Hanna Pokhmurska | Technische Universität Chemnitz (original) (raw)
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Papers by Hanna Pokhmurska
The results of controlled doping of CdxHg1yxTe epitaxial layers are presented. The investigated l... more The results of controlled doping of CdxHg1yxTe epitaxial layers are presented. The investigated layers were obtained by the evaporation–condensation–diffusion method in the process of isothermal growth. The process of auto diffusion from the solid phase was investigated. This process consists in the diffusion of As dopants from CdTe substrate into the grown epitaxial layer. Two types of CdTe substrates, uniformly doped in the process of synthesis and unalloyed with ion implanted surface layer, have been used as sources of As diffusant. Comparative analysis of galvanomagnetic measurements and SIMS spectra was carried out. The results of investigations indicate the very high, almost 100%, electrical activity of As dopants in the CdxHg1yxTe epitaxial grown layer.
Thin Solid Films, 2002
The results of controlled doping of CdxHg1−xTe epitaxial layers are presented. The investigated l... more The results of controlled doping of CdxHg1−xTe epitaxial layers are presented. The investigated layers were obtained by the evaporation–condensation–diffusion method in the process of isothermal growth. The process of auto diffusion from the solid phase was investigated. This process consists in the diffusion of As dopants from CdTe substrate into the grown epitaxial layer. Two types of CdTe substrates, uniformly
Thin Solid Films, 2002
The results of controlled doping of CdxHg1−xTe epitaxial layers are presented. The investigated l... more The results of controlled doping of CdxHg1−xTe epitaxial layers are presented. The investigated layers were obtained by the evaporation–condensation–diffusion method in the process of isothermal growth. The process of auto diffusion from the solid phase was investigated. This process consists in the diffusion of As dopants from CdTe substrate into the grown epitaxial layer. Two types of CdTe substrates, uniformly
The laser surface melting of AA2024-T3 alloy modified a structure of surface layer resulting in c... more The laser surface melting of AA2024-T3 alloy modified a structure of surface layer resulting in cells and/or cellular dendrites of very fine microstructure. There are mainly two phases, i.e. primary solid solution and precipitated Al2Cu phase, around the cell boundaries. Some minor traces of Fe and Mn are also present. The estimated decrease of Cu content in precipitates is approximately 25%. The susceptibility to pitting corrosion of laser melted AA2024-T3 surfaces characterised by pitting potential was not improved in comparison with as-received material, mainly due to non-uniform structure at subsequent laser tracks.
Surface & Coatings Technology, 2002
The technology of wear resistant coatings and new powder wire composites has been developed. New ... more The technology of wear resistant coatings and new powder wire composites has been developed. New coatings with low porosity and small grains were obtained by arc-spraying of FeCrB+ Al and FeCr+ Al+ C powder wires in a steel cover. A modified arc spraying torch ...
Journal of Thermal Spray Technology, 2007
Different posttreatment methods, such as heat treatment, mechanical processing, sealing, etc., ar... more Different posttreatment methods, such as heat treatment, mechanical processing, sealing, etc., are known to be capable to improve microstructure and exploitation properties of thermal spray coatings. In this work, a plasma electrolytic oxidation of aluminum coatings obtained by arc spraying on aluminum and carbon steel substrates is carried out. Microstructure and properties of oxidized layers formed on sprayed coating as well as on bulk material are investigated. Oxidation is performed in electrolyte containing KOH and liquid glass under different process parameters. It is shown that thick uniform oxidized layers can be formed on arc-sprayed aluminum coatings as well as on solid material. Distribution of alloying elements and phase composition of obtained layers are investigated. A significant improvement of wear resistance of treated layers in two types of abrasive wear conditions is observed.
Key Engineering Materials, 2008
A brief overview of existing methods of post-treatment of thermally sprayed coatings is given and... more A brief overview of existing methods of post-treatment of thermally sprayed coatings is given and the influence of mechanical and chemical as well as high-energy beam post-treatment methods on the coating microstructure formation and some exploitation properties is described. As a special example, the modification of thermally sprayed coatings on magnesium alloys using electron and laser beams and high-density irradiation of an infra-red beamer for the improvement of wear and corrosion resistance is presented.
