# 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  
For in-line inspection, which in this context is regarded as QC in a manufacturing process, during or between the processing stages, there is a limited number of usable methods even today. While there are some established measuring systems for the quality inspection at the end of the component manufacturing route, which are also partially automated and connected in series, such as conventional ultrasonic technology, eddy current testing, etc., it is essential to find systems that include other restrictions. The overriding goal of such systems is to observe the quality of a feedstock over the entire value chain until the finished component, in order to be able to react immediately in the event of any deviations. For this purpose, the targeted system requires complete networking and background calculations that can respond in real time, based on real process data. Computations of this kind can then decide, depending on the severity of the deviation, whether the existent deficiencies can be rectified by adjusting the production route, or whether it is rejected. Successful implementation of such systems can save a company an enormous amount of money, if a defective component is sorted out at an early stage. This does not only contribute to cost efficiency, but also to energy and resource efficiency, and thus leads to an enormous contribution to the sustainability of a company. The criteria that a system has to fulfill in order to be a fundamental contributor are:  
* Possibility of integration
* High measurement frequency
* Near real time data processing
* Robustness
* Reliability
* Innovaciousness
* Affordability
* Long service life  
According to these criteria, most of the methodologies used for the final inspection are not suitable for an in-situ implementation, mainly due to the possibility of implementation, in combination with the low data acquisition frequency. It is quite common for sensors to be installed in production facilities to monitor and control various process parameters in-situ, in a variety of ways. A decisive parameter in this case is the usually unavoidable temperature measurement, whether in the furnace, during the forming process, at the run-out table, or during galvanizing, to mention some examples. Pyrometers are mainly used for this purpose; thermal cameras are applied in rarer cases. Similarly developed are geometry measurements, which can also usually be checked in several manners, in a cost-effective manner, on the basis of a wide variety of measurement principles. However, the situation is different when it comes to analyzing the microstructure prevailing in the component. For the quality of a component, there are several parameters that directly affect the material, which decide on good parts and rejects. On the one hand, for multiphase alloys or for composites, the phase composition or layer thickness inside would be an essential aspect. For correlating mechanical properties, grain size, aspect ratio, or orientation, is also essential. For thermomechanical treated steels, for example, it has been demonstrated that the prior austenite grain size and texture have an enormous influence on the morphology of the martensite produced in the cooling zone. This is ultimately reflected in the anisotropy of the mechanical properties (in rolling, normal, and transverse directions) [52]. In order to be able to determine the austenite grain size, which will not remain stable at lower temperatures, in the laboratory, elaborative stabilization procedures of the microstructure and complex microscopic analyses are often necessary. Consequently, the research for possibilities to investigate the microstructure of materials at high temperatures and in-situ, e.g., during corresponding deformations, is intensified. This in turn is achieved by means of different physical or chemical properties of, for example, phases, lattice structures, grain sizes, or orientations, which can be measurably separated from one another.