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Showing 21 results for Sintering

Mirfakhraee B., Eshraghi H., Sar Poulaki H.,
Volume 2, Issue 1 (3-2005)
Abstract

Effect of MgO addition on reaction sintering of aluminium titanate was investigated using equimolar Al2O3 and TiO2 after firing the samples at 1400 C for four hours. Results showed that MgO addition enhanced the sintering process by magnesium aluminates formation, which led to lower porosity and improved densification of the samples. Physical and mechanical properties showed that samples containing 5 wt% MgO was the optimum composition.
Paydar M.h., Fadaei R., Shariat M.h.,
Volume 2, Issue 2 (6-2005)
Abstract

Copper coated SiC powders having three different amounts of copper, in the range of 20-60 wt%, were prepared via electroless coating process. The produced composite powders were uniaxially cold compressed and sintered at different temperatures and times under protective atmosphere. It was found that composite Cu/SiC powders and a relatively dense copper matrix composite with a uniform distribution of SiC reinforcing particles imbedded in copper matrix can be fabricated via electroless coating method followed by conventional cold pressing and sintering process. The results also show that SiC particles have a poor wettability with copper and so liquid phase sintering of the Cu/SiC composite powders did not enhance densification of the samples. Regarding this fact, optimum sintering temperatures, which depends on copper content, was determined to be in the range of 1050-1080?C.
Baradari H., Amani Hamedani H., Karimi Khoygani S., Rezaei H.r., Javadpour J., Sar Poulaki H.,
Volume 3, Issue 1 (6-2006)
Abstract

Ultrafine hydroxyapatite (HAp) powders with crystallite size in the range of 10-90 nm were synthesized by chemical precipitation process using Ca(OH)2 and H3PO4 solutions as starting materials. Molar ratio of Ca/P=1.68 was kept constant throughout the process and alkaline condition for the reaction was maintained using ammonium hydroxide. The role of raw material concentration on HAp crystallite size and morphology were investigated using X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques. The results revealed that variations in crystallite size and morphology of synthesized HAp are strongly affected by the concentration of acid solution. To study the sintering behavior of HAp particles, the powders were pressed at 200 MPa using a uniaxial press. Sintering experiments were carried out at temperatures of 1100, 1250 and 1300°C with various soaking times at maximum temperatures. XRD was also used in determining thephases present after sintering process. The results indicated the decomposition of HAp into a-tricalcium phosphate (TCP) and b-TCP phases at 1300°C. The microstructure of the sintered HAp ceramics was characterized by SEM.
Ali. A. Hosseini,, F. Ghaharpour, H. Rajaei ,
Volume 6, Issue 3 (9-2009)
Abstract

Abstract: In this paper‚ the physical and mechanical properties of Al nanocomposite reinforced with CNTs wereinvestigated. High purity Al powder and Carbon Nanotubes (CNTs) with different percentage were mixed by ballmilling method and the composite was fabricated by cold pressing followed by sintering technique. The variation ofdensity and hardness of composite with CNTcontent was investigated. The microstructure of composite was evaluatedby SEM (Scanning Electron Microscope) and XRD (X -Ray Diffraction). The results show that the density and hardnessincrease with CNTpercentage.
H. Momeni, H. Razavi, S. G. Shabestari,
Volume 8, Issue 2 (6-2011)
Abstract

Abstract: The supersolidus liquid phase sintering characteristics of commercial 2024 pre-alloyed powder was studied at different sintering conditions. Pre-alloyed 2024 aluminum alloy powder was produced via air atomizing process with particle size of less than 100 µm. The solidus and liquidus temperatures of the produced alloy were determined using differential thermal analysis (DTA). The sintering process was performed at various temperatures ranging from the solidus to liquidus temperatures in dry N2 gas atmosphere for 30 min in a tube furnace. The maximum density of the 2024 aluminum alloy was obtained at 610ºC which yields parts with a relative density of 98.8% of the theoretical density. The density of the sintered samples increased to the maximum 99.3% of the theoretical density with the addition of 0.1 wt. %Sn powder to the 2024 pre-alloyed powder. The maximum density was obtained at 15% liquid volume fraction for both powder mixtures.
A. R. Abbasian, M. R. Rahimipour, Z. Hamnabard,
Volume 10, Issue 3 (9-2013)
Abstract

