Papers by Keyword: Amorphous Materials

Abstract: Primary crystallization of amorphous Al₈₆Ni₆Y₆Ce₂ (at.%) alloy was investigated through differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and X-ray diffraction. Moreover, nanoindentation analysis was performed to relate the hardness to the structure of the alloy. The kinetic parameters of the first crystallization process were determined by Kissinger method. The average amount of Avrami exponent (n=1.7±0.21) was concluded the primary crystallization occurred through three dimensional diffusion-controlled growth with decreasing rate. The α-Al nanoparticles 58 nm in size homogeneously embedded in the glassy matrix were formed during primary crystallization. Significant changes in the hardness occurred due to the change of the crystalline structures. The hardness of 7.30±0.58 GPa was obtained by annealing at 618 K with a microstructure of Al nanoparticles and Al₃Ni intermetallic compound in an amorphous matrix.

Abstract: The aim of the paper was investigation of the effect of Cu addition on glass forming ability (GFA), thermal stability, structure and magnetic properties of Fe-Co-based bulk metallic glasses (BMGs). The raw materials used in this experiment for the production of BMGs were pure Fe, Co, Cu and industrial Fe-B, Fe-Si, Fe-Nb ferroalloy. Investigations were carried out on BMGs in rods shaped with square section with side of 1.5mm. The structure of the investigated BMGs in rod form is amorphous. The addition of small amounts of Cu is effective in changing GFA and magnetic properties. The melting temperature - Tm remained almost constant for both investigated alloy. Two alloy compositions are at or very close to the eutectics, what according to ref. [1] should guarantee the best metallic glass-forming alloys. The investigated alloys have good soft magnetic properties. The successful synthesis of the Fe36.00Co36.00B19.00Si5Nb4 and Fe35.75Co35.75B18.90Si5Nb4Cu0.6 alloys with high GFA and good soft magnetic properties by using starting industrial alloys are encouraging for the future industry applications.

Abstract: A series of wedge shape Fe24+XCo24-XCr15Mo14C15B6Y2 (x=0,2,4,6,8) samples were prepared by copper mold suction casting method. The effects of high Co contents on glass forming ability (GFA) and mechanical properties of Fe24+XCo24-X Cr15Mo14C15B6Y2 bulk metallic glasses (BMG) were investigated, respectively. The glass forming ability of bulk amorphous Fe24+XCo24-XCr15Mo14C15B6Y2 (x=0,2,4,6,8) and Fe41Co7Cr15Mo14C15B6Y2 alloys have been researched. Simultaneously, the thermal conductivity parameters of those alloys were tested. The maximum thickness of amorphous region of wedge-shaped samples are dm =7.80 mm for Fe28Co20Cr15Mo14C15B6Y2, dm =7.10 mm for Fe41Co7Cr15Mo14C15B6Y2 and the thermal conductivity are λ=7.11 w.m-1.k-1 and 7.19 w.m-1.k-1, the thermal diffusivity are α=1.875 mm2/s and 1.905 mm2/s for Fe28Co20Cr15Mo14C15B6Y2 and Fe41Co7Cr15Mo14C15B6Y2 BMGs, respectively. The glass forming ability of Fe28Co20Cr15Mo14C15B6Y2 alloy is bigger than that of well known Fe41Co7Cr15Mo14C15B6Y2 alloy. With the change of Co content, the Vickers hardness of Fe24+XCo24-XCr15Mo14C15B6Y2 (x=0,2,4,6,8) change from 1292 to 1322Hv.

Abstract: Titanium Silicalite-1 (TS-1) was successfully synthesized from amorphous silica and titania powders by using a ball-milling method. In this method, amorphous fumed silica and anatase titania powders were ground in a planetary ball mill to produce a silica-titania precursor. The obtained precursor was then hydrothermally treated where TPABr was used as a template to obtain titanium silicalite-1 (TS-1). The XRD and UV-vis spectra indicate that the titanium in anatase with octahedral coordination is incorporated into the silica-titania precursor and the final TS-1 framework with a tetrahedral coordination. SEM image shows that TS-1 synthesized in this work appears in a shape of elongated prism with a dimension of about 3μm×1μm×0.2μm. This method gives a simple new approach to the synthesis of TS-1 using inexpensive silicon source, titanium source and template.

