Tahar Sahraoui - Academia.edu (original) (raw)

Papers by Tahar Sahraoui

Research paper thumbnail of Structure and wear behaviour of HVOF sprayed Cr3C2–NiCr and WC–Co coatings

Materials & Design, 2003

Hard chrome plating is used to restore the original dimensions to worn surfaces of gas turbine sh... more Hard chrome plating is used to restore the original dimensions to worn surfaces of gas turbine shafts. However, its use is about to decrease due to some intrinsic limitations of its deposits and the toxic and carcinogenic characteristics of the hexavalent chromium. During the last decade high velocity oxy-fuel (HVOF) thermal sprayed cermet coatings play an important role in industrial applications where exceptional friction and wear resistance are required. The purpose of this study is to investigate and to compare the microstructure, wear resistance and potentials of HVOF sprayed Cr C -NiCr and WC-Co coatings for a possible 3 2 replacement of hard chromium plating in gas turbine components repair. It has been shown that coatings exhibit high hardness with a high volume fraction of carbides being preserved during the spraying, and have different wear behaviour. ᮊ

Research paper thumbnail of Effect of post-weld aging treatment on mechanical properties of Tungsten Inert Gas welded low thickness 7075 aluminium alloy joints

Materials & Design, 2011

This paper reports the influence of post-weld aging treatment on the microstructure, tensile stre... more This paper reports the influence of post-weld aging treatment on the microstructure, tensile strength, hardness and Charpy impact energy of weld joints low thickness 7075 T6 aluminium alloy welded by Tungsten Inert Gas (TIG). Hot cracking occurs in aluminium welds when high levels of thermal stress and solidification shrinkage are present while the weld is undergoing various degrees of solidification. Weld fusion zones typically exhibit microstructure modifications because of the thermal conditions during weld metal solidification. This often results in low weld mechanical properties and low resistance to hot cracking. It has been observed that the mechanical properties are very sensitive to microstructure of weld metal. Simple post-weld aging treatment at 140°C applied to the joints is found to be beneficial to enhance the mechanical properties of the welded joints. Correlations between microstructures and mechanical properties were discussed. j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / m a t d e s Unwelded 4.7 J As welded 2.2 J 5.1 J Post-welded 2.7 J 4.9 J

Research paper thumbnail of HVOF sprayed WC–Co coatings: Microstructure, mechanical properties and friction moment prediction

Materials & Design, 2010

This study aims at gaining a better understanding of the microstructural features that control th... more This study aims at gaining a better understanding of the microstructural features that control the mechanical and the tribological performances of WC-12 wt.% Co coatings under High Velocity Oxygen Fuel (HVOF) spraying conditions. This paper looks at the influences of the HVOF process parameters for WC-12Co material on the microstructural and the tribological behaviours of the coatings. The correlation between the coating microstructure and the wear behaviour is investigated by observing and analysing the microstructure and by studying the friction moment using enhanced statistical tool based on neural computations. According to the experimental and the numerical results, it has been shown that the spray parameters affect the phase composition, hardness and porosity of HVOF sprayed WC-12Co coatings and the correlations with HVOF process parameters are fully predictable in the steady-state regime.

Research paper thumbnail of Design and deformation behavior of high strength Fe–Mn–Al–Cr–C duplex steel

Materials Science and Engineering: A, 2009

The influence of cold rolling reduction on microstructures and mechanical properties at room temp... more The influence of cold rolling reduction on microstructures and mechanical properties at room temperature of the duplex Fe–28Mn–7Al–5Cr–0.3C steel was investigated. In the Fe–28Mn–7Al alloy system, the duplex microstructure was obtained by lowering the carbon content to about 0.3wt.%. The steel was austenito-ferritic with a low to moderate stacking fault energy. Two thermomechanical cycles were performed, which included cold rolling/annealing

Research paper thumbnail of Friction moment prediction of HVOF coatings and Electroplated Hard Chromium

Materials Letters, 2008

Wear is one of the most critical problems in mechanics, oil, and gas industries among other indus... more Wear is one of the most critical problems in mechanics, oil, and gas industries among other industrial fields. Electrolytic Hard Chromium (EHC) and HVOF thermal spraying for applications of various materials have proved to be effective against wear. In this study, the results of wear tests for WC-12Co, Cr 3 C 2 -25NiCr, Tribaloy©-400, and EHC are predicted and compared using an artificial intelligence methodology. It has been shown that predicted wear analysis permits to determine friction moment for different loading conditions. The best candidate seems to be WC-12Co for which worn surface reveals prevailing adhesion mechanism responsible for the lowering of the friction moment.

