中/高熵碳化物陶瓷及其基体/涂层改性碳/碳复合材料研究现状与展望OA

Improving the ablation resistance of C/C composites under ultra-high temperature environments is a prerequisite for their applications as thermal protection components in high-speed aircraft.When conventional silicide-modified C/C composites serve in an aerobic environment at>1700℃,the active oxidation of silicide is intensified,causing the formation and escape of gaseous SiO from unoxidized silicide.Concurrently,the decomposition pressure and saturation vapor pressure of SiO2 increase with temperature,accelerating their decomposition and volatilization from the oxide scale.These processes lead to a rapid consumption of silicide,preventing the formation of a dense and continuous oxygen barrier,and resulting in a gradual loss of thermal protection capability. Among ultrahigh-temperature ceramics(UHTCs),HfC and ZrC are preferred modified components for their high melting points(>3000℃)and good chemical stability,as well as high melting points of their oxidation products(i.e.,HfO2:2810℃and ZrO2:2677℃).Nevertheless,their protective oxide scales exhibit a loose structure after long-term oxidation/ablation due to the lack of a densification pathway capable of healing oxidation/ablation-induced defects(pores and cracks).To mitigate this issue,the liquid-phase sintering effect of low-melting oxide phases(i.e.,TiO2:～1840℃,Ta2O5:～1800℃,and Nb2O5:～1512℃)promotes their solid solution process with high-melting HfO2/ZrO2 and produces dense Hf/Zr-X-O compound(X=Ti,Ta and Nb),healing ablative defects during ablation.As a result,the ablation resistance of the coatings is significantly improved.Consequently,some multi-phase carbides are widely applied for C/C composites,including HfC-ZrC-TiC,HfC-TaC,ZrC-TaC,HfC-ZrC-TaC,HfC-NbC,and ZrC-NbC.However,they are typically prepared by mechanical blending through ball milling before spraying,showing an inhomogeneous elemental distribution in a microscale.It induces locally aggregated low-melting phases,having an insufficient mechanical denudation resistance,thus impeding further improvement of ablation resistance.Conventional silicide-and multi-phase carbide ceramic-modified C/C composites face some challenges,including insufficient high-temperature stability,limited long-term ablation resistance,and narrow protective temperature ranges. In comparison to these ceramics,medium-/high-entropy carbide(M/HEC)ceramics unique"four effects"and tunability of composition and microstructure endow excellent comprehensive properties.This review represented the preparation methods of M/HEC ceramics,which are composed of solid-phase reaction(i.e.,Carbothermal reduction method,Direct synthetic method,and Molten salt synthesis)and liquid-phase reaction(i.e.,Polymer-derived ceramics and Sol-gel)methods,and discussed their effects on the structure and properties of M/HEC ceramics.The preparation methods of M/HEC substrate-modified C/C(i.e.,Precursor infiltration and pyrolysis,Reaction melt infiltration,and Molten salt infiltration methods)and M/HEC coating-modified C/C(i.e.,Supersonic atmospheric plasma spraying method)were described,and the preparation cycles of different processes and their effects on the structure and properties of C/C composites were compared.Finally,the influence of different M/HEC on the ablation resistance was summarized,and some promising prospects for the future development of M/HEC substrate/coating-modified C/C composites were proposed. Summary and Prospects The focus and difficulties of M/HEC substrate/coating-modified C/C in future work mainly include the following aspects: 1)Efficient and rapid design of anti-oxidation/ablation ceramic components.With the rapid advancement of"Artificial Intelligence+Materials"and the proposal of the"Materials Genome Initiative",an increasing number of computational methods,integrated computing platforms,and databases are developed.This progress enables the use of AI-based high-throughput theoretical calculations(i.e.,thermodynamics,finite element,first principles calculations,and molecular dynamics)and experimental verification to establish the M/HEC performance databases and optimize the M/HEC components with the superior comprehensive performance. 2)Construction of substrate/coating and their microstructure control.The structural designs(i.e.,M/HEC zoned gradient modification,M/HEC nano-reinforcements,and M/HEC gradient coatings),stress distribution simulations(i.e.,at interface and within gradient sublayer),and multi-scale heterogeneous interface control can improve the interface bonding and stress distribution state between M/HEC and C/C substrates,leading to a synergistic enhancement in bonding strength,crack suppression,and ablation resistance. 3)Clarifying the oxidation/ablation protection mechanisms under extreme coupling environments involving thermal,mechanical,and medium factors.A comprehensive service environment evaluation system,such as the plasma or arc wind tunnel,should be used to simulate multi-field conditions,including thermal exposure,mechanical loads(i.e.,high-speed airflow and particle erosion),and corrosive medium(i.e.,oxygen and water vapor).An in-situ visualization system is used to monitor the long-term service stability of M/HEC substrate/coating modified C/C composites under extreme service environments,which involve ultra-high temperature oxidation/ablation,high-and low-temperature thermal impact,and strong airflow denudation.In addition,multi-scale theoretical calculations and advanced in-situ characterization techniques are conducted to elucidate their oxidation/ablation protection mechanisms. 4)Fabrication of large-sized components and acceleration of their engineering applications.The existing preparation of M/HEC substrate/coating modified C/C composites remains largely confined to laboratory-scale research.Producing large-sized components is a complex process,which requires a large-scale processing equipment and precisely controls over multiple steps to achieve uniform distribution of M/HEC internally and externally throughout the entire structure.It is urgent for overcoming the application bottlenecks of process stability,composition uniformity,stress control and structural/functional integration design of large-sized components to develop simple and efficient preparation techniques.