Helmut Klein

Texture analysis with high-energy synchrotron radiation

Texture measurement with short-wave X-ray synchrotron radiation in the range of λ ≃ 0.1 A is described. The measurements were carried out with the multipurpose diffraction instrument at the high-field wiggler, high-energy beamline BW5 at HASYLAB. The instrument was equipped with an on-line image-plate area detector for diffraction-image registration and a Eulerian cradle for sample orientation. The particular features of texture measurement with the BW5 instrument are: good resolution in the Bragg angle, extremely high angular resolution in crystal orientation (pole-figure angles) and particularly high penetration depth of several millimetres to centimetres, comparable with that of neutrons but at high spatial resolution. Several examples illustrate the particular advantages of this method for texture studies using large or encased samples (in situ studies in complicated environments, such as cryostats, furnaces, vacuum or pressure chambers, with no serious window problems). This allows, among others, non-destructive texture analysis in technological parts and whole components. Because of the extremely high beam intensity (short exposure times) compared with all other methods of texture measurement, the new technique is particularly suited for the study of large sample series (as is often necessary in industrial applications).

Texture and microstructure analysis with high-energy synchrotron radiation

High-energy synchrotron radiation with wavelengths in the range of 0.1 A is an excellent tool to measure the orientational and spatial distribution of crystallites in polycrystalline materials of any kind. A particular sweeping method for continuous imaging of texture and microstructure with high resolving power is described. In grain-resolved structures, the orientation stereology of the grains can thus be obtained. High-energy synchrotron radiation has penetration depths in most materials comparable with that of neutrons. It is thus very well suited for the study of big samples and for non-destructive testing of complex technological components.

Comparative in vitro study and biomechanical testing of two different magnesium alloys.

In this in vitro study, magnesium plates of ZEK100 and MgCa0.8 alloy similar to common titanium alloy osteosynthesis plates were investigated as degradable biomedical materials with a focus on primary stability. Immersion tests were performed in Hank’s Balanced Salt Solution at 37℃. The bending strength of the samples was determined using the four-point bending test according to ISO 9585:1990. The initial strength of the noncorroded ZEK100 plate was 11% greater than that of the MgCa0.8 plate; both were approximately 65% weaker than a titanium plate. The bending strength was determined after 48 and 96 h of immersion in Hank’s Balanced Salt Solution; both magnesium alloys decreased by approximately 7% after immersion for 96 h. The degradation rate and the Mg2+ release of ZEK100 were lower than those of MgCa0.8. Strong pitting and filiform corrosion were observed in the MgCa0.8 samples after 96 h of immersion. The surface of the ZEK100 plates exhibited only small areas of filiform corrosion. The results of this in vitro study indicate that the ZEK100 alloy may be more suitable for biomedical applications.

High-resolution imaging of texture and microstructure by the moving detector method

In order to describe texture and microstructure of a polycrystalline material completely, crystal orientation g = {ϕ1 Φ ϕ2} must be known in all points x = {x 1 x 2 x 3} of the material. This can be achieved by location-resolved diffraction of high-energy, i.e. short-wave, X-rays from synchrotron sources. Highest resolution in the orientation- as well as the location-coordinates can be achieved by three variants of a detector “sweeping” technique in which an area detector is continuously moved during exposure. This technique results in two-dimensionally continuous images which are sections and projections of the six-dimensional “orientation–location” space. Further evaluation of these images depends on whether individual grains are resolved in them or not. Because of the high penetration depth of high-energy synchrotron radiation in matter, this technique is also, and particularly, suitable for the investigation of the interior of big samples.

Calculation of anisotropic properties of dental enamel from synchrotron data.

Obtaining information about the intrinsic structure of polycrystalline materials is of prime importance owing to the anisotropic behaviour of individual crystallites. Grain orientation and its statistical distribution, i.e. the texture, have an important influence on the material properties. Crystallographic orientations play an important role in all kinds of polycrystalline materials such as metallic, geological and biological. Using synchrotron diffraction techniques the texture can be measured with high local and angular resolving power. Here methods are presented which allow the spatial orientation of the crystallites to be determined and information about the anisotropy of mechanical properties, such as elastic modulus or thermal expansion, to obtained. The methods are adapted to all crystal and several sample symmetries as well as to different phases, for example with overlapping diffraction peaks. To demonstrate the abilities of the methods, human dental enamel has been chosen, showing even overlapping diffraction peaks. Likewise it is of special interest to learn more about the orientation and anisotropic properties of dental enamel, since only basic information is available up to now. The texture of enamel has been found to be a tilted fibre texture of high strength (up to 12.5×). The calculated elastic modulus is up to 155 GPa and the thermal expansion up to 22.3 × 10(-6)°C(-1).

