Microstructure and mechanical properties of polycrystalline-Ag/amorphous-CoZrNb multilayers

Ag/CoZrNb multilayers were prepared by direct current magnetron sputtering. Their microstructure, hardness, elastic modulus and plastic deformation were investigated by X-ray diffraction, high-resolution transmission electron microscopy, X-ray absorption near-edge structure, field emission scanning electron microscopy and nanoindentation technique. The results show that the multilayers have well modulated structure. For all the multilayers, Ag layer is polycrystalline structure, while CoZrNb layer is amorphous structure. With the decrease of modulation periodicity the elastic modulus decreases due to the compliant interface. The polycrystalline Ag layer not only makes the hardness enhanced with the decrease of modulation periodicity, but also restricts the propagation of shear bands and promotes the nucleation of new shear bands, which may be of help for the plasticity enhancement of amorphous CoZrNb layer.     

Thermal stability of microstructure and mechanical properties of Ni/Ru multilayers

The microstructure, hardness and thermal stability of Ni/Ru multilayers prepared by evaporation deposition were investigated by X-ray diffraction, transmission electron microscopy, vacuum annealing and nanoindenation. The hardness values of as deposited multilayers increase, while their elastic modulus values decrease, with decreasing periodicity. After annealing at low temperature (below 450 °C), the decrease in hardness of multilayers with larger periodicity is more remarkable than that of multilayers with smaller periodicity due to coarsening of the in-plane grain size. The higher temperature (600 °C) annealing results in the breakdown of the periodical structure and a significant drop in hardness for multilayers with smaller periodicity. The results were discussed according to Orowan-type single dislocation bowing mechanism.     

Amorphous-CuTa/amorphous-CoZrNb multilayers: Structure, mechanical properties and thermal stability

CuTa/CoZrNb multilayers were prepared by direct current magnetron sputtering. The structure, mechanical properties and thermal stability were investigated by X-ray diffraction, high-resolution transmission electron microscopy, vacuum annealing and nanoindentation. The results show that the as-deposited multilayers possess amorphous/amorphous structure. The amorphous feature leads to the lack of hardness enhancement with decreasing modulation periodicity, which can be attributed to the absence of the dislocation movement. After thermal annealing, the density increases due to the decrease of the bond distance and the annihilation of defects with increasing annealing temperature. The densification results in the enhancement of the elastic modulus and hardness. The enhancement for the multilayers with smaller modulation periodicity is more sensitive to thermal annealing because of larger volume fraction of interfaces.     

磁控溅射沉积Al/AlN纳米多层膜的摩擦学性能

纳米多层膜因具有优异的力学性能与抗摩擦磨损性能使其在摩擦学领域具有重要的应用价值。采用磁控溅射沉积法制备了Al、AlN单层薄膜与Al/AlN纳米多层膜,探讨了纳米多层化对薄膜的力学性能和摩擦学性能的影响。采用纳米压痕仪和摩擦磨损试验机测量评价薄膜的纳米硬度和摩擦学性能。结果表明:Al/AlN纳米多层膜具有良好的周期调制结构,多层膜中的大量界面能显著提高薄膜的力学性能与摩擦学性能。多层膜的硬度为8.8GPa,高于采用混合法则计算出的硬度值6.6GPa;多层膜具有软质Al层和硬质AlN层的交替结构,在摩擦过程中,硬质AlN层可以起到良好的承载作用,软质层可以起到良好的减摩作用。相对于Al单层薄膜或AlN单层薄膜,Al/AlN纳米多层膜具有较低的摩擦因数(0.15)和优异的抗磨损性能。     

Evaluating modulus and hardness enhancement in evaporated Cu/W multilayers

The microstructure, hardness and elastic modulus of Cu/W multilayers prepared by evaporation deposition were investigated by X-ray diffraction, transmission electron microscopy and nanoindenation. The results show that the multilayers with good modulation structure have asymmetrical interfaces. The W on Cu interfaces are relatively sharp, while the Cu on W interfaces are diffuse, with significant intermixing. The intermixing results in compression of the out-of-plane interplanar spacing of the W layer. The compression increases with decreasing periodicity and leads to modulus enhancement. The hardness values also increase with decreasing periodicity, which is interpreted by the Lehoczky model.     

Sputter-deposited Cu/Cu(O) multilayers exhibiting enhanced strength and tunable modulus

By means of brief pauses in radiofrequency (RF) sputter deposition between individual layers, ultrathin copper oxide layers were formed through adsorption in the Cu/Cu multilayers. Their mechanical properties were compared with the Cu/Cu(O) multilayers whose oxide layers were deliberately deposited between copper layers. The mechanical hardness value of the Cu/Cu(O) multilayers approached that of nanostructured copper thin films. The Young’s modulus of the multilayers was tunable, in accordance with the elasticity theories of composites. In addition, the Hall–Petch slope of the RF sputter-deposited Cu monolayers indicated that their theoretical strength approached the shear modulus of copper.     

