Microstructure and oxidation resistance of in-situ silicide composite coating on Mo-2.5Zr-2.5ZrO2-xW (x=0, 20, 30) substrate

Abstract

In-situ silicide composite coatings were prepared on Mo-2.5Zr-2.5ZrO2-xW (x=0, 20, 30) substrates by pack cementation technique. The microstructure evolution, oxidation behavior and oxidation resistance mechanism of the composite coatings at 1300 °C were studied. The experimental results revealed that the coating thickness increases from 89 μm to 144 μm when the W content in the substrate increases from 0 at.% to 30 at.%. During the oxidation process, due to the presence of many cracks in the MoSi2 coating on the Mo-2.5Zr-2.5ZrO2 substrate, it was rapidly oxidized to form Mo5Si3 and volatile MoO3 in turn. When the oxidation time reached 150 h, the mass of MoSi2 coating increased to −937.19 mg/cm2, and the sample was completely destroyed. The mass gain of the coating on Mo-2.5Zr-2.5ZrO2-30W substrate (mainly (Mo,W)Si2) was only 2.86 mg/cm2 after 210 h cyclic oxidation. In the process of high temperature oxidation, the molten SiO2 oxide film with flowability formed on the surface can well isolate oxygen, while the presence of high melting point ZrO2 particles can form pinning effect on the surface of the oxide film, which limits the irregular flow of molten SiO2, and helps to improve the high temperature oxidation resistance of the coating.