This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
This study is focused on the high-temperature corrosion evaluation of selected thermally sprayed ... more This study is focused on the high-temperature corrosion evaluation of selected thermally sprayed coatings. NiCoCrAlYHfSi, NiCoCrAlY, NiCoCrAlTaReY, and CoCrAlYTaCSi coatings were sprayed on the base material 1.4923. This material is used as a cost-efficient construction material for components of power equipment. All evaluated coatings were sprayed using HP/HVOF (High-Pressure/High-Velocity Oxygen Fuel) technology. High-temperature corrosion testing was performed in a molten salt environment typical for coal-fired boilers. All coatings were exposed to the environment of 75% Na2SO4 and 25% NaCl at the temperature of 800 °C under cyclic conditions. Each cycle consisted of 1 h heating in a silicon carbide tube furnace followed by 20 min of cooling. The weight change measurement was performed after each cycle to establish the corrosion kinetics. Optical microscopy (OM), scanning electron microscopy (SEM), and elemental analysis (EDS) were used to analyze the corrosion mechanism. The CoC...
In order to extend the life of boilers by applying an anti-corrosion coating without the need to ... more In order to extend the life of boilers by applying an anti-corrosion coating without the need to dismantle them, it is advisable to find coatings that can be applied using cheaper and portable techniques, such as Twin Wire Arc Spray technology (TWAS). In this study, we compare selected NiCr-based coatings and two uncoated steel substrates (steel 1.7715 and 1.4903). Two coatings, Cr3C2 - 25% NiCr and Hastelloy C-276 are deposited using High velocity oxygen-fuel technology (HVOF) and three coatings, NiCrTi, NiCrMo, and Inconel 625, are deposited using TWAS. In addition to the corrosion weight gain during 50 cycles of loading in an 18% Na2SO4 and 82% Fe2(SO4)3 salt environment at 690 °C evaluated using the gravimetric method, the microstructure and phase composition of the coatings were analyzed on the samples after the exposure in order to compare the properties and gain a deeper understanding of the corrosion kinetics. Coating cross-sections and free-surfaces were observed with a sca...
At present, due to advanced fatigue calculation models, it is becoming more crucial to find a rel... more At present, due to advanced fatigue calculation models, it is becoming more crucial to find a reliable source for design S–N curves, especially in the case of new 3D-printed materials. Such obtained steel components are becoming very popular and are often used for important parts of dynamically loaded structures. One of the commonly used printing steels is EN 1.2709 tool steel, which has good strength properties and high abrasion resistance, and can be hardened. The research shows, however, that its fatigue strength may differ depending on the printing method, and may be characterized by a wide scatter of the fatigue life. This paper presents selected S–N curves for EN 1.2709 steel after printing with the selective laser melting method. The characteristics are compared, and conclusions are presented regarding the resistance of this material to fatigue loading, especially in the tension–compression state. A combined general mean reference and design fatigue curve is presented, which ...
The CoCrWC alloy, well known as Stellite Alloy 6, is the most widely used alloy in the Co-based g... more The CoCrWC alloy, well known as Stellite Alloy 6, is the most widely used alloy in the Co-based group of alloys. It has an excellent resistance to many forms of wear and corrosion over a wide range in temperature. Their exceptional wear resistance is due mainly to the unique inherent characteristics of the hard carbide phase dispersed in a CoCr alloy matrix. Stellite Alloy 6 has an outstanding resistance to seizing or galling as well as cavitation erosion and retains a reasonable level of hardness up to 500°C. It is available in many product forms – castings, wrought bars, sheets etc. It is ideally suited to a variety of hardfacing processes and can be turned with carbide tooling. Examples include valve seats and gates; pump shafts and bearings, erosion shields and rolling couples. The thermal spraying is one of the technologies that can be used for Stellite Alloy 6 deposition on the parts surface. To preserve its superior properties, it is necessary to find the optimal spraying par...
