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 opera- tion, 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 Ni3A1 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 tem- perature 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 ℃, 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 ℃, 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.

Enhancing anti-oxidation and thermal-radiation performance of the repaired borosilicate glass coating on C/C composites by Sm-doping

To repair the damaged SiC coated C/C composites,a double-layer system including a Sm-doped boro-silicate glass external layer and a SieSiC inner layer was prepared by a slurry-based laser cladding technique.Isothermal oxidation experiment and indirect/direct thermal-radiation measurements were performed.The results showed that the absorbance of borosilicate glass to the laser at 900e1200 nm was improved significantly by Sm-doping.Consequently,the repaired coating with a more compact structure and better oxidation resistance was obtained.After oxidation at 1773 K for 10 h,the mass loss of the damaged sample could be reduced by 74.98%with repairing.By increasing laser-absorption and reducing viscosity,the thermal-radiation property of the repaired coating was enhanced to decrease the surface temperature greatly.A repair system with excellent thermal protection performance was achieved.

Recovery in oxidation behavior of damaged SiCeZrB_(2)/SiC coating of carbon/carbon composites

Polysiloxane(PSO)was adopted as the matrix of the repair agents,and SiCeZrB_(2)powder was used as the filler,to repair the prefabricated defects on the SiCeZrB_(2)/SiC(SZS)coating of carbon/carbon(C/C)composites.The repair agents were brushed on the defect areas and then underwent preoxidation(PR)or heat-treatment(HR)in a vacuum.The effects of different treatment processes on the chemical composition,microstructure of the repair agents,and the oxidation resistance behavior of the repaired coating were investigated.The repaired agents after both processes were pyrolyzed and generated SiOC ceramics,and they were well combined with the original coating.The thermal stability of PSO after preoxidation is poorer than that after heat-treatment,resulting in a weight loss rate of 5.88%after oxidation at 1500℃for 270 min,while that of the HR coating is only-0.87%,yet both have been great improvement compared with the unrepaired coating.This work provides an effective and simple approach to repairing damaged coatings for high-temperature applications.