Luc Vernhes - Academia.edu (original) (raw)

Papers by Luc Vernhes

Journal of Thermal Spray Technology, 2016

Journal of Thermal Spray Technology, 2018

The load-carrying capacity and wear resistance of a duplex-coated 316 stainless steel were determ... more The load-carrying capacity and wear resistance of a duplex-coated 316 stainless steel were determined, and a finite element numerical approach was developed to predict and corroborate experimental observations. Lowstrength alloys are generally used for highly demanding valve applications due to their superior chemical stability, galvanic corrosion resistance, and lower susceptibility to stress corrosion cracking failure. Hardfacing (using thermal spraying, laser cladding, or plasma transferred arc welding) is currently the most common solution to protect valve components. Hardfacing provides a thick, hardened case that significantly improves tribological performance. However, hardfaced layers provide lower wear resistance compared to vacuum-deposited hard coatings. One solution to further improve hardfacing performance is a duplex approach, which combines the two processes. This study investigates the following materials: a 316 stainless steel base hardfaced with laser-cladded Co-Cr superalloy and topped with a CVD nanostructured W-WC coating. Tribological properties of three configurations were assessed for their ability to delay initiation of plastic deformation and surface cracking under quasistatic loading and for their resistance to dry reciprocal sliding wear. The results demonstrate that finite element modeling allows numerical prediction and comparison of the load-carrying capacity and wear resistance of duplex-coated AISI 316 stainless steel. Keywords hybrid coating systems Á laser cladding Á load-carrying capacity Á mechanical modeling Á tribomechanical properties Á wear-resistant coatings

Journal of Thermal Spray Technology, 2016

A detailed characterization project was undertaken by Velan, an international industrial valve de... more A detailed characterization project was undertaken by Velan, an international industrial valve designer and manufacturer, in collaboration with the National Research Council of Canada, Boucherville, and Polytechnique Montré al. The purpose was to assess the mechanical and tribological resistances of promising ceramic coatings for hydrometallurgy applications, including a novel n-TiO 2-Cr 2 O 3 blend. Hardness and shear strength were determined using microhardness indentation testers and universal tensile testing equipment. Wear resistance of the coatings under sliding wear, abrasion, and galling conditions were measured by standard pin-on-disk tests, abrasion tests, and custom-designed galling tests. The main result is that the synergy between Cr 2 O 3 and n-TiO 2 produced abrasion performance exceeding that of these materials alone. Also, an optimized balance between the hard and brittle Cr 2 O 3 phases and the soft and ductile n-TiO 2 phases resulted in higher abrasion, sliding, and galling resistance. The novel n-TiO 2-Cr 2 O 3 blend is therefore considered as a promising evolution of the current TiO 2-Cr 2 O 3 blend.

Journal of Thermal Spray Technology, 2015

The aim of this study was to investigate the effects of subsurface materials on the performance o... more The aim of this study was to investigate the effects of subsurface materials on the performance of a wearresistant thin film. The mechanical, tribological, and corrosion properties were assessed for two hybrid coating systems: (1) W-WC thin film and a laser cladded Co-Cr interlayer applied to a 316 stainless steel substrate and (2) the same W-WC thin film and a spray-and-fused Ni-W-Cr-B interlayer applied to an Inconel Ò 718 substrate. They were then compared to the same systems without an interlayer. The microstructures were analyzed by XRD, EDS, and SEM. The hardness and surface load-carrying capacity of the coating systems were determined by micro-and macrohardness testing. Rockwell indentation was used to assess coating adhesion (CEN/TS 1071-8). Tribological properties were assessed with a reciprocating tribometer, and corrosion resistance was determined by potentiodynamic polarization and electrochemical impedance spectroscopy. The originality of this work lies in the finding that, except for the Inconel 718/Ni-W-Cr-B/W-WC system, the wear rate decreases with decreasing hardness of the subsurface materials carrying the thin film due to the decreasing contact pressure for a given load. Another novel finding is the stress-induced phase transformation of the Co-Cr interlayer, which occurs beneath the thin film under high load.

Materials Chemistry and Physics, 2013

h i g h l i g h t s Tungsten/tungsten carbide (W/WC) and cobalt-phosphor (NCP) coatings are compa... more h i g h l i g h t s Tungsten/tungsten carbide (W/WC) and cobalt-phosphor (NCP) coatings are compared with hard chromium (HC). NCP and W/WC offer better tribological properties (wear rate and friction coefficient) than HC. W/WC has demonstrated a robust corrosion behavior with a breakdown potential greater than 1 V. NCP and W/WC are potential candidates to replace hard chromium as protective coating.