IOP Conference Series: Materials Science and Engineering, 2021
The components in coal power plants such as fire sides in boilers, preheaters, or heat exchangers... more The components in coal power plants such as fire sides in boilers, preheaters, or heat exchangers are significantly mechanically and chemically stressed. The main stress originates from high temperature corrosion caused by the aggressive atmosphere inside the boiler, but other influences such as erosion and abrasion by coal and flying ash, heat shocks, etc. also have significant negative effect. One of the options for increasing the service life and improving the utility properties of these components is a thermal spray coating. Because the disassembly of these components is impossible, the mobile TWAS deposition technology was used. In this paper, different types of TWAS-sprayed coatings suitable for application in such environment are compared and evaluated. Two types of coating materials were evaluated, FeCr-based ones and NiCr-based ones, in terms of microstructure and mechanical properties such as hardness, adhesion, abrasion and erosion resistance. The SEM microscopy evaluatio...
IOP Conference Series: Materials Science and Engineering, 2021
The NiCr coatings, deposited by modern Cold Spray technology, and by well-established Twin Wire A... more The NiCr coatings, deposited by modern Cold Spray technology, and by well-established Twin Wire Arc Spraying and High Velocity Oxygen Fuel technologies, was studied in terms of microstructure, mechanical, tribological and corrosion properties. Compared to other thermal spraying technologies, CS coatings achieve higher cohesive strength and associated tribological properties. The dense structure is responsible for the coatings’ high corrosion protection ability. The influence of CS technological parameters was found negligible, except the usage of nozzle for internal diameter spraying, which results to significant increase of coatings porosity.
The article aims to comprehend the microstructural changes, in Plasma Transfer Arc (PTA) deposite... more The article aims to comprehend the microstructural changes, in Plasma Transfer Arc (PTA) deposited M2 high speed steel (HSS) hardfacings upon incorporation of 10 wt% Mo alloying during deposition followed by laser surface melting. PTA deposited hardfacings were produced over 4140 steel. Then Mo alloyed and unalloyed PTA deposits were subjected to laser surface melting (LSM) process. A comprehensive microstructural characterization for all the resultant structures was carried out. Optical metallography using appropriate etching reagents and SEM microscopy in conjunction with XRD techniques were employed to ascertain the matrix structure and carbides morphology. The PTA microstructure was close to equilibrium structure of M2 HSS containing mixture of ferrite/austenite/martensite along with MC, M2C and M6C type carbides. While the LSM of M2 HSS caused higher fraction of martensite and finer grains in the structure resulting in increment in hardness. 10-wt% Mo addition changes the carbi...
Thermally sprayed hardmetal coatings were produced to provide improved erosion wear compared to c... more Thermally sprayed hardmetal coatings were produced to provide improved erosion wear compared to conventional cast GX4CrNi13-4 martensitic steel (CA6NM) used in hydro turbine components. Sprayed coatings and reference materials were tested with high-speed slurry pot tester using either fine or coarse quartz as the erosive media. Additional erosion tests were carried out with centrifugal dry erosion tester. Tungsten carbide based coatings provided the highest wear resistance due to the high hardness and even distribution of the fine carbide particles. The cast 13-4 steel samples experienced up to 180 times higher wear rates in fine quartz slurry and up to 36 times higher wear rates in coarse slurry compared to the sprayed coatings.
The 15th International Workshop on Advanced Infrared Technology and Applications, 2019
Thermographic testing is an inspection method, which primary indicates a presence of discontinuit... more Thermographic testing is an inspection method, which primary indicates a presence of discontinuities in a tested sample. Its application to coatings can indicate a presence of local thickness variations; however, it mostly does not bring a quantitative information about a thickness of the coatings. This contribution is focused on a quantification of the thermographic inspection, which would make possible an evaluation of coating thickness differences. A flash pulse thermographic testing was applied to thermally sprayed coatings. An importance of a precise synchronization of a flash-source and thermographic recording was determined. Different evaluation methods were analyzed and their comparison showed that a time-power transformation method is the most suitable for a quantification of the inspection results.
The present work aimed to clarify how the characteristics of WC-CoCr hardmetal feedstock powders,... more The present work aimed to clarify how the characteristics of WC-CoCr hardmetal feedstock powders, namely the grain size of the WC carbides and of the binder and the compressive strength of the sintered aggregates, affect the dry sliding wear and impact resistance of coatings deposited by High-Velocity Air Fuel (HVAF) spraying.
