Oxidation behavior of monolithic HfSi₂ and SiC fiber-reinforced composites fabricated by melt infiltration using Si–8.5 at%Hf alloy at 800–1200°C in dry air

Abstract

The low-temperature melt-infiltration method using eutectic Si alloys is a novel process of fabricating SiC fiberreinforced SiC-based matrix composites (SiC f /SiCs) for high-temperature structural applications. SiC f /SiCs were fabricated by the melt-infiltration method using a eutectic Si8.5 at%Hf alloy to evaluate their dry oxidation behavior at 8001200°C for times ranging from 10100 h. The oxidation behavior of monolithic HfSi 2 (Monolith) fabricated by spark plasma sintering was also evaluated in dry air. The oxidation behavior of the composite matrix and Monolith obeyed the parabolic law in dry conditions. The steps to form the oxidation layer were expected to produce HfO 2 and Si, followed by SiO 2 , and, finally, HfSiO 4 . The oxidation rate of the matrix was similar to that of Monolith and 10 2 10 4 times larger than that of Si. The oxidation activation energy employed in oxidation of HfSi 2 was calculated as 258 kJ/mol in dry air.

Research status of bond coats in environmental barrier coatings

“…SiO 2 reacts with HfO 2 to form HfSiO 4 during Si oxidation, which leads to the bond coat operating at higher temperatures, even over the melting point of Si. Formation of HfSiO 4 at temperatures above 1000°C followed by Equation () 19 : $$\begin{equation}{\rm{Si}}{{\rm{O}}_2}_{({\rm{s}})} + {\rm{Hf}}{{\rm{O}}_{2({\rm{s}})}} \to {\rm{HfSi}}{{\rm{O}}_{4({\rm{s}})}}.\end{equation}$$…”

“…In addition, improving the fuel efficiency of the gas turbine engine can reduce emissions such as CO 2 and NO x that are detrimental to the environment 16–18 . At present, CMCs have been applied to exhaust nozzles, turbine blades, combustion chambers, and so on, which are exposed to an extreme environment where the superalloys will melt and be damaged prematurely during operation 1,19,20 …”

Oxidation mechanisms of SiC‐fiber–reinforced Si eutectic alloy matrix composites at elevated temperatures

“…However, HfSi 2 in the Si-HfSi 2 alloy was oxidized prior to other phases in the composites, and the Si-HfSi 2 alloy showed the same oxidation rate as HfSi 2 . 45 The Si phase in the Si-HfSi 2 did not improve the oxidation resistance of HfSi 2 .…”

“…The present authors have studied the oxidation behavior of HfSi 2 and SiC f /SiC composites using Si‐HfSi 2 eutectic alloy, which contains a high amount of Si. However, HfSi 2 in the Si‐HfSi 2 alloy was oxidized prior to other phases in the composites, and the Si‐HfSi 2 alloy showed the same oxidation rate as HfSi 2 . The Si phase in the Si‐HfSi 2 did not improve the oxidation resistance of HfSi 2 .…”

“…41 On the other hand, reports on the oxidation behavior of Si eutectic alloys have been limited. [42][43][44] The present authors have studied the oxidation behavior of HfSi 2 and SiC f /SiC composites using Si-HfSi 2 eutectic alloy, 45 which contains a high amount of Si. However, HfSi 2 in the Si-HfSi 2 alloy was oxidized prior to other phases in the composites, and the Si-HfSi 2 alloy showed the same oxidation rate as HfSi 2 .…”