Abstract: Bulk Nd60-xCo15+xAl25 (where x =0, 2, 5, 8, 11) sheet alloys were prepared by argon arc melting and suction casting a copper mold. Glassing forming ability (GFA) of these alloys was investigated by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Due to the dissimilarity reflected from DSC curves the thermodynamic calculation was applied. The values of Gibbs free energy (∆Gl-x (Tg)) for the amorphous alloys were gave out and some GFA criterions were adopted to make a comparison among the samples.

Abstract: Bulk metallic glasses (BMGs) are well known for their promising properties. Surface properties can be further improved by using certain techniques such as electron beam melting (EBM), laser beam melting (LBM), ion irradiation, ion implantation and neutron irradiation. BMGs especially Zr-based BMGs have numerous applications as structural materials. In this manuscript, the results are presented on microstructural investigations and phase formations in Zr-based BMGs modified by using above mentioned techniques. Microstructure was studied by scanning electron microscopy (SEM). Phase analysis was done by X-ray diffraction (XRD) and confirmed by energy dispersive spectroscopy (EDS). Vickers hardness was measured and correlated with the microstructure. The phases identified in Zr-Cu-Al-Ni alloy samples modified by EBM, LBM and ion irradiation are Ni-Zr, NiZr₂, CuZr₂, Cu₁₀Zr₇ and Al₂NiZr₆. ZrSi₂ phase was detected in Zr₅₅Cu₃₀Al₁₀Ni₅ and Zr₆₅Cu₁₇Ni₁₀Al₈ BMGs irradiated with Si⁺ (ions). About 20-35 % increase in hardness and elastic moduli was achieved by surface modification. Modifications of BMGs by electron and laser beams melted the materials surfaces while ion irradiation improved the mechanical properties of localized zones without melting.

Abstract: A quaternary Ni₈₆Cr₇Si₄Fe₃ amorphous alloy was synthesized by melt spinning technique. Surface modification was done by electron beam melting (EBM), neutron irradiation and γ-rays. Microstructure of as cast, annealed and modified samples was examined by scanning electron microscope. Crystallization behavior was studied by annealing the samples in vacuum at different temperatures in the range 773-1073 K. Techniques of X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used for characterization. Differential scanning calorimetry (DSC) was conducted at various heating rates in the range 10-40 K/min. Thermal parameters like glass transition temperature T_g, crystallization temperature T_x, supercooled liquid region ΔT_x and reduced glass transition temperature T_rg were measured. The Ni₈₆Cr₇Si₄Fe₃ alloy exhibits wide supercooled liquid region of 60 K indicating good thermal stability. The activation energy was calculated to be 160±4 kJ/mol using Kissinger and Ozawa equations respectively which indicates high resistance against crystallization. The XRD results of the samples annealed at 773 K, 923 K, 973 K and 1073 K/20 min show nucleation of Ni₂Cr₃ and NiCrFe crystalline phases. Vickers microhardness of the as cast ribbon was measured to be 680.. About 30-50 % increase in hardness was achieved by applying EBM technique.

Abstract: Hydrogen and iron diffusion coefficients in molten zirconium have been calculated using a molecular dynamics (МD) model. The molecular dynamics method using micro-canonical (NVT) ensemble was used to analyze iron and zirconium diffusion coefficient dependence on electric field intensity and the presence of hydrogen in the zirconium melt. Results obtained are compared to the literature data on impurity removal in plasma-arc zirconium melting in the presence of hydrogen as well as in electron-beam and vacuum-arc melting. The limiting stage of iron removal from the melt is established. The contribution of the electric field to iron removal is estimated. We carried out systematization of the D_H^Me data for Zr, Nb, and Ta. An Arrhenius equation analysis for D_H^Me and its extrapolation to the premelting zone taking into account the Gorsky effect was carried out too. The analysis enabled the estimation of D_H^Me for the temperature interval where experiment encounters difficulties.

Abstract: Using microwave-assisted solid-state method, a series of zinc oxide-modified mesoporous SBA-15 materials were synthesized. The desulphurization test with a gas mixture containing 0.1 vol % hydrogen sulfide was carried out on these materials. Chemicals before and after the desulphurization test were analyzed using nitrogen adsorption, XRD, EDS, TEM, ICP and other standard methods. The results suggest that zinc oxide modification can accelerate the transformation from a mesoporous to a zeolite phase. The different zinc loading results in different zinc-phase dispersions on the materials.

Abstract: Amorphous alloys Ni64Zr36 and Ni36Zr64 structure and hydrogen mobility are researched by the molecular dynamics method. The analysis of structure factors and partial distribution functions of atoms revealed hydrogen affects the short order parameters of the disordered systems. Diffusion coefficients of hydrogen are shown to depend on its concentration.