金屬多層膜微觀結構與力學性能的尺度效應
發(fā)布時間：2018-12-15 14:55
【摘要】：納米金屬多層膜由于具有周期性的調(diào)制結構,晶粒生長受到組元層間尺度的約束和異質(zhì)界面的影響,與傳統(tǒng)的塊體材料或合金相比,多層膜材料往往表現(xiàn)出奇特的力學性能。在研究中發(fā)現(xiàn),多層膜的力學性能與結構的特征尺度密切相關。隨著納米多層膜尺度的改變,其層內(nèi)結構以及層間界面結構發(fā)生相應變化,從而導致性能表現(xiàn)出強烈的尺度效應。因此,研究多層膜的尺度效應規(guī)律,對實現(xiàn)多層膜結構與性能的有效調(diào)控及最優(yōu)化設計有著重要的科學意義。本文利用直流磁控濺射法在Si襯底上制備了一系列不同調(diào)制周期的Cu/Ta、Ag/Cu和Ag/Nb納米多層膜,借助X射線衍射儀、掃描電子顯微鏡、透射電子顯微鏡等表征了多層膜的微觀結構；利用納米壓痕儀對納米多層膜的硬度、彈性模量和室溫蠕變行為等力學性能進行了分析測試。系統(tǒng)地研究了其尺度變化對微觀結構及力學性能的影響及其相應機制的改變。結論如下：一、Cu/Ta納米多層膜的硬度隨單層厚度(h)的變化而表現(xiàn)出明顯的尺度效應。當單層厚度介于10-100 nm時,硬度值隨單層厚度的減小而增加,并且在h=10 nm時硬度達到最大值6.13 GPa,數(shù)值變化符合Hall-Petch關系,說明強化由位錯塞積造成。但是在單層厚度由10 nm降至5 nm時,硬度值出現(xiàn)了明顯的降低,原因是由于Ta層中β-Ta相的消失而造成,這種由于相結構改變而導致的軟化現(xiàn)象在金屬納米多層膜中尚屬首次報道。隨著單層厚度繼續(xù)減小至5 nm以下時,硬度值保持穩(wěn)定,此時以界面阻擋強化為主,位錯穿越界面受阻而產(chǎn)生強化。Cu/Ta納米多層膜的彈性模量隨單層厚度減小而增大,并在單層厚度為10 nm時達到最大值131 GPa。達到最大值后隨尺度的減小,彈性模量則呈逐漸降低趨勢。二、在Ag/Cu納米多層膜中獲得了高強度和高電導率結合的優(yōu)異綜合性能。Ag/Cu納米多層膜的硬度隨尺度的變化表現(xiàn)出非單調(diào)性。硬度值在5-20nm區(qū)間內(nèi)隨單層厚度的減小而增加,并在5 nm時硬度達到最大值3.86 GPa。當h=3 nm時,由于生成了超晶格使得硬度出現(xiàn)軟化。多層膜中孿晶界與堆垛層錯對位錯的阻擋作用與界面強化作用相結合,使得多層膜強化。另外,由于界面彎曲和晶粒取向差增大,使得多層膜在h=50 nm時出現(xiàn)反常強化,高于h=20 nm時的硬度。Ag/Cu納米多層膜的彈性模量隨單層厚度的減小而減小,沒有出現(xiàn)彈性模量的增強效應。彈性模量的降低與界面處錯配造成的晶面間距膨脹有關。Ag/Cu納米多層膜的電阻率在h≥10 nm時具有低電阻率并且穩(wěn)定,這是由于Ag/Cu納米多層膜中織構的生成,大角晶界數(shù)目減少,減少了晶界對電子的散射,阻止了電阻率的升高。從而解決了高強度與高導電性這一相互矛盾的問題,在Ag/Cu納米多層膜中獲得了高強度和高電導率相結合的優(yōu)異綜合性能。但是在h10 nm時由于界面與晶界對電子的散射使得電阻率隨尺度減小而急劇增加。另外,針對綜合性能的評價問題,首次提出并建立了一個簡單的模型,對Ag/Cu納米多層膜強度與電導率相結合的力/電綜合性能進行了評價,經(jīng)實驗數(shù)據(jù)證實該評價體系合理。該模型的建立為解決此類問題提供了一個很好的思路。三、Ag/Nb納米多層膜的微觀結構與力學性能對尺度變化表現(xiàn)出超常敏感性。隨著尺度的減小,晶體結構類型按照多晶→織構→超晶格的趨勢而變化,并且在單層厚度為20和50 nm時界面處出現(xiàn)了非晶層。Ag/Nb納米多層膜的硬度隨單層厚度的減小而增加,并且硬度值的增加趨勢逐漸加大。h=50 nm時,硬度值為3.53 GPa,而當減小至h=1 nm時,硬度值增加到6.79 GPa,與h=50 nm相比強化率高達92.4%。共格應力強化是Ag/Nb納米多層膜在小尺度下強化的主要因素。Ag/Nb納米多層膜的彈性模量隨單層厚度的變化呈現(xiàn)增加趨勢。在h=50nm時,由于界面處非晶層的存在,彈性模量有反常的降低行為。而單層厚度在20～1 nm之間時,由于晶格壓縮效應導致了彈性模量增強。四、Cu/Ta、Ag/Cu和Ag/Nb納米多層膜的室溫蠕變行為均表現(xiàn)出明顯的尺度效應。蠕變應力指數(shù)隨單層厚度的減小而增大。蠕變機制以位錯攀移為主,隨著尺度的減小,位錯攀移發(fā)生的位置由同質(zhì)晶界逐漸過渡到異質(zhì)界面,并且界面處的共格關系有利于蠕變應力指數(shù)的提高。另外,在Ag/Nb多層膜中非晶層的出現(xiàn)可抑制蠕變變形的進一步擴展。
[Abstract]:Due to the periodic modulation structure, the grain growth is influenced by the constraint of the inter-layer dimension and the heterogeneous interface, and the multi-layer film material tends to exhibit peculiar mechanical properties as compared with the conventional bulk material or alloy. It is found in the study that the mechanical properties of the multi-layer film are closely related to the characteristics of the structure. With the change of the scale of the nano-multilayer film, the structure of the layer and the interface structure of the interlayers have changed accordingly, resulting in a strong scale effect. Therefore, it is of great scientific significance to study the scale effect of multi-layer film and to realize the effective regulation and optimization of multi-layer film structure and performance. In this paper, a series of Cu/ Ta, Ag/ Cu and Ag/ Nb nano-multilayer films with different modulation periods were prepared on Si substrate by direct current magnetron sputtering. The microstructure of multilayer films was characterized by X-ray diffractometer, scanning electron microscope, transmission electron microscope and so on. The mechanical properties of the nano-multilayer film, such as the hardness, the elastic modulus and the room temperature creep behavior, were analyzed by means of the nanoindentation. The effect of scale change on microstructure and mechanical properties and its corresponding mechanism are studied systematically. The results are as follows: 1. The hardness of the Cu/ Ta nano-multilayer film shows a significant scale effect with the change of the thickness (h) of the single layer. When the thickness of the single layer is in the range of 10-100 nm, the hardness value is increased with the decrease of the thickness of the single layer, and the hardness reaches the maximum of 6.13 GPa at the time of h = 10 nm, and the numerical change is in line with the Hall-Petch relationship, and the reinforcement is caused by the dislocation plug product. However, when the thickness of the single layer