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Nadimpalli Raghukiran

Bio: Nadimpalli Raghukiran is an academic researcher from VIT University. The author has contributed to research in topics: Spray forming & Alloy. The author has an hindex of 4, co-authored 9 publications receiving 69 citations. Previous affiliations of Nadimpalli Raghukiran include Indian Institute of Technology Madras.

Papers
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Journal ArticleDOI
TL;DR: In this article, a nano-scale scandium rich phase, identified as AlSi 2 Sc 2 (V-phase) uniformly distributed in the alloy, was found to have high matrix hardness (1.34 GPa) in contrast to 1.04 GPa observed in the case of binary Al-Si alloys by nanoindentation.
Abstract: Hypereutectic Al– x %Si–0.8Sc alloys ( x =13, 16, 19 and 22 wt%) were produced by spray forming. The microstructures of all the alloys exhibited very fine silicon phase with average size of about 5–10 µm irrespective of the silicon content of the alloy. Transmission electron microscopy revealed the presence of a nano-scale scandium rich phase, identified as AlSi 2 Sc 2 (V-phase) uniformly distributed in the alloy. The presence of V-phase resulted in higher matrix hardness (1.34 GPa) in contrast to 1.04 GPa observed in the case of binary Al–Si alloys by nanoindentation. Isothermal heat treatment at 375 °C revealed insignificant coarsening of silicon phase in both binary and ternary alloys. The Al– x %Si–0.8Sc alloys exhibited higher flow stress and tensile strength in contrast to their binary alloy counterparts which was attributed to the bi-modal size distribution of the strengthening phases in the form of nano-scale V-phase and sub-micron to 10 µm size silicon particles. The pin-on-disk wear tests exhibited appreciable improvement in the wear performance of the relatively low-silicon content ternary alloys over their binary counterparts while the high-silicon content binary and ternary alloys exhibited no much difference in the wear performance.

36 citations

Journal ArticleDOI
TL;DR: In this article, the influence of spray deposition process on the refinement of silicon phase and the tribological performance of hyper-eutectic Al-Si alloys is reported.

27 citations

Journal ArticleDOI
TL;DR: In this paper, the authors used spark plasma sintered from corresponding gas-atomized powders and showed significant ductility of as high as 85% compressive strain without failure even with the presence of relatively higher weight fraction of the brittle silicon phase.
Abstract: Hypereutectic Al–Si and Al–Si–Sc alloys were spark plasma sintered from corresponding gas-atomized powders. The microstructures of the Al–Si and Al–Si–Sc alloys possessed remarkably refined silicon particles in the size range of 0.38–3.5 µm and 0.35–1.16 µm respectively in contrast to the silicon particles of size greater than 100 µm typically found in conventionally cast alloys. All the sintered alloys exhibited significant ductility of as high as 85% compressive strain without failure even with the presence of relatively higher weight fraction of the brittle silicon phase. Moreover, the Al–Si–Sc alloys have shown appreciable improvement in the compressive strength over their binary counterparts due to the presence of intermetallic compound AlSi2Sc2 of size 10–20 nm distributed uniformly in the matrix of those alloys. The dry sliding pin-on-disc wear tests showed improvement in the wear performance of the sintered alloys with increase in silicon content in the alloys. Further, the Al–Si–Sc ternary alloys with relatively lesser silicon content exhibited appreciable improvement in the wear resistance over their binary counterparts. The Al–Si–Sc alloys with bimodal distribution of the strengthening phases consisting of ultra-fine (sub-micron size) silicon particles and the nano-scale AlSi2Sc2 improved the strength and wear properties of the alloys while retaining significant amount of ductility.

11 citations

Journal ArticleDOI
TL;DR: In this paper, the effect of Si morphology on the microstructural stress distribution of the as-cast and as-sprayed alloys was estimated by simulating uni-axial tensile loads on microstructures using Object Oriented Finite Element code (OOF2).
Abstract: Near-eutectic Al–Si alloys were produced by conventional casting and spray forming resulting in microstructural differences due to process dependent cooling rates. The as-sprayed alloy exhibited fine equiaxed Si particles uniformly distributed throughout the matrix in contrast to the as-cast alloy, which exhibited acicular morphology with relatively large needle-like Si particles. The effect of Si morphology on the microstructural stress distribution of the as-cast and as-sprayed alloys was estimated by simulating uni-axial tensile loads on microstructures using Object Oriented Finite Element code (OOF2). Microstructures of the as-sprayed alloy experienced relatively low and uniform stress distribution, while the microstructural stress distribution in the as-cast alloy was significantly influenced by the orientation of the needle shaped silicon particles.

4 citations

Journal ArticleDOI
TL;DR: In situ age hardening phenomenon observed in as-sprayed Al-Sc binary alloys is reported in this article, along with substantial grain refinement in the as-Sprayed alloys exhibited hardness in the range of 605 MPa (Al-0.3 ) to 923 MPa(Al- 0.8 ) that are comparable to the optimum hardness values typically obtained by age hardness in similar as-cast alloys.

