Influence of Tempered Microstructures on the Transformation Behaviour of Cold Deformed and Intercritically Annealed Medium Carbon Low Alloy Steel

This research is focused on understanding the role of microstructural variables and processing parameters in obtaining optimised dual phase structures in medium carbon low alloy steels. Tempered Martensite structures produced at 300, 500, and 650 degrees C, were cold rolled to varied degrees ranging from 20 to 80% deformation. Intercritical annealing was then performed at 740, 760, and 780 degrees C for various time duration ranging from 60 seconds to 60 minutes before quenching in water. The transformation behaviour was studied with the aid of optical microscopy and hardness curves. From the results, it is observed that microstructural condition, deformation, and intercritical temperatures influenced the chronological order of the competing stress relaxation and decomposition phase reactions which interfered with the rate of the expected alpha -> gamma transformation. The three unique transformation trends observed are systematically analyzed. It was also observed that the 300 and 500 degrees C tempered initial microstructures were unsuitable for the production of dual structures with optimized strength characteristics.

Effect of indium doping on the electrical switching behaviour of Ge–Te glasses

Bulk Ge15Te85−x In x (1 ≤ x ≤ 11) series of glasses have been found to exhibit a threshold switching behaviour for an input current of 2 mA. An initial decrease is seen in the switching voltages (V T) with the addition of indium, which is due to the higher metallicity of indium. An increase is seen in V T above 3 at.% of indium, which proceeds until 8 at.%, with a change in slope (lower to higher) seen around 7 at.%. Beyond x = 8, a reversal in trend is exhibited in the variation of V T, with a well-defined minimum around x = 9 at.%. Based on the composition dependence of V T, it is proposed that Ge15Te85−x In x glasses exhibit an extended rigidity percolation threshold. The composition, x = 3, at which the V T starts to increase and the composition, x = 7, at which a slope change is exhibited correspond to the onset and completion, respectively, of the extended stiffness transition. Thermal studies and photoconductivity measurements also support the idea of an extended rigidity percolation in Ge15Te85−x In x glasses. In addition, the minimum seen in V T at x = 9 is associated with the chemical threshold (CT) of this glassy system.

Volume change behaviour of expansive soils

Understanding the volume change behaviour of expansive soils/clays becomes a dire necessity to obtain engineering solutions to structures founded on these soils. Behaviour of expansive soils does not conform to the natural behaviour of fine grained soils. Most of the cases, the permissible heave/settlement forms the design criteria. The paper discusses the basic properties, the role of effective stress concept, basic mechanism in controlling the volume change behaviour, the role of double layer repulsion and its validity and certain basic considerations of footing resting on an expansive soil with respect to heave or settlement and the soil reinforcement as a possible engineering solution.

Effect of scaling on the non-quasi-static behaviour of the MOSFET for RF ICs

The effect of scaling (1 μm to 0.09 μm) on the non-quasi-static (NQS) behaviour of the MOSFET has been studied using process and device simulation. It is shown that under fixed gate (Vgs) and drain (Vds) bias voltages, the NQS transition frequency (fNQS) scales as 1/Leff rather than 1/L2eff due to the velocity saturation effect. However, under the practical scaling guidelines, considering the scaling of supply voltage as well, fNQS shows a turn around effect at the sub 100 nm regime. The relation between unity gain frequency (ft) and fNQS is also evaluated and it is shown that ft and fNQS have similar trends with scaling.

Effect of strain rate and temperature on the plastic deformation behaviour of a bulk metallic glass composite

The composites consisting of amorphous matrix reinforced with crystalline dendrites offer extraordinary combinations of strength, stiffness, and toughness and can be processed in bulk. Hence, they have been receiving intense research interest, with a primary focus to study their mechanical properties. In this paper, the temperature and strain rate effects on the uniaxial compression response of a tailored bulk metallic glass (BMG) composite has been investigated. Experimental results show that at temperatures ranging between ambient to 500 K and at all strain rates; the onset of plastic deformation in the composite is controlled by that in the dendrites. As the temperature is increased to the glass transition temperature of the matrix and beyond, flow in the amorphous matrix occurs readily and hence it dictates the composite's response. The role of the constituent phases in controlling the deformation mechanism of the composite has been verified by assessing the strain rate sensitivity and the activation volume for deformation. The composite is rate sensitive at room temperature with values of strain rate sensitivity and activation volume being similar to that of the dendrites. At test temperatures near to the glass transition temperature, the composite however becomes rate-insensitive corresponding to that of the matrix phase. At low strain rates, serrated flow akin to that of dynamic strain ageing in crystalline alloys was observed and the serration magnitude decreases with increasing temperature. Initiation of the shear bands at the dendrite/matrix interface and propagation of them through the matrix ligaments until their arrest at another interface is the responsible mechanism for this. (C) 2011 Elsevier B.V. All rights reserved.

Microstructure and damping behaviour of consolidated magnesium chips

Chips produced by turning a commercial grade pure magnesium billet were consolidated by solid state recycling technique of cold compaction followed by hot extrusion. The cold compacted billets were extruded at four different temperatures: 250 degrees C, 300 degrees C, 350 degrees C and 400 degrees C. For the purpose of comparison, cast magnesium (pure) billets were extruded under similar conditions. Extruded products were characterized for damping properties. Damping capacity and dynamic modulus was measured as a function of time and temperature at a fixed frequency of 5 Hz 10 to 14% increase in damping capacity was observed in chip consolidated products compared to reference material. Microstructural changes after the temperature sweep tests were examined. Chip boundaries present in consolidated products were observed to suppress grain coarsening which otherwise was significant in reference material. The present work is significant from the viewpoint of recycling of machined chips and development of sustainable manufacturing processes. (C) 2012 Elsevier B.V. All rights reserved.