Papers by Author: Wei Tao Wu

Abstract: The specimens of O-phase Ti-22Al-25Nb (at%) intermetallics coated with silica-based enamel received mass gains of about 1 mg/cm2, after 300 h of oxidation or hot corrosion at 800 °C. These rates were much faster than the growth rates of silica films at the same temperature. To understand this phenomena, the specimens were analyzed using SEM, XRD, EPMA and TEM. An oxide layer with thickness of several μm was observed at the enamel/substrate interface of the coated specimens after either oxidation or hot corrosion. XRD and TEM analysis revealed the newly formed oxide layer was composed of α-Al2O3, Al2SiO5, Al2TiO5, rutile-TiO2 and NbO2. It was shown by EPMA profiling that an Al-depleted zone was located just beneath the oxides. It was proposed that the solid reactions between the enamel coating and the O-phase Ti-Al-Nb played important roles for the oxidation and hot corrosion behavior of the coated specimens.

Abstract: Composite metastable Ti0.5Al0.5N, Ti0.49Al0.49Y0.02N and Ti0.48Al0.48Y0.04N coatings were deposited on a wrought martensite steel 1Cr11Ni2W2MoV for aero-engine compressor blades by arc ion plating respectively all coatings possessed a dense surface and the same B1NaCl phase structure and the lattice parameter increased with increase of the incorporated element Y. Oxidation-resistance of (Ti,Al,Y)N coatings at 800
for up to 500 hr was investigated and the results showed that the introduction of yttrium into the coatings dramastically improved the oxidation-resistance of the coatings in air. The presence of Y in the nitride coatings suppresses the outer diffusion of Fe through the nitride coating. And the oxide of yttrium may segregate to the grain boundaries of oxides, suppressing the outward diffusion of metallic elements in coating and the inward diffusion of oxygen. Besides, the existence of adequate Y in the coatings is in favor of suppression of the growth of oxide crystals, formation layered oxide scale and decrease of compressive stress of oxidation.