Journal of Thermal Spray Technology, 2013

This case study is the result of an investigation on HVOF 80/20 Cr 3 C 2-NiCr coating failure of ... more This case study is the result of an investigation on HVOF 80/20 Cr 3 C 2-NiCr coating failure of on-off metal-seated ball valve (MSBV) used in supercritical steam lines in a power plant and solution. HVOF 80/20 Cr 3 C 2-NiCr coating is used to protect thousands of MSBVs without incident. However, in this case, the valves are challenged with exposure to rapid high-pressure and-temperature variations resulting in a unique situation where the coating experiences cracking and cohesive failure. It was found that carbide precipitation is a major factor causing embrittlement of the coating. Once the coating toughness and ductility is reduced, thermal, mechanical, and residual stresses can initiate and propagate cracks more easily, causing coating failure when exposed to thermal shock. To alleviate the above mentioned issues, possible coating alternatives were then evaluated.

Volume 14: Emerging Technologies; Engineering Management, Safety, Ethics, Society, and Education; Materials: Genetics to Structures, 2014

Wear of materials is a serious problem facing industry especially in mechanical applications wher... more Wear of materials is a serious problem facing industry especially in mechanical applications where moving parts are continuously subjected to friction. Hard coatings prepared by a variety of processes are nowadays considered as effective solutions to protect components against wear. Examples of such processes are: thermal spray coating, vacuum-based coating and hardfacing. In this paper, we study the mechanical, tribological and corrosion properties of two hard coating systems: CoCr Stellite 6 (ST6) hardfacing on 316 stainless steel and NiWCrB Colmonoy 88 (C88) thermal spray coating on Inconel 718. The effect of gas nitriding on the microstructure and wear performance of these coating systems is investigated. X-ray diffraction, energy dispersive spectroscopy and scanning electron microscopy were used for microstructural analysis. Micro-indentation technique was utilized to measure the surface and cross-sectional hardness of the coatings. Rockwell indentation technique was used to ev...

La robinetterie et la tuyauterie industrielles sont des appareils sous pression qui permettent de... more La robinetterie et la tuyauterie industrielles sont des appareils sous pression qui permettent de reguler le flux de materiaux (liquides, gaz et boues) en controlant les sections de passages. L’optimisation des processus, la reduction des couts et les reglementations gouvernementales exigent des equipementiers de maintenir leurs produits a la fine pointe de la technologie. La robinetterie a ete developpee il y a plus de 3000 ans pour alimenter en eau les fermes et les villes en utilisant des alliages de bronze, qui fournissent a la fois une resistance a la corrosion et des performances tribologiques acceptables. Durant la revolution industrielle, ces antiques robinets ont evolue et des materiaux tribologiques plus modernes tels que les alliages Monel cuivre-nickel, Stellite cobalt-chrome, et le chromage dur applique par placage electrolytique ont ete developpes au debut du XXe siecle pour optimiser le comportement tribologique et maximiser la duree de vie en service de ces equipemen...

Surface & Coatings Technology, 2020

In recent years, a major challenge facing the power generation industry is delamination of Stelli... more In recent years, a major challenge facing the power generation industry is delamination of Stellite-hardfaced coatings from high-temperature valves. In order to meet this challenge, IN82 buffer layer was evaluated to replace the problematic S21 buffer layer. S6 and either S21 or IN82 hardfacing alloys were deposited onto F91 steel substrates using plasma-transferred arc hardfacing. Aging was conducted at temperatures between 550 and 650 °C for three exposure durations within a one-year period. A comparative study was carried out on the microstructure and mechanical properties of IN82 and S21 hardfaced specimens. The F91/S21 interface is unstable during aging because a hard and brittle interfacial layer grows, which significantly reduces the impact energy of S21 hardfaced specimens. In contrast, the F91/IN82 interface is microstructurally much more stable than the F91/S21 interface; an interfacial band, part of the F91 steel, and some discrete M23C6 carbides along this band grow duri...

Journal of Thermal Spray Technology, 2013

This case study is the result of an investigation on HVOF 80/20 Cr 3 C 2 -NiCr coating failure of... more This case study is the result of an investigation on HVOF 80/20 Cr 3 C 2 -NiCr coating failure of on-off metal-seated ball valve (MSBV) used in supercritical steam lines in a power plant and solution. HVOF 80/20 Cr 3 C 2 -NiCr coating is used to protect thousands of MSBVs without incident. However, in this case, the valves are challenged with exposure to rapid high-pressure and -temperature variations resulting in a unique situation where the coating experiences cracking and cohesive failure. It was found that carbide precipitation is a major factor causing embrittlement of the coating. Once the coating toughness and ductility is reduced, thermal, mechanical, and residual stresses can initiate and propagate cracks more easily, causing coating failure when exposed to thermal shock. To alleviate the above mentioned issues, possible coating alternatives were then evaluated.

