Study on the Microstructure and High-Temperature Oxidation Performance of β-NiAl/γ′-Ni3Al Intermetallic Compounds Fabricated by Laser Metal Deposition

Abstract

Four Ni-Al intermetallic compounds with the Al concentrations in range of 28 to 35 (in atomic percentage) have been fabricated by laser metal deposition (LMD) through mixing appropriate contents of pure Ni powder with pre-alloyed high-Al nickel aluminide powder. Ni-35Al and Ni-32Al are both composed of more than 45 vol.% β-NiAl matrix phase dispersing γ′-Ni3Al, while Ni-30Al and Ni-28Al consisted of worm-like, needle-like γ′-Ni3Al mainly and less than 37 vol.% β-NiAl. After 20 h oxidation in air at 1000 °C, the results of thermobalance, X-ray diffraction and scanning electron microcopy, indicated that Ni-35Al and Ni-32Al are more oxidation-resistant than the Ni-30Al and Ni-28Al. Because the first two can thermally grow an external Al2O3 scale but the second two form a duplex oxide scale consisting of outer NiAl2O4 layer and inner Al2O3 layer.