Research paper thumbnail of Alternative to chromium: characteristics and wear behavior of HVOF coatings for gas turbine shafts repair (heavy-duty)

Journal of Materials Processing Technology, 2004

Hard chromium plating is usually used to restore to original dimensions the worn surfaces of gas ... more Hard chromium plating is usually used to restore to original dimensions the worn surfaces of gas turbine shafts. However, such a technology presents harmful effects on the environment and the public health and it exhibits, moreover some intrinsic technical limitations. HVOF (high-velocity oxy-fuel) thermal spraying process appears as more environmentally friendly than chromium plating process but exhibits also lower potential production costs when compared to hard chromium deposits.

Research paper thumbnail of Superplastic Deformation Behavior of 7075 Aluminum Alloy

Journal of Materials Engineering and Performance, 2003

A study has been made to investigate the effect of a prior amount of warm rolling on the superpla... more A study has been made to investigate the effect of a prior amount of warm rolling on the superplastic forming behavior of a standard grade 7075 aluminum alloy. The thermomechanical treatment process presented for grain refinement includes furnace cooling from the solution treatment temperature to the overaging temperature, warm rolling from 65–85% deformation, recrystallization, and artificial aging treatment. Increasing the amount of warm rolling beyond 80% deformation does not produce material with higher elongation to failure when the thermomechanical treatment process presented is used. The largest value of elongation to failure was 700%, which was obtained for a specimen having a grain size of 8 �m at a strain rate of 6�10−3S−1. The fracture surface exhibits a granular appearance indicative of an intergranular fracture mode. Dislocation activities within grains were observed, indicating the occurrence of dislocation slip during grain boundary sliding.

Research paper thumbnail of Wear behavior of alumina–titania coatings: analysis of process and parameters

Ceramics International, 2006

The effect of injection parameters of atmospheric plasma spray process is studied on tribological... more The effect of injection parameters of atmospheric plasma spray process is studied on tribological behavior of Al2O3–13% TiO2 plasma sprayed coatings.The suggested correlations between the process parameters and the friction coefficient were mainly explained by the effect of the process parameters on the in-flight particle characteristics and related to bounding mechanism during coating formation. This work demonstrated experimentally that the

Research paper thumbnail of Ab initio calculations and experimental studies of site substitution of ternary elements in WC

Materials Science and Engineering: B, 2004

Structural and electronic properties of the tungsten carbide (WC)–12% X (X = C, Cr, Co, Zr) alloy... more Structural and electronic properties of the tungsten carbide (WC)–12% X (X = C, Cr, Co, Zr) alloys are reported in this article. All calculations are based on density functional theory (DFT) within the generalized gradient approximation (GGA). We report the lattice parameters, bulk moduli and heat formation of the selected alloys. The stability mechanism and bond character studied in the

Research paper thumbnail of Structure and wear behaviour of HVOF sprayed Cr3C2–NiCr and WC–Co coatings

Materials & Design, 2003

Hard chrome plating is used to restore the original dimensions to worn surfaces of gas turbine sh... more Hard chrome plating is used to restore the original dimensions to worn surfaces of gas turbine shafts. However, its use is about to decrease due to some intrinsic limitations of its deposits and the toxic and carcinogenic characteristics of the hexavalent chromium. During the last decade high velocity oxy-fuel (HVOF) thermal sprayed cermet coatings play an important role in industrial applications where exceptional friction and wear resistance are required. The purpose of this study is to investigate and to compare the microstructure, wear resistance and potentials of HVOF sprayed Cr C -NiCr and WC-Co coatings for a possible 3 2 replacement of hard chromium plating in gas turbine components repair. It has been shown that coatings exhibit high hardness with a high volume fraction of carbides being preserved during the spraying, and have different wear behaviour. ᮊ

Research paper thumbnail of Effect of post-weld aging treatment on mechanical properties of Tungsten Inert Gas welded low thickness 7075 aluminium alloy joints

Materials & Design, 2011

This paper reports the influence of post-weld aging treatment on the microstructure, tensile stre... more This paper reports the influence of post-weld aging treatment on the microstructure, tensile strength, hardness and Charpy impact energy of weld joints low thickness 7075 T6 aluminium alloy welded by Tungsten Inert Gas (TIG). Hot cracking occurs in aluminium welds when high levels of thermal stress and solidification shrinkage are present while the weld is undergoing various degrees of solidification. Weld fusion zones typically exhibit microstructure modifications because of the thermal conditions during weld metal solidification. This often results in low weld mechanical properties and low resistance to hot cracking. It has been observed that the mechanical properties are very sensitive to microstructure of weld metal. Simple post-weld aging treatment at 140°C applied to the joints is found to be beneficial to enhance the mechanical properties of the welded joints. Correlations between microstructures and mechanical properties were discussed. j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / m a t d e s Unwelded 4.7 J As welded 2.2 J 5.1 J Post-welded 2.7 J 4.9 J

Research paper thumbnail of HVOF sprayed WC–Co coatings: Microstructure, mechanical properties and friction moment prediction

Materials & Design, 2010

This study aims at gaining a better understanding of the microstructural features that control th... more This study aims at gaining a better understanding of the microstructural features that control the mechanical and the tribological performances of WC-12 wt.% Co coatings under High Velocity Oxygen Fuel (HVOF) spraying conditions. This paper looks at the influences of the HVOF process parameters for WC-12Co material on the microstructural and the tribological behaviours of the coatings. The correlation between the coating microstructure and the wear behaviour is investigated by observing and analysing the microstructure and by studying the friction moment using enhanced statistical tool based on neural computations. According to the experimental and the numerical results, it has been shown that the spray parameters affect the phase composition, hardness and porosity of HVOF sprayed WC-12Co coatings and the correlations with HVOF process parameters are fully predictable in the steady-state regime.

