本文選題：難混溶合金熔體 + 結(jié)構(gòu)不均勻性　； 參考：《山東大學(xué)》2017年碩士論文

【摘要】：本文采用分子動(dòng)力學(xué)模擬的方法,運(yùn)用修正的鑲嵌原子勢(shì)(MEAM),研究了易混溶的Cu-Zr和難混溶的Cu-Ag合金熔體的結(jié)構(gòu)及動(dòng)力學(xué)特征的差異并探討了兩種體系非晶的動(dòng)態(tài)力學(xué)性能。以上研究對(duì)于認(rèn)識(shí)金屬玻璃的本質(zhì)、玻璃轉(zhuǎn)變機(jī)制以及變形機(jī)制具有重要意義。對(duì)于Cu-Zr合金熔體,當(dāng)溫度低于1200K,MSD曲線上出現(xiàn)一個(gè)平臺(tái),并且隨著溫度的降低,平臺(tái)逐漸明顯。而對(duì)于Cu-Ag體系,平臺(tái)出現(xiàn)的時(shí)間較短,甚至可以忽略。對(duì)擴(kuò)散系數(shù)研究發(fā)現(xiàn)Cu-Zr體系的擴(kuò)散系數(shù)遠(yuǎn)遠(yuǎn)低于Cu-Ag體系。非相干散射因子Fs(q,t)的計(jì)算結(jié)果與MSD曲線呈現(xiàn)相同的趨勢(shì),說(shuō)明Cu-Zr體系比Cu-Ag體系具有更明顯的β弛豫現(xiàn)象。根據(jù)MCT理論對(duì)擴(kuò)散系數(shù)和弛豫時(shí)間進(jìn)行了擬合,發(fā)現(xiàn)由兩者擬合得到的臨界溫度Tc值差別不大,說(shuō)明擴(kuò)散系數(shù)與弛豫時(shí)間之間的相關(guān)性。對(duì)兩個(gè)體系的結(jié)構(gòu)分析,發(fā)現(xiàn)Cu-Zr體系中0 0 12 0、0 2 8 1和0 2 8 0等正二十面體和五次對(duì)稱性強(qiáng)的類二十面體的數(shù)量遠(yuǎn)遠(yuǎn)高于Cu-Ag體系,并且這些團(tuán)簇?cái)?shù)量隨著溫度的降低逐漸增加;Cu-Ag體系中的多面體主要是0 3 6 3、0 3 6 4和0 2 8 2等一些非二十面體團(tuán)簇和類晶型團(tuán)簇。二十面體和類二十面體團(tuán)簇易形成骨架阻礙原子運(yùn)動(dòng),原子運(yùn)動(dòng)減慢,原子擴(kuò)散系數(shù)降低,弛豫時(shí)間增加,從而導(dǎo)致Cu-Zr體系的擴(kuò)散能力遠(yuǎn)遠(yuǎn)低于Cu-Ag體系,非晶形成能力遠(yuǎn)遠(yuǎn)高于Cu-Ag體系。兩種體系在過(guò)冷條件下弛豫時(shí)間與五次對(duì)稱符合關(guān)系τα=τ0expM/(1-W)σ擴(kuò)散系數(shù)與五次對(duì)稱符合關(guān)系D=A*(T*W)B,揭示了微觀結(jié)構(gòu)與動(dòng)力學(xué)的內(nèi)在聯(lián)系。對(duì)兩者非晶動(dòng)態(tài)力學(xué)性能的研究,發(fā)現(xiàn)Cu-Zr和Cu-Ag兩種體系的β弛豫都是以過(guò)剩尾的形式在損耗模量曲線體現(xiàn)出來(lái)的,但是Cu-Ag體系在αα弛豫峰左側(cè)部分高于Cu-Zr體系,這表明Cu-Ag體系的β弛豫比Cu-Zr體系更容易激活,這是由于Cu-Zr非晶的二十面體團(tuán)簇的數(shù)量遠(yuǎn)遠(yuǎn)高于Cu-Ag非晶。研究了機(jī)械應(yīng)變對(duì)兩種體系動(dòng)態(tài)力學(xué)性能的影響,發(fā)現(xiàn)升高溫度和增大振幅對(duì)兩種體系來(lái)說(shuō)對(duì)應(yīng)的弛豫過(guò)程是很相似的,說(shuō)明機(jī)械應(yīng)變和溫度對(duì)體系的弛豫動(dòng)力學(xué)起到相似的作用,機(jī)械應(yīng)變對(duì)弛豫動(dòng)力學(xué)的影響具有普遍性。同時(shí)研究了α弛豫與結(jié)構(gòu)不均勻性的相互關(guān)系,發(fā)現(xiàn)對(duì)于Cu-Zr體系,在α弛豫峰峰值溫度,原子最可能的位移距離與平均最近鄰原子間距的比值(up/rp)接近一個(gè)常數(shù),約為23%,而對(duì)于Cu-Ag體系,up/rp的數(shù)值約為21%。說(shuō)明α弛豫通常發(fā)生在原子移動(dòng)距離是平均原子間距的約為21%-23%處,這與文獻(xiàn)結(jié)果一致。進(jìn)一步研究了兩者內(nèi)耗關(guān)系,發(fā)現(xiàn)內(nèi)耗與快原子近似地滿足一次線性關(guān)系,由于Cu-Zr體系中正二十面體數(shù)量遠(yuǎn)遠(yuǎn)多于Cu-Ag體系,抑制了原子運(yùn)動(dòng),使快原子數(shù)量減少,因此導(dǎo)致了 Cu-Zr體系的內(nèi)耗小于Cu-Ag體系。
[Abstract]:In this paper, the structure and dynamic characteristics of the melt of easily miscible Cu-Zr and inmiscible Cu-Ag alloy are studied by means of molecular dynamics simulation and modified inlay atomic potential. The dynamic mechanical properties of the two systems are also discussed. The above studies are of great significance in understanding the nature, glass transition mechanism and deformation mechanism of metallic glass. For the melt of Cu-Zr alloy, a platform appears when the temperature is below 1200kg, and with the decrease of temperature, the platform becomes more and more obvious. For the Cu-Ag system, the platform appears in a short time, even can be ignored. The diffusion coefficient of Cu-Zr system is much lower than that of Cu-Ag system. The calculated results of the incoherent scattering factor (FslQ) show the same trend as the MSD curve, which indicates that the 尾 -relaxation of Cu-Zr system is more obvious than that of Cu-Ag system. According to the MCT theory, the diffusion coefficient and relaxation time are fitted. It is found that there is little difference