Muhammad Iqbal
材料科学技术（英）
Minor alloying plays an important role in the synthesis and improvement of thermal stability of bulk metallic glasses (BMGs). The present study was conducted to investigate the effect of minor additions of Y, Ti and Nb on crystallization behavior and thermal properties of Zr64.5Ni15.5Al11.5Cu8.5 base alloy. Thermal parameters and the activation energies for crystallization were calculated for four [Zr0.645Ni0.155Al0.115Cu0.085]100-xMx (M = Y, Ti and Nb while x = 0, 2 at. %) alloys. Parameters describing thermal stability in these systems, including the activation energies for crystallization, were determined. The present alloys have wide supercooled liquid region of ≥87 K. Maximum activation energy was found to be greater than 300 kJ/mol for the base alloy. Four crystalline phases were identified in the samples annealed at 823 K. Reduced glass transition temperature (Trg) and other thermal parameters like γ, δ and β improved by Y and Ti addition. Niobium addition resists crystallization below annealing temperature 713 K however its effect on thermal properties is not very promising.
关键词:
Activation energy
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null
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null
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null
H.B. Motejadded
材料科学技术（英）
Coarsening behavior of γ′ precipitates in the dendritic regions of a Ni3Al base alloy containing chromium, molybdenum, zirconium and boron was investigated. Annealing treatment was performed up to 50 h at 900, 1000 and 1100 °C. The alloy was produced by vacuum-arc remelting technique. Results show that coarsening of the γ′ precipitates in this complex alloy containing high volume fractions of γ′ phase follows Lifshitz-Slyozov-Wagner (LSW) theory. Coarsening activation energy of the γ′ precipitates was evaluated to be about 253.5 kJ?mol-1 which shows that the growth phenomenon is controlled by volume diffusion of aluminum. With an innovative approach, diffusion coefficient of the solute element(s) and the interfacial energy between γ′ precipitates and γ (matrix) were estimated at 900, 1000 and 1100 °C. Accordingly, the interfacial energies at 900, 1000 and 1100 °C are 4.49±1.48, 2.08±0.69 and 0.98±0.32 mJ?m-2, respectively. Also the diffusivities of solute element(s) at these temperatures are 3.41±1.08, 30±9.5 and 145.15±45.85 (10-15 m2?s-1), respectively.
关键词:
Ni3Al base intermetallic
Baowei QIAO
,
Yunfeng LAI
,
Jie FENG
,
Yun LING
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Yinyin LIN
,
TingAo TANG
,
Bingchu CAI
,
Bomy CHEN
材料科学技术（英）
The amorphous Ge2Sb2Te5 film with stoichiometric compositions was deposited by co-sputtering of separate Ge, Sb, and Te targets on SiO2/Si (100) wafer in ultrahigh vacuum magnetron sputtering apparatus. The crystallization behavior of amorphous Ge2Sb2Te5 film was investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and differential scanning calorimetry (DSC). With an increase of annealing temperature, the amorphous Ge2Sb2Te5 film undergoes a two-step crystallization process that it first crystallizes in face-centered-cubic (fcc) crystal structure and finally fcc structure changes to hexagonal (hex) structure. Activation energy values of 3.636±0.137 and 1.579±0.005 eV correspond to the crystallization and structural transformation processes, respectively. From annealing temperature dependence of the film resistivity, it is determined that the first steep decrease of the resistivity corresponds to crystallization while the second one is primarily caused by structural transformation from "fcc" to ``hex" and growth of the crystal grains. Current-voltage (I-V) characteristics of the device with 40~nm-thick Ge2Sb2Te5 film show that the Ge2Sb2Te5 film with nanometer order thickness is still applicable for memory medium of nonvolatile phase change memory.