IOP Conference Series: Materials Science and Engineering, 2018
For wear demanding applications, the coatings, consisting of WC in the nickel-based alloy are oft... more For wear demanding applications, the coatings, consisting of WC in the nickel-based alloy are often used due to their excellent properties. Nevertheless, there are still limits of these coatings, mainly deterioration of tungsten carbide due to heat load during laser cladding. The suppress the limits, a new type of coating material, consisting of the (TiW)C 1-x in nickel-based alloy, was designed. The goal of this study is to compare the microstructure and mechanical properties of new (TiW)C 1-x based coating with a usual WC-based coating to confirm its improved behaviour.
Thermally sprayed coatings can be remelted to improve their microstructure and functional propert... more Thermally sprayed coatings can be remelted to improve their microstructure and functional properties. Among other remelting technologies, laser remelting has the advantage of precise control of the remelting process by suitably chosen parameters. It enables the remelting of the whole thickness of the coating and creation of a metallurgical bonding with the substrate or remelting of the coating only to a certain depth and maintaining the advantage of thermally sprayed coatings´ lamellar microstructure. In this study, HVOF sprayed Stellite coatings on a steel substrate were remelted by a high power diode laser. The experiment was designed to evaluate the role of the process speed on the depth of remelting, comparing cases of a different coatings and sample thicknesses using Near-infrared (NIR) camera. The temperature field in the melting area was evaluated and related to the achieved depth of remelting. The study shows that the IR measurement can be used for prediction of the achieved depth of remelting during a laser remelting, regardless of the coating/substrate thickness ratio.
Lowering the thermal energy and increasing the kinetic energy of hard metal particles sprayed by ... more Lowering the thermal energy and increasing the kinetic energy of hard metal particles sprayed by the newly developed HVAF systems can significantly reduce their decarburization, and increases the sliding wear and corrosion resistance of the resulting coatings, making the HVAF technique attractive, both economically and environmentally, over its HVOF predecessors. Two agglomerated and sintered feedstock powder chemistries, WC-Co (88/12) and WC-CoCr (86/10/4), respectively, with increasing primary carbides grain size from 0.2 to 4.0 microns, have been deposited by the latest HVAF-M3 process onto carbon steel substrates. Their dry sliding wear behaviors and friction coefficients were evaluated at room temperature via Ball-on-disk (ASTM G99-90) wear tests against Al 2 O 3 counterparts, and via Pin-on-disk (ASTM G77-05) wear tests against modified martensitic steel counterparts in both dry and lubricated conditions. Sliding wear mechanisms, with the formation of wavy surface morphology and brittle cracking, are discussed regarding the distribution and size of primary carbides. Corrosion behaviors were evaluated via standard Neutral Salt Spray, Acetic Acid Salt Spray, accelerated corrosion test, and electrochemical polarization test at room temperature. The optimization of the tribological properties of the coatings is discussed, focusing on the suitable selection of primary carbide size for different working load applications.
Laser marking is an advanced application of surface optical properties modification. Processes oc... more Laser marking is an advanced application of surface optical properties modification. Processes occurring during the laser beam-surface interaction cause surface color changes. These processes can affect also other material properties, such as undesirable reduction of corrosion resistance in the case of stainless steels. Influence of laser marking processing parameters on stainless steel corrosion properties is shown in this contribution. Different material analysis methods for the evaluation of changes to the corrosion properties of stainless steel were tested. The results, including corrosion tests and GIXRD analyses of laser treated materials, are presented. Possibilities and limitations of laser marking of stainless steel in the context of its corrosion resistance reduction are discussed. http://www.valardocs.com/wp-content/uploads/2015/03/SMT28_EVERSION.pdf
This work compares the isolated nanoindentation with grid indentation on three HVOF coatings. The... more This work compares the isolated nanoindentation with grid indentation on three HVOF coatings. The bimodal and trimodal Gaussian fits are compared with the isolated indentation results and the reasons for the use of trimodal fit are given. The results are completed by comparison of conventional and instrumented micro indentation results.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
This study is focused on the high-temperature corrosion evaluation of selected thermally sprayed ... more This study is focused on the high-temperature corrosion evaluation of selected thermally sprayed coatings. NiCoCrAlYHfSi, NiCoCrAlY, NiCoCrAlTaReY, and CoCrAlYTaCSi coatings were sprayed on the base material 1.4923. This material is used as a cost-efficient construction material for components of power equipment. All evaluated coatings were sprayed using HP/HVOF (High-Pressure/High-Velocity Oxygen Fuel) technology. High-temperature corrosion testing was performed in a molten salt environment typical for coal-fired boilers. All coatings were exposed to the environment of 75% Na2SO4 and 25% NaCl at the temperature of 800 °C under cyclic conditions. Each cycle consisted of 1 h heating in a silicon carbide tube furnace followed by 20 min of cooling. The weight change measurement was performed after each cycle to establish the corrosion kinetics. Optical microscopy (OM), scanning electron microscopy (SEM), and elemental analysis (EDS) were used to analyze the corrosion mechanism. The CoC...
