6 results
Now showing1 - 6 of 6
- Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , In situ analysis of PCBN cutting tool materials during thermo-mechanical loading using synchrotron radiationPolycrystalline cubic boron nitride (PCBN) has outstanding properties in terms of hardness and chemical stability at elevated temperatures. Therefore, PCBN is used in cutting tool materials for hard machining applications e.g. hard turning of hardened steels. Due to the hardness of the workpiece, high forces act on a low contact area between tool and workpiece. Hence, severe thermo-mechanical loadings occur in such applications causing enhanced tool wear. Fundamental knowledge about the material behavior of PCBN-cutting-materials under thermo-mechanical loading is valuable as a basis for a better understanding of tool wear and finally for improvement of tool wear behavior. PCBN-materials are polycrystalline multi-phase compounds with strongly deviating material properties. In order to investigate the phase selective thermo-mechanical behavior of such materials lattice strain measurements are conducted under thermo-mechanical load using in situ X-ray diffraction with high energy synchrotron radiation. A four point bending test set-up and ceramic thermal heaters are used for the application of thermo-mechanical loading. Three different materials are investigated: a solid low PCBN-content material, a low PCBN-content material on a cemented carbide (CC) substrate and a high PCBN-content material on a CC-substrate. The low PCBN-content material exhibits a single phase binder material whereas the high PCBN-content material exhibits a multi-phase binder with up to five phases. Residual stresses are found in the samples with CC-substrate, only. Different phases of one material show different strains but nearly same stresses upon loading. Thus, thermo-mechanical loading can be seen as superposition of the respective mechanical and thermal loads. The space-resolved experimental data is used to validate an analytical model for the calculation of macroscopic stresses. The phase selective space-resolved strain and stress analysis presented in this paper provides a valuable method for the investigation and optimization of hard cutting tool materials and coatings under real cutting conditions.Publicationtype: Journal Article197 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , In situ high-energy X-ray diffraction during hot-forming of a multiphase TiAl alloy(Multidisciplinary Digital Publishing Institute (MDPI), 2015-11-30); ; ; ; Intermetallic γ-TiAl based alloys exhibit excellent high-temperature strength combined with low density. This makes them ideal candidates for replacing the twice as dense Ni base super-alloys, currently used in the medium temperature range (~700 °C) of industrial and aviation gas turbines. An important step towards the serial production of TiAl parts is the development of suitable hot-forming processes. Thermo-mechanical treatments often result in mechanical anisotropy due to the formation of crystallographic textures. However, with conventional texture analysis techniques, their formation can only be studied after processing. In this study, in situ high-energy X-ray diffraction measurements with synchrotron radiation were performed during hot-forming. Thus, it was possible to record the evolution of the phase constitution as well as the formation of crystallographic texture of different phases directly during processing. Several process temperatures (1100 °C to 1300 °C) and deformation rates were investigated. Based on these experiments, a process window can be recommended which results in the formation of an optimal reduced texture.Publicationtype: Journal ArticleScopus© Citations 18 435 294 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , In situ determination of internal stresses in mixed ceramic cutting tools during friction testing using synchrotron ratiationIn order to get a better understanding of wear mechanisms in cutting tool materials, the internal stress states caused by complex external thermo-mechanical loads during cutting processes should be investigated. This can be done using in situ X-ray diffraction with high energy synchrotron radiation. For this reason, in first model tests, the strain state in ceramic cutting tool materials (Al2O3–Ti(O,C)) for hard turning applications is determined during friction testing. An experimental set-up is presented which allows the measurement of lattice strain tensor components in the major phases of the mixed ceramic material under a two-dimensional loading condition during friction. Results show that during friction almost no lattice strains in lateral direction can be measured due to strain compensation. In contrast, in normal direction, lattice strains increase due to the addition of strains. Stress tensor components are calculated from lattice strains and show higher internal stress states for Ti(O,C) than for Al2O3 due to a higher Young’s modulus of Ti(O,C). The set-up represents a major step forward towards future in situ characterization of internal stress states in cutting tool materials exposed to complex thermomechanical loading conditions during cutting processes.Publicationtype: Review Article13 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , In situ measurement of lattice strains in mixed ceramic cutting tools under thermal and mechanical loads using synchrotron radiation(Springer, 2012-11-02); ; ; ; To completely understand wear mechanisms of mixed ceramic cutting tools (Al2O3-TiC), residual stress states and the superposition of external loads during hard turning should be investigated. This can be done via X-ray diffraction using high-energy synchrotron radiation to determine lattice strains in the material. For this reason, in first model tests, strain states in mixed ceramics were determined during the application of external loads. An experimental setup was developed to measure lattice strains in the different phases of the ceramic material in situ during thermal, mechanical and thermo-mechanical loading for first reference. The accuracy of the setup was sufficient to clearly determine shifts in lattice parameters in the different phases due to external loads. By applying a thermal load on the mixed ceramic material the two main phases showed different elastic lattice strains. Thus, a slightly lower coefficient of thermal expansion in the Al2O3-phase than in the Ti(O,C)-phase could be determined. This indicated the development of compressive stresses in the Al2O3-phase and tensile stresses in the Ti(O,C)-phase at room temperature. By applying external bending stresses to the mixed ceramic material, for both phases equal lattice strains could be determined. From these strains stresses could be calculated for both phases which were in the same order of magnitude as external stresses. With further in situ investigations of strain and stress states in the different phases of mixed ceramics during friction and turning experiments a more comprehensive characterization of wear mechanisms is possible. © 2012 German Academic Society for Production Engineering (WGP).Publicationtype: Journal Article55 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , In situ measurement of lattice strains in mixed ceramics under static thermal and mechanical loads(HASYLAB, 2012); ; ; ; Publicationtype: Journal Article8 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , X-ray characterization of a TiAlN-coating on a mixed ceramic substrate with a resolution of a few microns(HASYLAB, 2010); ; ; 4