Photoluminescence and concentration quenching of Pr3+ doped BaTa2O6 phosphor

The pure and Pr3+ doped TTB-BaTa2O6 phosphors were obtained by the solid state reaction method at 1 425 °C for 20hours. X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM) analyses confirmed a single phase of BaTa2O6up to 10 mol % Pr2O36. SEM analysis also shows that BaTa2O6 grain size decreased with the increasing Pr2O36 concentration.The chemical composition of Pr3+ doped BaTa2O6 structures was confirmed by Energy Dispersive Spectroscopy(EDS) analysis. BaTa2O6:Pr3+ phosphors exhibited on a strong red emission at 620,9 nm, a green emission at 548,3 nm and a red emission at 655,2 nm. Emission intensity increased with Pr3+ doping concentration up to 1,5 mol %, then decreased due to concentration quenching

Wear Behaviour of SiC reinforced 2618 Al matrix composites

<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:14.0pt; mso-bidi-font-size:10.0pt; font-family:Arial; mso-fareast-font-family:"Times New Roman"; mso-bidi-font-family:"Times New Roman"; mso-fareast-language:EN-US;} p.zetmetni, li.zetmetni, div.zetmetni {mso-style-name:"Özet metni"; mso-style-link:"Özet metni Char"; margin-top:6.0pt; margin-right:0cm; margin-bottom:0cm; margin-left:0cm; margin-bottom:.0001pt; text-align:justify; mso-pagination:widow-orphan; font-size:11.0pt; mso-bidi-font-size:10.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman"; mso-fareast-language:EN-US; font-style:italic; mso-bidi-font-style:normal;} span.zetmetniChar {mso-style-name:"Özet metni Char"; mso-style-locked:yes; mso-style-link:"Özet metni"; mso-ansi-font-size:11.0pt; mso-ansi-language:TR; mso-fareast-language:EN-US; mso-bidi-language:AR-SA; font-style:italic; mso-bidi-font-style:normal;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 70.85pt 70.85pt 70.85pt; mso-header-margin:35.4pt; mso-footer-margin:35.4pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> Metal matrisli kompozitlerin üretim ve kullanımları son 20 yılda teknolojik gelişmelerle birlikte, özellikle havacılık, savunma, otomotiv, spor ve denizcilik gibi uygulamalarda artış göstermiştir. Alüminyum alaşımları arasında, 2618 alüminyum alaşımı yüksek sıcaklık uygulamaları için (özellikle uçak motor parçası) geliştirilen Al-Cu-Mg-Fe-Ni içeren ısıl işlemle sertleştirilebilir bir dövme alüminyum alaşımıdır. Bu alaşımda bulunan Fe ve Ni elementleri sıcaklık altında mikroyapısal kararlılık sağlayarak alaşımın 200 °C’ye kadar mukavemetini korumaktadır. Bu çalışmada, sıkıştırma döküm yöntemi ile üretilmiş olan % 50 hacim oranında SiC partikül takviyeli döküm halindeki ve yaşlandırılmış durumdaki 2618 alüminyum matrisli kompozitin kuru kayma aşınma davranışları incelenmiştir. Kompozitlerin oda sıcaklığı mekanik özellikleri sertlik ve darbe deneyleri ile belirlenmiştir. % 50 SiC içeren 2618 aluminyum matrisli kompozitin sertliği yaşlandırma işlemi ile % 5 oranında artarken darbe direnci ise yaklaşık olarak % 12 oranında azalmıştır. Kompozitlerin aşınma davranışları ileri-geri aşınma deneyleri ile incelenmiştir. İleri-geri aşınma deneyleri 1.5-6.0 N yük aralığında, 0.02 m/s ve 0.09 m/s olmak üzere iki farklı kayma hızında Al2O3 topun sürtünmesi ile yapılmıştır. Aşınma deneyleri sonunda SiC ile takviye edilmiş 2618 alüminyum matrisli kompozitin döküm haline kıyasla, yaşlandırma ısıl işlemi ile aşınma direncinin düşük test yüklerinde ve yüksek kayma hızlarında değişmediği, ancak yüksek test yüklerinde ve düşük kayma hızlarında ise arttığı tespit edilmiştir.   Anahtar Kelimeler: Alümyum alaşımı, aşınma, kompozit, SiC.In the past two decades, a strong interest has been shown in the application of the aluminum matrix composites in the design of many engineering and non-engineering components. Potential uses of these materials are numerous in industries and they include such areas of application as aerospace (satellite struts), defense (electronic instrument racks), automotive (drive shafts and brake disks), sports goods (golf clubs and mountain bicycle frames), and marine (yacht fittings). Aluminum and its alloys with low density and high strength to weight ratio is an excellent candidature matrix material for compositing. Aluminum alloys can be divided into two categories: heat treatable and non-heat treatable alloys. Among aluminum alloys, 2618 (AA2618) is one of the most attractive matrix materials. 