Oxygen-penetration-induced large hardness enhancement in nanoscale Nb/Ti multilayers

Nb/Ti multilayers with different modulation periods were prepared by magnetron sputtering deposition. Microstructure and mechanical properties were investigated by XRD, SEM and Nanoindentation. It turns out that hardness of samples increases with decreasing modulation wavelength (Λ) and then dropped at small Λ. Through scrutinizing other results in literature, we found that the coherent stress rather than modulus mismatch played more important role for hardness enhancement with decreasing Λ of the bcc-hcp multilayers. Annealing of samples in low (or high) vacuum at 400 C for 30 min led to large (or medium) enhancement of hardness, while the modulated structure was still maintained. It was found that annealing in low vacuum resulted in oxygen penetration into the multilayers as revealed by auger electron spectroscopy, but hardly changed metallic sheet resistivity. XRD results suggested that some niobium oxides were formed in Nb layers and oxygen distributed interstitially in Ti layers. The large hardness enhancement after annealing is mainly due to the strengthening effect from dispersive distribution of nano-scale niobium oxides and interstitial oxygen in the multilayers. In addition, interfaces between adjacent layers were more distinct after annealing which indicated good thermal stability of laminated structure.     

Structural transition and magnetic properties of evaporated Fe/Gd multilayers

Fe/Gd multilayers were prepared by alternate vapor deposition of pure Fe and Gd at a rate of 0.01-0.03 nm/s in an ultra-high-vacuum electron-gun evaporation system.The effects of the constituent metal layer thickness on the microstructures and magnetic properties of the films were investigated by low angle X-ray diffraction,transmission electron microscopy,and vibrating sample magnetometer.The experimental results show that a transition from the polycrystalline to amorphous state in the Fe layers occurs with the decrease of Fe layer thickness in the Fe/Gd multilayers.The saturation magnetization of the muitilayers reduces significantly with decreasing Fe layer thickness and increasing Gd layer thickness.A superparamagnetic behavior at room temperature is observed for the [Fe(0.6 nm)/Gd(4.0 nm)]15 multilayer due to the formation of discontinuous Fe layers.     

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.     

Nanoindentation study of amorphous-Co79Zr13Nb8/Cr multilayers

The mechanical properties of Co₇₉Zr₁₃Nb₈/Cr multilayers were investigated using nanoindentation. The hardness is higher than the average value calculated by rule-of-mixture. The hardness and the resistance to plastic deformation characterized by the ratio of H³/E² vary similarly with periodicity (Λ). They all arrive to the maximum at Λ = 8 nm and decrease subsequently when the Λ increases. The hardness dependence on the Λ is fitted by Hall-Petch relation. The fitted index n is much lower than the normal value (~ 0.5) in many crystalline multilayers. The mutual restriction of shear band and dislocation in amorphous/crystalline structure, which is named structure barrier strengthening, should be main mechanism for the hardness enhancement. The SEM study of indents shows that the shear bands are distorted significantly at the smaller Λ (4 nm) and disappear at the larger Λ (> 20 nm). This morphology variation implies a potential improvement of plasticity caused by the restriction effect of the Cr crystalline layers on the shear bands propagation.     

气相沉积铁钇多层膜的磁学性能

研究了气相沉积技术制备的Fe/Y多层膜的磁学性能,试验结果表明,当多层膜中铁层厚度减少到1．4nm时,薄膜由铁磁性转变为超顺磁性;多层膜的饱和磁化强度随铁层厚度的减少和钇层厚度的增加而显著降低。     

TiN/Si3N4纳米多层膜硬度对Si3N4层厚敏感性的研究

通过反应磁控溅射制备了一系列不同Si3N4层厚的TiN/Si3N4纳米多层膜,利用X射线衍射仪、高分辨透射电子显微镜、扫描电子显微镜和微力学探针表征了多层膜的微结构和硬度,研究了其硬度随Si3N4层厚微小改变而显著变化的原因.结果表明,在TiN调制层晶体结构的模板作用下,溅射态以非晶存在的Si3N4层在其厚度小于0.7 nm时被强制晶化为NaCl结构的赝晶体,多层膜形成共格外延生长的{111}择优取向超晶格柱状晶,并相应产生硬度显著升高的超硬效应,最高硬度达到38.5GPa.Si3N4随自身层厚进一步的微小增加便转变为非晶态,多层膜的共格生长结构因而受到破坏,其硬度也随之降低.     

Cu/Co-W nanolayers electrodeposited from single bath and investigations of their nanohardness

For the first time thick (??8 ??m) Cu/Co-W multilayered coatings with individual layers ranging from 5 to 200 nm were electrodeposited from a single bath. The content of tungsten in rich-in Co-W layers was controlled by varying current densities in a citrate-borate bath. Continuous Multi-Cycle (CMC) nanoindentation technique was used to analyze mechanical properties of those deposits. Optical examination of the indented zone revealed the absence of cracks inside and outside the indentation area in the interval of the normal loads used. The hardness of Cu/Co-W multilayers varied with the bi-layer period and the electrodeposition parameters. The Cu/Co-W multilayers showed an increased hardness compared to that of Co-W coatings electrodeposited under the same conditions.     

