TEM study of the effect of high-temperature thermal cycles on the stability of the Y-Al-O oxides in MA956 ODS steel

MA956, a commercial ferritic grade of Oxide Dispersion-Strengthened (ODS) steel, was investigated using transmission electron microscopy (TEM) to evaluate the influence of high-temperature thermal cycles on the nanometric dispersed oxides. Analyses of the oxide size distribution were carried out on foils from the as-received MA956 and following treatment at 1285ºC for one hour, and show that growth of the oxides has occurred under the thermal cycle. Implications for the oxide stability in the steel matrix are discussed, in the light of the oxide chemical composition

Evolution of dislocation density, size of subgrains and MX-type precipitates in a P91 steel during creep and during thermal ageing at 600 °C for more than 100,000 h

International audienceThere are rather few quantitative data on the microstructure of the 9–12%Cr heat resistant steels after long-term creep. This paper presents results of the quantitative measurement of the size of MX precipitates, subgrain size and dislocation density in a P91 steel that had been creep tested for 113,431 h at 600 °C. The same measurements were conducted in the same P91 steel in the as received conditions. Transmission electron microscopy investigations were conducted using thin foils and revealed a decrease in dislocation density and an increase in subgrain size after creep exposure. MX carbonitrides are very stable during thermal and creep exposure of P91 steel at 600 °C up to 113,431 h. Electron backscatter diffraction (EBSD) investigations also revealed a significant change in the substructure of the steel after creep exposure

Effects of build orientation and element partitioning on microstructure and mechanical properties of biomedical Ti-6Al-4V alloy produced by laser sintering

Direct Metal Laser Sintering (DMLS) technology was used to produce tensile and flexural samples based on the Ti-6Al-4V biomedical composition. Tensile samples were produced in three different orientations in order to investigate the effect of building direction on the mechanical behavior. On the other hand, flexural samples were submitted to thermal treatments to simulate the firing cycle commonly used to veneer metallic devices with ceramics in dental applications. Roughness and hardness measurements as well as tensile and flexural mechanical tests were performed to study the mechanical response of the alloy while X-ray diffraction (XRD), electron microscopy (SEM, TEM, STEM) techniques and microanalysis (EDX) were used to investigate sample microstructure. Results evidenced a difference in the mechanical response of tensile samples built in orthogonal directions. In terms of microstructure, samples not submitted to the firing cycle show a single phase acicular α’ (hcp) structure typical of metal parts subject to high cooling rates. After the firing cycle, samples show a reduction of hardness and strength due to the formation of laths of the β (bcc) phase at the boundaries of the primary formed α’ plates as well as to lattice parameters variation of the hcp phase. Element partitioning during the firing cycle gives rise to high concentration of V atoms (up to 20 wt%) at the plate boundaries where the β phase preferentially forms

Atomic force microscopy studies of the surface scale formed during oxidation of incoloy MA956

The formation of thin oxide films on {111} and {110} single crystal specimens of Fe20Cr5A1 based oxide dispersion strengthened alloy during the early stages of oxidation up to 1000°C was investigated by atomic force microscopy. The atomic force microscopy results revealed the crystalline character of a corrosion layer. The alumina scale morphology (height and grain size of crystallites) was only slightly dependent on the crystallographic texture of the underlying bulk material. The results show that atomic force microscopy has the potential to study surface structure of oxide layers in the initial stages of an oxidation process

Gaya kepemimpinan KH. R. Sadad MB. Bukhori di Pondok Pesantren Asyrofuddin Conggeang Sumedang

