Papers by Keyword: Nickel Ni

Abstract: Metal-induced lateral crystallization (MILC) of patterned amorphous silicon(a-Si) thin film using Ni as a catalyst has been investigated. Ni-MILC grains are based on the growth of needle-like crystals due to the migration of NiSi2 precipitates, which located at the crystalline front, along the <111> directions. In the case where the needle-like crystallites collided at the a-Si pattern edge, not only “turn” or “branch” of the needle-like crystallites toward one of the possible <111> directions but also the growth along the pattern edge were observed. By limiting the growth area, the competitive growth of dendrite crystals that originated in needle-like crystallites was found to appear. This phenomenon resulted in the orientation alignment of MILC crystals in a wide area. Besides, the grain-filtering of MILC crystals was found to be possible by narrowing the pattern width.

Abstract: Ti-Ni based functionally graded alloy is a kind of the promising material, which has potential to be used in aero engines. Using laser rapid forming, a Ti-Ni graded alloy with a continuous compositional gradient from pure Ti to Ti-50wt.%Ni were fabricated. On comparison with the graded alloy, a series of homogenous deposits with the typical composition between pure Ti to Ti-50wt.%Ni were also laser rapid formed. The phase evolution along the compositional gradient direction in the graded alloy is: α+β→β+Ti2Ni →(TiNi +Ti2Ni)+ TiNi; and the phase evolution in the corresponding compositional homogeneous deposit is: α+β→ β+(β+Ti2Ni)→ β+Ti2Ni+(β+Ti2Ni)→ (TiNi+Ti2Ni)+TiNi. The phase transformation and microstructural evolution along the compositional gradient were analyzed by using the microstructure selection map.

Abstract: This study is considered as a method for producing multifunctional metal composite materials by using Single-walled Carbon Nanotubes (SWNTs). In this research, various metals (Ni, Cu, Ag ) were successfully deposited onto the surface of SWNTs. It has been found that homogenous dispersion and dense nucleation sites are the necessary conditions to form uniform coating on SWNTs. Functionalization has been applied to achieve considerable improvement in the dispersion of purified single-walled carbon nanotubes. A three-step electroless plating approach was used and the coating mechanism is described in the paper. The samples were characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and energy-dispersive X-ray spectroscopy (EDX). The application of coated SWNTs in Titanium will be discussed in this paper.

Abstract: In order to improve the hydrogenation property of Mg/Ti laminate composite, Ni was added as a third element. Hydrogen storage properties of the laminated Mg/Ti/Ni alloy films were studied. Laminated Mg/Ti/Ni multilayer alloy films were prepared by cold rolling of stacked Mg, Ti and Ni under ambient conditions. The stacked foils were subjected to repetition of rolling and stacking, resulting in super-laminated foils with the thickness less than 0.3mm, containing more than 15000 layers. Microstructures of the super-laminates were studied by scanning electron microscopy and X-ray diffractometry. Their hydrogenation behaviors were investigated by use of a Sieverts type apparatus. The hydrogen storage capacity (H/M) of the laminate with composition Mg/Ti/Ni=9.0/0.9/0.1 amounted H/M=1.6 at 573K, 0.4MPa. Initial activation property was improved by controlling the amount of Ni appropreately.

Abstract: Pulsed electric current sintering (PECS) was applied to the bonding of W (tungsten) to Cu (copper) using Nb or Ni powder as an intermediate layer. The influence of the intermediate layer on the bond strength of the joint was investigated by observation of the microstructure. The bonding process was carried out at carbon-die temperatures of 1073 and 1173 K for 1.8 ks at a bonding pressure of 130 MPa. The bond strength of the joint with an intermediate layer of Ni powder was 250 MPa. This joint fractured in the Cu base during the tensile test. SEM observations of the joint with an intermediate layer of Ni revealed that a diffusion layer formed at the joint interface.