between the critical temperature T _ c obtained from the two fitting results, which indicates the correlation between diffusion coefficient and relaxation time. It is found that the number of normal icosahedron and icosahedron with strong quintic symmetry in Cu-Zr system is much higher than that in Cu-Ag system, and the number of icosahedron and icosahedron in Cu-Ag system is much higher than that in Cu-Ag system. Moreover, the number of these clusters increases with the decrease of temperature, and the polyhedron in Cu-Ag system is mainly composed of some non-icosahedron clusters and crystal like clusters such as 0.363N 0.364 and 0.282. Icosahedron and icosahedron clusters are easy to form skeletons that hinder the movement of atoms, slow down the atomic movement, decrease the atomic diffusion coefficient and increase the relaxation time, resulting in the diffusion ability of the Cu-Zr system being much lower than that of the Cu-Ag system. The ability of amorphous formation is much higher than that of Cu-Ag system. The relaxation time and the quintic symmetry coincidence relation 蟿 偽 = 蟿 0expM / l W) 蟽 diffusion coefficient of the two systems under undercooling conditions and the five-order symmetry coincidence relation D _ (a) A ~ (1) T _ (T) W _ (B) reveal the intrinsic relationship between microstructure and dynamics. It is found that the 尾 -relaxation of both Cu-Zr and Cu-Ag systems is reflected in the loss modulus curve in the form of excess tail, but the Cu-Ag system is higher than the Cu-Zr system on the left side of 偽 relaxation peak. This indicates that 尾 -relaxation in Cu-Ag system is easier to activate than that in Cu-Zr system, which is due to the fact that the number of Cu-Zr amorphous icosahedron clusters is much higher than that of Cu-Ag amorphous. The effect of mechanical strain on the dynamic mechanical properties of the two systems is studied. It is found that the relaxation process corresponding to the two systems is very similar to the increase of temperature and amplitude. The results show that mechanical strain and temperature play a similar role in the relaxation kinetics of the system, and the influence of mechanical strain on the relaxation kinetics is universal. At the same time, the relationship between 偽 relaxation and structural inhomogeneity is studied. It is found that for Cu-Zr system, the ratio of the most probable displacement distance of atoms to the average nearest neighbor distance is close to a constant at the peak temperature of 偽 relaxation peak. About 23, and for the Cu-Ag system uprp is about 21. It is shown that 偽 -relaxation usually occurs at a distance of about 21% to 23% of the average atomic distance, which is consistent with the results in the literature. It is found that the linear relationship between internal friction and fast atoms is approximately linear. Because the number of normal icosahedrons in Cu-Zr system is much larger than that in Cu-Ag system, the atom motion is restrained and the number of fast atoms is reduced. Therefore, the internal friction of Cu-Zr system is smaller than that of Cu-Ag system.
【學(xué)位授予單位】：山東大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TG139.8

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本文編號(hào)：1821941