In order to evaluate the sintering behavior of lithium meta titanate (Li2TiO3) powder, the shrinkage of powder compact was measured under constant rates of heating. Densification curves for Li2TiO3 have been constructed with the help of shrinkage powder measured at different heating rates. The activation energy at the initial stage of sintering was determined by analyzing the densification curves and the value of Q=377 kJ/mol was obtained. The diffusion mechanism at the initial sintering stage was determined by the analytical method applied to the constant rates of heating data. This analysis exhibited that the dominant mechanism for initial sintering stage of Li2TiO3 is volume diffusion from grain boundary and surfaces.
M. Ahangarkani, K. Zangeneh-Madar, H. Abbaszadeh, A. A. Rahmani , S. Borgi,
Volume 11, Issue 3 (9-2014)
Abstract

In the present paper, the influence of cobalt additive on the sintering/infiltration behavior of W-Cu composite was studied. For this purpose, the mixed powders of tungsten and cobalt were compacted by CIP method and then sintered at 1450, 1550 and 1600 °C in a hydrogen atmosphere. The sintered specimens at 1550 °C were subsequently infiltrated with liquid copper at 1250 °C for 10, 60 and 120 min. The microstructure and composition of samples were evaluated using SEM, EDS as well as XRD techniques. The density of the sintered samples was measured by Archimedes method. Vickers indentation test was used to measurement hardness. It was found that sintering mechanism of tungsten powder depends on temperature and cobalt additive content. Also, the best infiltration behavior was observed in the samples with optimum cobalt value. In addition, it was found that the W-W contiguity as well as dihedral angle decreases as cobalt increases. Density and hardness of infiltrated specimens are attained 16.28-16.79 g.cm-3 and 220-251 VHN, respectively.
A. Mohammadzadeh, A. Sabahi Namini, M. Azadbeh,
Volume 11, Issue 3 (9-2014)
Abstract

The rapidly solidified prealloyed alpha brass powder with a size range of 40 to 100 μm produced by water atomization process was consolidated using liquid phase sintering process. The relationships between sintering temperature, physic-mechanical properties and microstructural characteristics were investigated. Maximum densification was obtained at 930 °C, under 600 MPa compacting pressure, with 60 min holding time. The microstructure of the sintered brass was influenced by dezincification and structural coarsening during supersolidus liquid phase sintering. As a consequence of Kirkendall effect atomic motion between Cu and Zn atoms caused to dezincification at the grain boundaries and formation of ZnO particles on the pore surfaces. It was concluded that microstructural analysis is in a well agreement with obtained physical and mechanical properties. Also, the amount of liquid phase, which depends on sintering temperature, results in different load bearing cross section areas, and it affects the type of fracture morphologies.
M. M. Mohammadi Samani, H. R. Baharvandi, H. Abdizadeh, J. Rezapour,
Volume 11, Issue 4 (12-2014)
Abstract

B4C and its composites with TiB2 as second phase continues to be extensively used as the preferred ceramic material in military applications as armor systems for absorbing and dissipating kinetic energy from high velocity projectiles. It also exhibits a high melting point (2427 °C), and high neutron absorption cross section. Pressureless sintering of the B 4C-nanoTiB2 nanocomposite using small amount of Fe and Ni (≤3 Wt%) as sintering aids was investigated in order to clarify the role of Fe and Ni additions on the mechanical and microstructural properties of B4C-nanoTiB2 nanocomposites. Different amount of Fe and Ni, mainly 1 to 3 Wt% were added to the base material. Pressureless sintering was conducted at 2175, 2225 and 2300 °C. It was found that Addition of 3 Wt% Fe and 3 wt% Ni and sintering at 2300 °C resulted in improving the density of the samples to about 99% of theoretical density. The nanocomposite samples exhibited high density, hardness, and microstructural uniformity.
A. Ahmadi, A. A. Youzbashi, A. Nozad, A. Maghsoudipour, T Ebadzadeh,
Volume 11, Issue 4 (12-2014)
Abstract

