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FARKLI KOMPOZİSYONLARDAKİ Fe-Mg ALAŞIMLARIN MEKANİK ÖZELLİKLERİNİN İNCELENMESİ
Abstract
z Toz metalurjisi, çok küçük boyutlu partikülleri birbirine bağlayarak karışık şekilli parçaların üretimini sağlayan bir yöntemdir. Bu çalışmada, Fe-Mg toz karışımları homojen bir şekilde toz karıştırıcıda 24 saat süreyle karıştırılmıştır. Elde edilen tozlar tek eksenli preste 300 bar basınç altında soğuk olarak preslendikten sonra Ar atmosfer ortamında 620 °C sıcaklıkta sinterleme işlemine tabi tutulmuşlardır. Sinterlenerek üretilen numunelere sırasıyla sertlik, yoğunluk ve gözeneklilik testleri uygulanmıştır. Metalografik analiz olarak XRD çalışması yapılmıştır. XRD analiz sonucu olarak Fe, Mg ve MgO faz değerleri bulunmuştur. Abstract Powder metallurgy is a method of producing mixed shaped parts by connecting very small sized particles together. In this work, Fe-Mg powder mixtures were homogeneously mixed in the powder mixer for 24 hours. The powders obtained were cold pressed under a uniaxial prestressing pressure of 300 bar and then subjected to sintering at 620 °C in Ar atmosphere. Hardness, density and porosity tests were applied to the samples produced by sintering, respectively. XRD work was done as a metallographic analysis. As a result of XRD analysis, Fe, Mg and MgO phase values were found.
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Ni-25Fe and Ni-15Fe-13Mg (at.%) alloy nanoparticles were fabricated by a thermal plasma method, and their catalytic properties for methanol decomposition were examined in the 513–793 K temperature range. Both nanoparticles started showing activity for methanol decomposition above 593 K, with activity rapidly increasing with temperature. Ni-15Fe-13Mg showed much higher activity and less carbon deposition than Ni-25Fe. These results indicated that the addition of Mg in the Ni-Fe alloy significantly increased the activity, but suppressed carbon deposition. Characterization of the nanoparticles revealed that the Mg was segregated and a thin layer of MgO was formed on the surface of the nanoparticles. It is likely that the formation of MgO suppressed carbon deposition, but enhanced the activity by delaying the coarsening of nanoparticles during the reaction.
The use of beta-tricalcium phosphate (β-TCP) ceramic as a bioresorbable bone substitute is limited to non-load-bearing sites by the material׳s brittleness and low bending strength. In the present work, new biocompatible β-TCP-based composites with improved mechanical properties were developed via reinforcing the ceramic matrix with 30vol% of a biodegradable iron-magnesium metallic phase. β-TCP-15Fe15Mg and β-TCP-24Fe6Mg (vol%) composites were fabricated using a combination of high energy attrition milling, cold sintering/high pressure consolidation of powders at room temperature and annealing at 400°C. The materials synthesized had a hierarchical nanocomposite structure with a nanocrystalline β-TCP matrix toughened by a finely dispersed nanoscale metallic phase (largely Mg) alongside micron-scale metallic reinforcements (largely Fe). Both compositions exhibited high strength characteristics; in bending, they were about 3-fold stronger than β-TCP reinforced with 30vol% PLA polymer. Immersion in Ringer׳s solution for 4 weeks resulted in formation of corrosion products on the specimens׳ surface, a few percent weight loss and about 50% decrease in bending strength. In vitro studies of β-TCP-15Fe15Mg composite with human osteoblast monocultures and human osteoblast-endothelial cell co-cultures indicated that the composition was biocompatible for the growth and survival of both cell types and cells exhibited tissue-specific markers for bone formation and angiogenesis, respectively.
We report on the formation of the ternary hydride Mg2FeH6 in mechanically activated powders. Powder mixtures with nominal composition Mg67Fe33 were ball-milled in an inert Ar atmosphere either at room temperature or at liquid nitrogen temperature (cryomilling), and subsequently hydrogenated at different pressures at 622K in a Sieverts-type apparatus. X-ray diffraction data from the hydrided products show Mg2FeH6 is formed directly from 2Mg+Fe+3H2. Cryomilling improves the hydrogen absorption kinetics, but also results in a decrease of the total yield of Mg2FeH6. This is likely due to MgH2 being kinetically favoured, and in turn acting as a competitor to the formation of the ternary hydride. The absorption data is discussed in the framework of the Johnson–Mehl–Avrami model, which suggests the formation of Mg2FeH6 occurs via interface-controlled growth processes.
The Mg–3%Al melt was treated by carbon inoculation and/or Fe addition. The effects of Fe addition and addition sequence on the carbon inoculation of Mg–3%Al alloy were investigated in the present study. The role of Fe in the grain refinement of Mg–3%Al alloy treated by carbon inoculation was closely associated with the operating sequence of carbon inoculation and Fe addition. Fe has no obvious effect on the grain refinement of Mg–3%Al alloy by carbon inoculation under the condition that Fe pre-existed in the Mg–3%Al melt before carbon inoculation. However, Fe played an inhibiting role under the condition that the Mg–3%Al melt had been inoculated by carbon before Fe addition. The Al–C–O particles were observed in the sample treated only by carbon inoculation. In addition to Al–C–O particles, Al–C–O–Fe particles could be observed in the sample treated by Fe addition and then carbon inoculation. These Al–C–O and Al–C–O–Fe particles, actually being Al–C and Al–C–Fe phases, should be the potent nucleating substrates for Mg grains, resulting in the grain refinement. However, the Al–C–O–Fe-rich intermetallic particles were mainly observed in the samples treated by carbon inoculation and then Fe addition. The Al–C–O–Fe particles, actually being Al–C–Fe phases, formed under this condition should not be the potent nucleating substrates for Mg grains, resulting in the grain coarsening.
Using density functional theory formulated within the framework of the exact muffin-tin orbital method, we investigate the elastic properties of hexagonal closed-packed Fe–Mg alloys, containing 5 and 10 at.% Mg, up to pressures of the Earth's inner core. We demonstrate the effect of Mg alloying on the hexagonal axial ratio, elastic constants, density and sound wave velocities. We find that 10% Mg alloying decreases the shear modulus of iron by 23% and reduces the transverse sound velocity, vS by 12% at core pressures. Although it is debated whether or not Mg can partition into the core, our results support Mg as a candidate light element in the core.
- M Moravej
- F Prima
- M Fiset
- D Mantovani
Moravej, M., Prima, F., Fiset, M., Mantovani,
D., (2010), Electroformed Iron As New
Biomaterial
For
Degradable
Stents:
Development
Process
and
Structure-Properties Relationship, Acta Biomaterialia, 6:
1726-1735.