Comparative Study of CGS, HVAF and VPS Coatings on Single Crystal Substrates for Turbine Blade Repair

The repair of high-value single-crystal turbine blades is essential for both sustainability and cost efficiency, as these components are susceptible to degradation when exposed to extreme operating conditions. This study investigates and compares coatings produced using three different thermal spraying processes, cold gas spraying, high-velocity air-fuel spraying, and vacuum plasma spraying, to identify the optimal method for repair applications requiring subsequent directed recrystallization. The comparison showed that VPS coatings offer the most promising properties: They exhibit the lowest oxygen content, near-zero residual stress, and superior adhesion and successfully achieved the required 2 mm coating thickness without delamination. While CGS and HVAF were limited in achievable thickness, the resulting columnar grain structure of the VPS coating may pose a challenge for the intended directed recrystallization process.