In order to extend the life of boilers by applying an anti-corrosion coating without the need to ... more In order to extend the life of boilers by applying an anti-corrosion coating without the need to dismantle them, it is advisable to find coatings that can be applied using cheaper and portable techniques, such as Twin Wire Arc Spray technology (TWAS). In this study, we compare selected NiCr-based coatings and two uncoated steel substrates (steel 1.7715 and 1.4903). Two coatings, Cr3C2 - 25% NiCr and Hastelloy C-276 are deposited using High velocity oxygen-fuel technology (HVOF) and three coatings, NiCrTi, NiCrMo, and Inconel 625, are deposited using TWAS. In addition to the corrosion weight gain during 50 cycles of loading in an 18% Na2SO4 and 82% Fe2(SO4)3 salt environment at 690 °C evaluated using the gravimetric method, the microstructure and phase composition of the coatings were analyzed on the samples after the exposure in order to compare the properties and gain a deeper understanding of the corrosion kinetics. Coating cross-sections and free-surfaces were observed with a sca...
At present, due to advanced fatigue calculation models, it is becoming more crucial to find a rel... more At present, due to advanced fatigue calculation models, it is becoming more crucial to find a reliable source for design S–N curves, especially in the case of new 3D-printed materials. Such obtained steel components are becoming very popular and are often used for important parts of dynamically loaded structures. One of the commonly used printing steels is EN 1.2709 tool steel, which has good strength properties and high abrasion resistance, and can be hardened. The research shows, however, that its fatigue strength may differ depending on the printing method, and may be characterized by a wide scatter of the fatigue life. This paper presents selected S–N curves for EN 1.2709 steel after printing with the selective laser melting method. The characteristics are compared, and conclusions are presented regarding the resistance of this material to fatigue loading, especially in the tension–compression state. A combined general mean reference and design fatigue curve is presented, which ...
The CoCrWC alloy, well known as Stellite Alloy 6, is the most widely used alloy in the Co-based g... more The CoCrWC alloy, well known as Stellite Alloy 6, is the most widely used alloy in the Co-based group of alloys. It has an excellent resistance to many forms of wear and corrosion over a wide range in temperature. Their exceptional wear resistance is due mainly to the unique inherent characteristics of the hard carbide phase dispersed in a CoCr alloy matrix. Stellite Alloy 6 has an outstanding resistance to seizing or galling as well as cavitation erosion and retains a reasonable level of hardness up to 500°C. It is available in many product forms – castings, wrought bars, sheets etc. It is ideally suited to a variety of hardfacing processes and can be turned with carbide tooling. Examples include valve seats and gates; pump shafts and bearings, erosion shields and rolling couples. The thermal spraying is one of the technologies that can be used for Stellite Alloy 6 deposition on the parts surface. To preserve its superior properties, it is necessary to find the optimal spraying par...
