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The working distance is an essential parameter of the laser metal deposition (LMD) process which has to be kept at a constant level for successful applications. Especially when applying LMD in additive manufacturing (AM) to generate large-scale components, distance control is crucial as these parts can take multiple hours to complete. If over time the working distance runs out of the processing limits, the process efficiency will decrease, and this can lead to a process break down destroying the component build. The development approach is to integrate an enhanced distance measurement system based on optical coherence tomography (OCT) into a commercial LMD powder processing head. By deflecting an elliptic measuring track around the processing area, the OCT system can detect the working distance as well as topological information (2D + d) compared to a standard 1D distance measurement (1D + d). By continuously collecting data when moving the processing head, a 3D-scan of the surface can be recorded online. This technology is beneficial for AM as well as LMD repair applications as the system allows the scanning of unknown surfaces prior to LMD processing. In a next development step, the position data of the laser-cell (robot or CNC-Machine) is linked to the 2D + d data gaining full 3D information with high spatial and temporal resolution in real-time. Based on these monitoring capabilities, a closed loop control can be set up by implementing stabilization methods. By adapting LMD process parameters like the powder feed rate or the processing speed, a work distance and LMD track height control can be achieved. [ABSTRACT FROM AUTHOR]

Corrosion causes costs of about 3–4% of each country's gross domestic product, and due to the climate change, the corrosion rates on infrastructure are likely to increase furtherly in the future1,2. For corrosion protection, hard chrome plating (HCP) is commercially used since the early 20th3. Yet the biggest drawback concerns environmental protection, since toxic and carcinogenic hexavalent chromium Cr6+ is used. As an alternative, thermal spray (TS) is increasingly used since the last 20 years. Nevertheless, the coatings are technologically constrained in regard to high porosity, low material efficiency and poor bonding to the base material. Therefore, the demand for an environmental friendly and economical process that produces high-quality coatings is increasingly coming into the research focus. With laser, dense, metallurgically bonded and therefore well-adhering coatings with high material efficiency of > 90% can be produced from a large number of metallic alloys without the need to use environmentally harmful chemicals or noise emissions. However, the typical area coating rate of < 0.4 m2/h is significantly lower than that of TS of about 10 m2/h4,5, and is too small for coating large-scale components. In this regard, a novel coating process with laser was developed in this work. By decoupling the melding of powder from the coating speed, the coating speed of < 2 m/min in conventional laser coating can be increased to > 500 m/min. Defect-free layers that metallurgically bond to the base material with a thickness of 50–250 µm and a material efficiency of > 90% can be achieved. According to the results, an area coating rate up to 20 m2/h is achievable. The pioneer work of applications in offshore and automobile sectors show, this process is already providing beneficial for the industry. [ABSTRACT FROM AUTHOR]

Highlights • Formed by HDR-LMD, IN625 seem have finer microstructure than that of IN718. • With approx. 2 kg/h deposition rate, IN625 is nearly whole density, IN718 porous. • There exists stronger convection in the melt pool of IN625 than in IN718. • The convection may cause faster heat transfer so that accelerates the solidification. • The convection may promote the escape of the gas that trapped in the process. Abstract Nickel-based super-alloys Inconel 718 (IN718) and Inconel 625 (IN625) have comparable chemical composition and similar physical constants such as density and melting range; however, in high-deposition-rate laser metal deposition (HDR-LMD), processes with IN625 are not transferable to that with IN718. In order to compare HDR-LMD process with IN718 and IN625, the current study has been conducted. Initially, parallel experiments have been performed, and the metallurgical analysis for macro- and microstructures have been carried out. Then, the strengthening effects of HDR-LMD for both alloys have been compared. Finally, in order to understand and explain the obtained results, both processes have been characterized by using a high-speed camera. According to the study, the following conclusions have been drawn: in comparison to IN718, there seems to have a stronger convection in the melt pool of IN625; this convection could be the reason for the faster solidification of IN625 since it may accelerate the dissipation of heat; As a further consequence of the stronger convection, the degassing during the solidification can be enhanced. [ABSTRACT FROM AUTHOR]