【摘要】：金納米線作為一維納米材料的主要組成,由于其良好的化學(xué)穩(wěn)定性和高電導(dǎo)率,較高的表面活性以及優(yōu)良的生物親和性,使其在納米結(jié)構(gòu)器件和生物傳感器等方面具有廣闊的應(yīng)用前景。本文采用分子動力學(xué)方法,以一維金納米線為研究對象,主要研究了單晶金納米線和孿晶結(jié)構(gòu)納米線拉伸力學(xué)行為和微觀形變機(jī)理,現(xiàn)主要結(jié)論如下:(1)單晶金納米線在拉伸作用下彈性模量受直徑的影響不大,受晶向影響較大,不同晶向彈性模量的大小順序為E[111]E[110]E100],同時[100]晶向納米線屈服應(yīng)變和屈服應(yīng)力遠(yuǎn)遠(yuǎn)高于其他晶向納米線,是[110]晶向納米線屈服應(yīng)變和屈服應(yīng)力的2.65倍和2.54倍。納米線在低和中等拉伸應(yīng)變率下,應(yīng)變率對金納米線彈性模量、屈服強(qiáng)度和斷裂應(yīng)變等力學(xué)特性影響較小,但在高應(yīng)變率下這些力學(xué)特性都迅速提高。孿晶結(jié)構(gòu)金納米線的彈性模量受孿晶間距影響不大,屈服應(yīng)力受孿晶面間距影響較大。隨著孿晶面間距的不斷增大,納米線屈服應(yīng)力不斷減小,當(dāng)孿晶間距達(dá)到一定值后,屈服應(yīng)力則屈于平衡,不在改變。(2) [100]晶向單晶金納米線在不同拉伸應(yīng)變率下呈現(xiàn)不同力學(xué)行為和微觀形變機(jī)理。低應(yīng)變率(ε1.0×109s-1)下,應(yīng)力-應(yīng)變曲線在塑性變形階段呈現(xiàn)周期性“鋸齒狀”變化特征,直至最后斷裂,塑性變形主要由滑移引起,位錯在每個屈服階段產(chǎn)生、擴(kuò)展并逃逸;中等應(yīng)變率(1.0×109s-1ε≤1.0×1010s-1)下,應(yīng)力-應(yīng)變曲線塑性變形階段平緩降低,直至最后斷裂,塑性變形由滑移和孿生引起,位錯在屈服過程不能充分?jǐn)U展并逃逸,而是相互交截并駐留在納米線內(nèi)部;高應(yīng)變率(ε1.00×1010s-1)下,應(yīng)力-應(yīng)變曲線在初始彈性變形階段呈現(xiàn)一個明顯凸起,在塑性變形階段呈現(xiàn)“波浪狀”起伏變化,直至最后斷裂,塑性變形由非晶化引起,體系在屈服過程迅速轉(zhuǎn)化為無序非晶態(tài)原子,而且斷裂應(yīng)變高達(dá)435.89%,呈現(xiàn)超塑性。(3)三種不同晶向納米線在低應(yīng)變率下的塑性變形機(jī)理均是由滑移引起。[100]晶向納米線拉伸塑性變形過程中具有四個滑移系,但只有其中一個滑移面對塑性變形起主要作用;[110]晶向納米線拉伸塑性變形過程中,層錯間距隨應(yīng)變量增加不斷增大,而后滑移方向改變,納米線滑移加劇導(dǎo)致納米線的最終斷裂;[111]晶向金納米線塑性形變主要由堆垛層錯引起。(4)孿晶間距對金納米線屈服應(yīng)力影響較大,當(dāng)TBS2nm(twin boundary spacing)時,位錯和孿晶面共同作用使得納米線頸縮區(qū)域?qū)\晶間距增大,而后孿晶面阻礙滑移并改變滑移方向,對納米線起強(qiáng)化作用;當(dāng)TBS2nm時,納米線被軟化。(5)孿晶結(jié)構(gòu)納米線軟化包括兩種機(jī)制。當(dāng)2nmTBBS5nm時,孿晶界未能有效阻止位錯滑移,當(dāng)位錯在孿晶面處積累到一定程度時,位錯打破孿晶面的限制,位錯作為產(chǎn)生源在鄰近孿晶塊內(nèi)再次生成位錯,并同時伴有部分不全位錯的分解和消失,納米線未能過早形成應(yīng)力集中,斷裂應(yīng)變相對較大;當(dāng)TBS5nm時,位錯的滑移使得納米線孿晶面被破壞,形成剪切帶,無序原子在孿晶面處大量堆積,使得納米線斷裂應(yīng)變變小。
[Abstract]:As one of the main components of one-dimensional nanomaterials, gold nanowires have broad application prospects in nanostructured devices and biosensors due to their good chemical stability, high conductivity, high surface activity and excellent biocompatibility. In this paper, molecular dynamics method is used to study one-dimensional gold nanowires. The main conclusions are as follows: (1) The elastic modulus of single crystal gold nanowires is not affected by the diameter, but by the crystal orientation. The order of elastic modulus of different crystal orientations is E [111] E [110] E100, and [100] crystal. The yielding strain and stress of nanowires are 2.65 times and 2.54 times higher than those of other nanowires. The strain rate has little effect on the elastic modulus, yield strength and fracture strain of gold nanowires at low and moderate tensile strain rates, but at high strain rates. The elastic modulus of the twin-structured gold nanowires is not affected by the twin spacing, but the yield stress is greatly affected by the twin spacing. With the increasing of the twin spacing, the yield stress of the nanowires decreases continuously. When the twin spacing reaches a certain value, the yield stress yields to equilibrium and does not change. The stress-strain curves exhibit periodic "zigzag" characteristics at low strain rates (e 1.0 x 109 s-1), and finally fracture. The plastic deformation is mainly caused by slip, and dislocations are produced at each yield stage. At moderate strain rate (1.0 The stress-strain curves show a distinct bulge at the initial elastic deformation stage, a "wave-like" fluctuation at the plastic deformation stage, and finally fracture. The plastic deformation is caused by amorphous deformation. The system rapidly transforms into disordered amorphous atoms during the yield process, and the fracture strain is as high as 435.89%, showing superplasticity. The plastic deformation mechanism of homocrystalline nanowires at low strain rates is caused by slip. [100] There are four slip systems in the tensile plastic deformation of nanowires, but only one slip plane plays a major role in the plastic deformation. [110] In the tensile plastic deformation of nanowires, the stacking fault spacing increases with the increase of strain. (4) The twin spacing has a great influence on the yield stress of gold nanowires. When TBS2 nm (twin boundary spacing) is used, the dislocation and twin face act together to cause the twin in the necking region of the nanowires. When TBS2 nm, the nanowires are softened by two mechanisms. (5) The softening of twin nanowires includes two mechanisms. When 2 nm TBBS 5 nm, the twin boundary can not effectively prevent the dislocation slip. When the dislocation accumulates at the twin surface to a certain extent, the dislocation breaks the twin surface. Restriction, dislocation as the source of generation in the adjacent twin block again generated dislocations, and accompanied by partial decomposition and disappearance of incomplete dislocations, nanowires failed to form stress concentration prematurely, fracture strain is relatively large; when TBS5 nm, dislocation slip makes the twin surface of nanowires destroyed, forming a shear band, disordered atoms piled up in the twin surface. The fracture strain of nanowires decreases with product.
【學(xué)位授予單位】：長安大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TB383.1;O341

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本文編號：2202009