金属多层膜微观结构与力学性能的尺度效应
发布时间:2018-12-15 14:55
【摘要】:纳米金属多层膜由于具有周期性的调制结构,晶粒生长受到组元层间尺度的约束和异质界面的影响,与传统的块体材料或合金相比,多层膜材料往往表现出奇特的力学性能。在研究中发现,多层膜的力学性能与结构的特征尺度密切相关。随着纳米多层膜尺度的改变,其层内结构以及层间界面结构发生相应变化,从而导致性能表现出强烈的尺度效应。因此,研究多层膜的尺度效应规律,对实现多层膜结构与性能的有效调控及最优化设计有着重要的科学意义。本文利用直流磁控溅射法在Si衬底上制备了一系列不同调制周期的Cu/Ta、Ag/Cu和Ag/Nb纳米多层膜,借助X射线衍射仪、扫描电子显微镜、透射电子显微镜等表征了多层膜的微观结构;利用纳米压痕仪对纳米多层膜的硬度、弹性模量和室温蠕变行为等力学性能进行了分析测试。系统地研究了其尺度变化对微观结构及力学性能的影响及其相应机制的改变。结论如下:一、Cu/Ta纳米多层膜的硬度随单层厚度(h)的变化而表现出明显的尺度效应。当单层厚度介于10-100 nm时,硬度值随单层厚度的减小而增加,并且在h=10 nm时硬度达到最大值6.13 GPa,数值变化符合Hall-Petch关系,说明强化由位错塞积造成。但是在单层厚度由10 nm降至5 nm时,硬度值出现了明显的降低,原因是由于Ta层中β-Ta相的消失而造成,这种由于相结构改变而导致的软化现象在金属纳米多层膜中尚属首次报道。随着单层厚度继续减小至5 nm以下时,硬度值保持稳定,此时以界面阻挡强化为主,位错穿越界面受阻而产生强化。Cu/Ta纳米多层膜的弹性模量随单层厚度减小而增大,并在单层厚度为10 nm时达到最大值131 GPa。达到最大值后随尺度的减小,弹性模量则呈逐渐降低趋势。二、在Ag/Cu纳米多层膜中获得了高强度和高电导率结合的优异综合性能。Ag/Cu纳米多层膜的硬度随尺度的变化表现出非单调性。硬度值在5-20nm区间内随单层厚度的减小而增加,并在5 nm时硬度达到最大值3.86 GPa。当h=3 nm时,由于生成了超晶格使得硬度出现软化。多层膜中孪晶界与堆垛层错对位错的阻挡作用与界面强化作用相结合,使得多层膜强化。另外,由于界面弯曲和晶粒取向差增大,使得多层膜在h=50 nm时出现反常强化,高于h=20 nm时的硬度。Ag/Cu纳米多层膜的弹性模量随单层厚度的减小而减小,没有出现弹性模量的增强效应。弹性模量的降低与界面处错配造成的晶面间距膨胀有关。Ag/Cu纳米多层膜的电阻率在h≥10 nm时具有低电阻率并且稳定,这是由于Ag/Cu纳米多层膜中织构的生成,大角晶界数目减少,减少了晶界对电子的散射,阻止了电阻率的升高。从而解决了高强度与高导电性这一相互矛盾的问题,在Ag/Cu纳米多层膜中获得了高强度和高电导率相结合的优异综合性能。但是在h10 nm时由于界面与晶界对电子的散射使得电阻率随尺度减小而急剧增加。另外,针对综合性能的评价问题,首次提出并建立了一个简单的模型,对Ag/Cu纳米多层膜强度与电导率相结合的力/电综合性能进行了评价,经实验数据证实该评价体系合理。该模型的建立为解决此类问题提供了一个很好的思路。三、Ag/Nb纳米多层膜的微观结构与力学性能对尺度变化表现出超常敏感性。随着尺度的减小,晶体结构类型按照多晶→织构→超晶格的趋势而变化,并且在单层厚度为20和50 nm时界面处出现了非晶层。Ag/Nb纳米多层膜的硬度随单层厚度的减小而增加,并且硬度值的增加趋势逐渐加大。h=50 nm时,硬度值为3.53 GPa,而当减小至h=1 nm时,硬度值增加到6.79 GPa,与h=50 nm相比强化率高达92.4%。共格应力强化是Ag/Nb纳米多层膜在小尺度下强化的主要因素。Ag/Nb纳米多层膜的弹性模量随单层厚度的变化呈现增加趋势。在h=50nm时,由于界面处非晶层的存在,弹性模量有反常的降低行为。而单层厚度在20~1 nm之间时,由于晶格压缩效应导致了弹性模量增强。四、Cu/Ta、Ag/Cu和Ag/Nb纳米多层膜的室温蠕变行为均表现出明显的尺度效应。蠕变应力指数随单层厚度的减小而增大。蠕变机制以位错攀移为主,随着尺度的减小,位错攀移发生的位置由同质晶界逐渐过渡到异质界面,并且界面处的共格关系有利于蠕变应力指数的提高。另外,在Ag/Nb多层膜中非晶层的出现可抑制蠕变变形的进一步扩展。
[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.
【学位授予单位】:南京大学
【学位级别】:博士
【学位授予年份】:2015
【分类号】:TB383.2
本文编号: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.
【学位授予单位】:南京大学
【学位级别】:博士
【学位授予年份】:2015
【分类号】:TB383.2
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