Effect of Ni-5Al Addition on the Properties of BaAl2O4-Based Coating Deposited with a Novel Explosive Spray Coating Technique

Abstract

A suitable mixture of Ba(NO3)2 and Al powders, known as pyrotechnic mixture, was burned to deposit pure BaAl2O4 and Ni-BaAl2O4 coatings on low-carbon steel by a new explosive spray coating method. Ni-5Al is a bonding coating material commonly used in thermal spraying to deposit ceramics on metal substrates to achieve strong coating-substrate adhesion. In addition, because it is hard in nature, this material has the potential to impart toughness to a brittle composite. Therefore, Ni-5Al powder was added to the explosive spray charge to deposit a Ni-BaAl2O4 composite coating. Various characterization techniques, such as x-ray diffraction, field emission scanning electron microscopy with energy-dispersive spectroscopy analysis, transmission electron microscopy (TEM), Vickers hardness test, scratch test, image analysis, and roughness estimation were used to compare various properties of the two coatings. It was found that the Ni-based globules are uniformly distributed in the Ni-BaAl2O4 coating. BaAl2O4 and Ba phases were observed in the pure BaAl2O4 coating, while Ni, BaAl2O4 and Ba2Al2O5 phases were mainly formed in the Ni-BaAl2O4 coating. The formation of Ni-Fe and Ni-Al based compounds and the interdiffusion of materials in the interface region of this type of coating significantly improved the coating-substrate adhesion. The TEM analysis confirmed the presence of brittle crystalline and amorphous phases in both coatings. The overall crystallinity of Ni-BaAl2O4 was higher than that of the pure BaAl2O4 coating material. The increase in hardness and reduction in crack formation in the Ni-BaAl2O4 composite also suggests an improvement in toughness. In addition, the average surface roughness and porosity of the Ni-BaAl2O4 coating were lower than that of the pure BaAl2O4 coating. The addition of Ni-5Al to the feedstock improved the mechanical properties of the explosively deposited BaAl2O4-based coating. © 2022, ASM International.