Surface & Coatings Technology, 2011
In the field of thermal spraying, cermets are known to have excellent wear-protecting properties.... more In the field of thermal spraying, cermets are known to have excellent wear-protecting properties. However, the high price of the spraying materials and the environmental aspects of nickel and cobalt utilization are often the limitations to their wider application. Within the frame of a multi-institutional cooperation of various German research centres, the AiF/DFG research cluster "Thermal Spraying" was organised, one of the main research goals of which is the development of economically attractive alternative spray materials with new property profiles. This paper presents some results of the project that deals with the development and thermal spraying of particle-reinforced iron-based composite alloys. High-alloyed steels serve as matrix materials into which hard CrB 2 particles are incorporated by means of a high-energy milling (HEM) process. The microstructure of the powder and the level of its amorphisation can be strongly influenced by appropriate milling parameters that allow the adjustment of the desired nanocrystalline structure. By using the highvelocity oxygen fuel thermal spraying process (HVOF), the microstructure of the particles can be transferred to the coatings. The deposited coatings exhibit low porosity and high microhardness values of more than 1000 HV0.3. The high abrasion wear resistance of newly developed coatings evaluated by means of the Miller test (ASTM G75-01) makes them promising for application for example in paper industry as an alternative to hard chromium coatings.
Surface & Coatings Technology, 2008
... 2.5. Coating characterization. The resulting microstructure of the electron beam modified sur... more ... 2.5. Coating characterization. The resulting microstructure of the electron beam modified surfaces is characterized materialographically using optical microscopy, scanning electron microscopy (LEO 1455VP) and energy dispersive X-ray microanalysis (EDISON). ...
Surface & Coatings Technology, 2006
Three actual trends in development of HVOF spraying technology are described and discussed. The t... more Three actual trends in development of HVOF spraying technology are described and discussed. The trends concern application fields as well as gun and feedstock characteristics. At the example of demountable draw bars it is shown that HVOF sprayed ...
Surface & Coatings Technology, 2006
Electroplated hard chromium and thermal spray hardmetal coatings are widely used in a variety of ... more Electroplated hard chromium and thermal spray hardmetal coatings are widely used in a variety of applications for wear protection of component surfaces. The two protective coating types are tested in direct comparison for tribological conditions of dry abrasive wear (Taber Abraser test) and dry oscillating wear load. Oscillating wear tests are carried out both with hardened 100Cr6 steel and alumina balls as counterbody. Different types of hardmetal coatings are imparted. Besides HVOF sprayed coatings also coatings sprayed by an APS gun with axial powder feed are tested. For HVOF spraying besides standard WC/Co(Cr) feedstock also coarse (d 50 = 5 μm) and fine carbide feedstock (d 50 = 0.8 μm) and ultrafine powders, i.e. 2 μm b d b 12 μm, are considered. Use of ultrafine powders is particularly interesting from the economical point of view, as belt grinding can be sufficient for finishing in many cases. The optimum coating solution for wear protection depends on the specific tribosystem. The choice of feedstock, spraying process, equipment and processing conditions does not only depend on the resultant tribological properties. Therefore simultaneous influence on corrosion protection capability and thermal conductivity might have to be considered.
ABSTRACT The main tendencies in the development of tungsten carbide coating applications are pres... more ABSTRACT The main tendencies in the development of tungsten carbide coating applications are presented. General properties of WC based coatings and their dependence on different factors are discussed. For comparative examination of the abrasive wear resistance of thermal spray coatings detailed Taber Abraser wear tests are carried out. Besides HVOF sprayed cermet and APS Cr 2 O 3 also electroplated hard chromium coatings are studied. The best results have been obtained for HVOF sprayed cermet coatings. For this kind of wear conditions the difference in wear behaviour depending on carbide size in WC-CoCr coatings is insignificant compared to the difference depending on the matrix composition.
