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This paper was attempted to investigate the microstructure degradation and low cycle fatigue (LCF) performance of a serviced K465 Ni‐based superalloy turbine blade. LCF tests were carried out with small‐scale plate specimens sampled from the blades. Relationship between residual LCF life and microstructure state was estimated. The results indicate that the coarsening of γ/γ′ phases was the most significant microstructure degradation mode for the serviced blades. Both the γ matrix width and the γ′ precipitate diameter increased with the increase of service duration, while the γ′ precipitate volume fraction slightly decreased. The most severe microstructure degradation occurred at the leading edge along the chord direction, particularly at 50–70 % airfoil spans. The residual LCF life exhibited an accelerated decrease characteristic as increases of microstructure degradation degree. The coarsened microstructure diminished shear resistance of the superalloy, which resulted in additional accumulated inelastic deformation and a corresponding reduction in LCF life. Highlights: Service induced microstructure evolution and LCF life decay of a blade were investigated.Coarsening was identified as the main degradation form of γ/γ' phases in serviced blade.Accelerated decrease of residual LCF life was identified as increases of coarsening.Reduced plastic deformation resistance owing to coarsening is crucial to decay LCF life. [ABSTRACT FROM AUTHOR]

The relaxation dynamics and glass transition in finite-sized metallic liquid droplets were investigated via molecular dynamic simulations in model monoatomic Ta and binary Cu50Zr50 metallic liquids. We find that the droplet size has a significant impact on liquid dynamics and glass transition. Glass transition temperature and structural relaxation time exhibit strong size dependence and decrease drastically as the droplet is smaller than a certain size. It is revealed that this results from a liquid-like surface layer (~1 nm thick) of droplets, in which the dynamics is much faster than the interior of droplets. A proposed scaling relationship can well describe the size dependent behavior of the glass transition temperature in metallic liquid droplets. These findings provide insight into the dynamics of metallic liquid droplets and plausible understanding of recent novel experimental observations. Apart from temperature and pressure, size may be another important parameter for potentially tuning the properties of metallic liquids and glasses in nanometer scale. [ABSTRACT FROM AUTHOR]

The β-relaxation, which is the source of the dynamics in glass state and has practical significance to relaxation and mechanical properties of glasses, has been an open question for decades. Here, we propose a flow unit perspective to explain the structural origin and evolution of β-relaxation based on experimentally obtained energy distribution of flow units using stress relaxation method under isothermal and linear heating modes. Through the molecular dynamics simulations, we creatively design various artificial metallic glass systems and build a direct relation between β-relaxation behavior and features of flow units. Our results demonstrate that the β-relaxation in metallic glasses originates from flow units and is modulated by the energy distribution of flow units, and the density and distribution of flow units can effectively regulate the β-relaxation behavior. The results provide a better understanding of the structural origin of β-relaxation and also afford a method for designing metallic glasses with obvious β-relaxation and better mechanical properties. [ABSTRACT FROM AUTHOR]

Till date, there have been no direct atomic-level experimental observations of the earliest stages of the nucleation and growth processes of nanocrystals formed by thermally induced crystallization in ultrathin metallic glasses (MGs). Here, we present a study of the crystallization process in atomically thin and highly stable MG films using double spherical aberration-corrected scanning transmission electron microscopy (Cs-TEM). Taking advantage of the stability of MG films with a slow crystallization process and the atomic-level high resolution of Cs-TEM, we observe the formation of the nucleus precursor of nanocrystals formed by atom aggregation followed by concomitant coalescence and stepwise evolution of the shape of the nanocrystals with a monodispersed and separated bimodal size distribution. Molecular dynamics simulation of the atomic motion in the glass film on a rigid amorphous substrate confirms the stepwise evolution processes of atom aggregation, cluster formation, cluster movement on the substrate, and cluster coalescence into larger crystalline particles. Our results might provide a better fundamental understanding of the nucleation and growth processes of nanocrystals in thin MG films. [ABSTRACT FROM AUTHOR]