Synthesis of YSZ nanopowder by alkoxide sol-gel method, through two different hydrolysis routes, one under careful control by using acetyacetone as ligand, and the other through basic hydrolysis, was investigated. The synthesized powders were characterized by various analytical techniques such as, XRD, STA, PSA, BET, SEM, and TEM. The results showed that, the YSZ powders prepared through the basic hydrolysis route consist of weakly agglomerated nanosized spherical particles whereas the products obtained through the controlled hydrolysis route, consist of hard irregular shaped agglomerates. Sinterability of these powders was examined at 1480 °C, which showed that the powder synthesized through the basic hydrolysis route attains a density of 94%, against 60% for the other case. It was therefore concluded that, alkoxide sol-gel method through basic hydrolysis route, can be more suitable for the synthesis of YSZ nanopowder and its subsequent sintering.
A. M. Zahedi, H. R. Rezaie, J. Javadpour,
Volume 12, Issue 4 (12-2015)
Abstract

Different volume fractions (1.3, 2.6, and 7.6 Vol.%) of carbon nanotubes (CNTs) were dispersed within 8Y-TZP nanopowders. Mixed powder specimens were subsequently processed by spark plasma sintering (SPS) and effects of CNTs on the sintering process of 8Y-TZP/CNT composites was studied. Maintenance of CNTs through the SPS process was confirmed using TEM and Raman Spectroscopy. Studies on the sintering profile of zirconia-CNT composites (Z-xC composites) could, to some extent, clarify the effect of CNTs’ volume fraction on the densification rates of Z-xC composites. The specimen with the highest content of CNT (Z-7.6C) showed the lowest sintering rate while it was unable to reach full density.

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Z. Sadeghian, R. Dezfulizadeh,
Volume 13, Issue 2 (6-2016)
Abstract

In situ Al2024- Mg2Si composite was fabricated by spark plasma sintering (SPS) of reactive powder. Reactive powder was obtained from mechanical alloying (MA) of elemental powders. Clad layers of in situ composite were fabricated on Al substrates by spark plasma sintering (SPS). Structural evolution during MA process and after SPS was investigated by X-ray diffractometery (XRD). Scanning electron microscopy (SEM) was utilized to study the microstructure of sintered samples. Hardness and tensile behavior of sintered samples were investigated. The results showed that SPS of mechanically alloyed unreacted powder can result in the in situ formation of Mg2Si and Mg2Al3 within the Al matrix. SPSed clad layer showed a sound and clear interface to the Al substrate with a hardness of about 140 HV. Sintered in situ composite exhibited a tensile strength of 288 MPa.

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T. Ebadzadeh, S. Ghaffari, M. Alizadeh, K. Asadian, Y. Ganjkhanlou,
Volume 16, Issue 1 (3-2019)
Abstract

The densification behavior, structural and microstructural evolution and microwave dielectric properties of Li2TiO3 + xZnO (x = 0, 0.5, 1, 1.5, 2, 3, and 5 mol%) ceramics have been investigated using X-ray diffraction, Field Emission Scanning Electron Microscopy, Raman spectroscopy and microwave resonant measurement. The Maximum density of 3.33 g/cm3 was obtained in Li2TiO3 + 2ZnO ceramic at low sintering temperature of 1100˚C. SEM investigations revealed good close packing of grains when x = 2 and preferential grain growth when x ≥ 3. The maximum values of Q × f = 31800 GHz and εr = 22.5 were obtained in Li2TiO3 + 3ZnO and Li2TiO3 + 2ZnO compositions, respectively. The observed properties are attributed to the microstructural evolution and grain growth (first case) or high density of the obtained ceramic (second case).
 
