فهرست مطالب reza gholamipour

In this article, the growth kinetic and optical property of amorphous carbon (a-C) nanolayers deposited by ion beam sputtering deposition technique on glass substrates are investigated. The atomic force microscopy is used to measure the variation of surface roughness versus deposition time. According to the calculations, the roughness of thin films increases during the growth process as a fractal scaling law. The Hurst exponent (α) has a value higher than 0.5, and the growth exponent (β) changes in the range of 0.02 to 0.22. These fractal exponents predict that the growth process of amorphous carbon nanolayers obeys the rules of the Wolf-Villain model belonging to the Edwards-Wilkinson universality class, in which the relaxation and surface diffusion happen during the growth process. The results indicate that the optical band gap decreases by reducing the surface roughness, Hurst exponent and the correlation length during thin film growth which is the first observation of this trend.

The growth kinetic of amorphous carbon (a-C) thin films was investigated in the relation to the surface morphology and structural transformations. The a-C thin films were deposited by ion beam sputtering technique on the glass substrate. According to Avrami's model, the growth at the thickness above 56 nm (after 900 s deposition) is two-dimensional and the proposed equation for investigating about the growth process of amorphous carbon thin film in the present study is as follows: V=1-exp⁡(-2×〖10〗^(-7) t^2 ). Transformations of the thickness is similar to proposed Avrami's model follow a characteristic s-shaped, or sigmoidal, profile during deposition time from 300s to 4500s, where the transformation rates are low at the beginning and the end of the transformation but rapid in between. Surface roughness and structural transformation depend on the film thickness. Raman spectra showed the maximum displacement in G peak position created in the film thickness equal 360 nm with the reduction of the growth rate. The ID/IG ratio, the size of graphite crystallites with sp2 bonds (La) and the roughness of this layer is equal to 1.2, 1.48 nm and 20.39±4.8 nm, respectively.

In this research microstructural evolution during high temperature brazing of dissimilar bonding of IN738 Ni-base superalloy to TiAl intermetallic compound using an amorphous Ni-Si-B ternary alloy was investigated. Phase transformations via solidification and solid state reactions are discussed. Observations indicated that the microstructure of IN738/MBF-30/TiAl joint consist of four different zones; isothermal solidification zone in both sides, athermally solidified zone in the bond center, diffusion affected zone in the IN738 side and reaction layer in the TiAl side. γ-Ni solid solution phase in ISZ of the IN738 side and binary isostructural solid solutions in ISZ of the TiAl side were formed during holding time at bonding temperature. Ni-Cr borides have been formed due to binary eutectics associated with γ-Ni solid solution in the ASZ during cooling. Cr-Mo borides and Ni-rich boride with different morphologies were precipitated in the DAZ. Ni element from MBF-30 molten interlayer reacted with γ-TiAl base, leading to the formation of the reaction layer containing single phase δ-Ti2Ni and triple phase τ2-Al2TiNi+τ4-AlNi2Ti+β1-NiAl layers adjacent to TiAl substrate. Microhardness evaluation of different zones indicated that some high hardness phases have formed in the bond region and presence of the γ-Ni solid solution in the ASZ cause to decrease the detrimental effects of them.

In this study, the graphitic amorphous carbon (g-C) thin films were deposited by the ion beam sputtering deposition (IBSD) technique on glass substrates. The effect of ion beam energy on the optical and structural properties of thin films was investigated in the wide range from 1.8 keV to 5 keV. The results of investigation about optical and structural properties using UV-visible spectroscopy and Raman spectroscopy respectively showed a direct correlation between structural and physical developments. Raman spectra indicated a structural transition from graphite to nano-crystalline graphite phase. The values of ID/IG ratio, optical transparency and optical band gap depend on the ion beam energy; all of them increased by increasing argon ion beam energy from 3 keV, which is associated with a decrease in the film thickness. Furthermore, the sheet resistance of the samples was measured by the four-point probe (FPP) followed similar trends of these structural properties. According to Tauc equation the maximum optical band gap was equal to 3.75 eV by the graphite crystallites (with sp2 bands (La )) equal to 5 nm in amorphous carbon thin film deposited with the highest argon ion beam energy of 5 keV.

