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Gestational diabetes mellitus (GDM) is one of the most common pregnancy complications characterized by insulin resistance and pancreatic β-cell dysfunction. Increasing evidence suggests that microRNAs (miRNAs) play key roles in the diverse types of diabetes, including GDM. However, the underlying mechanisms remain largely unknown. The purpose of this study is to investigate the role of microRNAs in GDM. The microarray data of dysregulated miRNAs in blood and placenta was retrieved in the GEO dataset under the accession number GSE19649. Quantitative reverse transcription PCR (qRT-PCR) was performed to analyze the expression levels of miR-494 in peripheral blood from twenty pairs of gestational diabetes (GDM) women and healthy women. Then, we investigated the effects of miR-494 on the insulin secretion of pancreatic β-cells. Moreover, the role of this miR-494 in regulating the proliferation and apoptosis of pancreatic β-cells were determined by MTT assay and flow cytometry, respectively in INS1 cells transfected with a miR-494 mimic or inhibitor. In addition, the direct target of miR-494 was confirmed using 3' untranslated region (UTR) luciferase reporter assay. Our data demonstrated that the miR-494 level was significantly decreased in the blood of GDM patients, and the low level was associated with a high concentration of blood glucose. Furthermore, overexpression of miR-494 improved pancreatic β-cell dysfunction by enhancing insulin secretion and total insulin content, inducing cell proliferation, and inhibiting cell apoptosis, whereas miR-494 knockdown exhibited decreased insulin secretion and proliferation, as well as stimulated apoptosis. In addition, phosphatase and tensin homolog (PTEN) which has been shown to play a pivotal role in apoptosis, was proved to be a direct target of miR-494 in pancreatic β-cells. More importantly, siRNA-induced downregulation of PTEN reversed the effects of miR-494 knockdown on insulin secretion, cell proliferation, and apoptosis of pancreatic β-cells., EXCLI Journal; 16:Doc1297; ISSN 1611-2156

Hot corrosion behavior of powder metallurgy (PM) Rene95 Ni-based superalloy in molten 25%NaCl + 75%Na2SO4 salts at 650 °C, 700 °C and 750 °C are investigated by weight loss measurements, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). Experimental results show that hot corrosion kinetics follow a square power law at 650 °C and linear power laws at 700 °C and 750 °C. The corrosion layers on the surface of PM Rene95 superalloy are detected to be mainly composed of Cr2O3, NiO, and Ni3S2 at each temperature. Besides, small amounts of NiCr2O4 at 700 °C and NaCl at 750 °C are observed respectively. Cross-sectional morphologies and corresponding elemental maps indicate that corrosion layers near scale/alloy interface are composed of oxides at 650 °C while duplex oxides and sulfides at 700 °C and 750 °C. According to these results, a cooperating mechanism of oxidation and sulfuration for hot corrosion of PM Rene95 Ni-based superalloy is confirmed.

Super304H austenitic heat resistant steel is based on 18/8 Cr-Ni stainless steel alloyed mainly with 3%Cu and a small amount of Nb combined with N,which is used as superheater/reheater tubes in ultra-super critical(USC) power plants all over the world,due to its good combination of elevated temperature strength with hot corrosion resistance.The excellent high temperature strengths of this steel are mainly contributed by the precipitation strengthening effect of fine Cu-rich phase.Comprehensive study of the characteristic of Cu-rich phase is very important to understand strengthening effect on this steel.However,the Cu-rich phase is very fine and difficult to be detected at the beginning of precipitation.In this paper,three dimensional atom probe(3DAP) was used to study the early stage of precipitation behavior and the composition change in Cu-rich phase of Super304H aged at 650℃for different times after solution treatment at high temperature.Cu-rich phase is formed from Cu-rich segregated rigion by the concentration of Cu atoms in it at very beginning stage of aging.Homogeneously distributed Cu-rich phase precipitates with about 1 nm radius are obviously detected after aging at 650℃for 5 h.With increasing aging time,Cu-rich phase is growing slowly while other elements in the Cu-rich phase decreased obviously.The copper element has almost concentrated to 90%in the center part of Cu-rich phase after 500 h aging.The homogenous distribution of fine Cu-rich phase in austenitic matrix effects excellent hardening with increasing aging time.The stability of fine Cu-rich phase is one of the most important reasons for keeping good strength of Super304H heat resistant steel at high temperature.