Journal of Thermal Spray Technology, 2016

Journal of Thermal Spray Technology, 2018

The load-carrying capacity and wear resistance of a duplex-coated 316 stainless steel were determ... more The load-carrying capacity and wear resistance of a duplex-coated 316 stainless steel were determined, and a finite element numerical approach was developed to predict and corroborate experimental observations. Lowstrength alloys are generally used for highly demanding valve applications due to their superior chemical stability, galvanic corrosion resistance, and lower susceptibility to stress corrosion cracking failure. Hardfacing (using thermal spraying, laser cladding, or plasma transferred arc welding) is currently the most common solution to protect valve components. Hardfacing provides a thick, hardened case that significantly improves tribological performance. However, hardfaced layers provide lower wear resistance compared to vacuum-deposited hard coatings. One solution to further improve hardfacing performance is a duplex approach, which combines the two processes. This study investigates the following materials: a 316 stainless steel base hardfaced with laser-cladded Co-Cr superalloy and topped with a CVD nanostructured W-WC coating. Tribological properties of three configurations were assessed for their ability to delay initiation of plastic deformation and surface cracking under quasistatic loading and for their resistance to dry reciprocal sliding wear. The results demonstrate that finite element modeling allows numerical prediction and comparison of the load-carrying capacity and wear resistance of duplex-coated AISI 316 stainless steel. Keywords hybrid coating systems Á laser cladding Á load-carrying capacity Á mechanical modeling Á tribomechanical properties Á wear-resistant coatings

Journal of Thermal Spray Technology, 2016

A detailed characterization project was undertaken by Velan, an international industrial valve de... more A detailed characterization project was undertaken by Velan, an international industrial valve designer and manufacturer, in collaboration with the National Research Council of Canada, Boucherville, and Polytechnique Montré al. The purpose was to assess the mechanical and tribological resistances of promising ceramic coatings for hydrometallurgy applications, including a novel n-TiO 2-Cr 2 O 3 blend. Hardness and shear strength were determined using microhardness indentation testers and universal tensile testing equipment. Wear resistance of the coatings under sliding wear, abrasion, and galling conditions were measured by standard pin-on-disk tests, abrasion tests, and custom-designed galling tests. The main result is that the synergy between Cr 2 O 3 and n-TiO 2 produced abrasion performance exceeding that of these materials alone. Also, an optimized balance between the hard and brittle Cr 2 O 3 phases and the soft and ductile n-TiO 2 phases resulted in higher abrasion, sliding, and galling resistance. The novel n-TiO 2-Cr 2 O 3 blend is therefore considered as a promising evolution of the current TiO 2-Cr 2 O 3 blend.

Journal of Thermal Spray Technology, 2015

The aim of this study was to investigate the effects of subsurface materials on the performance o... more The aim of this study was to investigate the effects of subsurface materials on the performance of a wearresistant thin film. The mechanical, tribological, and corrosion properties were assessed for two hybrid coating systems: (1) W-WC thin film and a laser cladded Co-Cr interlayer applied to a 316 stainless steel substrate and (2) the same W-WC thin film and a spray-and-fused Ni-W-Cr-B interlayer applied to an Inconel Ò 718 substrate. They were then compared to the same systems without an interlayer. The microstructures were analyzed by XRD, EDS, and SEM. The hardness and surface load-carrying capacity of the coating systems were determined by micro-and macrohardness testing. Rockwell indentation was used to assess coating adhesion (CEN/TS 1071-8). Tribological properties were assessed with a reciprocating tribometer, and corrosion resistance was determined by potentiodynamic polarization and electrochemical impedance spectroscopy. The originality of this work lies in the finding that, except for the Inconel 718/Ni-W-Cr-B/W-WC system, the wear rate decreases with decreasing hardness of the subsurface materials carrying the thin film due to the decreasing contact pressure for a given load. Another novel finding is the stress-induced phase transformation of the Co-Cr interlayer, which occurs beneath the thin film under high load.

Materials Chemistry and Physics, 2013

h i g h l i g h t s Tungsten/tungsten carbide (W/WC) and cobalt-phosphor (NCP) coatings are compa... more h i g h l i g h t s Tungsten/tungsten carbide (W/WC) and cobalt-phosphor (NCP) coatings are compared with hard chromium (HC). NCP and W/WC offer better tribological properties (wear rate and friction coefficient) than HC. W/WC has demonstrated a robust corrosion behavior with a breakdown potential greater than 1 V. NCP and W/WC are potential candidates to replace hard chromium as protective coating.