IOP Conference Series: Materials Science and Engineering, 2021
The components in coal power plants such as fire sides in boilers, preheaters, or heat exchangers... more The components in coal power plants such as fire sides in boilers, preheaters, or heat exchangers are significantly mechanically and chemically stressed. The main stress originates from high temperature corrosion caused by the aggressive atmosphere inside the boiler, but other influences such as erosion and abrasion by coal and flying ash, heat shocks, etc. also have significant negative effect. One of the options for increasing the service life and improving the utility properties of these components is a thermal spray coating. Because the disassembly of these components is impossible, the mobile TWAS deposition technology was used. In this paper, different types of TWAS-sprayed coatings suitable for application in such environment are compared and evaluated. Two types of coating materials were evaluated, FeCr-based ones and NiCr-based ones, in terms of microstructure and mechanical properties such as hardness, adhesion, abrasion and erosion resistance. The SEM microscopy evaluatio...
IOP Conference Series: Materials Science and Engineering, 2021
The NiCr coatings, deposited by modern Cold Spray technology, and by well-established Twin Wire A... more The NiCr coatings, deposited by modern Cold Spray technology, and by well-established Twin Wire Arc Spraying and High Velocity Oxygen Fuel technologies, was studied in terms of microstructure, mechanical, tribological and corrosion properties. Compared to other thermal spraying technologies, CS coatings achieve higher cohesive strength and associated tribological properties. The dense structure is responsible for the coatings’ high corrosion protection ability. The influence of CS technological parameters was found negligible, except the usage of nozzle for internal diameter spraying, which results to significant increase of coatings porosity.
The article aims to comprehend the microstructural changes, in Plasma Transfer Arc (PTA) deposite... more The article aims to comprehend the microstructural changes, in Plasma Transfer Arc (PTA) deposited M2 high speed steel (HSS) hardfacings upon incorporation of 10 wt% Mo alloying during deposition followed by laser surface melting. PTA deposited hardfacings were produced over 4140 steel. Then Mo alloyed and unalloyed PTA deposits were subjected to laser surface melting (LSM) process. A comprehensive microstructural characterization for all the resultant structures was carried out. Optical metallography using appropriate etching reagents and SEM microscopy in conjunction with XRD techniques were employed to ascertain the matrix structure and carbides morphology. The PTA microstructure was close to equilibrium structure of M2 HSS containing mixture of ferrite/austenite/martensite along with MC, M2C and M6C type carbides. While the LSM of M2 HSS caused higher fraction of martensite and finer grains in the structure resulting in increment in hardness. 10-wt% Mo addition changes the carbi...
Thermally sprayed hardmetal coatings were produced to provide improved erosion wear compared to c... more Thermally sprayed hardmetal coatings were produced to provide improved erosion wear compared to conventional cast GX4CrNi13-4 martensitic steel (CA6NM) used in hydro turbine components. Sprayed coatings and reference materials were tested with high-speed slurry pot tester using either fine or coarse quartz as the erosive media. Additional erosion tests were carried out with centrifugal dry erosion tester. Tungsten carbide based coatings provided the highest wear resistance due to the high hardness and even distribution of the fine carbide particles. The cast 13-4 steel samples experienced up to 180 times higher wear rates in fine quartz slurry and up to 36 times higher wear rates in coarse slurry compared to the sprayed coatings.
The 15th International Workshop on Advanced Infrared Technology and Applications, 2019
Thermographic testing is an inspection method, which primary indicates a presence of discontinuit... more Thermographic testing is an inspection method, which primary indicates a presence of discontinuities in a tested sample. Its application to coatings can indicate a presence of local thickness variations; however, it mostly does not bring a quantitative information about a thickness of the coatings. This contribution is focused on a quantification of the thermographic inspection, which would make possible an evaluation of coating thickness differences. A flash pulse thermographic testing was applied to thermally sprayed coatings. An importance of a precise synchronization of a flash-source and thermographic recording was determined. Different evaluation methods were analyzed and their comparison showed that a time-power transformation method is the most suitable for a quantification of the inspection results.
The present work aimed to clarify how the characteristics of WC-CoCr hardmetal feedstock powders,... more The present work aimed to clarify how the characteristics of WC-CoCr hardmetal feedstock powders, namely the grain size of the WC carbides and of the binder and the compressive strength of the sintered aggregates, affect the dry sliding wear and impact resistance of coatings deposited by High-Velocity Air Fuel (HVAF) spraying.
