(Ta,Hf)C基极高熔点固溶体陶瓷的烧结致密化、微结构剪裁与性能提升

Densification,microstructural tailoring and property improvement of(Ta,Hf)C-based ultra-high-temperature solid solution ceramics

立方相(Ta,Hf)C由TaC和HfC在全化学计量比范围内固溶得到,其中Ta_(0.8)Hf_(0.2)C体系的熔点近4000℃,被认为是目前热稳定性最佳的超高温陶瓷材料,有望用做高超声速飞行器的耐高温烧蚀结构部件。在近三年研究中,本人紧紧围绕(Ta,Hf)C基极高熔点陶瓷的固溶行为、烧结致密化、微结构裁剪设计、性能评价与提升的思路,系统梳理了(Ta,Hf)C基极高熔点陶瓷"组成-结构-性能"的关系。在常压烧结获得致密的单相Ta_(0.8)Hf_(0.2)C基础上,分别通过直接外加和原位引入SiC两种方式,实现Ta_(0.8)Hf_(0.2)C基复相陶瓷的微结构裁剪和性能优化提升;从过渡族金属碳化物的固溶机理出发,筛选低熔点Cr_(3)C_(2)瞬时液相助剂,以相对较低温度驱动实现(Ta,Hf)C固溶致密化。

Cubic(Ta,Hf)C solid solution could be obtained with TaC and HfC across the whole compositional ranges.Among this family,the melting point of Ta_(0.8)Hf_(0.2)C approaches 4000℃,is recognized as promising materials to serve as thermal protection system(TPS)in hypersonic aircraft.Our researches in recent three years were focused on the solid solution formation behavior,densification,microstructural tailoring,evaluation and properties improvement of(Ta,Hf)Cbased ultra-high-temperature ceramics,and revealed the relationship among’composition-microstructure-properties’systematically.Based on the results of pressureless densification of monolithic Ta_(0.8)Hf_(0.2)C ceramics,SiC was introduced in Ta0.8 Hf0.2 C-based ceramics in both in-situ and ex-situ ways for further optimization and property improvement.From the perspective of solid solution formation mechanism of transitional metallic carbides,transitional liquid assistant Cr_(3)C_(2) with a low melting point was selected.It can achieve densification at a relatively low temperature that accelerated by the solid solution of(Ta,Hf)C.Based on density functional theory(DFT)in conjunction with special quasi-random(SQS)structures,hardnes,modulus and transitional point of brittleness-ductility of Ta1-xHfxCy(0<x<1,0.8≤y≤1)was estimated.Based on this theory,the hardness increased from 34.351.86 GPa(Ta_(0.8)Hf_(0.2)C_(1.0))to 41.271.33 GPa(Ta_(0.8)Hf_(0.2)C_(0.8)).The carbon deficiency distributed unevenly in short atomic ranges,the dislocation movement was inhibited,thus resulting in the hardening effect.