Ni-Cu (70.4-29.6 ; wt%) alloy was prepared by a Vacuum Arc Remelting (VAR) furnace and the effect of thermal treatment on structure and Curie temperature was investigated. The results of Inductively Coupled Plasma (ICP) and EDS analysis showed that specimens with 4 times remelting were homogenized. The Curie temperature of alloy that measured by vibrating sample magnetometry (VSM) under condition of slow cooling across from order-disorder transition of alloy was higher than specimens quenched from recrystallization temperature. Curie temperature (TC) of alloy that quenched after melting was 60 ͦ C ,TC of sample that annealed in 1000 ͦ C for 24 hours then quenched in water was 40 ͦ C and sample that after annealing twice heated up to 70 ͦ C was 45.5 °C .
The d-spacing of the specimen without heat treatment, calculated by X-Ray Diffraction, had a little increase due to clustering. In addition, the surface morphology by optical microscope confirmed this behavior of Cu–Ni alloys in the different heat treatment.

In the present study, crystallization behavior of amorphous (Al90Ni8Zr2)98MM2 alloy have been investigated using X-ray diffraction, differential scanning calorimetry (DSC) and micro-hardness test. For this purpose, amorphous ribbons were manufactured using a melt-spinning apparatus. The average thickness of the produced ribbon was 20 micrometers. The results of the kinetic test showed that the crystallization in the amorphous alloy (Al90Ni8Zr2)98MM2 occurs at least in three steps. DSC graphs were analyzed using Kissinger's method and the activation energy for the first, second and a third stage of crystallization was 331, 241, and 330 kJ/mole, respectively. The results of micro-hardness test showed that the amorphous phase hardness at room temperature was 413 Vickers, which was reduced to 276Hv by isothermal heat treatment at temperatures close to first transformation temperatures. It has been observed that, after heat treatment at a temperature above α-Al phase transformation temperature, the hardness increases to 453Hv. Formation of intermetallic phases at 800K, cause the hardness drop to 269Hv.

In this study the effect of substrate temperature (from room temperature (RT) to 400°C) on the sructural and physical properties of cabon thin films were investigated. The films were prepared by ion beam sputtering deposition technique on glass substrate. Optical and structural properties were studied by UV-visible spectroscopy, Raman spectroscopy and atomic force microscopy, respectively. The results showed that optical transparency decreased with the increase in the substrate temperature. Raman spectra indicated a structural transition from amorphous to graphite-like phase by increasing temperatures since in the spectra; D peak disappeared in the layer at the substrate temperature of 400°C. The result of sheet resistance and the optical band gap showed the reduction trend by the increase in the substrate temperature from 100 to 400°C. However the enhancement of the surface roughness with the substrate temperature was observed. In the layer prepered with the substrate temperature equal to 100 °C , a minimum size of the graphite crystallites (with sp2 bands (La)) was equal to 0.36 nm and a maximum optical band gap was equal to 3 eV.

In this work, we have studied the influence of dc joule-heating thermal processing on the structure, magnetoimpedance (MI) and thermal properties of Co64Fe4Ni2B19-xSi8Cr3Alx (x = 0, 1, and 2) rapidly solidified melt-spun ribbons. The nanocrystallization process was carried out by the current annealing of as-spun samples at various current densities. As-spun and joule-heated samples were studied by X-ray diffraction (XRD), differential scanning calorimeter (DSC), and magnetoimpedance (MI) measurements. DSC results revealed that by the replacement of B by Al the first and second crystallization peaks are overlapped with each other and the initial nanocrystallization temperature is decreased with the increase in Al content of the alloy. Also it was shown that the replacement of B by Al atoms can improve soft magnetic properties confirmed by magnetoimpedance ratio (MIR%) results for the amorphous joule-heated ribbons. Furthermore, increase in dc joule current density increases the MI ratio first, however; after formation of crystalline phases, it decreases.