L. Ratke - Academia.edu (original) (raw)
Papers by L. Ratke
Materials Science and Engineering: R: Reports, 2004
Multiphase solidification in multicomponent alloys is pertinent to many commercial materials and ... more Multiphase solidification in multicomponent alloys is pertinent to many commercial materials and industrial processes, while also raising challenging questions from a fundamental point of view. Within the past few years, research activities dedicated to multiphase ...
Journal of Materials Science, 2010
ABSTRACT Using electromagnetic levitation under microgravity conditions, the interfacial properti... more ABSTRACT Using electromagnetic levitation under microgravity conditions, the interfacial properties of an Cu75Co25 alloy have been investigated in the liquid phase. This alloy exhibits a metastable liquid miscibility gap and can be prepared and levitated in a configuration consisting of a liquid cobalt-rich core surrounded by a liquid copper-rich shell. Exciting drop oscillations and analysing the frequency spectrum, both surface and (liquid–liquid) interfacial tension can be derived from the observed oscillation frequencies. This paper briefly reviews the theoretical background and reports on a recent experiment carried out on board the TEXUS 44 sounding rocket.
Advanced Engineering Materials, 2003
Scripta Metallurgica et Materialia, 1994
ABSTRACT
Scripta Metallurgica et Materialia, 1994
Scripta Metallurgica et Materialia, 1993
Materials Science and Engineering: R: Reports, 2004
Multiphase solidification in multicomponent alloys is pertinent to many commercial materials and ... more Multiphase solidification in multicomponent alloys is pertinent to many commercial materials and industrial processes, while also raising challenging questions from a fundamental point of view. Within the past few years, research activities dedicated to multiphase ...
Metallurgical and Materials Transactions A, 2007
ABSTRACT A model is developed to describe the microstructure evolution in a Cu-Co drop during coo... more ABSTRACT A model is developed to describe the microstructure evolution in a Cu-Co drop during cooling in the metastable miscibility gap in the liquid state. Rapid solidification experiments have been performed with Cu84Co16 alloy in a drop tube. The kinetic details of the liquid-liquid phase transformation in the Cu-Co drops have been calculated. The results demonstrate that the microstructure development is dominated by the common action of the nucleation and the diffusional growth of the minority phase precipitates under rapid solidification conditions. The calculated size distribution of the Co precipitates in powders and their average radius as a function of cooling rate are compared with the experimental results. The agreement is satisfactory.
IOP Conference Series: Materials Science and Engineering, 2012
Ternary eutectics provide a unique opportunity for studying the effects of complex microstructure... more Ternary eutectics provide a unique opportunity for studying the effects of complex microstructure formation, as three distinct phases must be formed simultaneously from the melt. In order to produce fully coupled three-phase growth, Al-Ag-Cu at the ternary eutectic composition was directionally solidified in a constant temperature gradient of 3 K/mm at velocities between 0.2 and 5.0 µm/sec. Under these conditions, the two intermetallic phases appear to grow as closely coupled rods in an α(Al) matrix, with the solidification velocity affecting the specific morphologies chosen by the rods and the general degree of alignment of the structure. Crystal orientations were examined by EBSD to determine if variations in morphology within a single sample are due to specific orientation relationships. Although no conclusive connection to morphology has yet been found, two different sets of orientation relationships between the three phases have thus far been identified.
International Journal of Materials Research, 2009
eutschesZentrumf ür Luft-und Raumfahrt (DLR),K öln,G ermany Microstructuree volution during aliqu... more eutschesZentrumf ür Luft-und Raumfahrt (DLR),K öln,G ermany Microstructuree volution during aliquid-liquid decompositionundert he common action of the nucleation,growthand Ostwald ripening of droplets
Advances in Space Research, 1995
In the Isothermal Heating Facility (IHF) of the Werkstofflabor on board the D2-mission we perform... more In the Isothermal Heating Facility (IHF) of the Werkstofflabor on board the D2-mission we performed directional melting and solidification experiments with liquid immiscible AlSiBi alloys. Their main objective was to investigate the Marangoni motion of a large number of Bi droplets within a well defined temperature field ahead of the solid-liquid interface, their hydrodynamic interaction and thus the collision and
Recent developments to reduce fuel consumption, emission and air pollution, size and weight of en... more Recent developments to reduce fuel consumption, emission and air pollution, size and weight of engines for automotive, truck, ship propulsion and electrical power generation lead to temperature and load conditions within engines that cannot be provided by conventional bearings. Therefore a European project has been established to develop a technically usable aluminium based lead free bearing material with sufficient hardness, wear and friction properties and good corrosion resistance to be produced with semi-continuous casting process. The paper describes the scientific challenges, approaches to tackle the solidification and casting problems and presents some illustrative research results.
