Department of Metallurgical & Materials Engineering

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Mg–3Al–1Zn (AZ31) alloy was caliber rolled isothermally at the temperature of 300 °C to develop fine grains of 3 µm size. The microstructure and texture evolution of caliber rolled bar during annealing at 300 °C was investigated for 5 to 6000 min. The grain growth from 6 to 17 µm was observed. The grain growth was noted to be faster initially but it became sluggish after ~60 min of annealing. The changes in pole figure intensity, mis-orientation angle, kernel average mis-orientation and grain orientation spread were observed after caliber rolling and after annealing. The microstructure and presence of twins after caliber rolling play a vital role in formation of texture after annealing. The changes in microstructure and texture were analysed and the mechanisms involved are discussed. © 2015, The Indian Institute of Metals - IIM.

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Transactions of the Indian Institute of Metals

Microstructure and Texture Evolution During Annealing of Caliber Rolled Mg–3Al–1Zn Alloy

The feasibility has been demonstrated for achieving high-strain-rate superplasticity with elongations beyond 2000% in Al-Mg-Sc-Zr alloy with the partially recrystallized structure, produced by warm equal-channel angular pressing to strain of e~3 only. Subsequent alloy ambient temperature rolling up to e~1.6 enhanced the superplastic elongations and moved the optimum of superplasticity toward the higher strain rates. © (2015) Trans Tech Publications, Switzerland.

Materials Science Forum

Microstructure and superplasticity of an Al-Mg-Sc-Zr alloy processed by ECAP and subsequent cold rolling

The present study investigates the role of titanium in grain refinement of Mg–3Al and Mg–9Al alloys. Minor amount of Ti addition (&lt;1 wt% of Al–Ti master alloy) brings about grain refinement in both Mg–3Al and Mg–9Al alloys. Ultrasonic treatment further improves the grain size reduction in Ti added Mg–Al alloys. The average grain size of Mg–Al alloys are reduced by 20–30 % from the non-refined alloy by the addition of 1 wt% of Al–Ti master alloy and ultrasonic treatment further enhances the grain refinement by 10–20 %. In addition, ultrasonic treatment transforms the network type β-Mg17Al12 phase into fine discontinuous precipitates in Ti containing Mg–9Al alloys. The mechanism of grain refinement in ultrasonic treated Ti containing Mg–Al alloy is discussed in terms of solute and heterogeneous nucleation perspective. © 2015, The Indian Institute of Metals - IIM.

Discussions on the Mechanism of Grain Refinement in Ultrasonic Treated Ti Containing Mg–Al Alloys

NiCo2S4 is a technologically important electrode material that has recently achieved remarkable performance in pseudocapacitor, catalysis, and dye-synthesized solar cell applications.1 5 Essentially, all reports on this material have presumed it to be semiconducting, like many of the chalcogenides, with a reported band gap in the range of 1.2-1.7 eV.6,7 In this report, we have conducted detailed experimental and theoretical studies, most of which done for the first time, which overwhelmingly show that NiCo2S4 is in fact a metal. We have also calculated the Raman spectrum of this material and experimentally verified it for the first time, hence clarifying inconsistent Raman spectra reports. Some of the key results that support our conclusions include: (1) the measured carrier density in NiCo2S4 is 3.18 × 1022 cm-3, (2) NiCo2S4 has a room temperature resistivity of around 103 cm which increases with temperature, (3) NiCo2S4 exhibits a quadratic dependence of the magnetoresistance on magnetic field, (4) thermopower measurements show an extremely low Seebeck coefficient of 5 V K-1, (5) first-principles calculations confirm that NiCo2S4 is a metal. These results suggest that it is time to rethink the presumed semiconducting nature of this promising material. They also suggest that the metallic conductivity is another reason (besides the known significant redox activity) behind the excellent performance reported for this material. © 2015 American Chemical Society.

Fulltext

Chemistry of Materials

Is NiCo2S4 Really a Semiconductor?

The nanoindentation technique was employed to examine the strain rate sensitivity, m, and its dependence on the structural state of a Zr-based bulk metallic glass (BMG). The free volume content in the BMG was varied by examining samples in the as-cast (AC), shot-peened (SP), and structurally relaxed (SR) states. Hardness values measured at different loading rates and over a temperature range of 300-423. K as well as the strain-rate jump tests conducted in the quasi-static regime at room temperature, show that m is always negative. All the load-displacement (. P-. h) curves in this temperature regime exhibit serrated load-displacement responses, indicating that the shear band mediated inhomogeneous plastic flow governs deformation. Such localization of flow and associated softening is the raison d'être for the negative m. Significant levels of pile-up around the indents were also noted. The order in the average values of hardness, pile-up heights, and the displacement bursts on the P-. h curves was always such that SR>AC>SP, which is also the order of increasing free volume content. These observations were utilized to discuss the reasons for the negative strain rate sensitivity, and its dependence on the structural state of metallic glasses. It is suggested that the positive values of m reported in the literature for them are possibly experimental artefacts that arise due to large pile ups around the indents which lead to erroneous estimation in hardness values. © 2014 Elsevier B.V.

