Hot Deformation of IN718 with Various Initial Microstrucures- Experiments and State-variable Modelling

Significant research has been directed towards characterising the precipitation and dissolution kinetics of the δ phase in IN718, a nickel-base superalloy, but rather less is known about the specific influence of the precipitate on microstructural evolution during thermo-mechanical processing. To investigate the effect of δ precipitate morphology on the hot deformation behaviour of IN718 a series of hot isothermal axi-symmetric compression 'upset' tests have been carried out at fixed nominal strain rates and temperatures relevant to industrial hydraulic press-forging (0.001-0.3/s and 990-1040°C). These test conditions span the δ solvus temperature for the alloy, 1015°C. In particular, three different types of material, each with its own distinct microstructure, were examined: I- solution-treated, δ-free material; II- material containing finely dispersed, intragranular, particulate δ; III- material containing a dense network of intragranular and grain boundary δ platelets along crystallographic habit planes. The presence of δ phase strongly influences both the peak stress and the rate of flow softening. Below the δ solvus temperature the type II material, containing dispersed particulate ö, exhibited the highest peak stress. The type III material, containing acicular δ, exhibited the most significant post-peak softening, whereas the δ-free, type I material, exhibited the lowest peak stresses of all materials. For testing above the solvus temperature the flow behaviour was found to be practically identical for the three microstructures, regardless of the initial presence of δ in two of them. The presence of δ in the microstructure had a marked effect on the evolution of recrystallised fraction and grain size. It also influenced the evolution of texture that resulted into markedly different texture from the classic FCC texture exhibited by solution-treated material after hot deformation. Model predictions from semi-empirical state-variable model in the form of constitutive equations, in the form of flow behaviour and volume fraction recrystallised for solutiontreated IN718, showed good qualitative agreement with measured data. It was found that the model predictions naturally divided the flow behaviour into two regimes of dynamic recovery and dynamic recrystallisation, based on the strain rates employed for hot deformation. This agreed well with observations from microstructure investigations. The model was successfully extrapolated to predict flow behaviour of IN718 available elsewhere in the literature, under temperature and strain rate conditions different from those used in the present work. To further validate the state-variable model, hot compression of a non-uniform double-trucated cone specimen was carried out and the measured volume fraction recrystallised was successfully predicted

Extreme self-organization in networks constructed from gene expression data

We study networks constructed from gene expression data obtained from many types of cancers. The networks are constructed by connecting vertices that belong to each others' list of K-nearest-neighbors, with K being an a priori selected non-negative integer. We introduce an order parameter for characterizing the homogeneity of the networks. On minimizing the order parameter with respect to K, degree distribution of the networks shows power-law behavior in the tails with an exponent of unity. Analysis of the eigenvalue spectrum of the networks confirms the presence of the power-law and small-world behavior. We discuss the significance of these findings in the context of evolutionary biological processes.Comment: 4 pages including 3 eps figures, revtex. Revisions as in published versio

Pitting studies of plain carbon steel in chloride containing borate buffer solution

Passivation is the process of temporary or permanent halt in degradation or corrosion rate of a metal due to the formation of different types of surface layers or films that protects the underlying metal. Pitting corrosion is the breakdown of the surface film due to presence of aggressive ions such as chloride ions. The breakdown of the passivity film is characterized by breakdown potential (Vc) which is dependent on the pH of the solution, concentration of the aggressive ions and the potential sweep rate. This study used the Point Defect Model to characterize the breakdown potential with respect to varying pH and concentration. The pH of the solution was kept a constant at 10.4. The breakdown potential is found to decrease with increasing chloride concentration and decrease with increasing pH. The cumulative distribution of the breakdown potential was found to be in well agreement with the experimentally obtained data. Optical micrographs showed stable and Meta stable pitting. The parameters from point defect model was found to be in well agreement with the experimental data

Reduced dynamics of a PT-symmetric evolution

Evolutions under non-Hermitian Hamiltonians with unbroken PT-symmetry can be considered unitary under appropriate choices of inner products, facilitated by the so-called metric operator. While it is understood that the choice of the metric operator has no bearing on the description of the system, in this work we show that this choice does dictate the properties of the subsystem. Subsystem dynamics therefore does depend on the choice of the metric. We argue that this result is a reformulation of the previously known result that the set of observables, chosen to characterize the state, determines its decomposition into subsystems. In this work we take a non-Hermitian PT-symmetric quantum walk with an internal and external degree of freedom to show this. The Hamiltonian of the quantum walk is chosen to not allow a metric operator with a tensor product structure over these subspaces. Under these constraints, we investigate the properties of the internal state of the system under different choices of the metric operator and show that properties like bipartite entanglement and non-Markovianity depend on the choice of the metric operator.Comment: 16 pages, 5 figures; Comments are welcom

Assessment of On-going tectonic deformation in the Goriganga River Basin, Eastern Kumaon Himalaya Using Geospatial Technology

The Goriganga river basin lies in the Northeast Kumaon Himalaya and is found suitable for assessing active tectonics at different scales. In addition, this study focuses on the assessment of ongoing tectonic activity through morphotectonic measurement of the Goriganga river basin, which is an ideal location for such analysis and Goriganga river basin transects with three major domains of Himalaya’s lithotectonic structures viz., Tethys, Vaikrita, and Lesser Himalayan Domain. To realize this task, the ASTER Digital Elevation Model was used and found suitable to extract different morphotectonic indices such as Stream Length Gradient (SL), Hypsometric Integral (HI), Length of Overland Flow (Lg), Drainage Density (Dd) and Channel Sinuosity (Cs).  Results of these important indices, including SL (18- 4737) HI (0.26- 0.57), and Lg (0.08- 0.19) depict greater variability in the tectonics activity while these values are correspondingly high in the close proximity of lithotectonic units, showing strong tectonic activity. In the extreme south, the Rauntis Gad basin strongly influences tectonism due to transecting syncline and anticline as well as unknown active faults.