Theoretical design and experimental verification of high-entropy carbide ablative resistant coating

Composition design of high-entropy carbides is a topic of great scientific interest for the hot-end parts in the aerospace field.A novel theoretical method through an inverse composition design route,i.e.initially ensuring the oxide scale with excellent anti-ablation stability,is proposed to improve the ablation resistance of the highentropy carbide coatings.In this work,the(Hf_(0.36)Zr_(0.24)Ti_(0.1)Sc_(0.1)Y_(0.1)La_(0.1))C1-δ(HEC)coatings were prepared by the inverse design concept and verified by the ablation resistance experiment.The linear ablation rate of the HEC coatings is1.45μm/s,only 4.78%of the pristine HfC coatings after the oxyacetylene ablation at 4.18 MW/m2.The HEC possesses higher toughness with a higher Pugh's ratio of 1.55 in comparison with HfC(1.30).The in-situ formed dense(Hf_(0.36)Zr_(0.24)Ti_(0.1)Sc_(0.1)Y_(0.1)La_(0.1))O2-δoxide scale during ablation benefits to improve the anti-ablation performance attributed to its high structural adaptability with a lattice constant change not exceeding 0.19%at 2000-2300℃.The current investigation demonstrates the effectiveness of the inverse theoretical design,providing a novel optimization approach for ablation protection of high-entropy carbide coatings.

Superior synergistic oxidation resistance of medium-entropy carbide ceramic powders rather than multi-phase carbide ceramic powders

To date,some questions about medium-entropy carbide ceramics and the corresponding multi-phase carbide ceramics with the same cations and proportions remain unclear.Regarding oxidation behavior,do both have synergistic oxidation abilities and what role does entropy stabilization play in medium-entropy carbides?In this work,the oxidation behaviors of HfC-ZrC-TiC multi-phase carbide(HZT-MPC)and(Hf_(1/3)Zr_(1/3)Ti_(1/3))C medium-entropy carbide(HZT-MEC)powders were investigated.After thermogravimetry(TG)oxidation,the TG curve of HZT-MPC had a bimodal distribution.The"preferential oxidation"of HfC/ZrC occurred within HZT-MPC,followed by the formation of multi-phase oxides(HfO_(2),ZrO_(2),and TiO_(2)).The uneven compositional distribution slowed their solid solution reactions to form Ti-doped(Hf,Zr)O_(2) and(Hf,Zr)TiO_(4).The TG curve of HZT-MEC had a single peak.A uniform compositional distribution at the atomic scale promoted the rapid interdiffusion of oxides,forming Ti-doped(Hf,Zr)O_(2) and(Hf,Zr)TiO_(4) without ZrO_(2),HfO_(2),and TiO_(2) after TG oxidation.Additionally,HZT-MEC had a higher onset oxidation temperature(To;470℃)than did HZT-MPC(430℃),and the TG single peak of HZT-MEC was between the TG bimodal peaks of HZT-MPC.Therefore,HZT-MEC showed superior oxidation resistance compared to HZT-MPC,which was attributed to the entropy stabilization effect of HZT-MEC suppressing the"preferential oxidation"of HfC/ZrC and the"delayed oxidation"of TiC,promoting the synergistic oxidation ability of multiple principal elements.

Influence of MoSi_(2) on oxidation protective ability of TaB_(2)-SiC coating in oxygen-containing environments within a broad temperature range

TaB_(2)-SiC coating modified by different content of MoSi_(2) was fabricated on graphite substrate with SiC inner coating by liquid phase sintering to elevate the anti-oxidation capability of the TaB_(2)-SiC coatings.As compared to the sample with the TaB_(2)-40wt% SiC coating,the coating sample modified with MoSi_(2) exhibited a weight gain trend at lower temperatures,the fastest weight loss rate went down by 76%,and the relative oxygen permeability value reduced from about 1% to near 0.More importantly,the large amount of SiO_(2) glass phase produced over the coating during oxidation was in contact with the modification of MoSi_(2),which was proved to be beneficial to the dispersion of Ta-oxides.A concomitantly formed continuous Ta-Si-O-B compound glass layer showed excellent capacity to prevent oxygen penetration.However,when the TaB_(2) content was sacrificed to increase the MoSi_(2) content,the relative oxygen permeability of the coating increased instead of decreased.Thus,on the basis of ample TaB_(2) content,increasing the MoSi_(2) content of the coating is conducive to reducing the relative oxygen permeability of the coatings in a broad temperature region.