جستجوی مقالات مرتبط با کلیدواژه "melt spinning" در نشریات گروه "مواد و متالورژی"

In the present work, the effects of substitution of Ag with Cu on thermal behaviors of Mg-Cu-Y based amorphous alloys were investigated. In this regards, four different (x=1, 4, 7, 10) Mg65Cu30-xAgxY5 alloys were melt spinned at same condition. The structural and thermal characteristics of prepared alloys were examined using X-ray diffraction (XRD) and differential scanning calorimetric (DSC) techniques. Based on results, the substitution of Ag with Cu in Mg-Cu-Y alloys had significant effects on thermal behavior of prepared samples. Although, the crystallization mechanism of prepared amorphous phase in different alloys was the same, the Mg65Cu23Ag7Y5 alloy (in the presence of 7 at. % of Ag) showed higher thermal stability in comparison to others. The crystallization activation energy of prepared amorphous alloys was estimated about 150-200 kJ mol-1. Based on the calculated values of Avrami exponent (1.5<n<1.7), the crystallization process in different systems were the same as a three-dimensional diffusion-controlled growth.

The structure of metals strongly depends on solidification parameters such as cooling rate and supercooling. It is obvious that the cooling rate is an important factor in order to refine metal structure, and especially affecting mechanical properties of metals. In this investigation melt spinning method is used to reach rapid solidification and ribbon shaped samples in Aluminum 5083 alloy were produced. The resulting ribbon samples were studied by optical microscopy (OM), scanning electron microscopy (SEM), micro hardness tester, X-ray difractometry, and were compared with their ingot counterparts. The results perfectly shown that the produced ribbons exhibits unique properties such as enhanced solid-solubility level of elements in the Al matrix (solid solution strengthening) and formation of spherically shaped intermetallic phases rich in Fe, Mn and Si and less than 50 nm in size homogenously dispersed in Al matrix which resulted in mechanical properties improvement and microstructural refinement of Al5083 alloy. As an example microhardness was approximately raised over 2 times more than conventional casting methods.

The aim of this study was optimization of the annealing process in melt spun Nd2Fe14B intermetallic magnetic alloy. In this regard, the melt spinning process was done at wheel speed of 40 m.s-1. In order to achieving the desired microstructure, the as-spun ribbons were subsequently annealed at temperature range of 500 to 700 ºC for different periods of time. Structural and magnetic characterization of produced samples were performed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). The results showed that the structure of as-spun ribbons at wheel speed of 40m.s-1 was composed of Fe-α, Nd2Fe14B and amorphous phases with the coercivity and saturation of magnetization in the range of 0.14 kOe and 120 emu/g, respectively. By annealing the produced ribbons and crystallization of the amorphous phase, the percentage of Fe-α and Nd2Fe14B was decreased and increased, respectively. The optimum annealing conditions for achieving the highest value of coercivity (about 9.2 kOe) was 600°C for 6h.

Co-based metallic glasses have attracted the attention of many researchers due to their excellent magnetic softness, as well as their high corrosion resistance. In the present research, Co-Fe-Ta-Hf-B glassy ribbon with a high thermal stability was prepared by melt-spinning and its isochronal crystallization kinetics at different heating rates was systematically investigated. The apparent and local activation energy of crystallization, the fraction of crystals at different temperatures and other kinetics parameters were calculated according to Ozawa method. In addition, the devitrification kinetics of the produced glass was studied based on the well-known Jahnson-Mehl-Avrami (JMA) and Sestak-Berggren (SB) models. The results indicated that the local activation energy increases with progress of crystallization. Furthermore, the average activation energy calculated based on the Kissinger model was 664 kJ/mol, which is larger than many other metallic glasses, and confirms a high thermal stability of this alloy. It was shown that the JMA model cannot be used for analysis of the crystallization behavior of the present alloy and due to a complex and autocatalytic nature of crystallization, the SB model gives more liable results for investigation of crystallization kinetics.

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.

