Effect of Pt on Stress Rupture Properties of Pt-Modified Nickel Aluminide Coatings at 1100 °C.

Platinum plays a crucial role in the superior high-temperature oxidation resistance of Pt-modified nickel aluminide (PtAl) coatings. However, PtAl coatings usually serve in thermo-mechanical coupling environments. To investigate whether Pt contributes to the high-temperature mechanical properties of PtAl coating, stress rupture tests under 1100 °C/100 MPa were performed on PtAl coatings with varying Pt contents. The different coatings were obtained by changing the thickness of the electroplated Pt layer, followed by a diffusion heat treatment and the aluminizing process in the present work. The results of the stress rupture tests indicated that an increasing Pt content resulted in a significant decrease in the stress rupture life of PtAl-coated superalloys under 1100 °C/100 MPa. Theoretical calculations and microstructural analysis suggested that an increased coating thickness due to the Pt content is not the main reason for this decline. It was found that the cracks generated close to the substrate in high-Pt-coated superalloys accelerated the fracture failure.

The Microstructure, Solidification Path, and Microhardness of As-Cast Ni-Al-Cr-Os Alloys in a Ni-Rich Region.

In this study, nine as-cast Ni-Al-Cr-Os alloys were prepared, and their constituent phases and microstructure were examined using X-ray diffraction and electron probe microanalysis techniques. The solidification paths of all the alloys in a Ni-rich corner were revealed based on a detailed analysis of the as-cast microstructure. The liquidus cube of the quaternary Ni-Al-Cr-Os system in a Ni-rich corner was established accordingly. A eutectic-type invariant reaction on the liquidus surface was explicitly identified, and its reaction can be expressed as L → α + ß + γ. No quaternary invariant reaction was found in the alloys following the addition of Os. The Ni-Al-Cr-Os alloy points were then vertically mapped onto the Ni-Al-Cr liquid phase projection to better observe the effect of Os addition on the solidification path of the Ni-Al-Cr system. It was found that the addition of a small amount of Os has no significant effect on the solidification path of the Ni-Al-Cr system. Furthermore, the microhardness of each alloy, which was determined to be in the range of 207 HV to 565 HV, was found to be closely related to the phase constitution and phase fraction of the alloy.

Automated Development of an Accurate Diffusion Database in Fcc AlCoCrFeNi High-Entropy Alloys from a Big Dataset of Composition Profiles.

This study aims to incorporate a big dataset of composition profiles of fcc AlCoCrFeNi alloys, in addition to those of the related subsystem, to develop a self-consistent kinetic description for quinary high-entropy alloys. The latest feature of the HitDIC (High-throughput Determination of Interdiffusion Coefficients) code was adopted in a high-throughput and automatic manner for accommodating a dataset of composition profiles with up to 87 diffusion couples. A good convergence for the optimization process was achieved, while satisfactory results regarding the composition profiles and previously evaluated diffusion properties were obtained. Here, we present an investigation into the elemental effect of Al towards interdiffusion and tracer diffusion, and their potential effect on creep and precipitation processes.

Depth-Sensing Indentation Creep Behavior of Nanostructured Thermal Barrier Coatings from As-Synthesized t'-8YSZ Feedstocks.

Nano-indentation is a popular method to characterize the micromechanical properties of nanostructured 8YSZ coatings. However, little research has focused on the creep behavior of nano-indentation and only the elastic modulus and nanohardness have been analyzed. Herein, for the first time, the nano-indentation creep behavior of plasma-sprayed nanostructured 8YSZ coatings using as-prepared nanostructured non-transformable tetragonal (t') feedstocks was investigated. The indentation creep behavior can be well characterized by the power-law equation and the strain rate sensitivity has been calculated in light of the equation. The strain rate sensitivity was sensitive to the load and the reasons were analyzed in detail. The current results can further guide and design thermal barrier coatings from the point of indentation creep property.

Involvement of multiple transcription factors in regulation of IL-ß-induced MCP-1 expression in alveolar type II epithelial cells.

