Showing 13 results for Intermetallic
S. M. Miresmaeili and S. Shabestari,
Volume 25, Issue 1 (7-2006)
Abstract
The formation of microporosity in modified Al-Si alloys has been reviewed in the present study. A major concern in modification is the increased tendency to form microporosity in the macro-shrinkage free Al-Si alloy castings. It has also been demonstrated that at low hydrogen contents (0.1cc/ 100g, Al), where only shrinkage porosity should occur, the effect of Sr-modification on porosity content is not considerable, indicating that the increase in porosity is due to an increase in gas porosity. Modification treatment, however, does not add hydrogen to the melt, nor does it increase the rate of regassing of the liquid, revealing that it can not enhance pore formation by increasing the melt hydrogen content. Modification treatment raises the freezing range (4-10 oC), but this increased freezing range exerts only a very small effect on microporosity formation, which cannot, by itself, explain the increased tendency to microporosity formation observed in modified alloys. The presence of modifiers slightly decreases the surface tension of the melt (5%), although this decrease in surface tension is not sufficiently high to considerably enhance pore formation in modified alloys. Many researchers have reported that modification treatment might favour the formation of porosity due to its effect on oxide use in the heterogeneous pore formation although the systematic observation of pores has shown that SrO does not take part in pore fomation in Sr-modified alloys. Strontium and other modifiers which increase pore formation (Na and Ca) in Al-Si alloys have a high chemical affinity to form complex intermetallic compounds with Si and Al. Systematic observation of pores have shown that Sr-rich intermetallics take part in pore formation. Thus, Sr-modification may increase the porosity content through the formation of Sr-rich compounds during solidification.
M. H. Enayati and M. Salehi,
Volume 25, Issue 2 (1-2007)
Abstract
Fabrication and characterization of aluminum matrix composites containing different volume fractions of Ni3Al powder (5-40 Vol%) were investigated. Ni3Al powder was produced by mechanical alloying of elemental nickel and aluminum powder mixture. Al-Ni3Al composite parts were prepared using a powder metallurgy route involving two stages Al and Ni3Al powder mixtures were first compacted under 500MPa and then hot-pressed under 250MPa at 420 oC for 10min. The microstructure and hardness of consolidated parts were investigated by x-ray diffractometery, optical and scanning electron microscopy and
hardness measurements. Results showed that consolidated Al-Ni3Al samples included no significant porosity with a nearly uniform distribution of Ni3Al particles. Additionally, structural examinations showed that no significant reaction between Ni3Al and aluminum matrix occurred during sintering process. Al-Ni3Al composites exhibited a higher hardness value compared with pure aluminum sample prepared under identical conditions. The hardness value of Al-Ni3Al composites increased linearly as Ni3Al content increased.
T. Mousavi, M. H. Abbasi, F. Karimzadeh, and M. H. Enayati,
Volume 26, Issue 2 (1-2008)
Abstract
M. Rajabi, R. A. Sedighi , S. M. Rabiee,
Volume 34, Issue 2 (7-2015)
Abstract
In this study, the effect of mechanical alloying on the microstructure and phase constituents of Mg-6Al-1Zn-1Si system was investigated. To understand the thermal behavior, isothermal annealing was performed at three different temperatures of 350, 400 and 450 °C for 1h. The results showed the grain size initially decreases with increasing the milling time up to 35h and then slightly increases. In contrast, the lattice strain increases sharply with increasing the milling time up to 35h and then decreases. Second-phase intermetallic particle Mg2Si was produced during annealing and the amount of this phase was increased with increasing annealing temperature. The mechanical alloying process decreased the formation temperature of Mg2Si.
M. Alizadeh, M. Hajizamani,
Volume 34, Issue 3 (12-2015)
Abstract
Sodium molybdate (Na2MoO4) as a grain refiner was used to refine the microstructure of Al-0.7Fe alloy. Al-Fe samples with the addition of 0.1, 0.2, 0.3, 0.4 and 0.5 wt.% sodium molybdate were fabricated by casting in sand molds at 750 ͦC. The microstructures of the as-cast samples were investigated by scanning electron microscopy (SEM) and the present phases were revealed by X-ray diffraction (XRD). The effect of sodium molybdate on the microstructure was examined by measuring the average grain sizes of the alloys, determining the widths of intermetallic compounds and carrying out hardness and tensile tests. The results showed that the addition of sodium molybdate modified the microstructure of Al-Fe alloy by reducing the average grain sizes. Also, it was found that the optimum amount of sodium molybdate to add to Al-0.7Fe alloy melt was 0.3 wt.% in this study.