关键词:
Co-sputtering
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H.B. Motejadded
材料科学技术（英）
In the present research, the dissolution mechanism of a Zr rich structure during annealing of a Ni3Al base alloy containing Cr, Mo, Zr and B, was investigated. The annealing treatments were performed up to 50 h at 900, 1000 and 1100 °C. The alloy used in this investigation was produced by vacuum-arc remelting technique. The results show that at the beginning of the process, a mixed interface reaction and local equilibrium (long range diffusion) mechanism controls the dissolution process. After a short time, this mechanism changes and the dissolution mechanism of the Zr rich structure changes to only long range diffusion of Zr element. According to this mechanism, the activation energy of this process is estimated to be about 143.3 kJ?mol-1. Also the
phases that contribute to this structure and the transformations that occur at the final steps of solidification of this alloy were introduced. According to the results, at the final step of solidification, a peritectic type reaction occurs in the form of L+ γ´→ γ+Ni7Zr2 and γ-Ni7Zr2 segregates from the melt. Following this transformation, γ-Ni7Zr2 eutectic separates from the remaining Zr rich liquid. The solidification process will be terminated by a ternary eutectic reaction in the form of L+→ γ+Ni5Zr+Ni7Zr2.
关键词:
Ni3Al base alloy
Bharat B.PANIGRAHI
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N.Subba REDDY
,
Karabi DAS
材料科学技术（英）
The effect of Al addition (2 and 5 at. pct) on sintering kinetics of Ti power was investigated. Al reduces the sintering rates, sinter density, increases activation energy of sintering and accelerates the grain growth. Sintering was controlled by mixed mode, i.e. transient liquid phase sintering, formation of intermetallics, and Ti grain boundary diffusion in TiAl2 and other intermetallics.
关键词:
Dilatometry
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Sintering
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Diffusion
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Activati
Ying LI
,
Yunfa CHEN
,
Jianghong GONG
材料科学技术（英）
The ac conductivities of Y2O3 or CaO-stabilized cubic zirconias were obtained from complex impedance measurements in the temperature range from 373 to 473 K. By analyzing the temperature-dependence of the resultant dc conductivities, it was shown that the activation energies for conduction are lower than those reported previously for the same materials at high temperatures. Comparing the activation energy data with the theoretically estimated values revealed that there may exist a certain, although very small, amount of free oxygen vacancies in the test samples at low temperatures and the conduction in the test samples is a result of the migration of these free oxygen vacancies.
关键词:
Ionic conductivity
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Haitao YE
,
Olivier GAUDIN
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Richard B.JACKMAN
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null
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null
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null
材料科学技术（英）
The first measurement of impedance on free-standing diamond films from 0.1 Hz to 10 MHz up to 300℃ were reported. A wide range of chemical vapour deposition (CVD) materials were investigated, but here we concentrate on `black' diamond grown by microwave plasma enhanced CVD (MWPECVD). The Cole-Cole (Z' via Z'') plots are well fitted to a RC parallel circuit model and the equivalent resistance and capacitance for the diamond films have been estimated using the Zview curve fitting. The results show only one single semicircle response at each temperature measured. It was found that the resistance decreases from 62 MΩ at room temperature to 4 kΩ at 300℃, with an activation energy around 0.51 eV. The equivalent capacitance is maintained at the level of 100 pF up to 300℃ suggesting that the diamond grain boundaries are dominating the conduction. At 400℃, the impedance at low frequencies shows a linear tail, which can be explained that the AC polarization of diamond/Au interface occurs.
关键词:
Black diamond
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diamond
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Impedance
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spectroscopy
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Act
Niwat Mookam
材料科学技术（英）
The growth, transformation, and lattice structure of intermetallic compounds formed between Sn-0.3Ag-0.7Cu lead-free solder and copper substrate were investigated. Dip soldering was used to initiate the reaction between the solder and substrate. An μ-Cu6Sn5 intermetallic phase possessing a hexagonal lattice structure was found at the as-soldered interface. Thermal aging at a number of conditions resulted in the formation of a Cu3Sn intermetallic phase between the Cu6Sn5 layer and the copper substrate. ε-Cu3Sn with an orthorhombic lattice structure was found together with hexagonal Cu3Sn. Subsequently, the activation energies of the intermetallic phases were calculated and compared to results obtained from the literature. The comparison showed that good agreement existed between the findings from this study and literature data within a similar temperature range.
关键词:
Soldering