The aim of the present study is to produce Sn base lead-free nanocomposite solders reinforced by nanoparticles with rapid solidification technique and compare their mechanical, electrical and thermal properties with conventional SAC (Sn-3.8Ag-0.7Cu) solder. Therefore, four lead-free soldering alloys Sn-3.8Ag-0.7Cu-XAl (X = 0, 0.25, 0.5, 1) were alloyed using a vacuum arc remelting (VAR) furnace. Then with melt spinning technique ribbons of nanocomposite solders reinforced with Cu6Sn5 and Ag3Sn intermetallic compounds nanoparticle were manufactured. The microstructural, mechanical, electrical and thermal properties of these nanocomposite solders were investigated using scanning electron microscopy, X-ray diffraction, Vickers hardness method, four-point resistance measurement method and differential scanning calorimetry (DSC). The results showed the uniform distribution of nanoparticles intermetallic compounds Cu6Sn5 and Ag3Sn in the solder matrix and a 30% significant increase of micro-hardness, negligible variation in the specific electrical resistance, and a 3 degrees increase in the melting temperature of the new nanocomposite solder compared to conventional SAC solder.

Cobalt-based amorphous alloys attracted the attention of many researchers to carry out fundamental research for their application in electronics¡ sensors and magnetic memory due to their special magnetic properties including close to zero Magnetostriction¡ magnetic permeability and high saturation magnetization. The purpose of this study is the formation and evaluation of microstructure and magnetic properties of cobalt-based amorphous alloy produced by melt spinning and mechanical alloying. The final compositions produced by both methods were studied by scanning electron microscopy¡ X-ray diffraction and vibrating magnetoresistance. The results showed that compound produced by chill block melt spinning has a better magnetic properties .

In this research, the TLP bonding of IN-738LC superalloy was investigated using MBF-20 amorphous foil produced by melt spinning process. The bonding process was carried out at 1035-1080°C for 30-60 min under the vacuum atmosphere. Microstructural investigations showed that the eutectic phases formed in non-isothermal solidified zone (ASZ) are consised of secondary phase borieds rich in nickel, chromium and nickel silicides. Nickel silicide fine precipitates are formed within γ solid solution via solid state precipitation during cooling. The centerline eutectic phases decreased with increase of the bonding time and decrease of amorphous foil thickness. It was found that isothermal solidification was completed when bonding was done at 1055°C for 30 min. However, the isothermal solidification rate decreased with increasing of the bonding temperature up to 1080°C. Unexpectedly, isothermal solidification rate decreased by increasing the tempretarure to 1080°C. The shear strength increased by completing isothermal solidification stage and eliminating brittle secondary phase particles in the centerline of bonding zone.

Residual stresses resulting from rapid quenching of molten metal in melt spinning process can be removed by structural relaxation of samples at temperatures lower than the crystallization temperature in order to improve the magnetic properties. In this research, amorphous Fe78Si9B13 ribbons (Metglas 2605S2 used in transformer cores) with the thickness of 26 µm were prepared by chill block melt spinning. DTA measurements on the ribbons heated with the rate of 20 K/min showed that the starting crystallization temperature is 535 °C. The ribbons were then heat treated in a protective gas for 15 to 60 minutes at temperatures in the range of 300-560 °C. XRD results revealed an amorphous structure for all the heat treated samples except for the samples annealed at 500 and 560 °C in which the structure were consisted of three crystalline phases of α-Fe, Fe2B and Fe3B. The measurement of magnetic properties by Hysteresisgraph indicated that the saturation induction increases by an increase in the annealing time and/or annealing temperature. The best combination of magnetic properties was obtained after annealing at 400 °C for 15 minutes.

The soft magnetic nanocrystalline Fe73.5Si13.5B9Cu1Nb3 alloy (FINEMET®) is produced by heat treatment of amorphous precursor. Determining kinetic parameters of amorphous structure transformation to nanocrystalline allows the control of microstructure (e.g. size and volume fraction of nanocrystalline grains) in order to achieve desired soft magnetic properties by optimizing the heat treatment conditions. In this research, the nanocrystallization kinetics of amorphous FINEMET alloy were studied using isoconversional and isokinetic methods under non-isothermal conditions of various heating rates ranging from 5 to 20°C/min. The changes in the microstructure and magnetic properties of amorphous ribbon during nanocrystallization process were studied using X-ray diffractometry and hysteresisgraph, respectively.