The results of controlled doping of CdxHg1yxTe epitaxial layers are presented. The investigated l... more The results of controlled doping of CdxHg1yxTe epitaxial layers are presented. The investigated layers were obtained by the evaporation–condensation–diffusion method in the process of isothermal growth. The process of auto diffusion from the solid phase was investigated. This process consists in the diffusion of As dopants from CdTe substrate into the grown epitaxial layer. Two types of CdTe substrates, uniformly doped in the process of synthesis and unalloyed with ion implanted surface layer, have been used as sources of As diffusant. Comparative analysis of galvanomagnetic measurements and SIMS spectra was carried out. The results of investigations indicate the very high, almost 100%, electrical activity of As dopants in the CdxHg1yxTe epitaxial grown layer.
Thin Solid Films, 2002
The results of controlled doping of CdxHg1−xTe epitaxial layers are presented. The investigated l... more The results of controlled doping of CdxHg1−xTe epitaxial layers are presented. The investigated layers were obtained by the evaporation–condensation–diffusion method in the process of isothermal growth. The process of auto diffusion from the solid phase was investigated. This process consists in the diffusion of As dopants from CdTe substrate into the grown epitaxial layer. Two types of CdTe substrates, uniformly
Thin Solid Films, 2002
The results of controlled doping of CdxHg1−xTe epitaxial layers are presented. The investigated l... more The results of controlled doping of CdxHg1−xTe epitaxial layers are presented. The investigated layers were obtained by the evaporation–condensation–diffusion method in the process of isothermal growth. The process of auto diffusion from the solid phase was investigated. This process consists in the diffusion of As dopants from CdTe substrate into the grown epitaxial layer. Two types of CdTe substrates, uniformly
The laser surface melting of AA2024-T3 alloy modified a structure of surface layer resulting in c... more The laser surface melting of AA2024-T3 alloy modified a structure of surface layer resulting in cells and/or cellular dendrites of very fine microstructure. There are mainly two phases, i.e. primary solid solution and precipitated Al2Cu phase, around the cell boundaries. Some minor traces of Fe and Mn are also present. The estimated decrease of Cu content in precipitates is approximately 25%. The susceptibility to pitting corrosion of laser melted AA2024-T3 surfaces characterised by pitting potential was not improved in comparison with as-received material, mainly due to non-uniform structure at subsequent laser tracks.
Surface & Coatings Technology, 2002
The technology of wear resistant coatings and new powder wire composites has been developed. New ... more The technology of wear resistant coatings and new powder wire composites has been developed. New coatings with low porosity and small grains were obtained by arc-spraying of FeCrB+ Al and FeCr+ Al+ C powder wires in a steel cover. A modified arc spraying torch ...
Journal of Thermal Spray Technology, 2007
Different posttreatment methods, such as heat treatment, mechanical processing, sealing, etc., ar... more Different posttreatment methods, such as heat treatment, mechanical processing, sealing, etc., are known to be capable to improve microstructure and exploitation properties of thermal spray coatings. In this work, a plasma electrolytic oxidation of aluminum coatings obtained by arc spraying on aluminum and carbon steel substrates is carried out. Microstructure and properties of oxidized layers formed on sprayed coating as well as on bulk material are investigated. Oxidation is performed in electrolyte containing KOH and liquid glass under different process parameters. It is shown that thick uniform oxidized layers can be formed on arc-sprayed aluminum coatings as well as on solid material. Distribution of alloying elements and phase composition of obtained layers are investigated. A significant improvement of wear resistance of treated layers in two types of abrasive wear conditions is observed.
Key Engineering Materials, 2008
A brief overview of existing methods of post-treatment of thermally sprayed coatings is given and... more A brief overview of existing methods of post-treatment of thermally sprayed coatings is given and the influence of mechanical and chemical as well as high-energy beam post-treatment methods on the coating microstructure formation and some exploitation properties is described. As a special example, the modification of thermally sprayed coatings on magnesium alloys using electron and laser beams and high-density irradiation of an infra-red beamer for the improvement of wear and corrosion resistance is presented.