Materials Science and Engineering A

On the strain rate sensitivity of plastic flow in metallic glasses

The development of microstructure and crystallographic texture with effective strain at three through-thickness locations (near rolls, center, and near mandrel) in a partly pilgered Zircaloy-4 tube is described. Pilgering is found to eliminate through-thickness variation in grain size in the starting hot-extruded material and to generate location-dependent asymmetries in crystallographic texture. Deformation texture development during pilgering is modeled with polycrystal plasticity by idealizing the metal flow pattern as axisymmetric flow through a convergent channel. Good qualitative comparison of the predicted and experimental post-pilgering textures is obtained, provided location-dependent transverse shear component is superposed on the gross flow field, and localized deformation at grain boundaries is allowed. Frictional forces between tube and die are deduced from these observations. © 2015, The Minerals, Metals & Materials Society and ASM International.

Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science

Texture Development and Plastic Deformation in a Pilgered Zircaloy-4 Tube

Al/2TiB2 in-situ composite was fabricated using salt-melt reaction method. Subsequently, it was re-melted and treated with high intensity ultrasonic waves for various time intervals. Substantial reduction in TiB2 particle size down to ~ 300 nm along with significant improvement in dispersion is achieved with the aid of ultrasonic treatment. Ultrasonic treatment has resulted significant increase in hardness of Al/2TiB2 in-situ composite. © (2015) Trans Tech Publications, Switzerland.

Effect of ultrasonic treatment on microstructure and mechanical property of in-situ Al/2TiB2 particulate composites

The effect of ultrasonic treatment (UT) on the synthesis of Al–MgAl2O4 master alloy has been studied by the reaction of SiO2 precursor with Al-2wt% Mg. The results show that SiO2 reaction is enhanced after UT and the corresponding mechanism is proposed. Grain refinement studies in pure Al showed that an increase in addition level of MgAl2O4 particles resulted in two to threefold reduction in grain size; whereas, UT intensified the grain size reduction by 11–12 fold. Significant grain refinement on UT is attributed to the cavitation enhanced wetting which activates MgAl2O4 particles as potent nucleating site for Al. © 2015, The Indian Institute of Metals - IIM.

Synthesis of Al–MgAl2O4 Master Alloy and its Grain Refinement Studies in Pure Aluminium

Current work outlines the thermodynamic prediction of Mg–Zn–X (X = Sn, Y) alloys amenable for both semi-solid metal (SSM) processing and age hardening treatment. Semi-solid processing capability of Mg–Zn–X (X = Sn, Y) alloy has been evaluated by measuring the metallurgical parameters such as ‘solidification interval’, ‘temperature liquid fraction sensitivity’ and ‘highest knee point’ from non-equilibrium Scheil solidification curve. According to thermodynamic prediction, binary Mg–Zn and ternary Mg–Zn–Sn alloys are suitable for heat treatment; however, wide solidification intervals in these systems restrict their SSM processing ability. Formation of binary Zn2Y and ternary W-Mg3Zn2Y3 intermetallic phases in Mg–Zn–Y alloy has been predicted to improve their SSM processing potential and at the same time Mg–Zn–Y alloy is found to be suitable for heat treatment process. © 2015, The Indian Institute of Metals - IIM.

Thermodynamic Designing of Heat Treatable Mg–Zn–X (X = Sn, Y) Alloy Suitable for Semi-solid Processing

A ZnO nanorods based superhydrophobic surface with extremely low roll-off angle is fabricated using a two-step solution based approach-Successive Ionic Layer Adsorption and Reaction (SILAR) and Chemical Bath Deposition (CBD). The grown ZnO nanorods have average diameter of 285nm with a predominant growth direction of [002]. The static contact angle of ZnO nanorods superhydrophobic surface is 155°, and the dynamic contact angles contact angle hysteresis and roll-off angle is 2°and 1°, respectively. Furthermore, to comprehend the mechanism governing the extremely low roll-off angle of ZnO nanorods based superhydrophobic surface, an analytical model has been developed by incorporating the topographical (diameter, density of nanorods and solid area fraction) and droplet parameters (surface tension, mass and volume). The theoretically calculated roll-off angle closely matches with the experimental results and reported results. © 2015 Elsevier B.V. All rights reserved.