M. Sarvari, M. Divandari,
Volume 35, Issue 2 (9-2016)
Abstract
In this study, centrifugal casting process was used for producing Al/Mg bimetal. Molten Mg was poured at 700 oC, with 1.5 and 3 melt-to-solid volume ratio (Vm/Vs) into the 450 oC preheated solid Al rotating at 800, 1200, 1600 and 2000 rpm. Castings were kept inside the centrifuged casting machine and cooled down to 150 oC. Investigating the effect of melt-to-solid volume ratio showed that increasing volume ratio from 1.5 to 3 results in diminishing metallurgical bonding in Al/Mg interface, because the force of contraction overcomes the resultant force acted on the interface. The results of study by scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) showed that bimetal compounds of Al3Mg2, Al12Mg17 and δ+Al12Mg17 eutectic structure (δ is the solid solution of Mg in Al) are formed in the interface. Atomic force microscopy (AFM) image of Al surface showed that the surface was rough in atomic dimentions, which can result in the formation of gas pores in the interface.
S. Tavassoli, M. Abbasi, R. Tahavvori,
Volume 35, Issue 2 (9-2016)
Abstract
The purpose of this article is to study the formation of intermetallic compounds (IMCs) at the interface of Al/Cu bimetal produced by compound casting of molten Al in solid copper tubes. The mechanism of the intermetallic compounds formations at the interface, the effects of molten aluminum pouring temperature and solid copper tubes preheating tempreture, were investigated on the IMCs type and thickness and Al/Cu interface microstructures were characterized by optical microscope (OM) and electron probe micro-analyzer (EPMA). Results show that the interface consists of three main layers, where Layer (I) is α-Al/Al2Cu eutectic structure, layer (II) is intermetal of Al2Cu and layer (III) constituites several intermetallic compounds such as AlCu, Al3Cu4, Al2Cu3 and Al4Cu9. Considering the components of hypereutectic melt at the interface, initially layer (II) was formed by θ phase nucleation and growth mechanism, then layer (I) was formed by Al and Cu dissolving and solidification. Finally layer (III) was formed by solid-state phase diffusion. Raising molten Al temperature and preheating solid Cu leads to increase of the intermetallic compounds thickness at interface which consequently increases the specific electrical resistance and decreases the Al/Cu bond strength. From experimental results it seems that the bond strength is affected by the thicknesses of layer II and III.
F. Mirarabshahi, A. Mashreghi, M. Kalantar, M. Mosalaei,
Volume 35, Issue 4 (2-2017)
Abstract
In this study, fabrication of an in-situ composite through aluminothermic combustion synthesis in An Al–V2O5-NiO system was investigated. Therefore, Al, V2O5 and NiO powders with stoichiometric ratio of 11:1:1, respectively, were milled for an hour and finally the mixtures were compressed. In order to investigate the temperatures of phase transformations, Differential Thermal Analysis (DTA) was utilized. Heat treatment was applied on the raw samples according to their peak temperatures treated in DTA. X Ray Diffraction (XRD) analysis for the samples shows formation of phases such as Al3V and Al3Ni2 at different sintering temperatures. Microstructure and phase analysis showed that during sintering of this sample, Al3V phase was not formed below 700 °C, at 880 °C Al3Ni2 it was formed and after 950 °C, it was transformed to Al4Ni3 phase. In addition, after 950°C, Al3V transformed into Al23V4 phase. Analysis of samples density and hardness showed that, due to increase of volume fraction percentages of reinforcing phase, these two parameters increase as well.
D. Azadrooy, H. Saghafian,
Volume 36, Issue 3 (11-2017)
Abstract
The effect of stir casting process on the modification of the Fe-containing intermetallics formed in a cast in-situ composite based on Al-319 matrix alloy was studied in the present work. Microstructural observations using optical and scanning electron microscopes showed that the undesirable needle-like shape of the Fe-containing intermetallics (β) and also the coarse star-like α compounds were modified into the disc and spheroid shape particles with much less length to width ratio. The effect of parameters such as stirring temperature, cooling rate and Fe contents on the shape, size and distribution of intermetallic particles and eutectic Si blades were also studied. Results showed that the best condition to improve the shape, size and distribution of intermetallic particles can be achieved at a stirring speed of 1200 rpm for 5 minutes at the vicinity of β needles nucleation temperature followed by casting into a metallic mold. Based on the results obtained from the current work, it can be concluded that the harmful morphology of the β intermetallic needles can be properly modified by applying a shearing force during stirring the molten alloy in the semi-solid state.
