Microstructure,thermal stability and wear resistance of additively manufactured single crystal Ni-based superalloys
The single crystal Ni-based superalloy SRR99 was fabricated by laser-directed energy deposition(LDED).Through microstructural characterization,hardness measurements and nanoscratch tests,the microstructural stability of LDED single crystal Ni-based superalloy at the service temperature was systematically investigated.The results show that the morphology and size(70 nm)of the γʹ precipitates in LDED samples remain stable after annealing at the service temperature(650℃)for 100 h.The hardness values of LDED samples keep almost unchanged(6.6 GPa)before and after annealing,and are more than 20%higher than that of the traditional cast samples.Furthermore,the coefficients of friction of the LDED samples before and after annealing are lower(0.19)and less scattering than those of their cast counterparts.This study demonstrates that Ni-based superalloy single crystals fabricated by LDED exhibit excellent thermal stability and friction properties,paving the way to the application of LDED technology in the repair and life extension of single-crystalline turbine blade dovetails.
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