本文關(guān)鍵詞：有限溫度和壓強(qiáng)對(duì)BCC金屬?gòu)椥孕再|(zhì)影響的第一性原理研究　出處：《太原理工大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： 密度泛函理論 彈性常數(shù) 有限溫度 高壓

【摘要】：固體的彈性性質(zhì)是固體本身的物理屬性,而彈性的大小則是由彈性常數(shù)來表示的。近年來,BCC(Body-Centered-Cubic)金屬材料Ta、Fe、W、Mo等被應(yīng)用于各行各業(yè)中,并在不同溫度壓強(qiáng)下工作,因此研究材料在一定的溫度和壓強(qiáng)下的彈性性質(zhì)具有重要的理論意義和實(shí)際價(jià)值。本文應(yīng)用基于密度泛函理論的第一性原理方法,利用VASP和Phonopy軟件包計(jì)算了BCC金屬材料的彈性常數(shù)隨溫度和壓強(qiáng)的變化關(guān)系,并預(yù)測(cè)了BCC材料的熱力學(xué)性質(zhì)及聲速隨溫度的的變化關(guān)系。主要研究?jī)?nèi)容如下:(1)首先采用兩種不同的交換關(guān)聯(lián)泛函(GGA-PAW、LDA)對(duì)BCC金屬材料的晶格常數(shù)進(jìn)行優(yōu)化。計(jì)算結(jié)果表明,根據(jù)不同的交換關(guān)聯(lián)泛函優(yōu)化得出的晶格常數(shù)與實(shí)驗(yàn)值對(duì)比有一定的不同。如果理論計(jì)算得到的晶格常數(shù)與實(shí)驗(yàn)測(cè)得的晶格常數(shù)越接近,計(jì)算得出的彈性常數(shù)就會(huì)與實(shí)驗(yàn)測(cè)得的彈性常數(shù)越接近。計(jì)算數(shù)據(jù)表明,使用GGA-PAW得到的晶格常數(shù)和彈性常數(shù)與實(shí)驗(yàn)值符合較好,因此在后續(xù)的計(jì)算工作中采用了GGA-PAW交換關(guān)聯(lián)泛函。(2)在密度泛函理論和密度泛函微擾理論基礎(chǔ)上,運(yùn)用第一性原理方法計(jì)算了BCC中Ta、Fe、W、Mo四種金屬材料在0-1500 K下的彈性常數(shù)。結(jié)果顯示,四種材料的三個(gè)彈性常數(shù)C11、C12和C44都隨溫度的升高而降低。并且,在溫度變化過程中,彈性常數(shù)滿足C11＞0,C44＞0,C11-C12＞0條件,這說明材料在該溫度范圍內(nèi)具有穩(wěn)定相。根據(jù)Voigt-Reuss-Hill方程中體積模量B和剪切模量G與彈性常數(shù)的關(guān)系計(jì)算出了0-1500 K間B/G的比值,并通過B/G的比值判斷出Ta、Fe、W、Mo四種材料材料在0-1500 K之間表現(xiàn)為韌性。(3)根據(jù)計(jì)算得到的彈性常數(shù)預(yù)測(cè)了聲速隨溫度的變化趨勢(shì),即聲速隨溫度的升高而降低,其原因是溫度升高加快原子振動(dòng)阻礙了聲速的傳播。預(yù)測(cè)了Ta、Fe、W、Mo的熱膨脹系數(shù)與溫度的關(guān)系,得到了BCC晶體體積隨溫度升高膨脹速率越大,彈性常數(shù)的降低速率也越大的結(jié)論。同時(shí)預(yù)測(cè)了Ta、Fe、W、Mo的熱力學(xué)性質(zhì)隨溫度的變化關(guān)系,在低溫區(qū)域(0-300K),等容熱容、等壓熱容隨溫度的增加變化較為明顯。在(300-1500 K)區(qū)域,等容熱容、等壓熱容隨溫度的升高而趨于平緩,尤其在1000-1500 K時(shí),CV遵循能量均分定理。(4)基于密度泛函理論計(jì)算了零溫下的彈性常數(shù)與壓強(qiáng)的關(guān)系,結(jié)果顯示彈性常數(shù)隨壓強(qiáng)的增加而增加,同時(shí)計(jì)算了Ta、Fe、W、Mo在高壓下和一定的溫度范圍內(nèi)與彈性常數(shù)的關(guān)系,結(jié)果發(fā)現(xiàn),壓強(qiáng)越高彈性常數(shù)隨溫度升高的降低速率越小,證明高壓下溫度對(duì)彈性常數(shù)的影響較小。
[Abstract]:The elastic property of a solid is the physical property of the solid itself, and the size of the elasticity is expressed by an elastic constant. The BCC-Body-Centered-Cubic-based metal material Tahfeite WNMo has been used in various industries and worked under different temperature and pressure. Therefore, it is of great theoretical significance and practical value to study the elastic properties of materials at a certain temperature and pressure. The first principle method based on density functional theory is applied in this paper. The relationship between temperature and pressure of BCC metal material was calculated by VASP and Phonopy software package. The thermodynamic properties of BCC materials and the relationship between the velocity of sound and temperature are predicted. The main research contents are as follows: 1) first, two different exchange correlation Functionals (GGA-PAW) are used. The lattice constants of BCC metal materials were optimized by LDA. the calculation results show that the lattice constants of BCC metal materials are optimized. The lattice constant obtained by different exchange correlation functional optimization is different from the experimental