Influence of Na2SO4 molten salts on the self-healing behavior of Ni/Al2O3 composites

ABSTRACT The objective of this study is to investigate the influence of Na2SO4 molten salt on the self-healing behavior of Ni/Al2O3 for its utilization as the middle pressure ceramic turbine blades of aircraft. Dense 5 vol% Ni/Al2O3 was prepared and cracks were introduced by the Vickers indentations. The samples were heat-treated ranging from 1000°C to 1150°C for 0.5 h to 48 h in air with Na2SO4 molten salt. The crack lengths of samples before/after the heat treatment were measured using scanning electron microscope (SEM) and the crack disappearance rate was calculated. X-ray diffraction (XRD) results show same peaks in the samples heat-treated with and without Na2SO4 molten salt. The crack disappearance rate of sample heat-treated with Na2SO4 molten salt is higher than that without molten salt and increases according to the parabolic manner. The apparent activation energies for crack disappearance are 354 kJ/mol for the sample heat-treated with Na2SO4 molten salt and 390 kJ/mol for that without Na2SO4 molten salt. The bending strength of the sample heat-treated with Na2SO4 molten salt is equivalent to that of the original sample. Ni/Al2O3 composite exhibits excellent corrosion resistance and self-healing function even in coexistence with Na2SO4 molten salt.