The interdendritic segregation along the mushy zone of directionally solidifi ed superalloy Inconel 718 has been measured by scanning electron microscope (SEM) and energy dispersion analysis spectrometry (EDAX)techniques and the corresponding liquid composition profile was presented. The liquid density and Rayleigh number (Ra) profi les along the mushy zone were calculated as well. It was found that the liquid density difference increased from top to bottom in the mushy zone and there was no density inversion due to the segregation of Nb and Mo. However carbide formation in the freezing range and the preferred angle of the orientated dendrite array could prompt the fl uid fl ow in the mushy zone although there was no liquid density inversion. The largest relative Rayleigh number appeared at 1,326 篊 for Inconel 718 where the fl uid fl ow most easily occurred.

Samples of forged and heat treated DA718 and STD718 were examined to determine the effects of long time thermal exposures at 1200 and 1250 °F on microstructures and mechanical properties. In addition to the coalescence of γ′/γ″ and the amount increasing of δ phase, the existence of a bcc chromium enriched α-Cr phase was confirmed by XRD and SEM. The weight fraction of α-Cr and other phases were determined by chemical phase analyses methods. The results showed that the fractions of α-Cr in both DA718 and STD718 were less than 1% but more α-Cr particles precipitated in DA718 than in STD718 because the retained strain in DA718 promoted α-Cr precipitation. The results also showed that more α-Cr particles precipitated in Alloy 718 at higher exposure temperatures and for longer exposure times. The thermal exposure at 1200 and 1250 °F did not have any deleterious effects on the 1200 °F creep crack growth rate (CCGR).

The growth of precipitate particles in precipitation-hardened alloys is very significant, because it can control the long-time mechanical properties of these alloys. The kinetics of this coarsening process have been accounted for in the theory of diffusion-controlled growth, based on the growth theory of Lifshitz and Slyozov and Wagner. The growth of {gamma}{prime} precipitate particles, which have an ordered fcc structure and precipitate coherently in many Ni-containing fcc alloys, follows the d {proportional_to} t{sup 1/3} law. Another commonly observed strengthening phase in many nickel alloys is {gamma}{double_prime}, which has a bct structure and precipitates coherently with a disk shape. A well-known example of this class of alloy, is the widely used commercial alloy, Inconel 718. Here, the measured coarsening kinetics of separate precipitation of {gamma}{double_prime} is found to be linearly related to the cube root of the aging time at 700 and 730 C. However, the coarsening behavior of {gamma}{double_prime} in a compact morphology of {gamma}{prime} + {gamma}{double_prime} in the modified alloy is different from that of Inconel 718. Initially the coarsening rate is very slow, but eventually it coarsens rapidly. The actual {gamma}{double_prime} particle size distribution of the modified alloy is skewed towards large particle size and differs significantlymore » from the theoretically predicted distribution. TEM observations also confirm the preferential dissolution of {gamma}{double_prime} during coarsening, which could be attributed to the presence of an easy-diffusion path or lies to in a short-circuit diffusion.« less

Turbine platform and blade are two main parts of aero engines and gas turbines. Due to different requirements in practice, platforms are always fabricated by single crystal superalloys, which have high temperature strength and resistance to hot corrosion and oxidation. The platforms employed at relatively lower temperatures can be made of powder superalloys. Therefore there is a great demand for bonding single crystal superalloys to powder superalloys. Because of high content offorming elements, traditional fusion welding methods employed in bonding the two materials are high susceptibility to cracking. Hot isostatic pressure (HIP) bonding is a preferable technique now to join nickel base superalloys. However, using experimental methods to explore appropriate HIP bonding parameters is time consuming and costly. This work puts forward a calculated method to simulate diffusion process and phase distribution of diffusion couples obtained by HIP diffusion bonding. In this work, the numerical model of HIP diffusion bonding was built, and distribution of elements and phases of DD407/FGH95 diffusion couples under different HIP temperature and bonding time were calculated