value, if the lattice constant obtained by theoretical calculation is closer to the lattice constant measured by experiment. The calculated elastic constants are closer to those measured experimentally. The calculated data show that the lattice constants and elastic constants obtained by GGA-PAW are in good agreement with the experimental values. Therefore, GGA-PAW exchange correlation functional is adopted in the subsequent calculation. Based on density functional theory and density functional perturbation theory, Ta in BCC is calculated by first-principle method. The results show that the three elastic constants C _ (11) C _ (12) and C _ (44) decrease with the increase of temperature. In the process of temperature change, the elastic constant satisfies the conditions of C11 > 0C44 > 0C11-C12 > 0. This indicates that the material has stable phase in the range of temperature. Based on the relationship between the volume modulus B and shear modulus G and the elastic constant in the Voigt-Reuss-Hill equation, 0-1500 is calculated. The ratio of B / G to K. According to the ratio of B / G, Tahe Few is determined. According to the calculated elastic constants, the variation trend of sound velocity with temperature is predicted, that is, the velocity of sound decreases with the increase of temperature. The reason is that the increase of temperature hinders the propagation of sound velocity, and the relationship between thermal expansion coefficient and temperature is predicted. It is concluded that the larger the expansion rate of BCC crystal with the increase of temperature, the greater the decreasing rate of elastic constant, and the relation of thermodynamic properties with temperature is predicted. In the low temperature region, the isovolumetric heat capacity and isobaric heat capacity change obviously with the increase of temperature, and in the region of 300-1500K), the isovolumic heat capacity is obvious. The isobaric heat capacity tends to be gentle with the increase of temperature, especially at 1000-1500K. The relationship between elastic constant and pressure at zero temperature is calculated based on density functional theory. The results show that the elastic constant increases with the increase of pressure. The relationship between the elastic constant and the elastic constant is obtained at high pressure and within a certain temperature range. The results show that the higher the pressure is, the smaller the decreasing rate of the elastic constant is with the increase of temperature, which proves that the influence of temperature on the elastic constant is small at high pressure.
【學(xué)位授予單位】：太原理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：O469

【參考文獻(xiàn)】

相關(guān)期刊論文 前3條

1 張修路;羅栶;郭志成;怓瑞娟;劉中利;劉成安;蔡靈倉(cāng);;高壓下鎢彈性和熱力學(xué)性質(zhì)的第一性原理研究[J];原子與分子物理學(xué)報(bào);2015年03期

2 何存富;魏曉玲;宋國(guó)榮;畢曉東;吳斌;;小尺寸材料彈性常數(shù)超聲測(cè)量系統(tǒng)的研制及其應(yīng)用[J];中國(guó)機(jī)械工程;2006年16期

3 陳麗;FCC晶體彈性常數(shù)的分子動(dòng)力學(xué)模擬及其適用性[J];機(jī)械工程學(xué)報(bào);2005年09期

，

本文編號(hào)：1408142