A. R. Abbasian, M. R. Rahimipour, Z. Hamnabard,
Volume 16, Issue 4 (12-2019)
Abstract

In this work, lithium meta titanate (Li2TiO3) nanocrystallites were synthesized by hydrothermal method and subsequent heat treatment. The shrinkage of the powder compact was measured under constant heating rate in order to study the sintering behavior of the synthesized powders. Densification curves of the synthesized powders were also constructed via the dilatometry analysis and evaluated at several heating rates. Two separate methods of analytical procedure and master curve sintering were employed to determine the activation energy of the initial sintering stage. The activation energy values were estimated based on these two distinct methods as 229±14 and 230 kJ/mol respectively, consistenting with each other. Moreover, surface diffusion was determined as the dominant mechanism of densification on initial sintering of Li2TiO3 nanocrystallites.
H. Aydın,
Volume 16, Issue 4 (12-2019)
Abstract

Mullite–zirconia composites were prepared using lanthanum oxide (La2O3) additive which three different mole ratio by the reaction sintering (RS) route of alumina, kaolinite and zircon. Starting materials were planetary milled, shaped into pellets and bars and sintered in the temperature range of 1450–1550 0C with 5 h soaking at peak temperature. In this work, the mullite-zirconia composites were characterized by thermal expansion coefficient, physical, microstructures and mechanical properties. The XRD method were employed for determining the crystalline phase composition of these composites. Microstructure of the composites was examined by SEM. ZrO2 takes part in both the intergranular as well as intragranular positions. However, intragranular zirconias are much smaller compared to intergranular zirconias.

H. Momeni, S. Shabestari, S.h. Razavi,
Volume 17, Issue 4 (12-2020)
Abstract

In this research, densification and shape distortion of the Al-Cu-Mg (Al2024) pre-alloyed powder compact in the supersolidus liquid phase sintering process (SLPS) were investigated. The effect of Sn on the sintering process was also studied. The powders were compacted at pressures ranging from 100 to 500 MPa in a cylindrical die. The sintering process was performed in a dry N2 atmosphere at various temperatures (580-620 ºC) for 30 min at a heating rate of 10 ºCmin-1. Results showed that the onset of densification process was observed at 600ºC and onset of distortion was occurred at 610ºC. Addition of 0.1 wt. %Sn to the alloy has increased the distortion of the samples produced from Al-Cu-Mg pre-alloyed powder, but their densification has been improved. The compact pressure of 200MPa caused the complete densification at the optimum sintering temperature and at the compact pressures greater than 200MPa; the sintered density was independent of green density. 
 

H. Mohebbi, S.m. Mirkazemi,
Volume 17, Issue 4 (12-2020)
Abstract

Flash sintering of 8 mol% yttria-stabilized zirconia (8YSZ) as solid oxide fuel cell (SOFC) electrolyte is studied. The relation between relative density, shrinkage, sample temperature during the flash, and incubation time, with the electric field strength, current density, as well as contact paste, are modeled by response surface methodology (RSM). The electric field strength and current density varied from 50 to 400V.cm-1 and 50 to 200mA.mm-2, respectively. Also, platinum (Pt) and lanthanum strontium manganite (LSM) used as contact paste. Results show that using LSM paste lead to higher density and more shrinkage compare with Pt paste. Contrary, the electric field strength has no significant effect on density and shrinkage. However, a minimum electric field strength equal to 80 V.cm-1 is necessary for flash onset. As the field increases, the incubation time decreases dramatically. Compare with samples with LSM paste, samples with Pt contact paste reach to a higher temperature during the flash. Flash sintered 8YSZ shows the mean grain size of 0.3μm, which is about half of the conventionally sintered 8YSZ. Electrochemical Impedance Spectroscopy reveals despite lower mean grain size, the resistivity of flash sintered 8YSZ is lower than conventionally sintered 8YSZ.
Sasan Ranjbar Motlagh, Hosein Momeni, Naser Ehsani,
Volume 18, Issue 1 (3-2021)
Abstract