The heat capacity jump ΔCp at glass transition and the dynamical heterogeneity are two of the most important features of glass forming liquids. In order to reveal the intrinsic relationship between the two properties, a model glass system (Na2O)x(SiO2)1-x (x=0.2-0.35) was studied by the systematic measurements of the ΔCp and the mechanical relaxation in the supercooled liquid region. A linear increase in ΔCp with increasing content of Na2O was found, indicating direct contributions of the locally fast dynamics around Na2O to ΔCp. This positive correlation between the locally heterogeneous dynamics and ΔCp was further confirmed by the dynamical heterogeneity analyses. Our results might be helpful for understanding the nature of glass transition. [ABSTRACT FROM AUTHOR]

Okra (Abelmoschus esculentus L.) regeneration frequency to a large extent depends on its genetic structure and its recalcitricity. In present study, the influence of silver nitrate (AgNO3) in combination with cytokinins such as 6-benzyl amino purine (BAP) and kinetin (KIN) to regenerate multiple shoots from cotyledonary node explants of A. esculentus were optimized. Cotyledonary node explants were excited from 10-days old okra in vitro seedlings and incubated on Murishage and Skoog (MS) medium supplemented with different concentration and the combination of BAP alone and in combination with KIN. The highest percentage of shoot bud regeneration (75%) was achieved on MS medium supplemented with 2.0 mgL-1 BAP. Highest percentage of shoot multiplication and proliferation (85%) with 6.75 shoots per explant having 3.75 cm length was obtained on MS medium containing 1.5 mgL-1 BAP + 1.5 mgL-1 KIN + 3.0 mgL-1 AgNO3. On the other hand, non-containing AgNO3, the combination of 1.5 mgL-1 BAP + 1.5 mgL-1 KIN, a maximum of 53% shoot multiplication with 2.3 shoots per explant having 3.75 cm length was recorded. Individual shoots were elongated on MS medium supplemented with 1.5 mgL-1 BAP + 1.5 mgL-1 GA3 (Gibberellic acid) (shoot length 5.60 ± 0.70a cm) and rooted on half strength MS medium + 1.0 mgL-1 IBA (Indole 3-butiric acid) + 200 mgL-1 AC (Activated charcoal), with highest root formation 83% with 5.20 roots per shoot having 4.8 cm length was achieved. The current protocol will be useful for the development of okra transgenic plant as a result of genetic transformation. [ABSTRACT FROM AUTHOR]

Temperature and potential effect on pitting occurrence of four austenitic stainless steels in 1 M sodium chloride solution are plotted, then the influence of scan rate and chloride concentration on potentiodynamic critical pitting temperature (CPT) are investigated. Basing on the independence and reliability analysis, the potentiodynamic CPT and potentiostatic CPT are compared. To improve the reproducibility of potentiostatic CPT, an elevated potential should be applied. On the other hand, crevice corrosion induced by transpassive etching is clarified, indicating the upper limit of applied potential in potentiostatic test. Consequently, a potential of 800 or 850 mV(SCE) is recommended for austenitic stainless steels. Additionally, regression analysis is carried out to confirm the linear relationship between potentiodynamic CPT and pitting resistance equivalent. [ABSTRACT FROM AUTHOR]

High-resolution x-ray diffraction reciprocal lattice mapping and low-temperature photo-luminescence (PL) were used to study the thermal strain in InP layers grown on Si (001) substrate by hydride vapor-phase epitaxial lateral overgrowth (ELO) technique. Good agreement is found between the PL and x-ray measurements. We show that strain in the grown ELO InP/Si layers is affected by the aspect ratio (width to height ratio) of the ELO InP layer. Almost strain-free InP layer with high crystallographic quality is obtained on Si substrate, which is similar to that of a homoepitaxial InP layer. [ABSTRACT FROM AUTHOR]