2618 aluminum alloy is a heat treatable Al-Cu-Mg-Fe-Ni forging alloy developed for high temperature applications, especially in the manufacture of aircraft engine components. This alloy has good elevated temperature strength up to 204 °C. The addition of small amounts of Fe and Ni produces microstructural stability under thermal exposure. It is anticipated that reinforcing 2618 aluminum alloy with SiC particles can lead to significant improvement in stiffness and strength, both at room and elevated temperatures besides improvement in wear resistance. In this study, structure and mechanical properties of squeeze cast 50 % SiC particle-reinforced 2618 aluminum matrix composites were investigated. 1 wt % Mg to enhance interfacial bonding between Al and SiC was added to commercially available 2618 Al alloy utilized as the matrix alloy. Composites were tested in as-cast and T6 temper states. The examined composite was fabricated by squeeze casting technique. During squeeze casting, the molten Al was poured into the pre-heated mold immediately after transferring the pre-heated SiCp?s. Subsequently, a high pressure of 600 MPa was applied on the mixture by a hydraulic press. Abrasive grade green SiCp?s having the mean size of 30 µm were used as the reinforcement. Structural characterization was carried out after grinding and polishing the samples by utilizing a light optical microscope (LOM), a scanning electron microscope (SEM) equipment with energy dispersive spectroscopy (EDS) and a X ray diffractometer. Room temperature mechanical properties of the composites were determined by hardness measurements and charpy impact tests. The hardness measurements were carried on a hardness tester under a load of 2 kg with a diamond Vickers indenter. Impact tests were conducted on a pendulum charpy-type impact tester on un-notched specimens having width and thickness of 5x5 mm. The results of impact tests were evaluated by averaging the results of three specimens. Wear performance of the composites was determined on a reciprocating wear tester designed according to ASTM G 133 standard. A 10 mm diameter Al2O3 ball was rubbed against the unlubricated surfaces at normal atmospheric conditions (room temperature and 50 % humidity). The stroke of the Al2O3 ball was 12 mm and test loads ranging from 1.5 to 6.0 N were applied for the total sliding distance of 120 m. Wear tests were carried out at two different sliding velocities (0.02 m/s and 0.09 m/s). During wear testing, frictional force data were continuously recorded. After wear test, the wear tracks formed on the composites were examined by a profilometry and a light optical microscope. Microstructural examination revealed presence of dense and pore free microstructure with a homogeneous distribution of SiC particles surrounded by matrix alloy. During microscopic examinations, only Al and SiC peaks were evident on the XRD patterns obtained from 2618 aluminum matrix composite in the as cast and aged states. Application of T6 temper to 50 vol.% SiC 2618 aluminum matrix composites increases the hardness (about 5 %) and decreases the impact resistance (about 12 %). Reciprocating wear tests carried out at two different sliding velocities (0.02 m/s and 0.09 m/s) and test loads in between 1.5 and 6.0 N revealed that the following results: the effect of T6 temper on wear resistance is almost negligible at low test loads and high sliding velocity. However, T6 temper improved the wear resistance (about 50%) at high test loads and low sliding velocity, when compared to as-cast state.   Keywords: Aluminum alloy, wear, composite, SiC

