The deformation and fracture behavior of an electrodeposited nanocrystalline Ni under compression

A bulk and dense nanocrystalline Ni with an average grain size of 19 nm and a thickness of 5.4 mm was fabricated by an electro-deposition technique. The nc Ni had a preferable (2 0 0) growth texture along the depositing direction. Under compression test, the nc Ni exhibited a high strength of 2920 MPa and an accepted good ductility of 16%. A novel fracture character, i.e., the triple-junction shaped micro-cracks with the size varying from few to several tens of micrometers which run through the holistic fracture body of the nc Ni, was observed. The reason for the formation of such cracks is attributed to GB activities, which leads to the formation of nano-sized void, and the subsequent formation of micro-crack.     

电沉积制备纳米镍的拉伸变形行为

为了系统研究纳米材料的超塑性变形特点,用电沉积方法制备了平均晶粒尺寸为70 nm的纳米镍.采用单向拉伸实验研究了其在室温和高温时的力学性能,并用透射电子显微镜TEM、扫描电子显微镜SEM和X射线能谱仪EDS观察分析了纳米镍变形前后的显微组织.实验结果表明:制备的纳米镍在室温时表现出的延伸率很低,但强度可达1000 MPa以上.当温度升高至450℃,应变速率为1.67×10-3 s-1时单向拉伸实验得到380%的延伸率,说明制备的纳米镍具有低温超塑性性能.实验过程中,材料内部的晶粒发生明显的长大与拉长.拉伸过程中形成的氧化物夹杂成为裂纹源,断口表现为沿晶断裂.     

Some observations on the fracture of electrodeposited single-crystal nickel films

Single-crystal films of nickel with (110), (111) and (211) as the film plane were fractured with the applied stress in different directions; the resulting fracture edges were examined using electron microscopy. The type of fracture depended upon the plane and orientation, varying from twin-free cleavage on (110) with the applied stress along the [001] to lattice distortion with no twins and disintegration of the sample on (110) with the applied stress along [1$\text{1}$0]. In the intermediate cases where twins were associated with the fracture, evidence of extrinsic faults was observed but no unambiguous evidence of intrinsic twins.     

Stripe domains in electrodeposited NiCo thin films

The presence of stripe domains (SD) in electrodeposited NiCo thin films was inferred from the specific form of the hysteresis loops. The critical field H_cr of this type of magnetization domain has been studied as a function of film composition, film thickness and annealing temperature. The range of the experimental parameters was: composition 0–50% Co in nickel, thickness 300–1000 nm and annealing temperature 300°–525°K.The experiments have shown that the magnetostriction-stress interaction (Saito et al.) and the columnar growth of crystallites separated by non-magnetic boundaries (Iwata et al.) are the two main causes for SD.     

Nanoindentation and micro-mechanical fracture toughness of electrodeposited nanocrystalline Ni-W alloy films

Nanocrystalline nickel-tungsten alloys have great potential in the fabrication of components for microelectromechanical systems. Here the fracture toughness of Ni-12.7 at.%W alloy micro-cantilever beams was investigated. Micro-cantilevers were fabricated by UV lithography and electrodeposition and notched by focused ion beam machining. Load was applied using a nanoindenter and fracture toughness was calculated from the fracture load. Fracture toughness of the Ni-12.7 at.%W was in the range of 1.49-5.14 MPa √m. This is higher than the fracture toughness of Si (another important microelectromechanical systems material), but considerably lower than that of electrodeposited nickel and other nickel based alloys.     

Differences observed in properties of ternary NiCoFe films electrodeposited at low and high pH

Ternary NiCoFe films were potentiostatically electrodeposited from the electrolytes with low (3.0) and high (3.6) pH levels, and differences in their compositional, structural, magnetic and magnetoresistance properties were studied. The compositional analysis demonstrated that the Ni content in the films decreased, and Co and Fe content increased while electrolyte pH was changed from low to high level. The structural analysis of the films was carried out using the X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The XRD data revealed that the films have a strong (111) texture of the face-centred cubic (fcc) structure at low pH, while for the films at high pH a mixture of dominantly fcc and hexagonal closed packed structure was observed. The SEM studies showed that films grown at low pH level had comparatively larger grains than those at high pH. The magnetic characteristics studied by a vibrating sample magnetometer and magnetotransport properties were seen to be changed by the electrolyte pH. However, all films have in-plane magnetic anisotropy. The differences observed in the magnetic and magnetotransport properties were attributed to the microstructural changes caused by the electrolyte pH.     