Research paper thumbnail of Design and deformation behavior of high strength Fe–Mn–Al–Cr–C duplex steel

Materials Science and Engineering: A, 2009

The influence of cold rolling reduction on microstructures and mechanical properties at room temp... more The influence of cold rolling reduction on microstructures and mechanical properties at room temperature of the duplex Fe–28Mn–7Al–5Cr–0.3C steel was investigated. In the Fe–28Mn–7Al alloy system, the duplex microstructure was obtained by lowering the carbon content to about 0.3wt.%. The steel was austenito-ferritic with a low to moderate stacking fault energy. Two thermomechanical cycles were performed, which included cold rolling/annealing

Research paper thumbnail of Friction moment prediction of HVOF coatings and Electroplated Hard Chromium

Materials Letters, 2008

Wear is one of the most critical problems in mechanics, oil, and gas industries among other indus... more Wear is one of the most critical problems in mechanics, oil, and gas industries among other industrial fields. Electrolytic Hard Chromium (EHC) and HVOF thermal spraying for applications of various materials have proved to be effective against wear. In this study, the results of wear tests for WC-12Co, Cr 3 C 2 -25NiCr, Tribaloy©-400, and EHC are predicted and compared using an artificial intelligence methodology. It has been shown that predicted wear analysis permits to determine friction moment for different loading conditions. The best candidate seems to be WC-12Co for which worn surface reveals prevailing adhesion mechanism responsible for the lowering of the friction moment.

Research paper thumbnail of Alternative to chromium: characteristics and wear behavior of HVOF coatings for gas turbine shafts repair (heavy-duty)

Journal of Materials Processing Technology, 2004

Hard chromium plating is usually used to restore to original dimensions the worn surfaces of gas ... more Hard chromium plating is usually used to restore to original dimensions the worn surfaces of gas turbine shafts. However, such a technology presents harmful effects on the environment and the public health and it exhibits, moreover some intrinsic technical limitations. HVOF (high-velocity oxy-fuel) thermal spraying process appears as more environmentally friendly than chromium plating process but exhibits also lower potential production costs when compared to hard chromium deposits.

Research paper thumbnail of Superplastic Deformation Behavior of 7075 Aluminum Alloy

Journal of Materials Engineering and Performance, 2003

A study has been made to investigate the effect of a prior amount of warm rolling on the superpla... more A study has been made to investigate the effect of a prior amount of warm rolling on the superplastic forming behavior of a standard grade 7075 aluminum alloy. The thermomechanical treatment process presented for grain refinement includes furnace cooling from the solution treatment temperature to the overaging temperature, warm rolling from 65–85% deformation, recrystallization, and artificial aging treatment. Increasing the amount of warm rolling beyond 80% deformation does not produce material with higher elongation to failure when the thermomechanical treatment process presented is used. The largest value of elongation to failure was 700%, which was obtained for a specimen having a grain size of 8 �m at a strain rate of 6�10−3S−1. The fracture surface exhibits a granular appearance indicative of an intergranular fracture mode. Dislocation activities within grains were observed, indicating the occurrence of dislocation slip during grain boundary sliding.

Research paper thumbnail of Wear behavior of alumina–titania coatings: analysis of process and parameters

Ceramics International, 2006

The effect of injection parameters of atmospheric plasma spray process is studied on tribological... more The effect of injection parameters of atmospheric plasma spray process is studied on tribological behavior of Al2O3–13% TiO2 plasma sprayed coatings.The suggested correlations between the process parameters and the friction coefficient were mainly explained by the effect of the process parameters on the in-flight particle characteristics and related to bounding mechanism during coating formation. This work demonstrated experimentally that the

Research paper thumbnail of Ab initio calculations and experimental studies of site substitution of ternary elements in WC

Materials Science and Engineering: B, 2004

Structural and electronic properties of the tungsten carbide (WC)–12% X (X = C, Cr, Co, Zr) alloy... more Structural and electronic properties of the tungsten carbide (WC)–12% X (X = C, Cr, Co, Zr) alloys are reported in this article. All calculations are based on density functional theory (DFT) within the generalized gradient approximation (GGA). We report the lattice parameters, bulk moduli and heat formation of the selected alloys. The stability mechanism and bond character studied in the