In situ Formation of Oxidation Resistant Refractory Coatings on SiC‐Reinforced ZrB₂ Ultra High Temperature Ceramics

Abstract

In situ oxidation resistant and solid refractory coatings have been generated on 20 vol% SiC-reinforced ZrB 2 ultra high temperature ceramics containing 10 wt% rare earth (RE) additives such as LaB 6 , La 2 O 3 , and Gd 2 O 3 fabricated by spark plasma sintering. Oxidation for 1 h at 1600°C in static air led to formation of a dense layer (up to 250 lm thick) of ZrO 2 and RE-zirconates on the composite systems underneath which were intermediate layers (50-100 lm) containing heterogeneous crystalline oxides such as La 2 Zr 2 O 7 and amorphous silicate phases. The benefits of predominating solid oxidation products over having substantial volumes of liquid present in aerospace leading edge applications are discussed. II. Experimental DetailsZrB 2 powder (>99%, d 50~4 5 lm, ρ = 6.85 g/cm 3 ; Sigma-Aldrich, Gillingham, U.K.) and SiC powder (a-SiC, 99%, d 50 0.7 lm, ρ = 3.217 g/cm 3 ; Good Fellow Chemicals, Hunting-J. Halloran-contributing editor Manuscript No. 29589.

Oxidation Behavior of Zirconium Diboride Silicone Carbide Based Materials at Ultra-High Temperatures

“…Given this temperature measurement uncertainty, the 1627°C transition temperature between oxidation regimes would be more accurately expressed as 1627°C±25. This temperature range is however supported by results in the literature 15,18,24,25,84 .…”

Microstructure evolution upon annealing of a ZrB2–SiC composite containing lanthana and magnesia

“…8,11,13 Specific investigations on ZrB 2 -SiC composites exploiting the eutectic composition of Y 2 O 3 and La 2 O 3 were performed by other authors to improve the oxidation resistance, [14][15][16] but the simultaneous addition of La 2 O 3 and MgO for ZrB 2 is a novelty.…”

The role of ceramic and glass science research in meeting societal challenges: Report from an NSF‐sponsored workshop

“…Use of UHTC composites with SiC additions leads to a passivating liquid silicate coating that is susceptible to ablation by turbulent flows and experiences volatilization above ~1600°C . Efforts to form solid protective coatings using rare‐earth additives lead to formation of refractory oxide scales, for example, LaZr 2 O 7 , but these too are unlikely to survive above ~1800°C due to thermal expansion mismatch. Conversely, environmental barrier coatings for CMCs based on rare‐earth disilicates are sufficiently refractory and better matched to the substrate than their rare‐earth monosilicate counterparts but have inferior resistance to volatilization in water vapor .…”