During acute lung injury, a large number of monocytes are recruited into the pulmonary tissue, which is mainly mediated by local production of monocyte chemotactic protein 1 (MCP-1). As an essential component of the lung tissues, alveolar type II epithelial cells are one of the major sources of MCP-1. Therefore, uncovering the mechanism whereby MCP-1 production is regulated in the alveolar type II cells will provide a pivotal theoretical basis for clinical intervention in acute lung injury. In the current study, we find that there is a κB binding site in the MCP-1 promoter region, and mutation of the site leads to reduced production of MCP-1 in alveolar type II epithelial cells. In contrast, overexpression of NF-κB p65 significantly increases MCP-1 expression. Furthermore, we elucidate that IKKα/ß-NF-κB p65 signaling pathway and phosphorylation of serine 534 in NF-κB p65 are required for the maximal expression of MCP-1. Also, Activator protein 1 (AP-1) site in the promoter region and JNK1/2-c-Jun signaling are required for MCP-1 generation in alveolar type II epithelial cells. Moreover, a CCAAT/enhancer-binding protein (C/EBP) element is identified in the MCP-1 promoter region through the point mutation technique, and further experiments demonstrate that both C/EBPß and C/EBPδ are involved in basic and IL-1ß-mediated MCP-1 expression. Of note, specificity protein 1-Sp1 expression is not changed in alveolar type II epithelial cells incubated with IL-1ß, but it still control MCP-1 production by binding to the consensus sequence in the promoter region. More importantly, we find that the results derived from the cell line-MLE-12 cells and primary cells are consistent. Taken together, our data provide insights into the molecular mechanism how MCP-1 expression in inflammatory alveolar type II epithelial cells is regulated at transcription level.

Inhibition of HBV-DNA replication and expression by siRNA based on magnetic nanoparticles transfering in HepG2 2.2.15 cells.

OBJECTIVE: To investigate the inhibitory effect of downregulation of hepatitis B virus (HBV) core gene (HBcAg) expression by RNA interference and magnetic nanoparticles on both HBV DNA replication and expression in vitro. METHODS: HepG2 2.2.15 cells were transfected with U6 promoter plasmids coding for small interfering RNA (siRNA) targeting HBV core gene using magnetic nanoparticles. RT-PCR and Western blot were used to assess the mRNA and protein expression HBV core antigen. Real-time PCR was used to evaluate the suppression efficiency of HBV-DNA replication and expression; and radioimmunoassay was used for HBV surface antigen (HBsAg), core antigen (HBcAg), and e antigen (HBeAg) detection. RESULTS: We successfully constructed nanoparticles with siRNA plasmid targeting HBV core antigen; HBcAg mRNA and HBV core antigen protein levels were significantly reduced in the transfected cells. HBV-DNA downregulation was estimated at 4-5 logs and the HBsAg and HBeAg levels were also reduced compared with the controls. CONCLUSION: Downregulation of HBV core gene using RNAi technology and magnetic nanoparticles can potentially be used as a therapeutic strategy for Hepatitis B.

Downregulation of xIAP expression by small interfering RNA inhibits cellular viability and increases chemosensitivity to methotrexate in human hepatoma cell line HepG2.

The aim of this study was to investigate whether downregulating the expression of xIAP by RNAi (RNA interference) technology can induce the apoptosis of HepG2 cells, inhibit cellular viability and increase chemosensitivity of cancer cells. HepG2 cells were transfected with U6 promoter plasmids coding for short interfering RNAs (siRNAs) targeting xIAP. RT-PCR and western blot analysis were used to assess the mRNA and protein levels of xIAP expression. T he suppression efficiency o f xIAPby RNAi was evaluated using the MTT assay for cellular viability and Annexin V-PI binding assay for apoptosis. These results showed that siRNAs reduced cellular viability and increased cellular apoptosis. Moreover, downregulation of xIAP expression enhanced the chemosensitivity of HepG2 cells to methotrexate. These results suggest that the downregulation of xIAP by RNAi could potentially be used as a therapeutic strategy for human hepatocellular carcinoma.