ChEMS Seminar: Repair of Nickel Base Superalloys by Cold Spray

Abstract: In the cold spray process, deposition of particles takes place through intensive plastic deformation upon impact in a solid state at temperatures well below their melting point. The high particle impact velocities and corresponding peening effects can lead to high compressive residual stresses in cold spray coatings. This can be advantageous with regard to mechanical properties as fatigue life, and hence, cold spray seems to be an ideal process for repair applications. In this study, Inconel 718 powder particles were cold sprayed on Inconel 718 substrates by using nitrogen gas for an application as a repair tool for aero engine components. First, velocities of the cold sprayed particles have been determined as a function of process conditions and particle size. Critical velocities have been determined considering the deposition efficiencies.

Furthermore, the magnitude of the residual stress and its distribution through the thickness of the cold sprayed coatings were measured by using the hole-drilling and bending methods. Mainly compressive residual stresses were observed in cold sprayed Inconel 718 coatings. Accumulation of residual stresses in the coatings is highly affected by peening during deposition and it decreases with increase in thickness. It has been observed that the bond- strengths of cold sprayed Inconel 718 coatings are highly influenced by coating thickness and residual stress states of the coating/substrate system. A detailed discussion will be given. In addition, further results on cold spraying different Ni base superalloys on CMSX 4 type substrates will be presented and discussed. Also, the influence of substrate temperature will be highlighted.

Bio: Robert Vaßen (Vassen) is the deputy director of the Materials Synthesis and Processing Division (IEK-1) of the Institute of Energy and Climate Research at the Forschungszentrum Jülich, Germany, and head of the Department of Materials Development for Advanced Power Plants. He received his diploma in physics in 1986 and his doctorate in 1990, both at the RWTH Aachen University. In 2004, he finished his abilitation at the Ruhr-University in Bochum. In 2009, he was appointed as professor at the Ruhr University. He also was a guest professor at the University West, Trollhättan, Sweden. His research focuses on the development of different coatings for advanced power plants as thermal barrier coatings or abradables for gas turbines and environmental barrier coatings for ceramic matrix composites. For many years, he also has been active in coating development for solid oxide fuel cells, membranes for oxygen and hydrogen separation and more recently, repair technologies especially by cold spray, aerosol deposition and ceramic matrix composites. He has published more than 300 papers (H-index of 36) and holds more than 20 patents. He has given around 100 invited talks and serves as a reviewer for several journals and as evaluator for different societies. In 2017, he was inducted into the Hall of Fame of the Thermal Spray Society (ASM).

Host: Daniel Mumm