Concentrated Solar Energy (CSE) processing is considered a promising renewable energy source tech... more Concentrated Solar Energy (CSE) processing is considered a promising renewable energy source technique for elaborating thick, wear-resistant claddings onto metallic surfaces of large dimensions that are expected to operate in heavy duty applications, such as excavator shovels, mineral crushers, etc. However, the prediction of surface processing effects on the microstructure and the properties of the main construction base metal are of crucial importance, as they are commonly required in all surface modification techniques. Thus, the present study is focused on the inverse thermal analysis and parametric modeling of heat deposition associated with CSE surface processing of metals. In this preliminary attempt, experimental findings that concern the elaboration of TiC- and chromium carbide-reinforced clads onto common steel base metals were used to quantify the evaluation of the temperature histories within the volume of workpieces undergoing solar heating, where direct temperature mea...
Abstract Having already demonstrated the feasibility of using Concentrated Solar Energy (CSE) as ... more Abstract Having already demonstrated the feasibility of using Concentrated Solar Energy (CSE) as a high temperature heat source for the in-situ elaboration of composite surface layers onto steel base metal, the present study focuses on the comparative evaluation of such “solar” titanium and chromium carbide hardfacings with respect to their microstructure characteristics and tribological performance. TiC and Cr3C2 powders were pre-deposited onto common steel base metal and the effects of solar irradiation time and repetition of solar exposure on the obtained microstructure of the surface layer were used as criteria for determining an adequate solar processing path for each specific carbide type. In the case of TiC powder, a single-step solar processing was sufficient to induce homogeneous dispersion of the carbide particles and, hence, surface reinforcement. For the Cr3C2 powder, single-step solar processing above a certain threshold solar processing time period was found to be necessary for the complete incorporation of the chromium carbide within the liquid metal pool, resulting in, however, carbides dissolution and surface alloying rather than carbides dispersion within the ferrous matrix. Thus, a second step of solar exposure of the previously obtained surface alloy above temperatures sufficient to cause re-melting, is necessary to obtain primary chromium carbide precipitates that provide the high wear resistance required. This was, indeed, demonstrated via dry sliding friction tests performed against an Al2O3 ball during which both “solar” surface layers exhibited relatively low specific wear rates. Microscopic observations on the worn surfaces indicated the synergy of distinct wear micro-mechanisms, different for each carbide particle type dispersed in the metallic matrix. These results in combination with the respective ones for WC-based hardfacing layers obtained via the same route and reported in the second part of this study, assist to identify the crucial metallurgical reactions that govern the successful implementation of the proposed “solar” technology.
The present paper discussed the development of a reliable and robust artificial neural network (A... more The present paper discussed the development of a reliable and robust artificial neural network (ANN) capable of predicting the tribological performance of three highly alloyed tool steel grades. Experimental results were obtained by performing plane-contact sliding tests under non-lubrication conditions on a pin-on-disk tribometer. The specimens were tested both in untreated state with different hardening levels, and after surface treatment of nitrocarburizing. We concluded that wear maps via ANN modeling were a user-friendly approach for the presentation of wear-related information, since they easily permitted the determination of areas under steady-state wear that were appropriate for use. Furthermore, the achieved optimum ANN model seemed to be a simple and helpful design/educational tool, which could assist both in educational seminars, as well as in the interpretation of the surface treatment effects on the tribological performance of tool steels.
