Improved mechanical properties of Ni-rich Ni₃Al coatings produced by EB-PVD for repairing single crystal blades

Active control of turbine blade tip clearance for aircraft engine continues to be a concern in engine operation, because turbine blades are subjected to wear and therefore cause an increasing tip clearance between the rotating blades and the shroud and also reduce the engine efficiency. In this work, a Ni-rich Ni₃Al coating with γ′/γ two-phase microstructure was deposited by electron beam physical vapor deposition (EB-PVD), which worked as repairing the worn blade tips of single crystal blades. Nb molten pool was used to increase the molten pool temperature and thus to enhance the deposition rate. The microstructures and mechanical properties can be modified by the deposition temperatures and the following heat treatments. All coatings consist of γ′ and γ phases. At deposition temperature of 600 °C, a dense microstructure can be achieved to produce a coating with grain size of ~1 μm and microhardness of ~HV 477. After being heated for 4 h at a temperature of 1,100 °C, the coatings have a more uniform microstructure, and microhardness maintains at a high level of ~HV 292. Effect of Hf and Zr on EB-PVD Ni₃Al repair coating will be further investigated.