High temperature anti‐oxidation behavior of in situ and ex situ nanostructured C/SiC/ZrB₂‐SiC gradient coatings: Thermodynamical evolution, microstructural characterization, and residual stress analysis

Abstract

Nanostructured C/SiC/ZrB2–SiC oxidation protective gradient coating was prepared by a two‐step reactive melt infiltration method. In order to reduce production cost, ZrB2 phase was synthesized by the in situ reactive that included low‐cost ZrO2 and B2O3 powders as raw materials. High‐temperature oxidation behavior of coatings was evaluated by isothermal oxidation test at 1773 K in air for 10 hours. Thermodynamical behavior of the coatings at various temperatures during oxidation test and coating process was predicted by HSC Chemistry 6.0 software. Compressive residual stresses of 36.9 MPa and 41 MPa were calculated for in situ and ex situ coatings by Williamson‐Hall method. After 10 hours of isothermal oxidation at 1773K, in situ and ex situ coatings showed 12.84% and 15.69% of weight losses with oxidation rates of 1.87 × 10−2 g cm−3 h−1 and 0.91 × 10−2 g cm−3 h−1, respectively. These results indicated that the oxidation protection ability of the coating produced by the in situ method was very close to ex situ coating.

Effect of processing parameters on microstructure and ablation behavior of SiC/ZrB2 coating for graphite

“…The intensity value of ZrB 2 peak decreased compared with XRD pattern of as‐sprayed coating, which may have been caused by its decomposition and oxidation at high temperature. Since the surface temperature of sample rises, SiC and ZrB 2 phases oxidize and transform to SiO 2 and ZrO 2 according to following reactions: …”

“…The intensity value of ZrB 2 peak decreased compared with XRD pattern of as-sprayed coating, which may have been caused by its decomposition and oxidation at high temperature. Since the surface temperature of sample rises, SiC and ZrB 2 phases oxidize and transform to SiO 2 and ZrO 2 according to following reactions 8 : Surface FE-SEM image of SiC/ZrB 2 coating after 60-second ablation test shows the ablated surface was covered by a relatively dense oxide layer (Figure 20A). Also, pores and cracks are observed in the protective oxide layer.…”

“…7 Reactive melt infiltration (RMI) is an attractive technique for preparing functionally gradient coating (FGC) which has many advantages including short fabrication time and low production cost. 8 During the RMI process, melted Si penetrates into the carbon substrate through porosities using capillary force. The molten Si fills the pores and reacts with the carbon and finally forms the SiC coating.…”

In situ synthesis mechanism of ZrC‐ZrB2/Cu composites prepared by SHS‐casting method

“…One of the solutions is to develop particle‐reinforced Cu matrix composites. ZrC and ZrB 2 possess high hardness, high melting point, excellent thermal stability, and superior electrical conductivity . These properties make them good candidates for acting as the reinforced particles in metal matrix composites.…”

Preparation and properties of dense ZrB2 composite reinforced by elongated SiC and Al3BC3 grains

“…The flexural strength and fracture toughness of composite were 458 MPa and 6.9 MPa m 1/2 , respectively. Addition of proper amounts of SiC particles can both improve the sinterability and enhance the oxidation resistance of ZrB 2 . Hwang et al reported that the addition of small size SiC particles imparted better oxidation resistance and improved the sinterability of ZrB 2 ceramics.…”