Showing papers by "S. Sankaran published in 2019"
TL;DR: In this paper, the effect of Nb addition on transformation kinetics, microstructure and mechanical properties of high carbon nano bainitic steels with 0.037 wt% Nb and without nb addition have been studied.
Abstract: Carbide free nano bainitic steels have recently become a promising material for several applications such as rails, armour etc. because of their impressive combination of mechanical properties. Very high strengths up to 2500 MPa have been achieved because of the very fine nano-scale microstructure obtained through transformations at low austempering temperatures. However, the low ductility and impact toughness are the limiting factors which prevent their use in several applications. It is well known that alloying elements such as Nb and V are added in very small quantity in order to improve strength and ductility of low and medium carbon steels through Nb, V (C, N) precipitates. Influence of these microalloying elements on the mechanical properties of nano bainitic steel is not well understood. In the present study, mechanical properties of two high carbon nano bainitic steels with 0.037 wt% Nb and without Nb addition have been studied. Nb addition results in a substantial increase in ductility (total % elongation) from 16 % to 28 %. Effect of Nb addition on transformation kinetics, microstructure and mechanical properties is also discussed.
9 citations
Posted Content•
TL;DR: In this paper, the grain boundary tracer diffusion of Ni, Fe and Cr was studied in a Ni-base 602CA coarse-grained alloy and a coexistence of several short-circuit contributions was distinguished at higher temperatures in Harrison's B-type regime (773-873 K), which were related to different families of high-angle grain boundaries with distinct coverages by precipitates and segregation levels.
Abstract: Grain boundary tracer diffusion of Ni, Fe and Cr was studied in a Ni-base 602CA coarse-grained alloy. A co-existence of several short-circuit contributions was distinguished at higher temperatures in Harrison's B-type regime (773-873 K), which were related to different families of high-angle grain boundaries with distinct coverages by precipitates and segregation levels as revealed by HAADF-STEM combined with EDX measurements. Annealing at 873 K for 18 hours resulted in Cr23C6-type carbides coexisting with an \alpha-Cr-Mn-enriched phase in addition to sequential segregation layers of Al, Fe and Ni around them. Curved and hackly grain boundaries showed a high density of plate-like carbides, whereas straight grain boundaries were composed of globular carbides with similar chemical composition variations and additionally with alternating layers of Cr and Ni in between the carbides, similar to microstructures after a spinodal decomposition. At lower temperatures, discontinuous interfaces with Cr and Cr-carbide enrichment dominated and the alloy annealed at 403 K for 72 hours contained plate-like Cr23C6-type carbides surrounded by a Ni-rich layer around them. The Ni grain boundary diffusion rates at these relatively low temperatures (formally belonging to C-type kinetics) showed an anomalous character being almost temperature independent. This specific diffusion behaviour was explained by a concomitant relaxation of transformation-induced elastic strains occurring on a longer time scale with respect to grain boundary diffusion. Thermodynamic insights into the probable mechanism of decomposition at grain boundaries are provided.
2 citations
18 Sep 2019
TL;DR: In this article, the role of the epoxy-CNT interface on damping by designing two systems of composites which differ in the interfacial area was determined by an experimental approach.
Abstract: In this report, we propose an experimental approach to determine the role of the epoxy-CNT interface on damping by designing two systems of composites which differ in the interfacial area. The composites are namely 'dispersed' and 'layered'. The CNTs were uniformly distributed in the epoxy matrix of the dispersed nanocomposites. Whereas, in the layered nanocomposite, a layer of CNT was sandwiched between two epoxy sheets. Image threshold technique was adopted to characterize the CNT spread area in the epoxy matrix. The epoxy-CNT interfacial area is assumed to be less than the CNT spread area due to the agglomeration of CNTs. The CNT spread area of dispersed nanocomposites was found to be 30 times higher than that of the layered composite. In addition to this, it is observed with microstructure analysis using scanning electron microscope and transmission electron microscope that the dispersed nanocomposites were comprised of more epoxy-CNT interfaces, and the layered nanocomposites have more CNT-CNT interfaces. At a particular CNT content, at the glass transition temperature, higher dynamic loss factor was characterized with dispersed nanocomposites. The energy dissipating nature of the epoxy-CNT and CNT-CNT interfaces were studied by analyzing the microstructural mechanisms of damping related to the system of composites dealt with this study.
1 citations