Abstract: Strength of nanostructured Cr-B and Cr-Ni alloys prepared by sputtering was related with grain size. The alloying of B or Ni to Cr reduces the grain size of the alloys. The increase in volume of grain boundaries or amorphous phase induced by alloying elements causes the departure of strength of nanostructured Cr alloys from the values estimated by the Hall-Petch relation. The formation and microhardness of Cr or Ti base amorphous alloys could be discussed by the chemical bonding between elements. The strength of dissimilar joints was dominated by the thickness and structure of the interfacial reaction zone between SiC and metal. The formation of interfacial reaction zone is discussed by the change of chemical potentials of elements between ceramics and metal.

Abstract: Notched tensile tests {orientation: tensile axis [001], direction of notching [010]or[110] } were performed to investigate the crack growth process in Ni-single crystal with hydrogen cathodic charging. Y-shaped hillocks and striation-like patterns were observed on the fracture surfaces of hydrogen embrittled specimens using the scanning electron microscope (SEM). The Y-shaped hillocks are exactly matched on both fracture surfaces of a specimen. In addition, cleavage fracture is occurred between a Y-shaped hillock and next one. It means that the cleavage fracture is occurred at first, and the Y-shaped hillock is secondary formed. It is considered that the striation-like pattern is formed by the localized slips and cleavage fracture between them. Peach-Koehler’s law leads that the dislocations on the equivalent slip systems with (111　)　[101] are subjected to the highest force of all dislocations at the crack tip. Furthermore, Ni-hydride was not observed on the surface of specimen just after charging hydrogen. Thus, it was concluded that Y-shaped hillock and striation-like pattern were occurred in Ni-single crystal with charging hydrogen under condition that Ni-hydride is not formed.

Abstract: Cyclic loading of metallic engineering components at constant elevated or fluctuating temperature causes a complex evolution of damage which be can hardly be described in a unique and straightforward manner. Often the thermal behaviour of the base metals is to weak, so thermal barrier coatings were needed. Nickel is generally used for such thermal barrier coatings. Therefore it is necessary to study the thermo-mechanical fatigue (TMF) of this material. The lifetime of these coatings is very strong affected by the temperature loading in general, both described by nodal temperatures and their local gradient. The thermal cyclic loading takes place as thermo-mechanical and low cycle fatigue (LCF) damage regime. To classify the thermo-mechanical failure mechanism of pure nickel, OP (out of phase) and IP-TMF (in phase) test series were examined. The use of damage parameters like the unified energy approach make sense, a more detailed life time calculation for pure Nickel can be done by using the Neu-Sehitoglu model. Summary, thermomechanical loadings activate multiple damage mechanism. Surface embrittlement by oxidation is the major distinctive mechanism in addition to pure fatigue damage. Different lifetime approaches were tested and analysed to fulfil the requirements for the fatigue analysis of nickel made components.

Abstract: In this work, ohmic contacts, formed by 100nm Ni layer RTA annealed or not, were investigated on 3C-SiC epilayers exhibiting different nitrogen doping levels. The epilayers were grown on (100) silicon. Doping level (N) and eventual dopant contamination (Al) were analyzed by C-V and/or SIMS. The specific contact resistance was determined by using Transmission Line Model (TLM) patterns for each condition (doping and annealing). Our results clearly evidence that very low specific contact resistance (~10-51.cm²) is obtained on highly doped 3C-SiC epilayers, enlightening the interest of both material and Ni contacts for future devices fabrication.

Abstract: A pure Ni single crystal of Cube orientation (001)/[100] have been deformed by reversible cold rolling to a reduction of 98% following an initial extrusion treatment. The microstructure in the as-deformed samples and in partly recrystallized specimens have been characterized in the scanning electron microscope using electron backscattered diffraction (EBSD). Line scans along the normal direction across the sample thickness show some evidence for a macroscopic pattern of subdivision. The EBSD measurements show that the deformed sample is characterized by large jumps in orientation between alternating S and Br orientations, related by misorientation angles of 50°~60°. In part of the sample a background cumulative change in orientation is seen, though local large change in orientation are also still seen. In annealed samples it is found that the orientations of the new grains