MoSi2 coating on Molybdenum substrate by Pack Cementation Method

Abstract

Despite being a high melting point metal with good mechanical properties the use of Molybdenum at high temperatures is limited due to its poor oxidation resistance above 600°C.Therefore the use of Molybdenum at high temperature is only possible after application of some suitable oxidation resistant coating. Such coating aspires to be a self-healing protective oxide layer, thus preventing direct atmospheric contact with the substrate. Many coatings which have been applied on Molybdenum alloys to provide oxidation protection include Au, Ni, Cr, Al-Si etc. Among various coatings applied onto Mo alloys, silicide coatings had shown outstanding performance under high temperature conditions. At temperatures above 1000°C, the formation of stable glassy silica scale accounts for the oxidation resistance of Molybdenum substrate. Such silica scale had been reported to self-heal small surface cracks formed on the surface of as-formed silicide coating due to difference between CTE of substrate and coating. This feature, in addition to some other features makes silicide coatings a strong candidate for application onto Mo metal for short term oxidation resistance. Various routes had been adopted by researchers to deposit silicide coating on Mo metal such as Chemical Vapor Deposition (CVD), Magnetron Sputtering, Pack Cementation, electro-thermal explosion ultrahigh speed spraying to name a few.