Mekanik alaşımlama ve sıcak presleme ile üretilen magnezyum kalsiyum alaşımlarının mikro yapı ve mekanik özelliklerinin araştırılması

Toz metalurjisi (TM), üreticilere diğer imal usullerine göre büyük avantajlar sunan bir üretim yöntemidir. Biyobozunur Mg alaşımları demir ve çinko alaşımlarına göre üstün özelliklere sahiptir. Magnezyum esaslı alaşımların yüksek bozunma hızı ve kayıpları sebebiyle kullanımları sınırlıdır. Bu çalışmada toz metalurjisi yöntemiyle üretilen biyobozunur Mg ve Ca tozlarının mekanik özelliklerini tahmin etmek için istatistiksel model CCD tasarımı kullanılarak yüksek mekanik performans sergileyen Mg-xCa alaşımları geliştirilmiştir. Anova analizi ve regresyon denklemi modelin doğruluğunu göstermiştir. Mg ve Ca tozları değişik sürelerde 11.99-14.43-18-21.5-24 saat alaşımlama işlemine tabi tutulmuş ve MA sonrası tozların tane boyut ölçümü ve SEM EDS, XRD analizleri yapılmıştır. Tozlar tek eksenli sıcak preste 46 MPa basınçta argon gazı altında vakumlu ortamda değişik sıcaklıklarda 325-370-437-504-549°C basılmış sinterlenmiş ve blok numuneler haline getirilmiştir. Mg-xCa alaşımlarının mikroyapıları, mekanik özellikleri basma dayanımları, yoğunluk değerleri ve sertlikleri birbirleri ile kıyaslamalı olarak incelenmiştir. İkincil faz Mg2Ca'nın artan Ca oranıyla beraber attığı gözlemlenmiştir. Mg-xCa alaşımlarının basma değerleri 251MPa sertlikleri 146 Brinell ve yoğunluk değerleri 1.7 g/cm3 olarak tesbit edilmiştir. Mg-xCa alaşımları saf Mg'ye göre üstün performans sergilemiştir.Powder metallurgy (PM) is a production method that provides better advantages to the producers comparing to the other methods. Biodegradable Mg alloys have superiorities compared to iron and zinc alloys. Mg-based alloys are still inhibited mainly by their high degradation rates and consequent loss in mechanical integrity. The broad studies in this subject are to increase the mechanical properties and corrosion performance. In this study, in order to predict the mechanical properties of biodegradable Mg and Ca which are produced with the powder metallurgy method, Mg-xCa alloys with high mechanical properties are developed by using statistical model CCD design, anova analysis and regression equation indicated that the model was accurate. In this study, the powder Mg and Ca have put to the process of alloying with different period of times. Grain sizes of the powders are measured and they have been analyzed for SEM EDS, XRD. Powders are pressed by a uniaxial hot compression in a vacuumed environment under argon gas in 46MPa pressure in different temperatures they have been sintered and sampled in blocks. Mg-xCa alloys have been analyzed comparatively for their microstructures, mechanical properties, pressure endurance, density rates and stiffness. It has been observed that secondary phase Mg2Ca increases with the increasing rate of Ca. The measured values of Mg-xCa alloys are 251MPa for compressive strength, 146 Brinel for hardness, and 1.7 g/cm3 for density. Mg-xCa alloys have performed much superior compared to pure Mg

Boron doping effect on the structural, spectral properties and charge transfer mechanism of orthorhombic tungsten bronze beta-SrTa2O6:Eu3+ phosphor

In the study, the effect of boron doping on spectral properties and CTB mechanism was investigated by using Eu3+ doped orthorhombic beta-SrTa2O6. A phosphor series of Eu3+ doped SrTa2O6, and Eu3+ and B3+ co-doped SrTa2O6 polycrystals were fabricated by solid-state reaction at 1400 degrees C for 20 h in an air atmosphere. The X-ray diffractions of the main phase structure for all the ceramics maintained up to 10 mol% Eu3+ concentration, while the increase of XRD intensity for Eu3+ and B3+ co-doped samples was attributed to somewhat improvement of crystallization. SEM morphologies of grains showed that the presence of boron promotes agglomeration and grain growth. The doping of boron up to 20 mol% led to an increase in PL intensity, CTB energy slightly shifted to low energy, and also an increase occurred in the asymmetry ratio of the phosphor. Therefore, the low crystal field symmetry of the Eu3+ sites and some improvement in crystal structure properties for Eu3+, B3+ co-doped samples supported the PL increase. The trend of Judd-Ofelt parameters (omega(2), omega(4)) is SrTa2O6:xEu(3+), 0.1B(3+) > SrTa2O6:xEu(3+). The high omega(2) parameter for boron co-doped samples showed a covalent Eu-O bond character with low symmetry of Eu3+ environment, while the high omega(4) value indicated the reduction in electron density of the ligands. Some increase in the short decays of Eu3+, B3+ co-doped samples is probably due to the surface effect and low crystal field symmetry. The quantum efficiency of 0.05Eu(3+), 0.1B(3+) co-doped phosphor with the highest PL intensity increased by about 21% compared to that without boron

Structural Properties, Photoluminescence, and Judd-Ofelt Parameters of Eu3+- Doped CoNb2O6 Phosphor

Trivalent Eu-activated CoNb2O6 phosphors were fabricated using the molten salt method, which provides enhanced homogeneity and low sintering temperature. The ceramic samples were examined by spectral and structural analyses. In X-ray diffractions, the single phase of orthorhombic columbite type CoNb2O6 structure was obtained for 0.5-10 mol% Eu3+ doping concentrations, while a two theta peak shift towards the smaller angles occurred. SEM examinations show an irregular morphology and sub-micron grain sizes. In photoluminescence (PL) spectra, the phosphors showed typical Eu3+ emissions with the 5F0 → 7FJ (J=0, 1, 2, 3, 4) transitions, and high emission peaks were observed at the 5D0 → 7F2 transition. The photoluminescence of CoNb2O6:Eu3+ decreased over 5 mol% because of the concentration quenching. The energy transfer mechanism and critical distance of the phosphor are the dipole-dipole (d–d) interaction, and 15.70 Å, respectively. The spectral features of the phosphors were assessed by calculating the Judd-Ofelt intensity parameters (Ω2, Ω4) from the PL emission spectrum. The low Ω2 parameter values or/and the Ω4>Ω2 trend for CoNb2O6:Eu3+ phosphors were related to the less covalent or more ionic character of the Eu3+–O2˗ bond and the high local symmetry of the Eu3+ sites, while the high Ω4 parameter values may be ascribed to the decrease in the electron density in the ligands

Investigation of Dry Sliding Wear Behavior of Mg-SiC Alloys Produced by Powder Metallurgy Method

In recent years, Mg alloys have great promise for weight-saving applications, because of their superior properties over mo nolithic metals, in the field of automotive and aerospace industries. In this study, the dry sliding wear behavior of Mg- SiC alloys with different sintering temperatures (375°C, 400°C, 425°C) were investigated. Mg with %10 weight SiC powders were mechanically mixed and alloyed and then fabricated successfully via fast heating under vacuumed argon atmosphere. The friction coefficient, hardness value, and wear resistance of the alloys were higher than those of the pure Mg. The increase in the sintering temperature of the Mg-SiC alloys up to 425°C caused an increase in the friction coefficient and a decrease in the wear mass loss respectively