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Showing papers by "S. Sankaran published in 2011"


Journal ArticleDOI
TL;DR: In this paper, the formation of intermediate metastable precipitates in the process of Mg 2 Si formation in Al-7Si-0.3Mg-TiB 2 in-situ composites with three different amounts of TiB 2 particles (2.5, 5 and 10 wt%) were studied using differential scanning calorimeter (DSC).
Abstract: Al-7Si-0.3Mg-TiB 2 in-situ composites were made by the salt-metal reaction i.e., the reaction of K 2 TiF 6 and KBF 4 salts with the molten alloy. The kinetics of the formation of intermediate metastable precipitates in the process of Mg 2 Si formation in Al-7Si-0.3Mg-TiB 2 in-situ composites with three different amounts of TiB 2 particles (2.5, 5 and 10 wt.%) were studied using differential scanning calorimeter (DSC) and also compared with the Al-7Si-0.3Mg base alloy. Kissinger analysis of non-isothermal DSC scans at various heating rates was carried out to evaluate the activation energies associated with the precipitation processes. The metastable precipitates were characterized by taking the solutionized samples to their respective DSC peak temperatures at a particular heating rate and the samples were then observed under a transmission electron microscopy. It was found that there is a decrease in the activation energies of the GP zones with increase in TiB 2 content.

16 citations


Journal ArticleDOI
TL;DR: In this article, the size distribution of TiB2 particles in the matrix was determined by scanning electron microscopy (SEM) analysis, and the results showed that there was no agglomeration of the particles throughout the matrix and that the dislocations are generated to accommodate the strain due to the difference in the coefficient of thermal expansion (CTE) of the particle and the Al-Cu matrix.
Abstract: Al-4Cu-xTiB2 (x=0, 2.5, 5, 10 wt %) in-situ composites were prepared by a mixed salt route technique. The composites were characterized by X-ray diffraction techniques, to confirm that no Al3Ti has formed, which is the advantage of mixed salt route technique. The scanning electron microscopy (SEM) analysis was carried out to determine the size distribution of TiB2 particles in the matrix. The results showed that there was no agglomeration of TiB2 particles throughout the matrix. The differential scanning calorimerty (DSC) studies were performed on the alloys as well as on composites to identify and characterize the precipitation sequence G.P.(I)→G.P.(II)/θ″→ θ′→ stable θ. To understand the precipitation kinetics of these precipitates in the presence of TiB2, the solutionized samples were heat treated at different temperatures of precipitation as indicated by the DSC Thermogram and subsequently quenched to room temperature to retain the precipitates that form at corresponding high temperatures. The TEM analysis was carried out to characterize the crystal structure and morphology of the different precipitates. The analysis suggested that the precipitation occur primarily on the dislocations in the matrix as well as in the TiB2 particle/Al-Cu matrix interface dislocations. It is believed that these dislocations are generated to accommodate the strain due to the difference in the coefficient of thermal expansion (CTE) of the TiB2 particles and the Al-Cu matrix. TEM results displayed that the interface contained large amount of dislocations which may possibly accelerate the precipitation sequence.

5 citations


Journal ArticleDOI
TL;DR: In this paper, a Nb-microalloyed structural steel with ferrite-pearlite microstructure was subjected to cold rolling and intercritical annealing to produce ultra-fine grained dual phase microstructures.
Abstract: A Nb-microalloyed structural steel with ferrite-pearlite microstructure was subjected to cold rolling and intercritical annealing to produce ultra-fine grained dual phase microstructure. Optical and transmission electron microscopy techniques were employed to characterise the microstructure. Initial results showed that the intercritical annealing (at 790°C for 90s) of samples rolled to a true strain of 2.4 resulted in a significant grain refinement from the average initial grain size of 20 μm to 1–2 microns. The microstructure primarily consisted of UFG ferrite matrix with homogeneously distributed islands of plate martensite with volume fraction of 27%.

4 citations


Journal ArticleDOI
TL;DR: In this article, the microstructure and texture of Nb-microalloyed steel following cold rolling and short intercritical annealing was investigated, and it was shown that cold rolling resulted in polygonal ferrite in the range of 1-2 μm in size.
Abstract: Severe cold rolling and short intercritcal annealing is often used to produce ultra-fine grained ferrite and martensite dual phase steels. In this paper, microstructure and texture of Nb-microalloyed steel following cold rolling and short intercritical annealing is investigated. The results show that cold rolling and annealing resulted in ultra-fine grained dual phase steel consisted of polygonal ferrite in the range of ~1-2 μm in size. In cold rolled material, the texture components are γ fiber (//normal direction) and α fiber (//rolling direction). Partial recrystallization texture was observed following intercritical annealing.

2 citations


Journal ArticleDOI
TL;DR: Using an Al 5083 alloy, in which an equi-axed microstructure is present from the beginning, it was shown that grain boundary sliding, accompanied by grain rotations, is the rate controlling mechanism.
Abstract: Even anisotropic superplastic flow, which is a result of an elongated grain shape and texture, can lead to extreme elongations to fracture (superplasticity). Therefore, to identify the mechanisms of deformation present during superplastic flow alone, the effects of the microstructure should be eliminated first. Using an Al 5083 alloy, in which an equi-axed microstructure is present from the beginning, it is shown that grain boundary sliding, accompanied by grain rotations, is the rate controlling mechanism.

1 citations


Journal ArticleDOI
TL;DR: A ferrite-bainite-martensite (F-B-M) microstructure was produced in a medium carbon microalloyed steel through two routes, namely, low temperature finish forging or rolling, followed by a two-step cooling and annealing as mentioned in this paper.
Abstract: A ferrite-bainite-martensite (F-B-M) microstructure was produced in a medium carbon microalloyed steel through two routes, namely, low temperature finish forging or rolling, followed by a two step cooling and annealing The texture formed in control forged and rolled material after two step cooling followed by annealing (TSCA) was examined Texture investigation was also carried out after low cycle fatigue testing at low and high total strain amplitudes Transmission electron microscopy was employed to study the microstructural evolution Fatigue tested F-B-M microstructure obtained through the rolling route was stable up to a total strain amplitude of 06% This paper reports the evolution of texture and microstructure in two-step cooled F-B-M microstructure and their stability during fatigue loading