Vortical and shear flows are common in turbomachinery. Multi-hole pressure probes are used in tur... more Vortical and shear flows are common in turbomachinery. Multi-hole pressure probes are used in turbomachinery flows in order to provide robust and accurate measurements of both pressure and velocity components. In this study, two different miniature five-hole probes are designed and fabricated, both with a cobra shape. The probe tip was 1.45 mm and it was maintained in that size for the length of the cobra shape formation, providing very close proximity to the solid boundaries and reduced flow blockage. The difference among the probes corresponded to the head geometry, as the one probe was formed with a pyramid tip shape, while the other was maintained with a flat shape. The calibration process was carried out in an open-circuit suction wind tunnel for the range of ±320 in yaw and pitch direction. The results showed that the pyramid probe exhibits a high flow angle spatial sensitivity and a reliable measurement range of ±280 in yaw and pitch direction. The flat probe provided unexpec...
Heat-treated and shot-peened lightweight steels with demanding requirements for durability are ap... more Heat-treated and shot-peened lightweight steels with demanding requirements for durability are applied in high-performance automotive leaf springs. Due to their heat-treatment they exhibit degraded properties in the surface-near area compared to the core. This area, which may extend until 300 μm from the surface to the core, experiences the highest bending stresses at operation. The microstructure in the surface and sub-surface layers determines the mechanical performance as well as the wear resistance. The present study refers to the material properties of a stress shot-peened 51CrV4 steel at various depths from the surface. The effect of the manufacturing process has been captured both by Vickers micro-hardness measurements and nanoindentation. The latter combined with a Fine Element Method (FEM)-based algorithm enables the determination of variations in the material’s stress–strain curves over the affected layers, which translate to internal stress changes. The nanoindentation te...
Nanoindentation is an effective technique to determine mechanical properties of bulk materials an... more Nanoindentation is an effective technique to determine mechanical properties of bulk materials and thin films. The prevailing measurement uncertainties in nanoindentation are induced by manufacturing inaccuracies of the indenter tip. Vickers indenters are not ideally pyramidal since their tips are always not exactly sharp and the tip geometry changes during the indenter lifetime, due to wear. The parameters of an equivalent indenter tip geometry, which can be used in the FEM-simulation of the nanoindentation, is attained by nanoindentations on reference materials with known Young's modulus, Poisson ratio and Martens hardness. The present paper deals with a fast method of indenter tip geometrical parameters determination, considering nanoindentation results on Si(100), as reference material. This procedure is based, on one hand, on the FEM supported calculation of Martens hardness taking into account the parameters of the equivalent indenter tip geometry and on the other hand, on...
This paper investigates the feasibility of increasing the wear resistance of cemented carbide too... more This paper investigates the feasibility of increasing the wear resistance of cemented carbide tools through water micro-blasting of their PVD-coatings. Nanohardness measurements were conducted to determine the influence of water micro-blasting on superficial films' hardness. Ball cratering tests were carried out at the flank and rake near the cutting edge to investigate the alteration of coating thickness due to micro-blasting.
The conduct of micro-blasting on PVD films has been documented as an efficient method to improve ... more The conduct of micro-blasting on PVD films has been documented as an efficient method to improve the cutting performance of coated tools. The increase of tool life is correlated to the applied conditions during micro-blasting. In this way the determi- nation of the optimum condition during micro-blasting is of great importance. In the frame of the present paper, the effect
ABSTRACT The performance of PVD films depends on the operational mechanical and thermal loads of ... more ABSTRACT The performance of PVD films depends on the operational mechanical and thermal loads of coated tools or components. To withstand these loads, sufficient film strength properties, at ambient and elevated temperatures are required. The present paper deals with the mechanical properties and the impact resistance of a TiAlN coating at temperatures up to 400°C. Nanoindentations were conducted by a nanoindentation device, enabling measurements at room and elevated temperatures in an inert gas atmosphere. The obtained results were evaluated using appropriate FEM algorithms for determining the film's stress–strain curves, at the temperatures of the conducted nanoindentations. Moreover, perpendicular impact tests on the coated specimens were carried out up to 400°C, for investigating the film's impact behaviour. The developed impressions were recorded by scanning electron microscopy and white light confocal measurements. The attained results demonstrate a non-linear dependence of the film fatigue properties versus the temperature, whereas a significant impact resistance improvement at approximately 150°C develops. Finally, a convergence between the yield and the fatigue endurance stress versus the temperature was revealed.
