With gas turbines, higher operating temperatures mean greater efficiency with a simultaneous reduction of CO2 emissions. The rising temperatures subject the turbine blades to increasingly severe loads. To prevent the tremendous heat from overly stressing the material and causing the blades to deform or crack, a two-layer coating developed by Siemens is applied to the blades. The outer fine-grained and porous ceramic thermal barrier coating is applied via a special plasma beam method. It can withstand temperatures of roughly 1,200 °C and insulates the turbine blade against this tremendous heat. A necessary adhesion layer also protects the blade metal against oxidation and corrosion. Together with active cooling, these coatings enable many years of safe operation at combustion temperatures of up to 1,400 °C.

The Siemens experts use a plasma cone as the heat source in the plasma spray method that is used to apply the ceramic material. The hot plasma stream melts the ceramic powder particles before depositing the coating by propelling the particles against the blade at high speed. The conventional method uses a standard coating nozzle with a powder injector for the material. This has proved to be very inefficient, however, because coating based on this method takes a relatively long time and the spray nozzle wears away very quickly. This wear causes a steady decrease in the performance of the coating burner. The results include a lot of wasted powder and a continuously changing process. Because a blade is coated in passes and layers, the thickness of the overall coating is uneven and the heat resistance of the blade is inhomogenous. With the latest generation, evenness of the thick thermal barrier coatings must be even more precisely guaranteed than ever before.

“We therefore went looking for a new spray method with which a blade could be coated more thickly, more quickly, and more evenly,” is how Ladru explains his approach. At the time, Ladru was still a Group Leader at Turbine Airfoil Coating and Repair GmbH (TACR Berlin), a joint venture between Siemens Energy and the turbine blade specialist Chromalloy Gas Turbine Corporation. By striving to optimize the spray method, he finally came up with his unique idea. Three spray injectors would be used instead of just one, and rather than adding the powder material after the plasma exits the nozzle, it would be added in the flow channel immediately downstream of the arc that generates the argon-hydrogen plasma. The three internal injectors distribute the material much more evenly and ensure optimal melting.

“The three rotating nozzles reduced the coating time by more than 30 percent,” says Ladru. The new method also has other advantages. The plasma spray system consumes around 40 percent less ceramic powder, while the service life of the nozzle increases from 40 to around 100 hours. What’s more, it is now much easier to set up the system correctly again after it had been shut down for maintenance or to change coatings, for example. Ladru developed the coating nozzle in collaboration with the Swiss company Medicoat AG, which specializes in coatings for medical technology. Ladru is particularly pleased about being named Inventor of the Year “because it underscores that innovative work driven by a pioneering spirit is also being performed at the Siemens joint venture company.”

A native of the Netherlands, Ladru has stayed true to the subject of materials since beginning his studies of material science in the Dutch city of Delft. “When I was young, I met a lot of friendly Germans while vacationing in Austria and while windsurfing on the Dutch coast. Given these positive experiences and my desire to learn German, I decided to write my degree thesis at RWTH Aachen University,” he reports. He also earned his PhD at the Surface Engineering Institute in Aachen. The subject of his doctoral thesis was very closely related to his later field of work: the “Development of an online process control for atmospheric plasma spraying for the production of thick thermal barrier coatings.” After receiving his PhD in 1999, he joined TACR in Berlin, where he worked for nearly 11 years before transferring to the parent company, Siemens, in 2010. He has 60 invention applications, 16 granted individual patents, and 36 IPR families to his name. As Head of the Technical Services Blades and Vanes group, he is responsible at Siemens for providing technical support to suppliers of compressor and turbine blades. His long years of experience working for a supplier and with the technology, plus his contacts throughout the world, are a great help to him in this field.

Ladru also has private roots in his new hometown of Berlin – he met his wife there. Both are passionate Salsa dancers, a hobby for which they have had little time since the birth of their child, however. Since the family built a house directly on the Havel River – ”a true Dutchman simply has to be close to the water” – Ladru has switched from windsurfing to sailing and can set sail from his own private dock.