is reduced from 10 nm to 5 nm, the hardness value is significantly reduced because of the disappearance of the Al-Ta phase in the Ta layer, which is first reported in the metal nano multilayer film due to the change of the phase structure. As the thickness of the single layer continues to decrease below 5 nm, the hardness value is stable. At this time, the interface barrier strengthening is the main, and the dislocation crossing interface is blocked to produce the reinforcement. The elastic modulus of the Cu/ Ta nano-multilayer film increases with the thickness of the single layer, and reaches a maximum value of 131 GPa when the thickness of the single layer is 10 nm. When the maximum value is reached, the elastic modulus decreases with the decrease of the scale. and 2, a high-strength and high-conductivity combined excellent comprehensive property is obtained in the Ag/ Cu nano multilayer film. The hardness of Ag/ Cu nano-multilayer film shows non-monotonicity with the change of the scale. The hardness value increases with the decrease of the single layer thickness in the interval of 5-20nm, and the hardness reaches the maximum value of 3.86GPa at the time of 5 nm. When h = 3 nm, the hardness is softened due to the generation of the superlattice. In the multi-layer film, the blocking effect of the grain boundary and the stacking layer on the dislocation is combined with the strengthening of the interface, so that the multi-layer film is strengthened. In addition, due to the increase of the interfacial bending and the crystal grain orientation, the multilayer film has an abnormal strengthening at h = 50 nm, and is higher than the hardness at h = 20 nm. The elastic modulus of the Ag/ Cu nano-multilayer film decreases with the decrease of the thickness of the single layer, and the reinforcing effect of the elastic modulus is not present. The reduction of the elastic modulus is related to the expansion of the crystal plane pitch due to the mismatch at the interface. the resistivity of the Ag/ Cu nano multilayer film has low resistivity and is stable at the time of h to 10 nm, which is due to the formation of the woven structure in the Ag/ Cu nano multilayer film, the number of the large-angle grain boundaries is reduced, the scattering of the electrons in the grain boundary is reduced, and the increase of the resistivity is prevented. so as to solve the problem that the high-strength and high-conductivity are mutually contradictory, and the excellent comprehensive property of the combination of high-strength and high-conductivity is obtained in the Ag/ Cu nano multilayer film. However, at h10 nm, the scattering of the electrons by the interface and the grain boundary causes the resistivity to increase sharply with the decrease in the scale. In addition, for the evaluation of the comprehensive performance, a simple model is proposed for the first time, and the combination of the strength and the electric conductivity of the Ag/ Cu nano-multilayer film is evaluated. The experimental data confirm that the evaluation system is reasonable. The establishment of the model provides a good idea for solving such problems. 3. The microstructure and mechanical properties of the Ag/ Nb nano-multilayer film show a supernormal sensitivity to the dimensional change. As the dimensions decrease, the crystal structure type changes according to the trend of the polycrystalline silicon-woven structure and the superlattice, and an amorphous layer is present at the interface at the time of the single-layer thickness of 20 and 50 nm. The hardness of the Ag/ Nb nano-multilayer film increases with the decrease of the thickness of the single layer, and the increase of the hardness value is gradually increased. When h = 50 nm, the hardness value is 3.53 GPa, and when it is reduced to h = 1 nm, the hardness value is increased to 6.79 GPa, and the strengthening rate is 92.4% higher than that of h = 50 nm. The strengthening of the co-lattice stress is the main factor of the strengthening of the Ag/ Nb nano-multilayer film at the small scale. The elastic modulus of the Ag/ Nb nano-multilayer film increases with the change of the