Conference Papers
Permanent URI for this collectionhttps://idr.nitk.ac.in/handle/123456789/28506
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Item Microstructure evolution in AI-7Si-0.3Mg alloy during partial melting and solidification from melt: A comparison(2006) Nyamannavar, S.; Ravi, M.; Prabhu, K.N.In the present work, a comparative study of microstructure evolution in Sr modified AI-7Si-0.3Mg alloy isothermally held at semi-solid state under conditions of (i) cooling from liquid state and (ii) partial melting from solid state to the semi-solid temperature was carried out. The effect of cooling rate (0.01 to 100 K/s) on the microstructure during solidification of semisolid alloy is studied. Partial melting of alloy results in the fine and more spherical solid phase compared to cooling of the same alloy from liquid state. Chemical modification of the eutectic silicon by Sr addition was found to remain same for both cooling the melt from liquid as well as partial melting from solid state, contrary to the reported results. The morphology of eutectic silicon corresponding to the liquid entrapped in solid phase is finer compared to that in interconnected liquid channel.Item Constitutional undercooling and growth of globuletic particle(2008) Nyamannavar, S.; Ravi, M.; Prabhu, K.N.Isothermal holding of an alloy at semi-solid temperature and quenching/cooling, results in formation of instabilities on the globuletic α-particles. The aspect of instability formation is necessary input for accurate simulation and modeling of microstructure evolution for semi-solid metal forming (SSM) process. In the present work instability formation is studied for Al-7Si-0.3Mg alloy. Small cylindrical samples (10 mm, height 10 mm) were subjected to isothermal holding at semisolid temperature followed by quenching/cooling to room temperature. Instabilities were found to form at cooling rates 30 and 100 K/s. Instability formation is explained by interface stabilization theory based on the constitutional undercooling of liquid ahead of the solid/liquid interface.Item Effect of Ni and Sr additions on the microstructure, mechanical properties, and coefficient of thermal expansion of Al-23%Si alloy(Elsevier Ltd, 2021) Vijayan, V.; Ravi, M.; Prabhu, K.N.In this paper, the combined and individual effect of strontium (Sr) and nickel (Ni) additions on the microstructure and mechanical properties of hypereutectic Al-23Si alloy was studied using an optical microscopy, universal tensile testing machine and Brinell hardness tester. The wear properties and coefficient of thermal expansion of the melt treated samples were determined using pin on disc wear testing machine and linear expansion measurement unit respectively. The results indicate that the Ni additions significantly enhanced the mechanical properties of the alloy, whereas, presence of Sr was detrimental. It was observed that the improvement in mechanical properties due to Ni was primarily due to refinement and transformation of the star shaped primary silicon into polyhedral crystals. However, the addition of Sr, both as separate and when combined with Ni, transformed the primary silicon into a faceted crystal and hence decreased the mechanical property. Among all, the Ni melt treated alloy samples showed lowest wear rate and coefficient of thermal expansion. © 2021 Elsevier Ltd. All rights reserved.