Journal of Thermal Spray Technology, 2013

This case study is the result of an investigation on HVOF 80/20 Cr 3 C 2-NiCr coating failure of ... more This case study is the result of an investigation on HVOF 80/20 Cr 3 C 2-NiCr coating failure of on-off metal-seated ball valve (MSBV) used in supercritical steam lines in a power plant and solution. HVOF 80/20 Cr 3 C 2-NiCr coating is used to protect thousands of MSBVs without incident. However, in this case, the valves are challenged with exposure to rapid high-pressure and-temperature variations resulting in a unique situation where the coating experiences cracking and cohesive failure. It was found that carbide precipitation is a major factor causing embrittlement of the coating. Once the coating toughness and ductility is reduced, thermal, mechanical, and residual stresses can initiate and propagate cracks more easily, causing coating failure when exposed to thermal shock. To alleviate the above mentioned issues, possible coating alternatives were then evaluated.

Volume 14: Emerging Technologies; Engineering Management, Safety, Ethics, Society, and Education; Materials: Genetics to Structures, 2014

Wear of materials is a serious problem facing industry especially in mechanical applications wher... more Wear of materials is a serious problem facing industry especially in mechanical applications where moving parts are continuously subjected to friction. Hard coatings prepared by a variety of processes are nowadays considered as effective solutions to protect components against wear. Examples of such processes are: thermal spray coating, vacuum-based coating and hardfacing. In this paper, we study the mechanical, tribological and corrosion properties of two hard coating systems: CoCr Stellite 6 (ST6) hardfacing on 316 stainless steel and NiWCrB Colmonoy 88 (C88) thermal spray coating on Inconel 718. The effect of gas nitriding on the microstructure and wear performance of these coating systems is investigated. X-ray diffraction, energy dispersive spectroscopy and scanning electron microscopy were used for microstructural analysis. Micro-indentation technique was utilized to measure the surface and cross-sectional hardness of the coatings. Rockwell indentation technique was used to ev...

La robinetterie et la tuyauterie industrielles sont des appareils sous pression qui permettent de... more La robinetterie et la tuyauterie industrielles sont des appareils sous pression qui permettent de reguler le flux de materiaux (liquides, gaz et boues) en controlant les sections de passages. L’optimisation des processus, la reduction des couts et les reglementations gouvernementales exigent des equipementiers de maintenir leurs produits a la fine pointe de la technologie. La robinetterie a ete developpee il y a plus de 3000 ans pour alimenter en eau les fermes et les villes en utilisant des alliages de bronze, qui fournissent a la fois une resistance a la corrosion et des performances tribologiques acceptables. Durant la revolution industrielle, ces antiques robinets ont evolue et des materiaux tribologiques plus modernes tels que les alliages Monel cuivre-nickel, Stellite cobalt-chrome, et le chromage dur applique par placage electrolytique ont ete developpes au debut du XXe siecle pour optimiser le comportement tribologique et maximiser la duree de vie en service de ces equipemen...

Surface & Coatings Technology, 2020

In recent years, a major challenge facing the power generation industry is delamination of Stelli... more In recent years, a major challenge facing the power generation industry is delamination of Stellite-hardfaced coatings from high-temperature valves. In order to meet this challenge, IN82 buffer layer was evaluated to replace the problematic S21 buffer layer. S6 and either S21 or IN82 hardfacing alloys were deposited onto F91 steel substrates using plasma-transferred arc hardfacing. Aging was conducted at temperatures between 550 and 650 °C for three exposure durations within a one-year period. A comparative study was carried out on the microstructure and mechanical properties of IN82 and S21 hardfaced specimens. The F91/S21 interface is unstable during aging because a hard and brittle interfacial layer grows, which significantly reduces the impact energy of S21 hardfaced specimens. In contrast, the F91/IN82 interface is microstructurally much more stable than the F91/S21 interface; an interfacial band, part of the F91 steel, and some discrete M23C6 carbides along this band grow duri...

Journal of Thermal Spray Technology, 2013

This case study is the result of an investigation on HVOF 80/20 Cr 3 C 2 -NiCr coating failure of... more This case study is the result of an investigation on HVOF 80/20 Cr 3 C 2 -NiCr coating failure of on-off metal-seated ball valve (MSBV) used in supercritical steam lines in a power plant and solution. HVOF 80/20 Cr 3 C 2 -NiCr coating is used to protect thousands of MSBVs without incident. However, in this case, the valves are challenged with exposure to rapid high-pressure and -temperature variations resulting in a unique situation where the coating experiences cracking and cohesive failure. It was found that carbide precipitation is a major factor causing embrittlement of the coating. Once the coating toughness and ductility is reduced, thermal, mechanical, and residual stresses can initiate and propagate cracks more easily, causing coating failure when exposed to thermal shock. To alleviate the above mentioned issues, possible coating alternatives were then evaluated.