Diamond-like carbon (DLC) films, hard carbon coatings, with unique physical and mechanical proper... more Diamond-like carbon (DLC) films, hard carbon coatings, with unique physical and mechanical properties which approach those of natural diamond, such as high hardness, low coefficient of friction and chemical inertness. In several applications, heavy loads and high friction forces are generated and lead to local temperature increase. In such cases these coatings must be thermal stable and with enhanced high temperature oxidation resistance in order to be good candidates for wear protection of metallic components. In the present study a radio frequency plasma deposition system was used for the deposition of 2 mum-thick amorphous DLC coatings onto AISI D2 substrates. The as deposited DLC covered samples were dense, homogeneous and well bonded to the substrate, while no cracks were observed. In order to study the thermal stability of the coatings' DLC nature, in-situ Transmission Electron Microscopic (TEM) observations were carried out during slow annealing of the specimen in the microscope vacuum chamber, as well as thermo-gravimetric (TG) measurements in argon atmosphere, up to 800° C. The first crystallites appeared within the DLC amorphous matrix at about 450° C as surface crystallization, while the mass crystallization started at 600° C as the TG measurements indicated. Finally, the nucleation was completed at 700° C. The oxidation results, performed from ambient temperature up to 1000° C, showed that DLC covered coupons are remarkably resistant as their mass gain was significantly lower than that of the uncovered substrates.
Despite the fact that ceramics and polymers have found numerous applications in several mechanica... more Despite the fact that ceramics and polymers have found numerous applications in several mechanical systems, metals and metallic alloys still remain the main materials family for manufacturing the bulk of parts and components of engineering assemblies. However, in cases of components that are serving as parts of a tribosystem, the application of surface modification techniques is required to ensure their unhampered function during operation. After a short introduction on fundamental aspects of tribology, this review article delves further into four representative case studies, where the inappropriate application of wear protection techniques has led to acceleration of the degradation of the quasi-protected metallic material. The first deals with the effects of the deficient lubrication of rolling bearings designed to function under oil lubrication conditions; the second is focused on the effects of overloading on sliding bearing surfaces, wear-protected via nitrocarburizing; the thir...
The term “tool steel” is used to describe a wide family of highly alloyed steels possessing speci... more The term “tool steel” is used to describe a wide family of highly alloyed steels possessing special properties rendering them from a techno-economic point of view suitable for manufacturing of severely loaded engineering parts. Depending on its chemical composition, a tool steel grade can exhibit: (a) Extreme toughness and shock resistance, required in applications such as punches, shear knives and air-operated chisels; (b) Excellent machinability, required in the manufacture of dies; (c) High hardenability and dimensional stability under heat treatments; (d) Excellent abrasion resistance, required in applications such as brick moulds; (e) Heat resistance, required in applications such as casting and forging dies, blades for hot shearing and hot extrusion tools. However, in many applications additional surface modification of the component is often necessary, in order to enhance its lifetime when operating under sliding and/or fatigue conditions and/or in corrosive environment. Liqu...
1 ABSTRACT Abradable seal coatings are engineered to minimise the clearance between blade tips an... more 1 ABSTRACT Abradable seal coatings are engineered to minimise the clearance between blade tips and casing to enhance gas-turbine performance. The gas path sealing has become an important method for this purpose. Abradable seals act as sacrificial layers between the blades and the casing, and are soft enough to avoid significant wear to blade tips, thus allowing much smaller clearances. The thermal sprayed abradable seal coating has been used because of its simple manufacturing processes, easy repair of the components, easy adjustment of its properties and good sealing effectiveness. In the present paper, we report on the surface microstructure and the tribological behavior of the widely used, abradable coating Al-Si polyester. Coatings were produced by using fully-automated atmospheric thermal spraying (APS) equipment. Microscopic examination revealed rounded polyester particles embedded in the Al-Si phase without forming any interfacial product. Porosity was estimated to be about 3...
In the present study two highly alloyed steel grades, intended for cold working applications, wer... more In the present study two highly alloyed steel grades, intended for cold working applications, were subjected to plane-contact, nonlubricating sliding friction testing in order to estimate the working regions (applied pressure and sliding velocity) that are governed by mild, moderate and severe wear mechanisms, before and after nitrocarburizing. For this purpose, both tool steel grades were initially pre-subjected to the proper heat treatments, in order to achieve a final bulk hardness of 40, 50 and 60 HRC whereas, after heat treatment, half of the material specimens were further subjected to nitrocarburizing surface treatment. The comparative experimental study of heat-treated and heat-/ surface-treated grades within a wide range of applied pressure and sliding velocity values, in combination to the development of a relevant Artificial Neural Network, allowed to determine the areas of recommended operation of such tribosystems. In all cases, the positive influence of the post-harden...