To explain the coating and substrate wear behaviour, when applying cemented car- bide (HM) tools ... more To explain the coating and substrate wear behaviour, when applying cemented car- bide (HM) tools with different grain sizes in milling, two variations of HM inserts, a fine- and an ultra-fine-grained one were coated with the same PVD AlTiN film. These inserts were examined by nanoindentations and impact tests concerning me- chanical properties and by milling experiments regarding wear. The investigations revealed an enhanced cutting performance of the less hard and more ductile fine- grained substrate compared to the ultra-fine-grained one. In turn, the coating depos- ited on the ultra-fine-grained insert showed increased mechanical properties and impact resistance, compared to the corresponding one deposited on the fine-grained substrate. Moreover, an improved cutting performance was obtained in the latter case at a width of flank wear land less than 0.1 mm. At greater flank wear values, the fine-grained substrate withstands more effective the cutting loads, due to its bet- ter duc...
Based on analytical and experimental test methods, an evaluation of coated tools efficiency in mi... more Based on analytical and experimental test methods, an evaluation of coated tools efficiency in milling Ti6Al4V with coated cemented carbide inserts is introduced. The stress-strain curves and the fatigue critical loads of the investigated coating were determined at various temperatures by nanoindentations and impact tests respectively, employing FEM-supported algorithms for results evaluation. The stress and temperature fields in the cutting wedge region were obtained by force measurements and FEM calculations of the milling process at various cutting conditions. A sufficient correlation of the coating’s impact resistance at various temperatures with their cutting performance at corresponding cutting conditions is revealed.
Precision glass molding is a technology for the medium to large scale production of complex optic... more Precision glass molding is a technology for the medium to large scale production of complex optical components with high surface quality and form accuracy. However, the process is only economically viable if a long lifetime of the molding tools can be guaranteed. This can be achieved by using protective coatings on the optical surfaces of the molding tools. The most
A novel methodology based on analytical and experimental test methods for predicting coated tool ... more A novel methodology based on analytical and experimental test methods for predicting coated tool efficiency in milling Inconel 718 and Ti6Al4V by coated cemented carbide inserts is introduced. The applied coatings were CrAlN films, containing alternatively Zr or Y dopants. The stress–strain curves and the fatigue critical loads of the applied coatings were determined at various temperatures by nanoindentations and
High power pulsed magnetron sputtering (HPPMS), substrate pretreatments and adhesive interlayers ... more High power pulsed magnetron sputtering (HPPMS), substrate pretreatments and adhesive interlayers can enhance tool life significantly. In the conducted research, TiAlN PVD-films and W-, Ti- or Cr-adhesive nanointerlayers were deposited by HPPMS on different superficially treated hardmetal inserts. The mechanical properties of the coatings were determined via nanoindentations and mathematical analysis. Additionally, inclined impact tests and milling investigations were performed
Vortical and shear flows are common in turbomachinery. Multi-hole pressure probes are used in tur... more Vortical and shear flows are common in turbomachinery. Multi-hole pressure probes are used in turbomachinery flows in order to provide robust and accurate measurements of both pressure and velocity components. In this study, two different miniature five-hole probes are designed and fabricated, both with a cobra shape. The probe tip was 1.45 mm and it was maintained in that size for the length of the cobra shape formation, providing very close proximity to the solid boundaries and reduced flow blockage. The difference among the probes corresponded to the head geometry, as the one probe was formed with a pyramid tip shape, while the other was maintained with a flat shape. The calibration process was carried out in an open-circuit suction wind tunnel for the range of ±320 in yaw and pitch direction. The results showed that the pyramid probe exhibits a high flow angle spatial sensitivity and a reliable measurement range of ±280 in yaw and pitch direction. The flat probe provided unexpec...
Heat-treated and shot-peened lightweight steels with demanding requirements for durability are ap... more Heat-treated and shot-peened lightweight steels with demanding requirements for durability are applied in high-performance automotive leaf springs. Due to their heat-treatment they exhibit degraded properties in the surface-near area compared to the core. This area, which may extend until 300 μm from the surface to the core, experiences the highest bending stresses at operation. The microstructure in the surface and sub-surface layers determines the mechanical performance as well as the wear resistance. The present study refers to the material properties of a stress shot-peened 51CrV4 steel at various depths from the surface. The effect of the manufacturing process has been captured both by Vickers micro-hardness measurements and nanoindentation. The latter combined with a Fine Element Method (FEM)-based algorithm enables the determination of variations in the material’s stress–strain curves over the affected layers, which translate to internal stress changes. The nanoindentation te...
Nanoindentation is an effective technique to determine mechanical properties of bulk materials an... more Nanoindentation is an effective technique to determine mechanical properties of bulk materials and thin films. The prevailing measurement uncertainties in nanoindentation are induced by manufacturing inaccuracies of the indenter tip. Vickers indenters are not ideally pyramidal since their tips are always not exactly sharp and the tip geometry changes during the indenter lifetime, due to wear. The parameters of an equivalent indenter tip geometry, which can be used in the FEM-simulation of the nanoindentation, is attained by nanoindentations on reference materials with known Young's modulus, Poisson ratio and Martens hardness. The present paper deals with a fast method of indenter tip geometrical parameters determination, considering nanoindentation results on Si(100), as reference material. This procedure is based, on one hand, on the FEM supported calculation of Martens hardness taking into account the parameters of the equivalent indenter tip geometry and on the other hand, on...