Materials Science and Engineering: R: Reports, 2004
Multiphase solidification in multicomponent alloys is pertinent to many commercial materials and ... more Multiphase solidification in multicomponent alloys is pertinent to many commercial materials and industrial processes, while also raising challenging questions from a fundamental point of view. Within the past few years, research activities dedicated to multiphase ...
Journal of Materials Science, 2010
ABSTRACT Using electromagnetic levitation under microgravity conditions, the interfacial properti... more ABSTRACT Using electromagnetic levitation under microgravity conditions, the interfacial properties of an Cu75Co25 alloy have been investigated in the liquid phase. This alloy exhibits a metastable liquid miscibility gap and can be prepared and levitated in a configuration consisting of a liquid cobalt-rich core surrounded by a liquid copper-rich shell. Exciting drop oscillations and analysing the frequency spectrum, both surface and (liquid–liquid) interfacial tension can be derived from the observed oscillation frequencies. This paper briefly reviews the theoretical background and reports on a recent experiment carried out on board the TEXUS 44 sounding rocket.
Advanced Engineering Materials, 2003
Scripta Metallurgica et Materialia, 1994
ABSTRACT
Scripta Metallurgica et Materialia, 1994
Scripta Metallurgica et Materialia, 1993
Materials Science and Engineering: R: Reports, 2004
Multiphase solidification in multicomponent alloys is pertinent to many commercial materials and ... more Multiphase solidification in multicomponent alloys is pertinent to many commercial materials and industrial processes, while also raising challenging questions from a fundamental point of view. Within the past few years, research activities dedicated to multiphase ...
Metallurgical and Materials Transactions A, 2007
ABSTRACT A model is developed to describe the microstructure evolution in a Cu-Co drop during coo... more ABSTRACT A model is developed to describe the microstructure evolution in a Cu-Co drop during cooling in the metastable miscibility gap in the liquid state. Rapid solidification experiments have been performed with Cu84Co16 alloy in a drop tube. The kinetic details of the liquid-liquid phase transformation in the Cu-Co drops have been calculated. The results demonstrate that the microstructure development is dominated by the common action of the nucleation and the diffusional growth of the minority phase precipitates under rapid solidification conditions. The calculated size distribution of the Co precipitates in powders and their average radius as a function of cooling rate are compared with the experimental results. The agreement is satisfactory.
IOP Conference Series: Materials Science and Engineering, 2012
Ternary eutectics provide a unique opportunity for studying the effects of complex microstructure... more Ternary eutectics provide a unique opportunity for studying the effects of complex microstructure formation, as three distinct phases must be formed simultaneously from the melt. In order to produce fully coupled three-phase growth, Al-Ag-Cu at the ternary eutectic composition was directionally solidified in a constant temperature gradient of 3 K/mm at velocities between 0.2 and 5.0 µm/sec. Under these conditions, the two intermetallic phases appear to grow as closely coupled rods in an α(Al) matrix, with the solidification velocity affecting the specific morphologies chosen by the rods and the general degree of alignment of the structure. Crystal orientations were examined by EBSD to determine if variations in morphology within a single sample are due to specific orientation relationships. Although no conclusive connection to morphology has yet been found, two different sets of orientation relationships between the three phases have thus far been identified.
International Journal of Materials Research, 2009
eutschesZentrumf ür Luft-und Raumfahrt (DLR),K öln,G ermany Microstructuree volution during aliqu... more eutschesZentrumf ür Luft-und Raumfahrt (DLR),K öln,G ermany Microstructuree volution during aliquid-liquid decompositionundert he common action of the nucleation,growthand Ostwald ripening of droplets
Advances in Space Research, 1995
In the Isothermal Heating Facility (IHF) of the Werkstofflabor on board the D2-mission we perform... more In the Isothermal Heating Facility (IHF) of the Werkstofflabor on board the D2-mission we performed directional melting and solidification experiments with liquid immiscible AlSiBi alloys. Their main objective was to investigate the Marangoni motion of a large number of Bi droplets within a well defined temperature field ahead of the solid-liquid interface, their hydrodynamic interaction and thus the collision and
Recent developments to reduce fuel consumption, emission and air pollution, size and weight of en... more Recent developments to reduce fuel consumption, emission and air pollution, size and weight of engines for automotive, truck, ship propulsion and electrical power generation lead to temperature and load conditions within engines that cannot be provided by conventional bearings. Therefore a European project has been established to develop a technically usable aluminium based lead free bearing material with sufficient hardness, wear and friction properties and good corrosion resistance to be produced with semi-continuous casting process. The paper describes the scientific challenges, approaches to tackle the solidification and casting problems and presents some illustrative research results.