... a coatingsubstrate interface. Gaëlle Rosa a , Pandora Psyllaki a , Roland Oltra Correspondin... more ... a coatingsubstrate interface. Gaëlle Rosa a , Pandora Psyllaki a , Roland Oltra Corresponding Author Contact Information , E-mail The Corresponding Author , a , Sophie Costil b and Christian Coddet b. a Laboratoire de Recherches ...
Excimer laser may be used in the micromachining of various materials, especially in cases where s... more Excimer laser may be used in the micromachining of various materials, especially in cases where surface finishing by a conventional machining method is difficult. In this study, the process was applied onto two high performance alloys: CMSX2 and TA6V, widely used in the aircraft industry. An attempt was made to determine the relationship between the laser parameters (fluence, frequency, pulse
... a coatingsubstrate interface. Gaëlle Rosa a , Pandora Psyllaki a , Roland Oltra Correspondin... more ... a coatingsubstrate interface. Gaëlle Rosa a , Pandora Psyllaki a , Roland Oltra Corresponding Author Contact Information , E-mail The Corresponding Author , a , Sophie Costil b and Christian Coddet b. a Laboratoire de Recherches ...
Laser Techniques and Systems in Art Conservation, 2001
ABSTRACT In the present work, the effects of nanosecond pulsed laser irradiation on oxidised meta... more ABSTRACT In the present work, the effects of nanosecond pulsed laser irradiation on oxidised metallic surfaces were investigated, in order to estimate the possibility of using laser techniques for cleaning applications. After oxidation, the oxidate layer developed on the metallic surfaces depends on the composition of the substrate and also on oxidation conditions. In the study a modelling system: pure Fe oxidised at 500°C, has been investigated. The influence of the optical properties of the oxide films on the removal mechanisms and the cleaning efficiency of the laser technique was illustrated by performing specific electrochemical treatments.
Concentrated Solar Energy (CSE) processing is considered a promising renewable energy source tech... more Concentrated Solar Energy (CSE) processing is considered a promising renewable energy source technique for elaborating thick, wear-resistant claddings onto metallic surfaces of large dimensions that are expected to operate in heavy duty applications, such as excavator shovels, mineral crushers, etc. However, the prediction of surface processing effects on the microstructure and the properties of the main construction base metal are of crucial importance, as they are commonly required in all surface modification techniques. Thus, the present study is focused on the inverse thermal analysis and parametric modeling of heat deposition associated with CSE surface processing of metals. In this preliminary attempt, experimental findings that concern the elaboration of TiC- and chromium carbide-reinforced clads onto common steel base metals were used to quantify the evaluation of the temperature histories within the volume of workpieces undergoing solar heating, where direct temperature mea...
Abstract Having already demonstrated the feasibility of using Concentrated Solar Energy (CSE) as ... more Abstract Having already demonstrated the feasibility of using Concentrated Solar Energy (CSE) as a high temperature heat source for the in-situ elaboration of composite surface layers onto steel base metal, the present study focuses on the comparative evaluation of such “solar” titanium and chromium carbide hardfacings with respect to their microstructure characteristics and tribological performance. TiC and Cr3C2 powders were pre-deposited onto common steel base metal and the effects of solar irradiation time and repetition of solar exposure on the obtained microstructure of the surface layer were used as criteria for determining an adequate solar processing path for each specific carbide type. In the case of TiC powder, a single-step solar processing was sufficient to induce homogeneous dispersion of the carbide particles and, hence, surface reinforcement. For the Cr3C2 powder, single-step solar processing above a certain threshold solar processing time period was found to be necessary for the complete incorporation of the chromium carbide within the liquid metal pool, resulting in, however, carbides dissolution and surface alloying rather than carbides dispersion within the ferrous matrix. Thus, a second step of solar exposure of the previously obtained surface alloy above temperatures sufficient to cause re-melting, is necessary to obtain primary chromium carbide precipitates that provide the high wear resistance required. This was, indeed, demonstrated via dry sliding friction tests performed against an Al2O3 ball during which both “solar” surface layers exhibited relatively low specific wear rates. Microscopic observations on the worn surfaces indicated the synergy of distinct wear micro-mechanisms, different for each carbide particle type dispersed in the metallic matrix. These results in combination with the respective ones for WC-based hardfacing layers obtained via the same route and reported in the second part of this study, assist to identify the crucial metallurgical reactions that govern the successful implementation of the proposed “solar” technology.