Synthesis and characterization of resol type phenolic resins

Farklı ön polimerizasyon sıcaklıkları ve çeşitli formaldehit / fenol (F: P) oranları, resol fenolik reçinenin sentezinde kritik bir öneme sahiptir. Polimerizasyon reaksiyonlarında reaksiyon parametrelerinin anlaşılması, fenolik reçine bazlı kompozit malzemelerin üretimi için ön şarttır. Farklı ön polimerizasyon sıcaklıkları ve çeşitli F:P oranlarının etkisini gözlemlemek için, X-Işını difraksiyonu (XRD), Fourier dönüşümlü infrared spektroskopisi (FTIR), Diferansiyel taramalı kalorimetri (DSC) ve mikro sertlik analizleri yapılmıştır. XRD ve FTIR analizlerinin sonuçları, sentezlenmiş reçinelerin yapısal konformasyonunun anlaşılmasını sağlamıştır. DSC ve mikro sertlik analiz sonuçlarıyla, ön-polimerizasyon sıcaklığı 50 °C ve F:P oranı 1,3 iken sentezlenen reçinenin (PFR250) artan eter köprülerine paralel olarak kristalleşme eğiliminin arttığı tespit edilmiştir.The different pre-polymerization temperatures and various formaldehyde/phenol (F:P) ratios have a critical importance in the synthesis of resol phenolic resin. Understanding the reaction parameters in polymerization reactions is a prerequisite for the production of phenolic resinbased composite materials. X-Ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR), Differential scanning calorimetry (DSC) and microhardness analysis were performed to observe the effect of different pre-polymerization temperatures and various F: P ratios. The results of XRD and FTIR analysis provided an understanding of the structural conformation of synthesized resins. It was also found by the DSC and microhardness analysis that the tendency of crystallization increased for the synthesized resin (PFR250) when the prepolymerization temperature was 50 °C and the F:P ratio was 1,3, especially in parallel with increasing ether bridges

Effect of heat treatment on the wear and corrosion behaviors of a gray cast iron coated with a COLMONOY 88 alloy deposited by high velocity oxygen fuel (HVOF) thermal spray

The present work has been conducted in order to determine the influence of heat treatment on the wear and corrosion behaviours of a gray cast iron substrate coated with a Ni base coating deposited by HVOF thermal spray. The wear resistance of the coatings was obtained using a reciprocating wear tester by rubbing a 10 mm diameter steel ball on the coatings at normal atmospheric conditions. Corrosion tests were performed using potentiodynamic polarization measurements in a 3,5 % NaCl solution. It was observed that the corrosion and wear resistance of the coatings increased along with the reduction of porosity and roughness by the heat treatment

Effect of Mill Type on Morphology of AA6013 Aluminium Powder

ABSTRACTIn conventional recycling method, metal chips are cast after pressing and melting in electric arc furnace. Material loss occurs during the recycling from liquid metal due to the several reasons. Direct recycling method which produces the aluminium powder from aluminium chips using mechanical mill can be an alternative to conventional recycling method. Thus material and energy losses, and labour cost will be reduced by direct recycling method without melting.In this study, the particle morphology of powder direct recycled from AA6013 aluminium alloy chips with cryogenic, disc and ball type grinders is investigated. Mechanical milling resulted flaky and irregular shaped AA6013 particles. It was ascertained that the chips did not break sufficiently in despite of the long duration milling mechanisms by ball mill. Cryogenic mill provides the energy required for milling mechanisms to act. Disc mill has the highest impact energy was determined. Consequently, efficiency of ball mill is lower than the efficiency of cryogenic and disc type mills. Shape factors of powders produced with ball and cryogenic mills were found greater than that of the powder produced by disc mill. Disc mill has the most efficient and effective impact energy which produces the smaller particles per minute, was determined.Keywords: Direct recycling method, powder production, scrap chips, aluminium alloy.

