# The Key Role of Laser Ultrasonics in the Context of Sustainable Production in an I 4.0 Value Chain
## 3 Quality Control Using In-Situ Methods
### In-Situ Methods for R&D Purposes
#### 3.2.1 High Temperature X-ray Diffraction (HT-XRD)  
This method is frequently used to perform in-situ qualitative or quantitative phase analysis, precipitation formation, as well as phase dissolution. The underlying principle is based on the classical XRD method, except that the sample can be heated in a heating chamber and XRD scans are continuously generated during the heating or holding time. Using the time-resolved generated diffractograms, the characteristic peak intensities and the peak shifts for individual phases can be evaluated, providing information about phase composition, transformation, phase precipitation, or dissolution kinetics. The peak intensities can also be used to obtain information about the quantitative fractions. On the other hand, the crystallite size, as well as the dislocation density, can also be analyzed via selective peak profile analysis. These analyses are mostly performed using either the modified Williamson-Hall or the modified Warren-Averbach procedure [72; 73; 74; 75]. Difficulties may arise in the analysis of the diffractograms due to the difference in peak positions between room temperature and higher temperatures, as a consequence of thermal expansion and therefore a peak profile shift. In addition, with the latter analysis methods, there can be an overlap of the residual stresses and the crystallite size, where both are analyzed based on the peak profile, while residual stresses dissipate at elevated temperatures, as the crystallite size increases. Therefore, the analysis requires enormous expertise for the interpretation of the data obtained [76]. This method is used in the laboratory scale for characterizing the above-mentioned effects of a material. Various verified reaction kinetics are used to create thermokinetic models for simulation software, such as MatCalc. A major disadvantage of this method is that characterization can only be performed in the near surface region. Consequently, this can lead to difficulties, if oxidation reactions occur, or if there are local differences in the chemical composition. Also, a grain size below 10\(\upmu\)m and a statistical distribution is required for a reliable analysis. Furthermore, the sample preparation is a decisive criterion to ensure valid investigations [77]. 2.2 High Temperature Scanning Electron Microscopy and Electron Backscatter Diffraction (HT-SEM/EBSD)  
This method is also based on the classical SEM or EBSD method with an integrated heating chamber, where images are acquired at a certain frequency. In contrast to the HT-XRD method, actual images can be generated here, which are based on the interactions of the sample surface with the electron beam. This enables high-resolution imaging and tracking of changes in the microstructure. For example, the displacements of individual grain boundaries during grain growth or recrystallization phenomena or even twinning effects can be displayed [78]. By using the EBSD arrangement, the time- and temperature-resolved changes in grain size and grain orientation can be detected. In this context, the application of test facilities for the evaluation of mechanical properties and for the application at high temperatures is increasingly envisaged. To date, there are already a variety of mechanical testing equipment, such as tensile test equipment, which can be implemented in the chamber of an SEM. If such a setup is installed in a HT-SEM/EBSD, this opens up a wide range of new methods to apply mechanical properties in-situ, at high resolution [79; 80; 81; 82]. Within the scope of deformation possibilities, such as the in-situ tensile test in the SEM, digital image correlation methods are also increasingly being used. By integrating camera systems, displacements of the previously applied patterns can be recorded with high precision, which allows conclusions to be drawn about strains in one or more spatial directions. Depending on the magnification adjusted in the SEM, strain localizations in the subgrain range can be determined.