M. Soltani Samani, A. Bahrami, F. Karimzadeh,
Volume 38, Issue 4 (1-2020)
Abstract
In this study, joining of Ni3Al intermetallic compounds using the transient liquid phase (TLP) process with Cu interlayer was investigated. The binding process was carried out in a vacuum furnace at a temperature of 1050 °C for different times of 30, 60, 90 and 120 minutes. The effect of time variation on microstructure and mechanical properties of the joint zone was investigated. The EDS analysis results of the joints proved formation of the athermally solidified zone (ASZ), isothermally solidified zone (ISZ) and diffusion affected zone (DAZ) at different times. After 90 minutes, brittle eutectic phases still exist in the joint line. However, by increasing the process time to 120 minutes, a copper-rich solid solution was formed in the joint line. Maximum hardness was attained in DAZ region and due to formation of more brittle compounds. By increasing the process time to 90 min, the hardness in the joint center-line increased. After 120 min, the hardness in the joint center-line decreased to about 224 HV. Maximum shear strength was achieved to be about 60 MPa at a process time of 30 minutes and due to formation of Ni-rich matrix at the joint. With increasing time to 90 min, the shear strength decreased to about 34 MPa. After 120 minutes and due to formation of copper-rich solid solution as well as disappearance of eutectic compounds, shear strength again increased to about 44 MPa. Investigation of fracture surfaces showed that until 90 minutes, fracture mode was mainly brittle whereas by increasing time to 120 minutes, a more ductile fracture occurred.
S. Arjmand, M. Tavoosi,
Volume 39, Issue 3 (12-2020)
Abstract
The present work aims to modify surface properties of pure Ti by development of Ti-Al-N intermetallic composite coatings. In this regard, tungsten inert gas (TIG) cladding process was carried out using Al 1100 as filler rod with Ar and Ar+N2 as shielding gases. Phase and structure of the samples were investigated by X-ray diffraction (XRD) technique, optical microscopy (OM) and scanning electron microscopy (SEM). Hardness values and corrosion behavior of the obtained coatings were also compared using Vickers microhardness tester and potentiostat, respectively. The results showed that composite structure containing Al3Ti, Ti3Al2N2 and Ti3Al intermetallic compounds could be formed on the surface of pure Ti. Amounts of brittle phases and welding defects at the titanium-coating interface were least by welding under pure Ar shielding. Despite the increasing amount of structural defects such as porosity and non-uniformity under Ar+N2 shielding, the prepared coatings had higher hardness (more than 100 HV) and corrosion resistance (more than twice) compared with those obtained under Ar shielding.
S. Arjmand, G. H. Akbari, G. R. Khayati,
Volume 39, Issue 4 (2-2021)
Abstract
The purpose of the present work is to investigate the influence of the number of weld-passes on microstructure, hardness and residual stresses of composite coatings composed of Ti-Al-Si intermetallic compounds. In this regard, surface coating of pure Ti was carried out using one and two passes of tungsten inert gas (TIG) welding with an Al filler alloy (grade 4043). Phase and structural evaluations of the coatings were investigated by X-ray diffraction, optical and scanning electron microscopies. microhardness and residual stress values of the coatings were measured using ASTM E384-HV device and the Sin2ψ method, respectively. The results showed that as the number of welding passes increased or the dilution ratio decreased, the volume fraction of Ti5Si3-Al3Ti intermetallic phases within the fusion zone increased and the volume fraction of martensite phase in the heat affected zone decreased. As a result, the average hardness value of the coating increased to be about 130 % compared to that of the pure Ti substrate. The tensile residual stresses at the center line of fusion zone were 165 ± 30 and 210 ± 35 MPa for the coatings prepared in one and two welding passes, respectively.
S. Sarafrazian, M. Tavoosi, A. Ghasemi ,
Volume 40, Issue 2 (9-2021)
Abstract
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.
