Repairing turbine blades via additive manufacturing

The project aims to make the repair process more stable, reliable and suitable for demanding industrial applications.

Turbine blades are exposed to extreme operating conditions, including high temperatures, strong mechanical loads and rapidly changing pressure conditions. Nickel-based superalloys are commonly used for these components because they retain their mechanical strength and resistance to heat and corrosion under challenging conditions.

Despite their durability, turbine blades experience wear and damage over time. Replacing them can be costly and resource-intensive, particularly because they are made from high-value materials and manufactured to precise specifications. Repairing damaged areas can therefore offer an attractive alternative by potentially extending component service life, conserving valuable materials and reducing the need to manufacture replacement parts.

However, the repair of turbine blades places exceptional demands on the production process. Even very small defects, including pores, insufficient bonding or microcracks in the repaired areas, can affect the performance and service life of a blade. Reliable monitoring and consistent process conditions are therefore essential.

Developing DED for High-Quality Repairs

As part of the “Sensor-supported qualification of regenerated turbine blades” project, known as SAMrep, the Additive Manufacturing – Metals group at LZH is advancing a laser- and powder-based additive manufacturing process called Directed Energy Deposition (DED).

During DED, metal powder is delivered to a precisely defined area of the damaged component. A laser melts the powder together with a thin layer of the existing base material, forming a metallurgical bond. The material is then deposited layer by layer until the damaged section has been rebuilt.

Unlike conventional manufacturing processes that produce an entirely new component, DED can apply material only where it is required. This makes the technology particularly promising for the repair and regeneration of complex, high-value components.

The process can also be adapted to different repair geometries. Nevertheless, variations in powder flow, laser energy, temperature distribution and the condition of the existing component can influence the quality of the deposited material. These variables make effective process monitoring especially important when working with sensitive nickel-based superalloys.

Sensor Technology for Greater Process Stability

To detect and help prevent defects during the DED process, the project partners are employing advanced sensor technology and multispectral process monitoring. By capturing information from different spectral ranges, the monitoring system is intended to provide a more comprehensive view of the conditions inside the processing zone.

The researchers aim to identify relevant changes and irregularities as the new material is being deposited. This approach could allow defects or unstable process conditions to be recognised at an early stage, rather than only during inspections performed after the repair has been completed.

The project is intended to enable non-destructive inspection directly during the deposition process. Integrating quality assurance into production could provide valuable information about each deposited layer and support a more reliable assessment of the repaired area.

In-process monitoring could also help researchers gain a better understanding of the relationship between sensor signals, process parameters and the resulting material quality. These findings may support the optimisation of DED parameters and the development of more stable process windows for turbine-blade repair.

Towards More Reliable and Resource-Efficient Repair

By combining additive manufacturing with sensor-based quality assurance, SAMrep addresses one of the central challenges involved in repairing safety-critical components: ensuring that the regenerated area meets demanding quality requirements.

A more reliable repair process could support the wider industrial use of DED for turbine components. It may also help reduce material consumption and extend the useful life of expensive parts. Instead of replacing an entire blade because of damage in a limited area, manufacturers could rebuild the affected section while retaining most of the original component.

The knowledge generated by the project may also be relevant to other industries that use high-value metal components under demanding conditions. Potential application areas include energy technology, aerospace, mechanical engineering and other sectors in which component reliability and traceable production quality are essential.

About SAMrep

The SAMrep project— “Sensor-supported qualification of regenerated turbine blades”—is funded by the Investment and Promotion Bank of Lower Saxony (NBank) using resources from the European Social Fund Plus and the European Regional Development Fund.

The project partners are 4D Photonics GmbH and Laser Zentrum Hannover e.V. Through their collaboration, the partners are combining expertise in additive manufacturing, laser processing and optical sensor technology to develop more dependable quality-assurance methods for the repair of turbine blades.