Surface & Coatings Technology, 2011
In the field of thermal spraying, cermets are known to have excellent wear-protecting properties.... more In the field of thermal spraying, cermets are known to have excellent wear-protecting properties. However, the high price of the spraying materials and the environmental aspects of nickel and cobalt utilization are often the limitations to their wider application. Within the frame of a multi-institutional cooperation of various German research centres, the AiF/DFG research cluster "Thermal Spraying" was organised, one of the main research goals of which is the development of economically attractive alternative spray materials with new property profiles. This paper presents some results of the project that deals with the development and thermal spraying of particle-reinforced iron-based composite alloys. High-alloyed steels serve as matrix materials into which hard CrB 2 particles are incorporated by means of a high-energy milling (HEM) process. The microstructure of the powder and the level of its amorphisation can be strongly influenced by appropriate milling parameters that allow the adjustment of the desired nanocrystalline structure. By using the highvelocity oxygen fuel thermal spraying process (HVOF), the microstructure of the particles can be transferred to the coatings. The deposited coatings exhibit low porosity and high microhardness values of more than 1000 HV0.3. The high abrasion wear resistance of newly developed coatings evaluated by means of the Miller test (ASTM G75-01) makes them promising for application for example in paper industry as an alternative to hard chromium coatings.
Surface & Coatings Technology, 2008
... 2.5. Coating characterization. The resulting microstructure of the electron beam modified sur... more ... 2.5. Coating characterization. The resulting microstructure of the electron beam modified surfaces is characterized materialographically using optical microscopy, scanning electron microscopy (LEO 1455VP) and energy dispersive X-ray microanalysis (EDISON). ...
Surface & Coatings Technology, 2006
Three actual trends in development of HVOF spraying technology are described and discussed. The t... more Three actual trends in development of HVOF spraying technology are described and discussed. The trends concern application fields as well as gun and feedstock characteristics. At the example of demountable draw bars it is shown that HVOF sprayed ...
Surface & Coatings Technology, 2006
Electroplated hard chromium and thermal spray hardmetal coatings are widely used in a variety of ... more Electroplated hard chromium and thermal spray hardmetal coatings are widely used in a variety of applications for wear protection of component surfaces. The two protective coating types are tested in direct comparison for tribological conditions of dry abrasive wear (Taber Abraser test) and dry oscillating wear load. Oscillating wear tests are carried out both with hardened 100Cr6 steel and alumina balls as counterbody. Different types of hardmetal coatings are imparted. Besides HVOF sprayed coatings also coatings sprayed by an APS gun with axial powder feed are tested. For HVOF spraying besides standard WC/Co(Cr) feedstock also coarse (d 50 = 5 μm) and fine carbide feedstock (d 50 = 0.8 μm) and ultrafine powders, i.e. 2 μm b d b 12 μm, are considered. Use of ultrafine powders is particularly interesting from the economical point of view, as belt grinding can be sufficient for finishing in many cases. The optimum coating solution for wear protection depends on the specific tribosystem. The choice of feedstock, spraying process, equipment and processing conditions does not only depend on the resultant tribological properties. Therefore simultaneous influence on corrosion protection capability and thermal conductivity might have to be considered.
ABSTRACT The main tendencies in the development of tungsten carbide coating applications are pres... more ABSTRACT The main tendencies in the development of tungsten carbide coating applications are presented. General properties of WC based coatings and their dependence on different factors are discussed. For comparative examination of the abrasive wear resistance of thermal spray coatings detailed Taber Abraser wear tests are carried out. Besides HVOF sprayed cermet and APS Cr 2 O 3 also electroplated hard chromium coatings are studied. The best results have been obtained for HVOF sprayed cermet coatings. For this kind of wear conditions the difference in wear behaviour depending on carbide size in WC-CoCr coatings is insignificant compared to the difference depending on the matrix composition.