Ta_(1–x)Hf_(x)C和Ta_(1–x)Zr_(x)C固溶体的结构稳定性和力学性质的第一性原理研究

First-principles study of structural stability and mechanical properties of Ta_(1-x)Hf_(x)C and Ta_(1-x)Zr_(x)C solid solutions

随着航空航天领域的飞速发展,极端的环境要求超高温陶瓷材料具有更好的力学性能和超高熔点.目前,单金属碳化物的超高温陶瓷材料承受的压力日渐增大.为了解决过渡金属单碳化物性能不足的问题,我们基于密度泛函理论系统地研究了Ta_(1–x)Hf_(x)C和Ta_(1–x)Zr_(x)C (0≤x≤1)固溶体的物理性质.通过调节Hf和Zr的浓度来研究它们的结构稳定性、晶格参数、力学性能、熔点和电子结构.我们的计算结果表明碳化物固溶体的稳定性随Hf/Zr含量的增加而增加,并且当Hf/Zr含量相同时, Ta_(1–x)Zr_(x)C比Ta_(1–x)Hf_(x)C的结构更稳定.我们还发现随着Hf/Zr含量的增加,固溶体的晶格常数和体积会膨胀. Ta_(1–x)Hf_(x)C和Ta_(1–x)Zr_(x)C固溶体的体积模量随着Hf/Zr含量的增加而减小,而固溶体的熔点、杨氏模量、剪切模量、维氏硬度和断裂韧性在掺杂含量x=0.2处会出现峰值.而且,添加Hf和Zr可以提高TaC的耐磨性.电子态密度结果显示随着Hf/Zr含量的增加,固溶体费米能级处的态密度值逐渐降低,这表明固溶体的结构稳定性逐渐增强.

With the rapid development of the aerospace field,the harsh environment requires ultra-high temperature ceramic materials with better mechanical properties and ultra-high melting points.At present,the ultra-high temperature ceramic materials of single metal carbides are required more and more urgently.In order to solve the problem about the insufficient performance of transition metal single carbides,we systematically study the various physical properties of Ta_(1-x)Hf_(x) and Ta_(1–x)Zr_(x)C solid solutions in an entire content range(0≤x≤1)based on density functional theory,including the formation energy,impurity formation energy,mixing energy,lattice parameters,elastic constants,elastic modulus,Vickers hardness,fracture toughness,wear resistance,melting point and electronic density of states.The results of formation energy show that with the increase of Hf and Zr doping concentration,the structural stability of Ta_(1-x)Hf_(x) and Ta_(1–x)Zr_(x)C solid solutions gradually increase.And the structure of Ta_(1–x)Zr_(x)C solid solution is more stable than that of Ta_(1-x)Hf_(x) solid solution when the doping content of Hf and Zr are the same.The results of mixing energy indicate that the formation of binary metal carbides from single metal carbides is an exothermic process.Furthermore,we also find that with the increase of Hf and Zr doping content,the lattice constant and volume of Ta_(1-x)Hf_(x) and Ta_(1–x)Zr_(x)C solid solutions can expand,which is mainly attributed to the atomic radii of Hf and Zr being larger than the radius of Ta.The results of mechanical properties show that the Ta_(1-x)Hf_(x) and Ta_(1–x)Zr_(x)C solid solution are brittle materials in the entire Hf/Zr content range and have mechanical stability.The bulk modulus of Ta_(1-x)Hf_(x) and Ta_(1–x)Zr_(x)C solid solutions decrease with the increase of Hf and Zr content,while the melting point,Young’s modulus,shear modulus,Vickers hardness and fracture toughness of Ta_(1-x)Hf_(x) and Ta_(1–x)Zr_(x)C solid solutions have peaks with the doping content x=0.2.Moreover,the addition of Hf/Zr can enhance the wear resistance of TaC.The results of the electronic density of states show that as the doping content increases,the density of states at the Fermi level of Ta_(1-x)Hf_(x) and Ta_(1–x)Zr_(x)C solid solutions decrease,which also indicates that the solid solution structure becomes more and more stable.