2 citations


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TL;DR: In this article, the effect of annealing on the tribological and corrosion properties of Al-12Si samples produced by selective laser melting (SLM) is evaluated via sliding and fretting wear tests and weight loss experiments and compared to the corresponding material processed by conventional casting.
Abstract: The effect of annealing on the tribological and corrosion properties of Al–12Si samples produced by selective laser melting (SLM) is evaluated via sliding and fretting wear tests and weight loss experiments and compared to the corresponding material processed by conventional casting. Sliding wear shows that the as-prepared SLM material has the least wear rate compared to the cast and heat-treated SLM samples with abrasive wear as the major wear mechanism along with oxidation. Similar trend has also been observed for the fretting wear experiments, where the as-prepared SLM sample displays the minimum wear loss. On the other hand, the acidic corrosion behavior of the as-prepared SLM material as well as of the cast samples is similar and the corrosion rate is accelerated by increasing the heat treatment temperature. This behavior is due to the microstructural changes induced by the heat treatment, where the continuous network of Si characterizing the as-prepared SLM sample transforms to isolated Si particles in the heat-treated SLM specimens. This shows that both the wear and corrosion behaviors are strongly associated with the change in microstructure of the SLM samples due to the heat-treatment process, where the size of the hard Si particles increases, and their density decreases with increasing annealing temperature.

121 citations

Journal ArticleDOI
TL;DR: In this paper, the effect of Sc addition and T6 aging treatment on the secondary dendritic arm spacing (SDAS), modification of eutectic Si morphology, β-Al 5 FeSiand π-Al 8 Mg 3 Si 6 Fe 1 phases and its effect on mechanical properties in A356 alloy has been investigated.
Abstract: Effect of Sc addition and T6 aging treatment on the secondary dendritic arm spacing (SDAS), modification of eutectic Si morphology, β-Al 5 FeSiand π-Al 8 Mg 3 Si 6 Fe 1 phases and its effect on mechanical properties in A356 alloy has been investigated. Addition of 0.4 wt%Sc in A356 alloy resulted in a 50%reduction in the secondary dendritic arm spacing (SDAS). Sc addition changed the morphology of eutectic Si from plate like to fibrous and globular. The needle like morphology of β-Al 5 FeSi phase in A356 alloy changed to Al 5 Fe(Si,Sc) phase having smaller size and irregular morphology. Transmission electron microscopy (TEM) diffraction pattern and Energy dispersive spectroscopy (EDS) analysis revealed the presence of β-Al 5 FeSiand π-Al 8 Mg 3 Si 6 Fe 1 phases in A356 alloy which changed to β-Al 5 Fe(Si,Sc), π-Al 8 Mg 3 (Si,Sc) 6 Fe 1 and additional V-AlSi 2 Sc 2 phase was observed in Sc containing alloys. Addition of 0.4 wt%Sc to A356 alloy improved its Vickers hardness, Ultimate tensile strength (UTS), Yield strength (YS) and ductility by 20%, 25%, 20% and 30% respectively. Artificial aging treatment resulted in significant improvement in the tensile properties for both A356 and Sc added A356 alloys.

54 citations

Journal ArticleDOI
TL;DR: In this paper, a novel Al-Si alloy eutectic Si modifier was proposed and prepared, and the microstructure, metamorphism mechanism and mechanical properties of the eutectoric Si of the alloy after adding Mg-15La master alloy were investigated.

43 citations

Journal ArticleDOI
TL;DR: In this article, a nano-scale scandium rich phase, identified as AlSi 2 Sc 2 (V-phase) uniformly distributed in the alloy, was found to have high matrix hardness (1.34 GPa) in contrast to 1.04 GPa observed in the case of binary Al-Si alloys by nanoindentation.
Abstract: Hypereutectic Al– x %Si–0.8Sc alloys ( x =13, 16, 19 and 22 wt%) were produced by spray forming. The microstructures of all the alloys exhibited very fine silicon phase with average size of about 5–10 µm irrespective of the silicon content of the alloy. Transmission electron microscopy revealed the presence of a nano-scale scandium rich phase, identified as AlSi 2 Sc 2 (V-phase) uniformly distributed in the alloy. The presence of V-phase resulted in higher matrix hardness (1.34 GPa) in contrast to 1.04 GPa observed in the case of binary Al–Si alloys by nanoindentation. Isothermal heat treatment at 375 °C revealed insignificant coarsening of silicon phase in both binary and ternary alloys. The Al– x %Si–0.8Sc alloys exhibited higher flow stress and tensile strength in contrast to their binary alloy counterparts which was attributed to the bi-modal size distribution of the strengthening phases in the form of nano-scale V-phase and sub-micron to 10 µm size silicon particles. The pin-on-disk wear tests exhibited appreciable improvement in the wear performance of the relatively low-silicon content ternary alloys over their binary counterparts while the high-silicon content binary and ternary alloys exhibited no much difference in the wear performance.

36 citations

Journal ArticleDOI
TL;DR: In this article, the relationship between surface porosity and corresponding wear behavior was investigated under low load range of 1.5 - 5 N against AISI 52100 bearing steel ball using a reciprocating ball-on-flat configuration and frequency of 10 Hz.
Abstract: Due to light weight, high specific strength, high corrosion resistance and good heat transfer ability, aluminium alloys are becoming attractive for critical structural applications. These alloys can be manufactured using powder metallurgy techniques in which porosity is a common characteristic. The presence of pores is responsible for decreasing effective load bearing cross sectional area and inducing stress concentration sites for strain localization and damage, decreasing both strength and ductility. The present study aims to establish a better understanding of the relationship between surface porosity and corresponding wear behavior. In this study, porous specimens were produced using powder metallurgy technique and the extent of wear damage and the type of wear was investigated under low load range of 1.5 - 5 N against AISI 52100 bearing steel ball using a reciprocating ball-on-flat configuration and frequency of 10 Hz. Scanning electron microscopy of the wear tracks and wear debris was carried out to understand wear mechanisms. This study revealed that due to combined effect of high stress intensity and subsurface cracking, wear rate increases with increasing porosity content. The friction and wear behavior of pure Al and Al 6061 as a function of porosity content can be attributed to their hardness and corresponding wear mechanism.

28 citations