Microstructure and magnetic behavior of electrodeposited CoPt thick films upon annealing

CoPt films with a thickness about 5-μm consisting of a disordered face-centered cubic phase have been prepared by using the electrodeposition technique. X-ray diffraction measurements and transmission electron microscopy studies reveal that the annealed CoPt films possess a nanocomposite microstructure of A1 + L1₀ CoPt and the size and volume fraction of the L1₀ ordered phase increase with annealing time. A strong magnetic exchange coupling between the A1 phase and the L1₀ ordered phase is observed after annealing for 2.5 h, which yields a large coercivity H_c = 14.2 kOe and a high remanence ratio M_r/M_s = 0.88 for the nanocomposite thick films of A1 + L1₀ CoPt.     

Optical and electrical properties of electrodeposited silver based thin films

The electrodeposited superionic conductor Ag₆I₄WO₄ was doped with various concentrations of [CrO₄]^2– to form the quarternary compound Ag₆I₄WO_4(1–xCrO_4(x). The doping level,x, was varied from 0 to 0.6 and the optimum compound was used for further analysis. X-ray diffraction (XRD) analysis indicated major peaks occurring atd values of 3.75,2.29,1.96 and 3.96 in the order of decreasing intensity. The energy dispersive analysis of X-rays (EDAX) technique verified quantitatively the ratio of the components in the solid electrolyte. From the fringes seen in the interference pattern of the transmission spectrum, the refractive index and thickness of the film was calculated. The absorption spectrum indicated the characteristic chromate peak at 310 nm when the dopant was present. An open circuit voltage (OCV) of 670 mV was observed for the fabricated cells with optimum performance at a doping level ofx=0.1, where the best discharge characteristics were observed. The subsequent conductivity was calculated to be of the order 10^–3–1 cm^–1 from the Cole-Cole plot.     

A modified layer-removal method for residual stress measurement in electrodeposited nickel films

Combining the traditional layer-removal method with a cantilever beam model, a modified layer-removal method is developed and used to measure residual stress in single and multi-layer electrodeposited nickel films with thickness of 2.5 μm. The out-of-plane displacement of the free tip of a cantilever beam is measured by the digital speckle correlation method. The results show that residual stress in a single semimat nickel film is compressive, while in a multi-layer system composed of dark, semimat and holophote nickel, residual stress in the surface layer is tensile. Residual stress decreases gradually with the increase of etching depths of single and multi-layer films. These findings are in qualitative agreement with nanoindentation tests, which confirms the reliability of the modified layer-removal method.     

Quantitative analysis of delayed fracture observed in stress rate tests on brittle materials

Delayed fracture in brittle materials may be demonstrated by observing the change in bend strength over a range of constant stress rates to failure. A simple technique has been developed to analyse this behaviour making efficient use of the experimental data. Based on a model incorporating theories of stress corrosion and brittle fracture, with Weibull statistics, the technique provides estimates of relevant parameters using the method of maximum likelihood. Confidence intervals of estimates, the significance of any observed rate effect, and the validity of the model are also assessed. The technique is demonstrated by applying it to data from bend tests on soda-lime glass and WC-Co materials.     

Morphology,structure, and magnetic properties of electrodeposited Ni films obtained from different pH solutions

Nanocrystalline nickel (Ni) films were obtained by electrodeposition from chloride aqueous solution with different pH values. The influence of electrolyte pH on the morphological, structural, and magnetic properties is studied, using scanning electron microscopy (SEM), X-ray diffraction (XRD), and alternating gradient force magnetometry (AGFM) techniques. SEM studies revealed a granular and compact structure of the surface of the electrodeposited Ni layers, and the variation of film roughness with bath pH is established. XRD analysis gives evidence of strongly textured Ni films along the (111) direction, with the face-centered cubic (fcc) structure for all baths pH. Magnetic properties such as coercivity, remanence, saturation magnetization, and squareness showed strong dependence on the baths pH and crystallite size. High coercivity was attributed to the presence of the small crystallite size of deposits. The properties of the deposit are greatly influenced by the solution pH.     

