Musa Gogebakan

The effect of Si addition on crystallization behavior of amorphous Al-Y-Ni alloy

This article reports the effect of silicon (Si) addition upon the crystallization behavior and mechanical properties of an amorphous AlYNi alloy. An amount of 1 at.% Si was added to a base alloy of Al85Y5Ni10 either by substitution for yttrium (Y) to form Al85Y4Ni10Si1, or by substitution for nickel (Ni) to form Al85Y5Ni9Si1. Differential scanning calorimetry (DSC) of all three alloys showed three exothermic peaks. Comparing the peak temperature for the first exothermic peak, a significant shift occurs toward the lower temperature. This indicates that 1 at.% substitutions of Y or Ni by Si decreases the stability of the amorphous phase. DSC study of these amorphous alloys during isothermal annealing at temperatures about 5–15 K lower than their first crystallization peaks showed that the formation of α-Al nanocrystals via primary crystallization occurred without an incubation period. The Avrami time exponent (n) of the primary crystallization from the amorphous structure was determined to be 1.00–1.16 using the Johnson-Mehl-Avrami (JMA) analysis. This suggested a diffusion-controlled growth without nucleation. However, a DSC study of these amorphous alloys during isothermal annealing at higher temperatures between 585 and 605 K showed a clear incubation period during the formation of the Al3Ni and Al3Y intermetallic phases. An n value of 3.00–3.45 was determined using JMA analysis. This suggested that the transformation reaction involved a decreasing nucleation rate and interface-controlled growth behavior. The tensile strength σf and Vickers hardness for these amorphous alloys are in the range 1050–1250 MPa and 380–398 diamond pyramid hardness number (1 diamond pyramid hardness number=1 kg/mm2=9.8 MPa), respectively.This article reports the effect of silicon (Si) addition upon the crystallization behavior and mechanical properties of an amorphous AlYNi alloy. An amount of 1 at.% Si was added to a base alloy of Al85Y5Ni10 either by substitution for yttrium (Y) to form Al85Y4Ni10Si1, or by substitution for nickel (Ni) to form Al85Y5Ni9Si1. Differential scanning calorimetry (DSC) of all three alloys showed three exothermic peaks. Comparing the peak temperature for the first exothermic peak, a significant shift occurs toward the lower temperature. This indicates that 1 at.% substitutions of Y or Ni by Si decreases the stability of the amorphous phase. DSC study of these amorphous alloys during isothermal annealing at temperatures about 5–15 K lower than their first crystallization peaks showed that the formation of α-Al nanocrystals via primary crystallization occurred without an incubation period. The Avrami time exponent (n) of the primary crystallization from the amorphous structure was determined to be 1.00–1.16 using the Johnson-Mehl-Avrami (JMA) analysis. This suggested a diffusion-controlled growth without nucleation. However, a DSC study of these amorphous alloys during isothermal annealing at higher temperatures between 585 and 605 K showed a clear incubation period during the formation of the Al3Ni and Al3Y intermetallic phases. An n value of 3.00–3.45 was determined using JMA analysis. This suggested that the transformation reaction involved a decreasing nucleation rate and interface-controlled growth behavior. The tensile strength σf and Vickers hardness for these amorphous alloys are in the range 1050–1250 MPa and 380–398 diamond pyramid hardness number (1 diamond pyramid hardness number=1 kg/mm2=9.8 MPa), respectively.

Characterization of the icosahedral quasicrystalline phase in rapidly solidified Al- -Cu- -Fe alloys

Abstract The present research aimed to characterize the microstructure of icosahedral quasicrystalline phase (i-phase) in different chemical compositions of Al–Cu–Fe alloys. The ternary alloys with the nominal compositions of Al70Cu20Fe10, Al65Cu20Fe15 and Al63Cu25Fe12 (at%) were rapidly solidified by melt-spinning technique. The melt-spun ribbons were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential thermal analysis (DTA). According to the XRD results, diffraction patterns of Al70Cu20Fe10 alloy showed the presence of the i-phase together with tetragonal θ-Al2Cu phase. However, XRD pattern of the melt-spun Al63Cu25Fe12 alloy showed the formation of i-phase together with a small amount of β-phase. The single quasicrystalline phase was observed only in the rapidly solidified Al65Cu20Fe15 alloy. The SEM examinations showed that the melt-spun Al70Cu20Fe10 and Al63Cu25Fe12 alloys composed of i-phase with an average grain size of 1–5 μm. However, for the Al65Cu20Fe15 alloy, the quasicrystalline particles in the star-shape dendritic formations were observed. The melting point of i-phase was determined as 890 °C by DTA examinations.

Crystallization studies of Al85Y10Fe5-xNix (X = 0, 2.5, 5) alloys

The crystallization behavior of melt-spun A85Y10Fe5−xNx (x=0, 2.5, 5) amorphous alloys has been investigated by a combination of differential scanning calorimetry (DSC) and x-ray diffractometry (XRD). XRD traces of these alloys consisted of a single broad peak corresponding to fully amorphous structure. Continuous DSC results showed that, the first crystallization peak temperature of Al85Y10Fe5 amorphous alloy was about 60 K higher than that of Al85Y10Ni5. The activation energies for the first crystallization peak increased from 210 kJ/mol for Al85Y10Ni5 to 280 for Al85Y10Fe5. These results indicate that 5 at.% substitutions Ni by Fe increases the stability of the amorphous phase.The crystallization behavior of melt-spun A85Y10Fe5−xNx (x=0, 2.5, 5) amorphous alloys has been investigated by a combination of differential scanning calorimetry (DSC) and x-ray diffractometry (XRD). XRD traces of these alloys consisted of a single broad peak corresponding to fully amorphous structure. Continuous DSC results showed that, the first crystallization peak temperature of Al85Y10Fe5 amorphous alloy was about 60 K higher than that of Al85Y10Ni5. The activation energies for the first crystallization peak increased from 210 kJ/mol for Al85Y10Ni5 to 280 for Al85Y10Fe5. These results indicate that 5 at.% substitutions Ni by Fe increases the stability of the amorphous phase.

