Prediction of high temperature flow stress in 9Cr–1Mo ferritic steel during hot compression

Constitutive analysis was performed on the experimental true stress-true strain data obtained from hot isothermal compression tests on 9Cr–1Mo steel in a wide range of temperatures (1173–1373 K, i.e. 900–1100 °C) and strain rates (0.01–100 s^?1). The constitutive equation for hot deformation is represented by a hyperbolic–sine Arrhenius type equation relating flow stress, strain rate and temperature, and could be described by the Zener–Hollomon parameter in an exponential type equation. The influence of strain was incorporated in the constitutive equation by considering the variation of material constants as a function of strain. It is observed that the compensation for strain could not accurately predict the flow stress for the entire strain rate and temperature regime. The constitutive equation was revised incorporating compensation for both strain and strain rate by suitably modifying the Zener–Hollomon parameter and the modified constitutive equation is found to give good prediction of flow stresses for most strain rate and temperature combinations.     

The reactive processing of silicides

Interest in silicides as advanced materials for high-performance applications has focused significant attention on the processing of these materials. In recent years, various processing methodologies have been evaluated. This article provides a comprehensive review of reactive processing techniques and the results of various investigations.     

Structural study of device quality silicon germanium thin films deposited by pulsed RF plasma CVD

Microstructures in silicon germanium thin films deposited by pulsed rf plasma CVD have been studied with the help of small-angle X-ray scattering (SAXS) and high-resolution transmission electron microscopy (HRTEM). With lowering of the pulse duty cycle the size of the particles incorporated in the films from the plasma decreases. However, the particles become more symmetric in shape and crystalline in nature. At 75% duty cycle the films have the highest photosensitivity. The increase in SAXS scattering at 75% has been explained by the formation of uniform-size nanocrystallites of SiGe. Urbach energy variation with the duty cycle also suggests the formation of nanocrystallites.     

Distributed Identification of Top-l Inner Product Elements and its Application in a Peer-to-Peer Network

The inner product measures how closely two feature vectors are related. It is an important primitive for many popular data mining tasks, for example, clustering, classification, correlation computation, and decision tree construction. If the entire data set is available at a single site, then computing the inner product matrix and identifying the top (in terms of magnitude) entries is trivial. However, in many real-world scenarios, data is distributed across many locations and transmitting the data to a central server would be quite communication intensive and not scalable. This paper presents an approximate local algorithm for identifying top-l, inner products among pairs of feature vectors in a large asynchronous distributed environment such as a peer-to-peer (P2P) network. We develop a probabilistic algorithm for this purpose using order statistics and the Hoeffding bound. We present experimental results to show the effectiveness and scalability of the algorithm. Finally, we demonstrate an application of this technique for interest-based community formation in a P2P environment.     

An alternate method for determination of brittleness of ceramics and polymers

As opposed to a pendulum scratching test for the determination of brittleness parameter for ceramics and polymers, this paper proposes an alternate brittleness parameter based on indentation analysis. The important advantages are that (i) no elaborate experiments are needed, and (ii) the proposed brittleness parameter has physical implications. The proposed parameter is as effective as the pendulum test for categorizing the brittleness of ceramics and polymers.     

Electrical Conductivity of Alumina/Aluminum Composites Synthesized by Directed Metal Oxidation

Electrical conductivities of Al₂O₃/A1 composite synthesized by directed oxidation of an aluminum alloy, and sintered Al₂O₃–4% MgO are measured. The high conductivity of the Al₂O₃/A1 composite compared to sintered Al₂O₃–4% MgO is shown as proof of the presence of continuous metal channels in the composite. Furthermore, the conductivity data are used to determine the activation energy for the diffusion of the dominant charge carrier in the oxide matrix.     

Characterization of deformation instability in modified 9Cr–1Mo steel during thermo-mechanical processing

In this study, various existing instability criteria were employed to delineate the unstable flow regions in modified 9Cr–1Mo steel during hot deformation. Experimental stress–strain data obtained from isothermal hot compression tests, in a wide range of temperatures (1123–1373 K) and strain rates (10⁻³–10 s⁻¹), were employed to develop instability maps. The domains of these instability maps were validated through detailed microstructural study. It has been observed that Hart’s stability criterion, Jonas’s criterion and Semiatin’s criterion under-predicts the instability regions in the studied temperatures and strain rates regime. Gegel’s and Alexander’s criteria as well as Murty’s metallurgical instability criterion, on the other hand, found to over-predict the instability domains. The instability map developed based on Dynamic Materials Model criterion has been found to precisely predict the instability domains. This instability map revealed four major unstable domains. Microscopic examination in these domains revealed that the instability is manifested in the specimens either as localized deformation band primarily along one of the diagonal or inhomogeneous distribution of martensite lath in the prior austenite grains.