Microstructural development of an electrodeposited Ni layer

This study investigated the microstructural development of an electrodeposited Ni layer formed from an additive-free Watt's bath. The major texture component of the electrodeposited Ni layer is strong < 110> fiber. The electrodeposited Ni layer consists of epitaxial regions with a thickness of about 100 nm and fine columnar grains extending along the growth direction. The fine columnar grains contain a high density of twins parallel to the growth direction. These twins were formed at side {111} facets during the lateral growth of the electrodeposited Ni layer. We surmise that the twins formed in order to change the orientation so that the energy of boundary between the existing grain, on which twin related grains nucleated, could be reduced.     

Brush electrodeposited CdS films on low temperature substrates

Cadmium sulphide films were deposited by the brush plating technique on titanium and conducting glass substrates using a current density of 80 mA cm^− 2. X-ray diffraction studies indicated the polycrystalline nature of the films with hexagonal structure. As the deposition temperature decreased, the peaks were broad indicating the formation of nanocrystallites. Optical absorption measurements yielded band gap values in the range of 2.39-3.10 eV as the deposition temperature decreases. XPS studies confirmed the formation of CdS. Atomic force microscope studies indicated the roughness of the films decreases with the decrease of deposition temperature. The as deposited films were photoactive.     

Characteristics of pulse electrodeposited PbS thin films

PbS thin films were deposited for the first time using the pulse electrodeposition technique at different duty cycles in the range of 9 to 50% and at room temperature using lead nitrate and sodium thiosulphate. The thickness of the films increased from 0.5 to 1.0 μm with increase of duty cycle. The films were polycrystalline and exhibited cubic structure. The band gap of the films deposited at 50% duty cycle is 0.42 eV. The resistivities of the films decreased from 0.9 to 0.5 × 10⁵ ohm cm as the duty cycle increased. Films with grain size in the range of 20 to 35 nm were deposited. Films with refractive index varying in the range of 4.45–3.75 with increase of wavelength were obtained. Films with higher photosensitivity and higher detectivity compared to earlier reports were obtained.     

Characteristics of pulse electrodeposited AgGaSe2 films

In this work, the pulse electrodeposition technique has been employed for the first time to deposit AgGaSe₂ films. The films were deposited at room temperature from a bath containing Analar grade 10 mM silver nitrate, 10 mM gallium nitrate and 10 mM SeO₂. The deposition potential was maintained as—0.68 V (SCE). Tin oxide coated glass substrates (5.0 ohms/sq) was used as the substrate. The duty cycle was varied in the range of 6–50 %. The XRD profile of the thin films deposited at different duty cycles indicate the peaks corresponding to AgGaSe₂. Atomic force microscopy studies indicated that the surface roughness increased from 0.95 to 1.25 nm with duty cycle. The transmission spectra exhibited interference fringes. Refractive index of 2.71 was observed in the wavelength range 600–1,000 nm. Electrochemical Impedance studies indicated a single semicircle. The grain boundary resistance decreased with increase of duty cycle.     

Electrical properties of electrodeposited CdTe thin films

The electrical properties of electrodeposited CdTe thin films have been studied. The temperature-dependent electrical conductivity data obtained have been used to determine the conductivity type and semiconductor parameters (E _g, B, and α) of the films.     

Characteristics of electrodeposited single-walled carbon nanotube films

Thin films of chemically-functionalized single walled carbon nanotubes (SWNTs) were fabricated by using a direct current (DC) electrodeposition method. SWNTs were shortened and then functionalized with acid chloride group to combine with amine group-terminated gold substrate. The electrodeposited SWNT films were characterized by using Raman spectroscopy, attenuated total reflectance infrared (ATR/IR) spectrometry and atomic force microscopy. We demonstrated that the SWNT film was well distributed on an electrode with robust adhesion.     

恒电位电化学沉积Fe-Pt-B合金薄膜的研究

Fe-Pt合金薄膜作为最具有发展潜力的高密度磁记录材料而成为研究的热点．通过循环伏安法，得到了Fe-Pt-B合金薄膜最佳沉积电位。在优化条件下，采用电化学沉积法制备了Fe-Pt-B合金薄膜。利用X荧光光谱仪（EDX）、振动样品磁强计（VSM）和透射扫描电镜（SEM）对薄膜的组成、磁性能和形貌进行了初步研究．结果表明Fe-Pt合金薄膜中B的掺入可以增强薄膜的结晶度．