High temperature oxidation behavior of HVOF-sprayed unreinforced and reinforced molybdenum disilicide powders

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• 作者：Reisel ; Guido ; Wielage ; Bernhard ; Steinhä ; user ; Siegfried ; Morgenthal ; Ingrid ; Scholl ; Roland
• 关键词：High temperature ; HVOF-sprayed ; Molybdenum disilicide ; Powders
• 刊名：Surface and Coatings Technology
• 出版年：2001
• 出版时间：September - October, 2001
• 年：2001
• 卷：146-147
• 期：Complete
• 页码：19-26
• 全文大小：733 K

文摘

Intermetallics like silicides are useful for protective coatings against high-temperature corrosion. Especially molybdenum disilicide which has a great potential as protective coating e.g. in aircraft engines and gas turbines in the temperature range between 1400 and 1800°C due to its high melting point and its low brittle-ductile transition temperature of approximately 800–1100°C. Four types of coatings were produced by high velocity oxyfuel spraying (HVOF): unreinforced MoSi₂ with low porosity, unreinforced MoSi₂ with high porosity, with silicon carbide reinforced MoSi₂ and with alumina reinforced MoSi₂. The coatings as sprayed were characterized by XRD, SEM and EDX. Microhardness and porosity were measured. The oxidation behavior of the coatings was determined at 500, 1000 and 1500°C. The influence of the heating rate was investigated during oxidation tests at 1000°C. The tests at 500°C showed that the pesting depends on the porosity of the coating. SiC as reinforcing phase seems to accelerate pesting, while alumina reduces this reaction. Unreinforced MoSi₂ coatings form a protective SiO₂ layer on the surface with a thickness below 10 μm during oxidation at 1500°C. The layer seems to be glassy with cristobalite inclusions. The microstructure of the coating changes to a high crystalline two-phase system of α-MoSi₂ and hexagonal Mo₅Si₃.