Kepemimpinan di lembaga pendidikan Islam mempengaruhi lingkungan dalam merealisasikan visi dan misi, termasuk kepemimpinan di pondok pesantren. Keberhasilan suatu kepemimpinan bergantung pada gaya kepemimpinan seseorang. Pondok Pesantren Asyrofuddin bertujuan untuk melahirkan generasi yang berakhlak mulia, cerdas, mandiri dan memiliki tanggung jawab. Tujuan itu dapat tercapai dengan pengelolaan yang baik oleh pimpinannya. Peneliti melihat beberapa pondok pesantren ada yang berkembang dan tidak berkembang. Peneliti menemukan bahwa salah satu faktor berkembang dan tidak berkembangnya di sebabkan oleh pengaruh gaya kepemimpinan. Penelitian ini difokuskan pada gaya kepemimpinan KH. R. Sadad MB. Bukhori di Pondok Pesantren Ayrofuddin Metode yang digunakan dalam penelitian ini adalah deskriptif dengan pendekatan kualitatif. Data yang diperoleh berasal dari sumber primer yang diambil dari hasil penelitian dan data sekunder diambil dari buku-buku dan dokumen-dokumen. Sedangkan tekhnik pengumpulan data dengan cara melakukan observasi, dan wawancara. Kepemimpinan KH. R. Sadad MB. Bukhori berdasarkan penelitian mampu mempengaruhi para anggota kepengurusan supaya bekerja sama guna mencapai tujuan yang sama pada Pondok Pesantren Asyropuddin. Pondok Pesantren Asyropuddin tidak lepas dari peran beliau dengan tipe kepemimpinan demokratis, dikatakan demokratis yaitu, beliau mampu menetapkan faktor manusia sebagai faktor utama dan terpenting. Dalam kepemimpinan ini setiap individu sebagai manusia diakui, sehingga setiap keputusan dan pengawasan beliau tidak ditetapkan oleh sepihak namun di tetapkan secara bersama-sama. Upaya-upaya yang dilakukan KH. R. Sadad MB. Bukhori dalam kepemimpinannya di Pondok Pesantren Asyrofuddin, yaitu pengambilan keputusan dengan proses tidak secara sepihak namun dilakukan dengan proses musyawarah begitupun di setiap pengambilan keputusan beliau melakukan pengambilan keputusan dengan cepat dan sigap walaupun permasalah tersebut merupakan permasalahn kecil, komunikasi dengan proses dimana para anggota melakukan komunikasi atasan terhadap bawahan begitupun bawahan terhadap atasan sehingga menimbulkan timbal balik yang menguntungkan antara dua belah pihak namun dalam hal semua itu tidak ada kecanggungan ataupun batasan dalam berpendapat, dan yang terakhir upaya dalam hal pengawasan dengan proses secara langsung terhadap bawahannya namun dengan cara kekeluargaan adapun pengawasan yang dilakukan beliau bukan untuk mencari kesalahan namun lebih kepada mencari solusi. Keberhasilan yang dicapai dari kepemimpinan beliau secara signifikan meningkatnya, yaitu dapat dilihat dari adanya sistem pendidikan yang diterapkan oleh pesantren dan dari perkembangan sarana yang membaik

ZnO quantum dots modified bioactive glass nanoparticles with pH-sensitive release of Zn ions, fluorescence, antibacterial and osteogenic properties

Zinc (Zn)-containing materials have osteogenic and antibacterial activities while bioactive glass nanoparticles (BGN) show bone-bonding ability, as well as osteoconductive and osteoinductive properties. Zn-containing BGN are therefore considered to be promising materials for various biomedical applications, particularly in bone regeneration. In this study, we report a convenient method to prepare Zn-containing BGN by coating ZnO quantum dots (QDs) on BGN via electrostatic interactions. The synthesized ZnO–BGN nanocomposite particles are spherical and highly dispersed, and exhibit a unique fluorescence behavior under UV excitation, emitting three wavelengths in the violet, blue and green range. ZnO–BGN showed apatite-forming ability upon immersion in simulated body fluid, but their apatite formation was delayed compared to BGN. Interestingly, ZnO–BGN showed a rapid release of Zn ions at pH 4 but a far slower release at pH 7.4. ZnO–BGN also exhibited antibacterial effects on both Gram-positive and Gram-negative bacteria at the concentrations of 1, 0.1, and 0.01 mg mL−1. Higher concentrations could lead to stronger antibacterial effects. The LDH and live/dead assays indicated that ZnO–BGN had no significant cytotoxicity towards human mesenchymal stem cells (hMSC) at concentration of 0.1 and 0.01 mg mL−1, but ZnO–BGN inhibited the relative proliferation of hMSC compared to BGN and the control according to the MTT assay. Notably ZnO–BGN improved the osteogenic differentiation of hMSC as indicated by the determination of the alkaline phosphatase activity. In conclusion, coating quantum dots on BGN is a promising strategy to produce Zn-containing BGN. The synthesized ZnO–BGN are potential materials for bone regeneration, considering their apatite-forming ability, unique ion-release behavior, effective antibacterial activity, non-cytotoxicity, and osteogenic potential