In this study, the effect of annealing treatment on microstructure and mechanical properties of Nb-10Hf-1Ti wt.% produced by Spark Plasma Sintering (SPS) was investigated. Scanning electron microscope (SEM), optical microscopy, X-ray diffraction analysis, hardness, and uniaxial tension test were used. Annealing treatment was carried out in a vacuum of 10-3 Pa at 1150 °C for 1, 3, 5, and 7 hours and in an argon atmosphere at 1350 °C for 5 hours. Internal oxidation and subsequent hafnium oxide formation causes the hardening of the C103 alloy and drastically increases hardness and tensile strength. Although HfO2 particles formed in the grain boundary cause brittleness and cleavage fracture of samples. Volume fraction, particle size, and mean interparticle spacing of oxides significantly change by annealing and subsequently the mechanical properties are affected. The SPSed sample at 1500 ℃ is softened by annealing at 1150 ℃ for 5 hours and its hardness and yield strength are reduced from 303 Hv to 230 Hv and 538 MPa to 490 MPa respectively. While annealing at 1350 ℃for 5 hours increases hardness and yield strength increases to 343 Hv and 581 MPa. 
Dillibabu Surrya Prakash, Narayana Dilip Raja,
Volume 18, Issue 4 (12-2021)
Abstract

Hybrid composites consisting of AA6061 matrix reinforced with TiB2 (2, 4, 6, and 8 wt. %), Al2O3 (2 wt. %) particles were produced by the sintering process. In comparison to the base material AA6061, the composite produced had improved mechanical properties. The sintered composites' mechanical properties, such as tensile strength and hardness, are measured and compared to the wear-tested specimen. Optical micrographs reveal that composites were riddled with defects like blowholes, pinholes, and improper bonding between the particulates before sintering. However, the post-sintered optical micrograph showed that the defects were greatly suppressed. Micrographic images revealed the changes in surface characteristics before and after wear. Until a sliding distance of 260 m, the wear rate of the hybrid composites was kept lower than that of the base material. The coefficient of all the composite materials produced for this study was noted to be less than that of the base material. The results reveal that the hardness of hybrid composites having 4 wt. % and 6 wt. % of TiB2 particulates increased by 5.98 % and 1.35 %. Because of the frictional heating during the wear test, the tensile properties lowered by up to 49.6%. It is concluded that the hybrid composites having 4 wt. % and 6 wt. % of TiB2 particulates exhibited less wear rate for extended sliding distance, good hardness, moderate tensile strength, and decent elongation percentage compared to its counterparts.

Sara Ahmadi, Bijan Eftekhari Yekta, Hossein Sarpoolaky, Alireza Aghaei,
Volume 18, Issue 4 (12-2021)
Abstract

In the present work, monolithic gels were prepared through different drying procedures including
super critical, infrared wavelengths and traditional drying methods. Dense and transparent glasses
were obtained after controlled heat treatment of the dried porous xerogels in air atmosphere.
The chemical bonding as well as different properties of the prepared gels and the relevant glasses
were examined by means of Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmitt-
Teller (BET) and UV-Vis spectrometer. Based on the obtained results, different drying conditions
affect the average pore size and the total pore volume of the studied gels. The mean pore size was
found to be 8.7 nm, 2.4 nm and 3.2 nm for super critical, IR radiation and slow drying in air
atmosphere, respectively. The glass network structure was significantly changed by heat treatment  temperature so that the B-O-Si bonds were formed only after 450 °C. It was found that the gel dried under super critical condition was unable to reach to its full density all over the selected sintering temperature interval.
 


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