Structural, electrical and magnetic properties of Nd – A – CoO 3 (A = Sr, Ca) Perovskite Powders by Mechanical Alloying

In this work, NdCoO3 (NCO), Nd0.8Sr0.2CoO3 (NSCO) and Nd0.9Ca0.1CoO3 (NCCO) perovskite cobaltites were synthesised by mechanical alloying method. Structural evolutions, magnetic and electrical properties of these perovskite were systematically examined through X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive X-ray detection (SEM-EDX), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), vibration sample magnetometer (VSM) and impedance analyser (IA). The XRD and SEM results revealed that the microstructure of the perovskite materials changed during mechanical alloying. The average crystallite size of the perovskite materials was calculated by Debye Scherrer equation and was confirmed by TEM, and it was determined ~19 nm. From the VSM results, the all perovskites had soft ferromagnetic properties. IA measurements showed that relatively dielectric constants of the perovskites decreased with increasing frequency. Therefore, for the first time, nanostructured NCO, NSCO and NCCO perovskites exhibiting good properties were produced in only two steps which are milling and heating.

Phase Identification and Size Evaluation of Mechanically Alloyed Cu-Mg-Ni Powders

Ternary mixture of Cu, Mg, and Ni with the nominal composition of nanocrystalline Cu50Mg25Ni25 (in at.%) was milled for 25 hours. Analysis of an X‐ray diffraction pattern (XRD) and transmission electron microscopy (TEM) was used to characterize the chemi‐ cal phases and microstructure of the final product, which is shown to consist of ternary alloy of Cu‐Mg‐Ni with FCC structure along with small amounts of FCC MgO and Mg0.85Cu0.15. The good agreement between the size values obtained by XRD and TEM is attributed to the formation of defect‐free grains with no substructure during ball milling. Dynamic recrystallization may be a possible mechanism for the emergence of such small grains (<20 nm). The particle size distribution and morphological changes of Cu–Mg–Ni powders were also analyzed by scanning electron microscopy (SEM). According to the SEM results, the particle size of the powders decreased with increasing milling time. Lattice parameter of the Cu‐Mg‐Ni ternary FCC alloy formed during mechanical alloying increased with increase in milling time from 3.61 to 3.65 Å after 20 hours milling.

Structure and Mechanical Behaviour of Cu‐Zr‐Ni‐Al Amorphous Alloys Produced by Rapid Solidification

The amorphous ribbons of Cu50Zr40Ni5Al5 alloy were manufactured by rapid solidifica‐ tion. The ribbons were investigated by X‐ray diffraction (XRD), scanning electron microscopy coupled with energy dispersive spectroscopy (SEM‐EDX) and differential scanning calorimetry (DSC). The activation energy of the crystallisation in amorphous alloys was determined by Kissenger technique. The mechanical properties of the ribbons were characterized using Vickers microhardness (HV) tester. According to the XRD and SEM results, the Cu50Zr40Ni5Al5 alloys have a fully amorphous structure. The EDX analysis of the ribbons showed that compositional homogeneity of the Cu50Zr40Ni5Al5 alloy was fairly high. From the DSC curves of the amorphous ribbons, it was deter‐ mined that glass transition temperature (Tg) is around 440–442°C and super‐cooled liquid region (ΔTx = Tx Tx) before crystallisation is around 61–64°C. The microhard‐ ness of the as‐quenched ribbons was measured about 550 HV. However, this micro‐ hardness value decreased with increasing annealing temperature and it was calculated about 465 HV after annealing temperature of 800°C.

Thermal Properties of Amorphous Al‐Ni‐Si Alloy

Thermal properties of the amorphous phases in rapidly solidified Al70Ni13Si17 alloy has been investigated by a combination of differential scanning calorimetry DSC. During continuous heating, three exothermic crystallization peaks were observed. Activation energies for the three crystallization peaks were calculated by the Kissinger and Ozawa methods give good agreement. This study describes the thermal properties of rapidly solidified Al70Ni13Si17 amorphous alloy.

Production of Cu‐Al‐Ni Shape Memory Alloys by Mechanical Alloy

The mechanical alloying technique has been used to produce shape memory Cu83Al13Ni4 alloy. The structure and thermal properties were examined by using scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The morphology of the surface suggests the presence of martensite.

Crystallization Behaviour of Amorphous Al‐Ni‐Nd Alloy

In this study, crystallization behaviour of rapidly solidified Al85Ni5Nd10 alloy has been investigated by differential scanning calorimetry (DSC). Continuous heating DSC trace of amorphous Al85Ni5Nd10 alloy consisted of three exothermic peaks. This indicated that; crystallization of amorphous Al85Ni5Nd10 alloy during continous heating takes places in three stages. Before the first exothermic peak, a glass transition temperature was observed.

Formation and Microstructure of Quasicrystalline Al‐Fe‐Cu Alloy by Mechanical Alloy

In the present investigation, we examined the i‐phase formation during Mechanical Alloying (MA) of Al70Cu20Fe10 elemental blend using X‐ray diffraction (XRD).