The Study of Electroless Ni-P/Ni-B Duplex Coating on HVOF-Sprayed Martensitic Stainless Steel Coating

High velocity oxygen fuel sprayed stainless steel coatings have been widely used in various industries to repair damaged components. However, its broad application is limited due to its comparatively low hardness and inferior tribological properties. In this work, electroless Ni-P/Ni-B duplex coating with a thickness of ≈ 40 μm was deposited on surfaces of HVOF-sprayed 420 martensitic stainless steel substrate, and its structural, corrosion and tribological properties were characterized. Experimental results showed that upper Ni-B coating deposited on the surface of first Ni-P layer by duplex treatment exhibited superior hardness, wear and corrosion resistances as compared to the HVOF-sprayed 420 martensitic stainless steel coating with a thickness of about 150 μm

Electroless Ni–B Coating of Pure Titanium Surface for Enhanced Tribocorrosion Performance in Artificial Saliva and Antibacterial Activity

In the present study, the surface of commercial pure (Grade 2) titanium was coated with electroless Ni–B. The surface morphology, microstructure and phase identification were analysed by X-Ray Diffraction (XRD) and Field Emission Gun Scanning Electron Microscope (FEG-SEM) equipped with Energy Dispersive X-ray Spectroscopy (EDS). The tribocorrosion performance in a laboratory simulated artificial saliva was investigated using a reciprocating ball-on-plate tribometer coupled to an electrochemical cell. The antibacterial property of the electroless Ni–B film coated on pure titanium was basically investigated. From this study, it may be concluded that this electroless Ni–B coating process cannot only improve the hardness and tribocorrosion performance of the pure titanium, but can also provide antimicrobial activity

Effect of B4CB_4C Content on the Mechanical and Tribological Performances of Polypropylene

Boron carbide ($B_4C$) reinforced polypropylene (PP) was prepared by twin-screw extrusion and injection molding. In the present study, the effect of $B_4C$ content on the mechanical properties and wear behavior of the PP composites was studied. The tribological properties of the PP composites were investigated by a reciprocating wear tester under dry friction conditions. The results of the mechanical and wear test showed that the hardness and yield strength increased with increasing $B_4C$ content, while the incorporation of $B_4C$ into PP largely increased wear and friction under dry sliding. The composites have higher wear rates in comparison with unfilled PP and the greater the difference, the greater are the sliding velocities

Grafen oksit (GO) ve indirgenmiş grafen oksit (RGO) dolgulu PVC kompozitlerin mekanik özelliklerinin karşılaştırılması

Grafen türevleri (grafen oksit-GO, indirgenmiş grafen oksit-RGO, çok tabakalı grafen-MLG vb.) polimer malzemelerin özelliklerini iyileştirmek için yüksek potansiyele sahip dolgu maddeleri olarak bilinmektedirler. Bu çalışmada kompozitlerin mekanik özelliklerinde ki değişim dolgu tipine ve dolgu miktarına göre incelenmiştir. Kompozitler, dolgu maddeleri olarak GO ve RGO, matriks olarak polivinil klorür (PVC) ile hazırlanmıştır. X-ışını kırınımı (XRD) sonuçları, GO ve RGO tabakalarının polimer matriksde homojen dağıldığını göstermiştir. Taramalı elektron mikroskobu (SEM) çalışmaları, RGO içeren kompozitin düz ve pürüzsüz, GO içeren kompozitin ise dolgu- matriks etkileşimi daha iyi olduğu için yüksek oranda gözenekli morfoloji sergilediklerini ortaya koymuştur. Yüksek GO (ağırlıkça %1) ve düşük RGO (ağırlıkça %0.1) içeren kompozitlerin mekanik özellikleri önemli bir iyileşme sergilemiştir. Dolgu maddesi içermeyen PVC’ye nazaran ağırlıkça %1 GO ve %0.1 RGO içeren kompozitlerin çekme mukavemetleri sırasıyla %84 ve %42 artmıştır. RGO ilavesi kompozit yapıyı rijitleştirdiğinden, RGO içeren kompozitler GO içeren kompozitlere kıyasla daha yüksek mikrosertlik ve daha düşük yüzde uzama değerleri sergilemişlerdir