不同调制波长Cu/Ag多层膜硬度分析

用直流电沉积双槽法在纯铜基体上制备了不同调制波长的Cu/Ag多层膜,研究了多层膜硬度与调制波长之间的关系.实验结果表明,当调制波长位于600～300nm时,Cu/Ag多层膜的硬度与调制波长之间较好地符合基于位错塞积模型的Hall-Petch关系;当调制波长小于300 nm时,硬度与调制波长的关系偏离了HaU-Petch关系.由实验结果分析得出了Cu/Ag多层膜的位错稳定存在极限晶粒尺寸约为25 nm,与基于程开甲等人的位错稳定性理论得出的Ag晶体极限晶粒尺寸27 nm接近,验证了程开甲等人的位错稳定性理论.     

Ag/Cu和Cu/Ni纳米金属多层膜强度软化的理论分析

用电沉积法分别制备了具有不同调制波长的Ag/Cu和Cu/Ni金属多层膜,研究了多层膜的硬度与调制波长之间的关系.结果表明,当调制波长λ>300 nm时,两种多层膜的硬度与调制波长符合位错塞积机制的Hall-Fetch关系,当λ<300 nm时,都偏离了Hall-Fetch关系;Ag/Cu和Cu/Ni多层膜分别在λ=50nm和100nm处取得硬度峰值.基于Cheng等人的电子理论分别求出了Ag,Cu和Ni金属晶体的位错稳定的临界晶粒尺寸,进而定量地解释了Ag/Cu和Cu/Ni金属多层膜硬度峰值位置.     

Cu/Ni多层膜中交变应力场对可动位错的制约

Cu／Ni多层膜的强化作用来自于多层膜结构中交变应力场对位错运动的约束．该交变应力场主要包括两部分：在共格界面处由于剪切模量差而导致的镜像力,以及多层膜内由于晶格常数差而形成失配位错网的应力．如果位错在膜层内运动的临界应力值小于交变应力场的约束,位错会被限制在单层膜内运动,多层膜被强化;反之,则位错很容易通过界面到达临近的膜层,多层膜开始出现弱化．交变应力场的变化幅值与多层膜的调制波长相关．理论计算结果表明,Cu／Ni多层膜的临界调制波长为1．9nm,但失配位错网的交变应力场在多层膜的调制波长λ=9nm时振幅达到极值．     

双槽电沉积法制备Cu/Ag纳米多层膜

双槽电沉积法制备了不同调制波长的Cu/Ag金属多层膜(Cu膜和Ag膜等厚),用扫描电子显微镜观察了多层膜的层状结构,并研究了不同调制波长下多层膜的显微硬度变化.结果表明:双槽电沉积法制备的Cu/Ag多层膜层状结构明显.当调制波长大于100 nm时,显微硬度随调制波长减小而增加;当小于100 nm时,硬度随调制波长减小而...     

Cu-Cr纳米金属多层膜屈服强度/硬度的尺寸依赖性

采用磁控溅射方法分别在聚酰亚胺基体以及单晶硅基体上制备恒定调制比(η)以及恒定调制周期(λ)的Cu-Cr纳米金属多层膜;通过单轴拉伸试验以及纳米压痕试验系统研究Cu-Cr多层膜屈服强度及硬度的尺度依赖性。微观分析结果表明:基体对多层膜的微观结构无影响,Cu-Cr多层膜在生长方向上均呈现Kurdjumov-Sachs取向关系,即{111}Cu//{110}Cr和-110-Cu//-111-Cr。力学测试结果表明:调制比恒定的Cu-Cr多层膜的屈服强度及硬度随调制周期的缩短而增加;调制周期恒定的Cu-Cr多层膜的屈服强度/硬度随调制比的增加而增加。Cu-Cr多层膜变形机制在临界调制周期(λc≈25 nm)和临界调制比(ηc≈1)由Cu层内单根位错滑移转变为负载效应。     

Cu/X(X=Cr,Nb)纳米多层膜力/电学性能的尺度依赖性

利用纳米压痕实验以及四探针法,系统研究了相同层厚Cu/X(X=Cr,Nb)纳米金属多层膜的力学性能(强/硬度)和电学性能(电阻率)的尺度依赖性.微观分析表明:Cu/X多层膜调制结构清晰,Cu层沿{111}面择优生长,X层沿{110}面择优生长.纳米压入结果表明,Cu/X多层膜的强度依赖于调制周期,并随调制周期的减小而增加.多层膜变形机制在临界调制周期(λ~c≈25 nm)由Cu层内单根位错滑移转变为位错切割界面.多层膜的电阻率不仅与表面/界面以及晶界散射相关,而且在小尺度下受界面条件显著影响.通过修正的FS-MS模型可以量化界面效应对多层膜电阻率的影响.Cu/X纳米多层膜可以通过调控微观结构实现强度-电导率的合理匹配.     