The present paper discussed the development of a reliable and robust artificial neural network (A... more The present paper discussed the development of a reliable and robust artificial neural network (ANN) capable of predicting the tribological performance of three highly alloyed tool steel grades. Experimental results were obtained by performing plane-contact sliding tests under non-lubrication conditions on a pin-on-disk tribometer. The specimens were tested both in untreated state with different hardening levels, and after surface treatment of nitrocarburizing. We concluded that wear maps via ANN modeling were a user-friendly approach for the presentation of wear-related information, since they easily permitted the determination of areas under steady-state wear that were appropriate for use. Furthermore, the achieved optimum ANN model seemed to be a simple and helpful design/educational tool, which could assist both in educational seminars, as well as in the interpretation of the surface treatment effects on the tribological performance of tool steels.
Diamond-like carbon (DLC) films, hard carbon coatings, with unique physical and mechanical proper... more Diamond-like carbon (DLC) films, hard carbon coatings, with unique physical and mechanical properties which approach those of natural diamond, such as high hardness, low coefficient of friction and chemical inertness. In several applications, heavy loads and high friction forces are generated and lead to local temperature increase. In such cases these coatings must be thermal stable and with enhanced high temperature oxidation resistance in order to be good candidates for wear protection of metallic components. In the present study a radio frequency plasma deposition system was used for the deposition of 2 mum-thick amorphous DLC coatings onto AISI D2 substrates. The as deposited DLC covered samples were dense, homogeneous and well bonded to the substrate, while no cracks were observed. In order to study the thermal stability of the coatings' DLC nature, in-situ Transmission Electron Microscopic (TEM) observations were carried out during slow annealing of the specimen in the microscope vacuum chamber, as well as thermo-gravimetric (TG) measurements in argon atmosphere, up to 800° C. The first crystallites appeared within the DLC amorphous matrix at about 450° C as surface crystallization, while the mass crystallization started at 600° C as the TG measurements indicated. Finally, the nucleation was completed at 700° C. The oxidation results, performed from ambient temperature up to 1000° C, showed that DLC covered coupons are remarkably resistant as their mass gain was significantly lower than that of the uncovered substrates.
Despite the fact that ceramics and polymers have found numerous applications in several mechanica... more Despite the fact that ceramics and polymers have found numerous applications in several mechanical systems, metals and metallic alloys still remain the main materials family for manufacturing the bulk of parts and components of engineering assemblies. However, in cases of components that are serving as parts of a tribosystem, the application of surface modification techniques is required to ensure their unhampered function during operation. After a short introduction on fundamental aspects of tribology, this review article delves further into four representative case studies, where the inappropriate application of wear protection techniques has led to acceleration of the degradation of the quasi-protected metallic material. The first deals with the effects of the deficient lubrication of rolling bearings designed to function under oil lubrication conditions; the second is focused on the effects of overloading on sliding bearing surfaces, wear-protected via nitrocarburizing; the thir...
The term “tool steel” is used to describe a wide family of highly alloyed steels possessing speci... more The term “tool steel” is used to describe a wide family of highly alloyed steels possessing special properties rendering them from a techno-economic point of view suitable for manufacturing of severely loaded engineering parts. Depending on its chemical composition, a tool steel grade can exhibit: (a) Extreme toughness and shock resistance, required in applications such as punches, shear knives and air-operated chisels; (b) Excellent machinability, required in the manufacture of dies; (c) High hardenability and dimensional stability under heat treatments; (d) Excellent abrasion resistance, required in applications such as brick moulds; (e) Heat resistance, required in applications such as casting and forging dies, blades for hot shearing and hot extrusion tools. However, in many applications additional surface modification of the component is often necessary, in order to enhance its lifetime when operating under sliding and/or fatigue conditions and/or in corrosive environment. Liqu...