It is an urgent thing how to control the quality of large size GH4169 ingots nowadays. The high Nb element content in this alloy can increase the tendency of freckle defect formation. Though almost all the investigators consider that the segregation of Nb-riched Laves phase is the key factor of the freckle defect, how to avoid this phenomenon is still a hard-to-solve problem in engineering practice. In this work, a new prototype system based on classical dynamical model related to basic metallurgy theory was established to simulate the dynamical dissolving process of precipites evolution in nickel base superalloys. In this prototype system, the parameters related to the thermodynamic equilibrium state can be got from thermodynamic software of Thermo-Calc, the solute element diffusion coefficient at any temperature and time iterative can be got from dynamic software of Dictra. By using this prototype system, the dissolution process of Laves phase during homogenization process with different initial particle sizes for GH4169 alloy was simulated, and then series remelting experiments with different cooling rates and different Laves phase distributions were carried out, and the calculated results were in good agreement with the experimental results. This newly developed prototype system may give great help to homogenization process design in engineering use.

Based on the classical nucleation theory,and considering the effects of heat temperature and preservation time on precipitation,the 7' precipitation model in nickel-based superalloy was established.In combination with the characteristic value data of 7' precipitation which was got by isothermal aging experiment of GH738 alloy,the relative accuracy of simulation result was verified. Results show that the classic dynamic model of the precipitation can better forecast that 7' phase of multiple complex nickel-based alloy system mainly precipitate by uniform nucleation.Further,precipitation model was combined with four typical superalloys GH80A,GH738,U720Li and DD407.The effects of the contents of Al,Ti and its ratio change on the precipitation of 7' were calculated and analyzed.Results showed that the better role of Al than Ti on equilibrium content.Under the premise of equal amount of Al + Ti,the increasing of Ti had a greater contribution to the driving force of precipitation and complete precipitation time,and increased the volume fraction of the beginning of precipitation,but reduced the size of precipitated phase.

Copper has been used as a strengthening element in newly developed Fe–Cr–Ni type austenitic heat resistant steel for inducing Cu-rich phase precipitation to meet high temperature strength requirement for 600 °C Ultra Super-Critical (USC) coal fired power plants for many years. However, the precipitation behavior and strengthening mechanism of Cu-rich phase in these advanced austenitic heat resistant steels is still unclear. In order to understand the precipitation strengthening behavior of Cu-rich phase and to promote high strength austenitic heat resistant steel development, 18 Cr9 NiCuNb steel which is a Cu-added Nb contained advanced Fe–Cr–Ni type austenitic heat resistant steel has been selected for this study to be aged at 650 °C till to 10,000 h. Micro-hardness and room temperature tensile test were conducted after long-time aging. SEM, TEM, HRTEM and three dimensional atom probe (3DAP) technology accompanying with thermodynamic calculation have been used to investigate the Cu-rich phase precipitation behavior during 650 °C aging. The experimental results showed that Cu atoms can quickly concentrate in clusters at very early precipitation stage to form the fine nano-size Cu-rich “segregation areas” within less than 1 h at 650 °C. With increasing aging time at 650 °C Cu atoms continuously concentrate to Cu-rich segregation areas (clusters) and simultaneously other kinds of atoms such as Fe, Cr and Ni diffuse away from Cu-rich segregation areas to austenitic matrix, and finally to complete the transformation from Cu-rich segregation areas to Cu-rich phase. However, there is only Cu atoms concentration but not crystallographic transformation from early stage of Cu-rich clusters forming to the final Cu-rich phase formation. Even the Cu atom becomes the main composed element after 500 h aging at 650 °C the Cu-rich phase still keeps coherent relationship with austenitic matrix. According the experimental results in this study, Cu-rich phase precipitation sequence which starts from the Cu atom segregation followed by the Cu diffusing from matrix to segregation areas and Fe, Cr and Ni atoms diffuse out from Cu-rich areas to matrix without crystallographic transformation is proposed. The Cu-rich phase is the most dispersed phase and contributes the most important strengthening effect among all precipitated phases (M23C6, MX and Cu-rich phase). It has been found that Cu-rich phase is very stable and still keeps in nano-size even for 10,000 h aging at 650 °C. The unique precipitation strengthening of Cu-rich phase in combination with nano-size Nb-rich MX phase and grain-boundary M23C6 carbide contributes excellent strengthening effect to 18 Cr9 NiCuNb austenitic heat resistant steel.