离子束增强沉积Ti–Mo多层膜和TiMo合金膜及其性能

采用离子束增强磁控溅射沉积技术制备了Ti-Mo金属多层膜和TiMo合金膜,评价了膜层的结合强度、韧性、硬度等力学性能和摩擦学性能.结果表明:不同调制周期及不同调制比的Ti-Mo多层膜的硬度均比Ti、Mo金属单层膜的硬度高,调制周期小于200 nm的多层膜呈现出明显的超硬度现象,调制周期为20 nm的多层膜硬度达到最大值,多层膜硬度随Ti膜:Mo膜调制比的减小而提高.Mo过渡层比Ti过渡层更能有效改善膜层的结合强度,离子辅助轰击能明显提高膜层的结合力.TiMo合金膜的硬度与Mo金属单层膜相近,明显低于调制周期20～200 nm的Ti-Mo多层膜,其韧性也明显低于调制周期60 nm以上的Ti-Mo多层膜.调制周期20～200 nm的Ti-Mo多层膜的耐磨性能优于TiMo合金膜.     

TiN/ZrO2 multilayers synthesized on GCr15 bearing steel using plasma immersion ion implantation and deposition

TiN/ZrO₂ multilayers with different modulation periods were synthesized on GCr15 bearing steel using plasma immersion ion implantation and deposition (PIIID). The total thickness of the TiN/ZrO₂ multilayers was approximately 2 μm and the modulation period was varied from 8 to 400 nm. The as-deposited films were characterized by scanning electron microscopy (SEM), micro-hardness, friction, scratch and corrosion tests. The SEM result indicates that the structure of the TiN/ZrO₂ multilayers has a good periodicity. Micro-hardness testing results show that the hardness enhancement effect takes place at the specific period of 15 nm, 100 nm and 200 nm. In addition, the friction coefficient declined from 0.8 to 0.1-0.3 and the cut-through number was increased greatly. The critical load in the scratch test exceeds 100 N, which shows a high adhesion strength. Moreover, the corrosion resistance of the TiN/ZrO₂ multilayers was improved significantly at the modulation period of 100 nm and 200 nm.     

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.     

Microstructure and mechanical properties of TiN/AlN multilayers deposited by filtered vacuum arc deposition

Nanometer TiN/AlN multilayers were prepared on silicon substrate by filtered vacuum arc deposition.The structures of the nanometer TiN/AlN multilayer were studied by using X-ray diffraction. The 12 nm TiN/AlN multiplayer is composed of cubic TiN structure and hexagonal wurzite AlN structure, but the 2 nm period multilayer is composed of face centered cubic structure TiN and AlN with strong (200) texture. The surface roughness, hardness and elastic modulus of multilayer are dependent on the period of multilayer. The hardness of the TiN/AlN multilayers is higher than that suggested by a simple rule of mixture. The peaking hardness of nanometer TiN/AlN multilayers at period of 2 nm is about 42 GPa, much higher than that of 12 nm. The wear resistance of the nanometer TiN/AlN multilayers was also studied.     

钛工业的研究开发现状——2002国际钛协会年会暨展览会见闻

研究了W/Mo纳米多层膜的微结构及超硬效应，W/Mo纳米多层膜采用磁控溅射技术制备，并采用XRD、TEM和显微硬度计研究了薄膜的微结构和硬度。结果表明，W/Mo纳米多层膜形成多晶外延生长的超晶格结构，界面共格畸变使W/Mo两调制层的晶面间距随调制周期的减小而相互接近，在多层膜中形成交变应力场，从而使薄膜得到强化。     

Magnetron sputtering deposition of [FePt/Ag]n multilayers for perpendicular recording

[FePt/Ag]n multilayers were deposited on glass substrates by RF magnetron sputtering and ex situ annealed at 550℃ for 30 min. The effects of inserted Ag layer thickness and the number of bilayer repetitions （n） on the structure and magnetic properties of the multilayers were investigated. It was found that the difference between in-plane and out-of-plane coercivities varied with an increase of inserted Ag layer thickness in the [FePt 2 nm/Ag x nm]10 multilayers. The ratio of out-of-plane coercivity to in-plane coercivity reached the maximum value with the Ag layer thickness of 5 nm, indicating that the Ag layer thickness plays an important role in obtaining perpendicular orientation. For the [FePt 2 nm/Ag 5 um]n multilayers, perpendicular orientation is also influenced by n. The maximum value of the ratio of out-of-plane coercivity to in-plane coercivity appeared when n was given as 8. It was found that the [FePt 2 nm/Ag 5 nm]8 had a high perpendicular coercivity of 520 kA/m and a low in-plane one of 88 kA/m, which shows a strong perpendicular anisotropy.     

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.