IOP Conference Series: Materials Science and Engineering, 2018
For wear demanding applications, the coatings, consisting of WC in the nickel-based alloy are oft... more For wear demanding applications, the coatings, consisting of WC in the nickel-based alloy are often used due to their excellent properties. Nevertheless, there are still limits of these coatings, mainly deterioration of tungsten carbide due to heat load during laser cladding. The suppress the limits, a new type of coating material, consisting of the (TiW)C 1-x in nickel-based alloy, was designed. The goal of this study is to compare the microstructure and mechanical properties of new (TiW)C 1-x based coating with a usual WC-based coating to confirm its improved behaviour.
Thermally sprayed coatings can be remelted to improve their microstructure and functional propert... more Thermally sprayed coatings can be remelted to improve their microstructure and functional properties. Among other remelting technologies, laser remelting has the advantage of precise control of the remelting process by suitably chosen parameters. It enables the remelting of the whole thickness of the coating and creation of a metallurgical bonding with the substrate or remelting of the coating only to a certain depth and maintaining the advantage of thermally sprayed coatings´ lamellar microstructure. In this study, HVOF sprayed Stellite coatings on a steel substrate were remelted by a high power diode laser. The experiment was designed to evaluate the role of the process speed on the depth of remelting, comparing cases of a different coatings and sample thicknesses using Near-infrared (NIR) camera. The temperature field in the melting area was evaluated and related to the achieved depth of remelting. The study shows that the IR measurement can be used for prediction of the achieved depth of remelting during a laser remelting, regardless of the coating/substrate thickness ratio.
Lowering the thermal energy and increasing the kinetic energy of hard metal particles sprayed by ... more Lowering the thermal energy and increasing the kinetic energy of hard metal particles sprayed by the newly developed HVAF systems can significantly reduce their decarburization, and increases the sliding wear and corrosion resistance of the resulting coatings, making the HVAF technique attractive, both economically and environmentally, over its HVOF predecessors. Two agglomerated and sintered feedstock powder chemistries, WC-Co (88/12) and WC-CoCr (86/10/4), respectively, with increasing primary carbides grain size from 0.2 to 4.0 microns, have been deposited by the latest HVAF-M3 process onto carbon steel substrates. Their dry sliding wear behaviors and friction coefficients were evaluated at room temperature via Ball-on-disk (ASTM G99-90) wear tests against Al 2 O 3 counterparts, and via Pin-on-disk (ASTM G77-05) wear tests against modified martensitic steel counterparts in both dry and lubricated conditions. Sliding wear mechanisms, with the formation of wavy surface morphology and brittle cracking, are discussed regarding the distribution and size of primary carbides. Corrosion behaviors were evaluated via standard Neutral Salt Spray, Acetic Acid Salt Spray, accelerated corrosion test, and electrochemical polarization test at room temperature. The optimization of the tribological properties of the coatings is discussed, focusing on the suitable selection of primary carbide size for different working load applications.
Laser marking is an advanced application of surface optical properties modification. Processes oc... more Laser marking is an advanced application of surface optical properties modification. Processes occurring during the laser beam-surface interaction cause surface color changes. These processes can affect also other material properties, such as undesirable reduction of corrosion resistance in the case of stainless steels. Influence of laser marking processing parameters on stainless steel corrosion properties is shown in this contribution. Different material analysis methods for the evaluation of changes to the corrosion properties of stainless steel were tested. The results, including corrosion tests and GIXRD analyses of laser treated materials, are presented. Possibilities and limitations of laser marking of stainless steel in the context of its corrosion resistance reduction are discussed. http://www.valardocs.com/wp-content/uploads/2015/03/SMT28_EVERSION.pdf
This work compares the isolated nanoindentation with grid indentation on three HVOF coatings. The... more This work compares the isolated nanoindentation with grid indentation on three HVOF coatings. The bimodal and trimodal Gaussian fits are compared with the isolated indentation results and the reasons for the use of trimodal fit are given. The results are completed by comparison of conventional and instrumented micro indentation results.
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