thickness of the single layer. At h = 50nm, the elastic modulus is abnormally reduced due to the presence of the amorphous layer at the interface. while the single layer thickness is between 20 and 1 nm, the elastic modulus is enhanced due to the lattice compression effect. The temperature creep behavior of the four, Cu/ Ta, Ag/ Cu and Ag/ Nb nano-multilayer films showed obvious scale effect. The creep stress index increases with the decrease of the thickness of the single layer. The creep mechanism is mainly based on the dislocation climbing, with the reduction of the scale, the position of the dislocation climbing is gradually transited from the homogeneous grain boundary to the heterogeneous interface, and the co-lattice relationship at the interface is beneficial to the improvement of the creep stress index. In addition, the occurrence of the amorphous layer in the Ag/ Nb multilayer film can suppress further expansion of the creep deformation.
【學位授予單位】：南京大學
【學位級別】：博士
【學位授予年份】：2015
【分類號】：TB383.2
本文編號：2380844
[Abstract]:Due to the periodic modulation structure, the grain growth is influenced by the constraint of the inter-layer dimension and the heterogeneous interface, and the multi-layer film material tends to exhibit peculiar mechanical properties as compared with the conventional bulk material or alloy. It is found in the study that the mechanical properties of the multi-layer film are closely related to the characteristics of the structure. With the change of the scale of the nano-multilayer film, the structure of the layer and the interface structure of the interlayers have changed accordingly, resulting in a strong scale effect. Therefore, it is of great scientific significance to study the scale effect of multi-layer film and to realize the effective regulation and optimization of multi-layer film structure and performance. In this paper, a series of Cu/ Ta, Ag/ Cu and Ag/ Nb nano-multilayer films with different modulation periods were prepared on Si substrate by direct current magnetron sputtering. The microstructure of multilayer films was characterized by X-ray diffractometer, scanning electron microscope, transmission electron microscope and so on. The mechanical properties of the nano-multilayer film, such as the hardness, the elastic modulus and the room temperature creep behavior, were analyzed by means of the nanoindentation. The effect of scale change on microstructure and mechanical properties and its corresponding mechanism are studied systematically. The results are as follows: 1. The hardness of the Cu/ Ta nano-multilayer film shows a significant scale effect with the change of the thickness (h) of the single layer. When the thickness of the single layer is in the range of 10-100 nm, the hardness value is increased with the decrease of the thickness of the single layer, and the hardness reaches the maximum of 6.13 GPa at the time of h = 10 nm, and the numerical change is in line with the Hall-Petch relationship, and the reinforcement is caused by the dislocation plug product. However, when the thickness of the single layer is reduced from 10 nm to 5 nm, the hardness value is significantly reduced because of the disappearance of the Al-Ta phase in the Ta layer, which is first reported in the metal nano multilayer film due to the change of the phase structure. As the thickness of the single layer continues to decrease below 5 nm, the hardness value is stable. At this time, the interface barrier strengthening is the main, and the dislocation crossing interface is blocked to produce the reinforcement. The elastic modulus of the Cu/ Ta nano-multilayer film increases with the thickness of the single layer, and reaches a maximum value of 131 GPa when the thickness of the single layer is 10 nm. When the maximum value is reached, the elastic modulus decreases with the decrease of the scale. and 2, a high-strength and high-conductivity combined excellent comprehensive property is obtained in the Ag/ Cu nano multilayer film. The hardness of Ag/ Cu nano-multilayer film shows non-monotonicity with the change of the scale. The hardness value increases with the decrease of the single