Cu/Ni多层膜在多冲与压压载荷下的失效行为

采用磁控溅射技术在TC4钛合金表面制备Cu/Ni多层膜,利用多冲和动态循环压压试验装置对膜层的力学性能进行了评价,探讨了冲击条件、多层膜调制周期及结构等对多层膜失效行为的影响,比较了多层膜和单层Cu、Ni膜在多冲条件下的失效行为,以及多冲与循环压压载荷对多层膜失效行为的影响.结果表明:多冲法能够较好地表征Cu/Ni多层膜的结合强度、韧性、内聚强度.压压载荷作用下多层膜的失效主要表现为单一的开裂现象,因而压压法更适合评价膜层的韧性.采用合适的过渡层、离子辅助和基材加热方法可以获得高的多层膜强度和韧性;调制周期小于600 nm的Cu/Ni多层膜的内聚强度、韧性及多冲承载能力高于Cu、Ni单层膜;调制周期小于200 nm的多层膜呈现出明显的超硬度现象,且具有良好的强韧性能.     

溅射沉积Cu/W纳米多层膜结构与性能

以单晶硅和聚酰亚胺为衬底,用磁控溅射沉积调制周期λ=25~150 nm、调制比η=0.5~2的Cu/W纳米多层膜,用XRD、SEM、EDS、AFM、微力测试系统、纳米压痕仪和四探针法对多层膜微观结构、表面形貌和力学及电学性能进行研究。结果表明:λ和η显著影响多层膜结构和性能。多层膜Cu层和W层均为纳米晶结构,分别呈Cu(111)和W(110)择优取向。W(110)晶面间距减小且减幅与1/λ或η值呈正相关,Cu/W层间界面处存在扩散混合层。表面Cu层晶粒尺寸随Cu层厚增加而增大。裂纹萌生临界应变εc总体上随λ增大或η减小而下降,屈服强度σ0.2、显微硬度H和电阻率ρ总体上均与λ或η呈负相关。因Cu层和W层厚度随λ或η的变化而改变,相应地改变了Cu层晶粒度及其晶界密度、W层体积分数和Cu/W层间界面数量,使位错运动能力及电子散射效应变化,最终改变Cu/W纳米多层膜性能。     

Cu/Ni多层膜对Ti811合金微动磨损和微动疲劳抗力的影响

在Ti811钛合金表面利用离子辅助磁控溅射沉积技术制备20～1200nm不同调制周期的Cu/Ni金属多层膜,分析多层膜的结构,测试膜基结合强度、膜层显微硬度和韧性,对比研究不同调制周期的Cu/Ni多层膜对钛合金基材常温下微动磨损性能和微动疲劳(FF)抗力的影响。结果表明:利用离子辅助磁控溅射技术可以获得致密度高、晶粒细化、膜基结合强度高的Cu/Ni多层膜,该类多层膜具有良好的减摩润滑作用,因而改善了Ti811钛合金常温下抗微动磨损和微动疲劳性能;Cu/Ni多层膜对钛合金FF抗力的改善程度随膜层调制周期呈现非单调变化趋势,调制周期为200nm的Cu/Ni多层膜对钛合金FF抗力的提高程度最大,原因归于该膜层具有良好的强韧和润滑综合性能。     

MOLECULAR DYNAMICS SIMULATION OF STRENGTH ENING MECHANISM OF Cu/Ni MULTILAYERS

运用分子动力学方法模拟了Cu/Ni薄膜结构在纳米压入和微摩擦过程位错的运动规律, 探讨了薄膜结构中位错与界面的相互作用规律. 结果表明: Cu/Ni多层膜结构中的层间界面会阻碍位错继续向材料内部扩展, 阻碍作用主要来自于两个方面: 界面失配位错网对位错运动的排斥阻力使其难以到达或穿过界面; 由弹性模量差而产生的界面镜像力使位错被限制在Cu单层膜内运动. 这种阻碍作用有利于提高Cu/Ni多层薄膜的力学性能.     

Electron theory based explanation and experimental study on deformation behavior of Cu/Ni multilayers

Cu/Ni multilayers with various defined thickness of Cu and Ni layers were electrodeposited on low carbon steel substrates. Hardness measurements indicated that the increase in yield strength (one-third of hardness) with a decrease of layer thickness for Cu/Ni multilayers with single layer thickness at sub-micron length scale could be described by the Hall-Petch formula of the dislocation pile-up model. In the regime of few tens to a hundred nanometers of single layer thickness, the dislocation pileup-based Hall-Petch model broke down. This could be explained quantitatively according to the criterion condition on the limit size of dislocation derived from a modified Thomas-Fermi-Dirac electron theory.     