This paper investigates the feasibility of increasing the wear resistance of cemented carbide too... more This paper investigates the feasibility of increasing the wear resistance of cemented carbide tools through water micro-blasting of their PVD-coatings. Nanohardness measurements were conducted to determine the influence of water micro-blasting on superficial films' hardness. Ball cratering tests were carried out at the flank and rake near the cutting edge to investigate the alteration of coating thickness due to micro-blasting.
The conduct of micro-blasting on PVD films has been documented as an efficient method to improve ... more The conduct of micro-blasting on PVD films has been documented as an efficient method to improve the cutting performance of coated tools. The increase of tool life is correlated to the applied conditions during micro-blasting. In this way the determi- nation of the optimum condition during micro-blasting is of great importance. In the frame of the present paper, the effect
ABSTRACT The performance of PVD films depends on the operational mechanical and thermal loads of ... more ABSTRACT The performance of PVD films depends on the operational mechanical and thermal loads of coated tools or components. To withstand these loads, sufficient film strength properties, at ambient and elevated temperatures are required. The present paper deals with the mechanical properties and the impact resistance of a TiAlN coating at temperatures up to 400°C. Nanoindentations were conducted by a nanoindentation device, enabling measurements at room and elevated temperatures in an inert gas atmosphere. The obtained results were evaluated using appropriate FEM algorithms for determining the film's stress–strain curves, at the temperatures of the conducted nanoindentations. Moreover, perpendicular impact tests on the coated specimens were carried out up to 400°C, for investigating the film's impact behaviour. The developed impressions were recorded by scanning electron microscopy and white light confocal measurements. The attained results demonstrate a non-linear dependence of the film fatigue properties versus the temperature, whereas a significant impact resistance improvement at approximately 150°C develops. Finally, a convergence between the yield and the fatigue endurance stress versus the temperature was revealed.
To explain the coating and substrate wear behaviour, when applying cemented car- bide (HM) tools ... more To explain the coating and substrate wear behaviour, when applying cemented car- bide (HM) tools with different grain sizes in milling, two variations of HM inserts, a fine- and an ultra-fine-grained one were coated with the same PVD AlTiN film. These inserts were examined by nanoindentations and impact tests concerning me- chanical properties and by milling experiments regarding wear. The investigations revealed an enhanced cutting performance of the less hard and more ductile fine- grained substrate compared to the ultra-fine-grained one. In turn, the coating depos- ited on the ultra-fine-grained insert showed increased mechanical properties and impact resistance, compared to the corresponding one deposited on the fine-grained substrate. Moreover, an improved cutting performance was obtained in the latter case at a width of flank wear land less than 0.1 mm. At greater flank wear values, the fine-grained substrate withstands more effective the cutting loads, due to its bet- ter duc...
Based on analytical and experimental test methods, an evaluation of coated tools efficiency in mi... more Based on analytical and experimental test methods, an evaluation of coated tools efficiency in milling Ti6Al4V with coated cemented carbide inserts is introduced. The stress-strain curves and the fatigue critical loads of the investigated coating were determined at various temperatures by nanoindentations and impact tests respectively, employing FEM-supported algorithms for results evaluation. The stress and temperature fields in the cutting wedge region were obtained by force measurements and FEM calculations of the milling process at various cutting conditions. A sufficient correlation of the coating’s impact resistance at various temperatures with their cutting performance at corresponding cutting conditions is revealed.
Precision glass molding is a technology for the medium to large scale production of complex optic... more Precision glass molding is a technology for the medium to large scale production of complex optical components with high surface quality and form accuracy. However, the process is only economically viable if a long lifetime of the molding tools can be guaranteed. This can be achieved by using protective coatings on the optical surfaces of the molding tools. The most
A novel methodology based on analytical and experimental test methods for predicting coated tool ... more A novel methodology based on analytical and experimental test methods for predicting coated tool efficiency in milling Inconel 718 and Ti6Al4V by coated cemented carbide inserts is introduced. The applied coatings were CrAlN films, containing alternatively Zr or Y dopants. The stress–strain curves and the fatigue critical loads of the applied coatings were determined at various temperatures by nanoindentations and
High power pulsed magnetron sputtering (HPPMS), substrate pretreatments and adhesive interlayers ... more High power pulsed magnetron sputtering (HPPMS), substrate pretreatments and adhesive interlayers can enhance tool life significantly. In the conducted research, TiAlN PVD-films and W-, Ti- or Cr-adhesive nanointerlayers were deposited by HPPMS on different superficially treated hardmetal inserts. The mechanical properties of the coatings were determined via nanoindentations and mathematical analysis. Additionally, inclined impact tests and milling investigations were performed
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