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The structure of silicon coatings obtained on TZM molybdenum alloy by slurry method DOI:10.15199/28.2017.5.7

  1. INTRODUCTION Molybdenum base refractory alloys are potential candidate materials for a new generation high temperature nuclear reactors. TZM alloy (Titanium Zirconium Molybdenum) is one of the promising materials for aerospace applications, high temperature compact and fusion reactors. Its sublimation is fairly low, even at temperature higher than 1700°C in vacuum or inert atmosphere. The TZM alloy offers several attributes for high temperature structural applications including high melting point (>2600°C), high creep strength at elevated temperature, good corrosion compatibility with many molten metals and alloys. However, this alloy is easily oxidized when subjected to hot working even at 540°C in the oxidizing environment. The TZM alloy in air forms non-protective and volatile MoO3 oxides on the alloy surface. These oxides evaporate at 790°C. In consequence, the TZM alloy loses its material integrity due to catastrophic mass loss. Properties of the alloy are not relevant under these conditions [1]. The resistance to corrosion and oxidation of TZM alloy can be improved by adding the appropriate amount of silicon and obtaining a thin passive layer of oxide on MoSi2. Oxidation resistance of MoSi2 is derived from the formation of an adherent and continuous SiO2 film on its surface. Molybdenum disilicide has long been known as an attractive coating material for the protection of Mo and Mo-based alloys used in an oxidizing atmosphere at high temperature [2]. Methods for silicide coating have been studied for a long time, such as vacuum deposition, chemical vapour deposition, solid reaction with silicon powder, the pack-cementation method or the slurry cementation method [3]. 2. EXPERIMENTAL PROCEDURES Manufacturing of protective layers was conducted with the slurry method on TZM alloy containing approximately (wt %): 0.5% Ti, 0.1% Zr, 0.02% C, the balance is Mo. The slurry was prepared taking powdered silicon, an organic bind[...]

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