Analytic treatment of metallic multilayer strength at all length scales: Influence of dislocation sources

Metallic multilayers exhibit a very pronounced size effect where the mechanical strength depends on the layer thickness. Traditionally the Hall–Petch relation is used to account for the size effect. However, rigorous application of dislocation pileup theory predicts significant deviation from the Hall–Petch relation due to elastic inhomogeneity, discreteness of dislocations and dislocation source operation. Elastic inhomogeneity leads to anomalous scaling where the scaling exponent deviates from 1/2 of the classical Hall–Petch relation. The discrete dislocation effect is properly accounted for by a piecewise approach that can be applied at all length scales. In this article, a key step in the formulation is taken: the dislocation source characteristics are taken into consideration. Thus, all the three effects are accounted for. Analytic formulas linking yield stress to microscopic interface strength, dislocation source activation stress and other easily obtainable parameters (the Burgers vector, the elastic constants of constituent materials, crystal structure and layer thickness) are provided for all length scales. The model is then applied to Cu/Ni multilayers and the predicted strength is compared with experimental data.     

[Co／Ti],[Co／Cu（Ni）]多层膜的结构与磁性

用双对向靶溅射方法制备了具有非晶磁性的「Ｃｏ／Ｔｉ」３０，「Ｃｏ／Ｃｕ（Ｎｉ）３０」两组多层膜，分别用Ｘ射线衍射，透射电镜和振动样品磁强计做了结构和磁性测量，在以非晶Ｃｏ和Ｃｉｕ－Ｎｉ合金构成的「Ｃｏ／Ｃｕ（Ｎｉ）」多层膜中，发现饱和磁化强度Ｍｓ随非磁性层厚度ｄｓ的增国发生振荡变化；在以非晶Ｃｏ和Ｔｉ构成的「Ｃｏ／Ｔｉ」多层膜中，ＭＳ和则随ｄｓ的增加而减小。     

On plasticity and fracture of nanostructured Cu/X (X = Au,Cr) multilayers: The effects of length scale and interface/boundary

Plastic deformation and fracture behavior of two different types of Cu/X (X = Au, Cr) multilayers subjected to tensile stress were investigated via three-point bending experiments. It was found that the plastic deformation ability and fracture mode depended on layer thickness and interface/boundary. The Cu/Au multilayer showed significant features of plastic flow before fracture, and such plasticity was gradually suppressed by premature unstable shearing across the layer interface with decreasing layer thickness. In comparison, Cu/Cr multilayers were prone to a quasi-brittle normal fracture with decreasing layer thickness. Both experimental observations and theoretical analyses revealed differences in plasticity and fracture mode between the two types of metallic multilayers and the relevant physical mechanism transition due to length scale constraint and interface/boundary blocking of dislocation motion.     

Length-scale-dependent deformation mechanisms in incoherent metallic multilayered composites

Nano-indentation hardness as a function of bilayer period has been measured for sputter-deposited Cu–Nb multilayers. For this face-centered cubic/body-centered cubic system with incoherent interfaces, we develop dislocation models for the multilayer flow strength as a function of length scale from greater than a micrometer to less than a nanometer. A dislocation pile-up-based Hall–Petch model is found applicable at the sub-micrometer length scales and the Hall–Petch slope is used to estimate the peak strength of the multilayers. At the few to a few tens of nanometers length scales, confined layer slip of single dislocations is treated as the operative mechanism. The effects of dislocation core spreading along the interface, interface stress and interface dislocation arrays on the confined layer slip stress are incorporated in the model to correctly predict the strength increase with decreasing layer thickness. At layer thicknesses of a few nanometers or less, the strength reaches a peak. We postulate that this peak strength is set by the interface resistance to single dislocation transmission, and calculate the transition from confined layer slip to an interface cutting mechanism.     

Microstructures and strength of nanoscale Cu–Ag multilayers

Cu–Ag multilayers were found to have lower peak hardness than Cu–Ni in spite of lower misfit dislocation spacing that is expected to increase the resistance of interfaces to glide dislocation transmission. This is attributed to misfit dislocation core spreading in the interface plane in Cu–Ag.     

Interfacial Structures Governed Plastic Deformation Behaviors in Metallic Multilayers

In this work, we have investigated the mechanical properties of Cu/Ta, Ag/Cu and Ag/Nb multilayers with different heterogeneous interfaces. The results suggest that when individual layer thickness(h) is larger than 5–10 nm, the hardness/strength of three different multilayer systems has the similar length scale effect with decreasing layer thickness,while when h B 5 nm, the three multilayer systems show remarkably different plastic deformation behaviors. The strength curves exhibit the variation trends of unchanging, softening and increasing corresponding to Cu/Ta, Ag/Cu and Ag/Nb multilayers, respectively. The microstructure analysis shows that three kinds of multilayers have totally different interfacial structures, which lead to the different strengthening or softening mechanisms.