layer thickness in the interval of 5-20nm, and the hardness reaches the maximum value of 3.86GPa at the time of 5 nm. When h = 3 nm, the hardness is softened due to the generation of the superlattice. In the multi-layer film, the blocking effect of the grain boundary and the stacking layer on the dislocation is combined with the strengthening of the interface, so that the multi-layer film is strengthened. In addition, due to the increase of the interfacial bending and the crystal grain orientation, the multilayer film has an abnormal strengthening at h = 50 nm, and is higher than the hardness at h = 20 nm. The elastic modulus of the Ag/ Cu nano-multilayer film decreases with the decrease of the thickness of the single layer, and the reinforcing effect of the elastic modulus is not present. The reduction of the elastic modulus is related to the expansion of the crystal plane pitch due to the mismatch at the interface. the resistivity of the Ag/ Cu nano multilayer film has low resistivity and is stable at the time of h to 10 nm, which is due to the formation of the woven structure in the Ag/ Cu nano multilayer film, the number of the large-angle grain boundaries is reduced, the scattering of the electrons in the grain boundary is reduced, and the increase of the resistivity is prevented. so as to solve the problem that the high-strength and high-conductivity are mutually contradictory, and the excellent comprehensive property of the combination of high-strength and high-conductivity is obtained in the Ag/ Cu nano multilayer film. However, at h10 nm, the scattering of the electrons by the interface and the grain boundary causes the resistivity to increase sharply with the decrease in the scale. In addition, for the evaluation of the comprehensive performance, a simple model is proposed for the first time, and the combination of the strength and the electric conductivity of the Ag/ Cu nano-multilayer film is evaluated. The experimental data confirm that the evaluation system is reasonable. The establishment of the model provides a good idea for solving such problems. 3. The microstructure and mechanical properties of the Ag/ Nb nano-multilayer film show a supernormal sensitivity to the dimensional change. As the dimensions decrease, the crystal structure type changes according to the trend of the polycrystalline silicon-woven structure and the superlattice, and an amorphous layer is present at the interface at the time of the single-layer thickness of 20 and 50 nm. The hardness of the Ag/ Nb nano-multilayer film increases with the decrease of the thickness of the single layer, and the increase of the hardness value is gradually increased. When h = 50 nm, the hardness value is 3.53 GPa, and when it is reduced to h = 1 nm, the hardness value is increased to 6.79 GPa, and the strengthening rate is 92.4% higher than that of h = 50 nm. The strengthening of the co-lattice stress is the main factor of the strengthening of the Ag/ Nb nano-multilayer film at the small scale. The elastic modulus of the Ag/ Nb nano-multilayer film increases with the change of the thickness of the single layer. At h = 50nm, the elastic modulus is abnormally reduced due to the presence of the amorphous layer at the interface. while the single layer thickness is between 20 and 1 nm, the elastic modulus is enhanced due to the lattice compression effect. The temperature creep behavior of the four, Cu/ Ta, Ag/ Cu and Ag/ Nb nano-multilayer films showed obvious scale effect. The creep stress index increases with the decrease of the thickness of the single layer. The creep mechanism is mainly based on the dislocation climbing, with the reduction of the scale, the position of the dislocation climbing is gradually transited from the homogeneous grain boundary to the heterogeneous interface, and the co-lattice relationship at the interface is beneficial to the improvement of the creep stress index. In addition, the occurrence of the amorphous layer in the Ag/ Nb multilayer film can suppress further expansion of the creep deformation.
【學位授予單位】：南京大學
【學位級別】：博士
【學位授予年份】：2015
【分類號】：TB383.2
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