surrounding the M 23 C 6 carbides like a shell, Laves phases can slow down their growth and so contribute in solid solution hardening. X-ray diffraction analysis lead to determine the temperature-time dependence of the matrix and M 23 C 6 lattice parameter.

This study deals with microstructural evolution, mechanical properties and oxidation/carburizatio... more This study deals with microstructural evolution, mechanical properties and oxidation/carburization behaviour of an ASTM A213 T91 super-heater tube after long term service in a power plant ; approximately 157.000 hours (about 18 years) in subcritical conditions (542 • C and 174 bar). This work provides good experience data to better evaluate the performances of this material, it can be referential for readers who are interested in martensitic heat-resistant steels, because the major previous studies were conducted in laboratories focusing on short creep experiences and oxidation behaviour. Our investigations suggest remarkable changes in the core and the walls of the tube. In the bulk material, the recovery of the tempered martensitic matrix and the coarsening of the M 23 C 6 carbides were observed, but the mechanical properties and the creep strength are still good. However, carburization/oxidation represents a major life time limiting factor by affecting about 20% of the tube thickness. The mechanisms of carburization, oxidation and microstructure evolution are here discussed.

Teaching Documents by Seifallah Fetni

Ce manuscrit propose quelques exemples de systèmes mécaniques industrialisés. L'étudiant sera sol... more Ce manuscrit propose quelques exemples de systèmes mécaniques industrialisés.
L'étudiant sera sollicité à achever la phase de l'avant-projet, dans le but de concevoir un système qui pourrait concurrencer les produits existants sur le marché.
Les étapes suivantes sont vivement recommandés à suivre dans le travail (du groupe):
- L'Analyse du besoin
- L'Analyse Fonctionnelle Technique
- L'Élaboration du cahier des charges fonctionnel
- La Proposition de quelques Schémas Cinématiques
- Le développement des Calculs analytiques ou numériques nécessaires
- Le Choix des solutions technologiques.
- La préparation du dossier des Devis des composants du produit.

Ce fascicule de travaux pratiques est principalement destiné aux étudiants en filières technologi... more Ce fascicule de travaux pratiques est principalement destiné aux étudiants en filières technologiques.
Il introduit d'une façon progressive les méthodes et les pré-requis nécessaires permettant à l'étudiant d'étudier les systèmes mécanique : lectures des dessins, mise en plan, élaborations des schémas fonctionnels, proposition de solutions partielles.
Un accent est notamment mis sur les roulements vu leurs utilité dans les majorités des systèmes mécaniques. On aborde ainsi les techniques de choix et de montage adéquates au problème posé.
En plus du manuscrit proposé, vous aurez accès à des ressources en ligne utiles pour le bon déroulement des exercices.

Ce cours couvre les principales techniques de mise en oeuvre des matériaux métalliques, notamment... more Ce cours couvre les principales techniques de mise en oeuvre des matériaux métalliques, notamment les travaux de forge, les
métaux en feuilles, les travaux de fonderie et de soudage.
Pour chaque procédé, on vous présente essentiellement: le principe, les applications visées ainsi que les méthodes de mise au point.
Ce cours est dédié principalement aux étudiants en filières technologiques.

Le critère de Von Mises stipule que la déformation plastique est dueà la partie totalement déviat... more Le critère de Von Mises stipule que la déformation plastique est dueà la partie totalement déviatorique du tenseur des contraintes. Il fait l'intervention d'un seul paramètre σe , qui dépend du matériau et peutêtre obtenu par des essais expérimentaux.

International Journal of Renewable Energy Research, 2019

Materials & Design, 2021

International Journal of Renewable Energy Research-IJRER, 2018

Procedia Manufacturing, 2020

Engineering Failure Analysis Volume 97, March 2019, Pages 43-52, 2019

Thermal exposure changes in the microstructure of the 9Cr-1Mo steel, largely used in thermal powe... more Thermal exposure changes in the microstructure of the 9Cr-1Mo steel, largely used in thermal power plants and petrochemical industry, have been investigated, through long term experience at 550 • C in furnace, up to 7000 hours. Detailed analysis of the microstructural evolution and changes in secondary carbides (M 23 C 6) were carried out through SEM, XRD and EDX analysis. Electrochemical extractions were done because of the small volume of carbides. A progressive restoration of the tempered martensite matrix was observed. Moreover, a continuous increase of M 23 C 6 size is revealed until stabilization after about 5000 hours of exposure. The nucleation of Laves phases is here found ; two inverse contributions may be concluded. When nucleating far from secondary precipitates, these phases grow by consuming matrix elements, which can trigger creep damages. Nevertheless, by surrounding the M 23 C 6 carbides like a shell, Laves phases can slow down their growth and so contribute in solid solution hardening. X-ray diffraction analysis lead to determine the temperature-time dependence of the matrix and M 23 C 6 lattice parameter.