Location Depending Textures of the Human Dental Enamel

Dental enamel is the most highly mineralised and hardest biological tissue in human body [1]. Dental enamel is made of hydroxylapatite (HAP) - Ca5(PO4)3(OH), which is hexagonal (6/m). The lattice parameters are a = b = 0.9418 nm und c = 0.6875 nm [1]. Although HAP is a very hard mineral, it can be dissolved easily in a process which is known as enamel demineralization by lactic acid produced by bacteria. Also the direct consumption of acid (e.g. citric, lactic or phosphoric acid in soft drinks) can harm the dental enamel in a similar way. These processes can damage the dental enamel. It will be dissolved completely and a cavity occurs. The cavity must then be cleaned and filled. It exists a lot of dental fillings, like gold, amalgam, ceramics or polymeric materials. After filling other dangers can occur: The mechanical properties of the materials used to fill cavities can differ strongly from the ones of the dental enamel itself. In the worst case, the filling of a tooth can damage the enamel of the opposite tooth by chewing if the interaction of enamel and filling is not equivalent, so that the harder fillings can abrade the softer enamel of the healthy tooth at the opposite side. This could be avoided if the anisotropic mechanical properties of dental enamel would be known in detail, hence then another filling could be searched or fabricated as an equivalent opponent for the dental enamel with equal properties. To find such a material, one has to characterise the properties of dental enamel first in detail for the different types of teeth (incisor, canine, premolar and molar). This is here exemplary done for a human incisor tooth by texture analysis with the program MAUD from 2D synchrotron transmission images [2,3,4].

Recrystallization Texture and Microstructure in Ni and AlMg1Mn1 Determined with High-Energy Synchrotron Radiation

The newly developed “sweeping detector” technique with high energy synchrotron radiation allows to measure textures and microstructures of materials with high location and orientation resolution. This method was applied to hot rolled aluminium manganese alloys and to rolled nickel samples in different recrystallization stages. The grain-resolved measurements show, impressively, many details of the recrystallization process which can otherwise not be seen. That can be the base for comprehensive recrystallization theories.

Gas hydrate crystallite size investigations with high-energy synchrotron radiation

Abstract The grain sizes of gas hydrate crystallites are largely unknown in natural samples. Single grains are hardly detectable with electron or optical microscopy. For the first time, we have used high-energy synchrotron diffraction to determine grain sizes of six natural gas hydrates retrieved from the Bush Hill region in the Gulf of Mexico and from ODP Leg 204 at the Hydrate Ridge offshore Oregon from varying depth between 1 and 101 metres below seafloor. High-energy synchrotron radiation provides high photon fluxes as well as high penetration depth and thus allows for investigation of bulk sediment samples. Gas hydrate grain sizes were measured at the Beam Line BW 5 at the HASYLAB/Hamburg. A ‘moving area detector method’, originally developed for material science applications, was used to obtain both spatial and orientation information about gas hydrate grains within the sample. The gas hydrate crystal sizes appeared to be (log-)normally distributed in the natural samples. All mean grain sizes lay in the range from 300 to 600 µm with a tendency for bigger grains to occur in greater depth. Laboratory-produced methane hydrate, aged for 3 weeks, showed half a log-normal curve with a mean grain size value of c. 40 µm. The grains appeared to be globular shaped.

High-resolution texture imaging with hard synchrotron radiation in the moving area detector technique

Abstract The orientation distribution of crystallites in polycrystalline materials (called texture) is usually measured by polycrystal X-ray diffraction by “step-scanning” the sample in angular intervals in the order of 1°. This technique is not suited to fully exploit the low angular divergence of hard synchrotron radiation in the order of “milliradian”. Hence, step-scanning was replaced by a continuous “sweeping” technique using a continuously shifted area detector. In order to avoid overlapping from different reflections ( hkl ) a Bragg-angle slit was introduced. The “moving-detector” technique can be applied to obtain images of orientation as well as of location distributions of crystallites in polycrystalline samples. It is suitable for imaging continuous “orientation density” distribution functions as well as of “grain-resolved” textures. The excellent features of high-energy synchrotron radiation combined with the moving area detector technique will be illustrated with several examples including very sharp deformation textures, fully and partially recrystallized samples and materials with steep texture gradients.

Grain Growth Analyses of AlMn Alloys Using Texture and Microstructure Imaging Techniques with High-Energy Synchrotron Radiation

Abstract Annealed AlMn alloys with different amounts of manganese (0.4; 0.7 and 1 wt.-%) were analyzed with texture and microstructure imaging techniques using high-energy synchrotron radiation. These techniques allow getting reliable information about grain shape and grain size distribution in the different crystallographic directions due to high orientation and location resolution. The observed trends of the grain growth in dependence on the AlMn alloys composition and the crystallographic directions, are well correlated with the different texture components occurring with increasing annealing time. In comparison to the SEM/EBSD technique, these methods allow to get orientation dependent information about the grain size and shape related with additionally good statistics.