1 ABSTRACT Abradable seal coatings are engineered to minimise the clearance between blade tips an... more 1 ABSTRACT Abradable seal coatings are engineered to minimise the clearance between blade tips and casing to enhance gas-turbine performance. The gas path sealing has become an important method for this purpose. Abradable seals act as sacrificial layers between the blades and the casing, and are soft enough to avoid significant wear to blade tips, thus allowing much smaller clearances. The thermal sprayed abradable seal coating has been used because of its simple manufacturing processes, easy repair of the components, easy adjustment of its properties and good sealing effectiveness. In the present paper, we report on the surface microstructure and the tribological behavior of the widely used, abradable coating Al-Si polyester. Coatings were produced by using fully-automated atmospheric thermal spraying (APS) equipment. Microscopic examination revealed rounded polyester particles embedded in the Al-Si phase without forming any interfacial product. Porosity was estimated to be about 3...
In the present study two highly alloyed steel grades, intended for cold working applications, wer... more In the present study two highly alloyed steel grades, intended for cold working applications, were subjected to plane-contact, nonlubricating sliding friction testing in order to estimate the working regions (applied pressure and sliding velocity) that are governed by mild, moderate and severe wear mechanisms, before and after nitrocarburizing. For this purpose, both tool steel grades were initially pre-subjected to the proper heat treatments, in order to achieve a final bulk hardness of 40, 50 and 60 HRC whereas, after heat treatment, half of the material specimens were further subjected to nitrocarburizing surface treatment. The comparative experimental study of heat-treated and heat-/ surface-treated grades within a wide range of applied pressure and sliding velocity values, in combination to the development of a relevant Artificial Neural Network, allowed to determine the areas of recommended operation of such tribosystems. In all cases, the positive influence of the post-harden...
... a coatingsubstrate interface. Gaëlle Rosa a , Pandora Psyllaki a , Roland Oltra Correspondin... more ... a coatingsubstrate interface. Gaëlle Rosa a , Pandora Psyllaki a , Roland Oltra Corresponding Author Contact Information , E-mail The Corresponding Author , a , Sophie Costil b and Christian Coddet b. a Laboratoire de Recherches ...
Excimer laser may be used in the micromachining of various materials, especially in cases where s... more Excimer laser may be used in the micromachining of various materials, especially in cases where surface finishing by a conventional machining method is difficult. In this study, the process was applied onto two high performance alloys: CMSX2 and TA6V, widely used in the aircraft industry. An attempt was made to determine the relationship between the laser parameters (fluence, frequency, pulse
... a coatingsubstrate interface. Gaëlle Rosa a , Pandora Psyllaki a , Roland Oltra Correspondin... more ... a coatingsubstrate interface. Gaëlle Rosa a , Pandora Psyllaki a , Roland Oltra Corresponding Author Contact Information , E-mail The Corresponding Author , a , Sophie Costil b and Christian Coddet b. a Laboratoire de Recherches ...
Laser Techniques and Systems in Art Conservation, 2001
ABSTRACT In the present work, the effects of nanosecond pulsed laser irradiation on oxidised meta... more ABSTRACT In the present work, the effects of nanosecond pulsed laser irradiation on oxidised metallic surfaces were investigated, in order to estimate the possibility of using laser techniques for cleaning applications. After oxidation, the oxidate layer developed on the metallic surfaces depends on the composition of the substrate and also on oxidation conditions. In the study a modelling system: pure Fe oxidised at 500°C, has been investigated. The influence of the optical properties of the oxide films on the removal mechanisms and the cleaning efficiency of the laser technique was illustrated by performing specific electrochemical treatments.
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