文章信息/Info

Title:

Thermal Properties of Rare�睧arth Disilicates:Material Genome and Coordinated Mechanism

作者:

羅頤秀;  王京陽

（中國科學(xué)院金屬研究所，遼寧，沈陽，110016）

Author(s):

Luo Yixiu;  Wang Jingyang

(Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China)

關(guān)鍵詞:

稀土雙硅酸鹽; 多功能熱障/環(huán)境障一體化涂層; 熱導(dǎo)率; 熱膨脹; 聲子非簡諧性

Keywords:

Rare-earth disilicate;  Multifunctional thermal and environmental barrier coating (TEBC);  Thermal conductivity;  Thermal expansion;  Phonon anharmonicity

分類號:

V25

DOI:

10.7502/j.issn.1674-3962.201906043

文獻(xiàn)標(biāo)志碼:

A

摘要:

在未來航空發(fā)動機先進(jìn)技術(shù)中，以硅基陶瓷復(fù)合材料高溫結(jié)構(gòu)部件為基體，發(fā)展先進(jìn)的多功能熱障/環(huán)境障一體化涂層（TEBC）以實現(xiàn)有效防護(hù)是一個重要的研究方向。TEBC材料的發(fā)展和優(yōu)化需滿足低熱導(dǎo)率（κL）和合適的熱膨脹系數(shù)（CTE），以提高涂層體系的隔熱性-RE2Si2O7（RE=Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu）多晶型材料的晶體結(jié)構(gòu)、鍵合非均勻性、聲子色散關(guān)系及非簡諧性特征，計算了材料本征晶格熱導(dǎo)率和熱膨脹系數(shù)，揭示了控制材料低熱導(dǎo)率和熱膨脹系數(shù)大小的“基因”。研究發(fā)現(xiàn)，RE2Si2O7多晶型材料具有明顯的低頻光學(xué)-聲學(xué)聲子耦合效應(yīng)，且低頻聲子較大的非簡諧性是材料低熱導(dǎo)率的根源。同時，晶格中Si—O—Si“橋”結(jié)構(gòu)的線性或彎折形態(tài)導(dǎo)致了低頻聲子非簡諧性的“正負(fù)”差異及體模量差異，是決定β-和γ-RE2Si2O7熱膨脹系數(shù)遠(yuǎn)低于δ�睷E2Si2O7的關(guān)鍵因素。研究結(jié)果闡明了低頻聲子非簡諧性的“大小”和“正負(fù)”特征對RE2Si2O7多晶型材料熱學(xué)性能協(xié)調(diào)機制的關(guān)鍵作用，為實現(xiàn)TEBC熱學(xué)性能的優(yōu)化設(shè)計提供了指導(dǎo)。

Abstract:

In the future of aeroengine technology, silicon based ceramic matrix composite (CMC) has important applications as structural materials for the hot�瞫ection components, which, in the combustion environment, needs to be protected by multifunctional thermal and environmental barrier coating (TEBC). The threshold requirements for the design of advanced TEBC system include low thermal conductivity, which protects the CMC substrates from thermal attack; and compatible thermal expansions with substrates, in order to minimize the thermal stress during thermal cycling. Therefore, a comprehensive understanding of the coordinated mechanism of thermal conduction and thermal expansion for candidate materials, from the perspective of “material genome”, is a key challenge. In this paper, the structural characteristics, heterogeneity of interatomic bonding, phonon dispersions and phonon anharmonicity for rare�瞖arth disilicates (β-, γ- and δ-RE2Si2O7, RE=Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) are studied based on first�瞤rinciples calculations combined with lattice dynamics. Intrinsic lattice thermal conductivity (κL) and coefficient of thermal expansion (CTE) are calculated, and the “gene” that controls the thermal properties of RE2Si2O7 polymorphs are discussed. It is found that low�瞗requency optical phonons are obviously coupled with acoustic phonons, and the high anharmonicity for low�瞗requency phonons is the origin of low κL for β��, γ- and δ-RE2Si2O7. Besides, the “gene” that controls the thermal expansions of RE2Si2O7 polymorphs are found to be the linear or bent configuration of Si—O—Si “bridge”, which determines the positive or negative anharmonicity for low�瞗requency phonons, as well as the bulk modulus, and finally lead to obviously lower CTE for β- and γ-RE2Si2O7 as compared with δ-RE2Si2O7. These results highlight that, the anharmonicity for low-frequency phonons, i.e. the “magnitude” and the “positive or negative” values, is the key for coordinated tuning of κL and CTE for RE2Si2O7. These understandings bring new inspirations for the design and optimization of TEBC systems.