Modeling of thermally sprayed coatings on light metal substrates: – layer growth and residual stress formation

Automotive lightweight engineering is indispensable for fuel saving and reduction of emissions. The substitution of cast iron engine blocks by light metal components yields significant weight savings. Thereby, protective coatings, which can be applied by thermal spraying, are essential for cylinder liner surfaces to resist mechanical and tribological load during operation of the internal combustion engine. Aluminum alloys and ceramic coating materials show a principal mismatch in their thermophysical and mechanical properties. Due to the fast and dynamic heat and mass transfer processes during thermal spraying this leads to the formation of residual stresses in the layer composite. Hence, residual stress analysis and understanding their generation mechanisms are essential for the optimization of the manufacturing process and for the operational reliability of the component. Numerical finite element analysis (FEA) provides the facility to examine stress formation in real-time depending on temporary heat distribution in the component during the manufacturing process. A cylinder liner tube is modeled and an inside coating process with continuous material deposition is simulated. To analyze the influence of heat transfer manipulation during manufacturing, different simultaneous cooling techniques are adopted to the model. Finally, FEA results are verified (or supplemented) by measurements with the microhole drilling and milling method. Combined, this yields a deeper understanding of residual stress formation and a tool for an effective optimization of thermal spray processes.