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Bhuyan R.K.,Indian Institute of Technology Guwahati | Kumar T.S.,Indian Institute of Technology Guwahati | Goswami D.,Indian Institute of Technology Guwahati | James A.R.,Defense Metallurgical Research Laboratory | And 2 more authors.
Materials Science and Engineering B: Solid-State Materials for Advanced Technology | Year: 2013

We report the study of the effects of processing parameters and additive concentration on the structure, microstructure and microwave dielectric properties of MTO-CeO2 (x wt.%) ceramics with x = 0, 0.5, 1.0 and 1.5 prepared by solid-state reaction method by adding CeO2 nanoparticles as a sintering aid. The pure Mg2TiO4 ceramics were not densifiable below 1450 °C. However, when CeO2 nanoparticles were added to MTO, the densification achieved at 1300 °C along with the increase in average grain size with the uniform microstructure and improved microwave dielectric properties. This is mainly driven by the large surface energy of CeO2 nanoparticles and their defect energy during the sintering process. While the addition of CeO2 nanoparticles in MTO ceramics does not change the dielectric constant (εr), the unloaded quality factor (Qu) was altered significantly. MTO-CeO2 (1.5 wt.%) ceramics sintered at 1300 °C exhibit superior microwave dielectric properties (εr ∼ 14.6, Q × f0 ∼ 167 THz), as compared to the pure Mg2TiO4 ceramics. The observed results are correlated to the enhancement in density and the development of uniform microstructure with the enhanced grain size. © 2013 Elsevier B.V. All rights reserved. Source

Chander G.S.,Swarna Bharathi Institute of Science and Technology | Reddy G.M.,Defense Metallurgical Research Laboratory | Tagore G.R.N.,National Institute of Technology Warangal
International Journal of Advanced Manufacturing Technology | Year: 2013

Dissimilar joints between austenitic stainless steel and low alloy steel are extensively used in many high temperature applications in the energy conversion systems. In the present investigation, emphasis is made on the influence of process parameters on the impact toughness and hardness of the friction welded joints between these two materials. The important process parameters in friction welding such as friction force, forge force, and burn-off lengths are considered for optimization by Taguchi method using L8 27 orthogonal array. It is found that under low friction force, forging force, and burn-off conditions, the impact toughness is high due to the observed acicular martensite. Low impact toughness is reported for the welds made at higher levels of the parameters. Carbon depletion is also observed close to interface in low alloy steel side. Microhardness at the weld center is less than the microhardness on either side at the interface of low alloy steel and austenitic stainless steel close to weld center. The contribution of each parameter and significance of interactions of these parameters is determined by Taguchi method. Among these parameters, friction force has significant influence and forging force has negligible influence on microhardness. The burn-off has maximum influence while forge force has minimum effect on toughness of the welds. Statistical analysis of variance is carried out, optimum process parameters are evaluated, and regression equations are obtained. © 2012 Springer-Verlag London Limited. Source

Rao T.S.,ACE Engineering College Ghatkesar | Reddy G.M.,Defense Metallurgical Research Laboratory | Rao S.R.K.,SSN College of Engineering
Metallurgia Italiana | Year: 2016

High strength aluminum alloy 7075 is widely used in aerospace applications. In this investigation, Al-Zn-Mg-Cu alloy- AA7075-T651 was friction stir welded, in two thicknesses-10 mm and 16 mm, in order to investigate variations in microstructure and hardness profiles across the joint in through thickness direction. Process parameters resulting in defect free welds were identified using trial and error method. The variations in microstructures and hardness profiles were studied by means of optical microscopy, transmission electron microscopy (TEM) and hardness tests. 10 mm thick welds were found to show better performance in terms of hardness compared to 16 mm thick welds. However, both welds were found to exhibit significant loss in the hardness in the heat-affected zone (HAZ). Furthermore, the loss of hardness due to the welding is more in 16 mm thick welds. Hardness across the joint increases as the survey moves away from the surface of the specimen to the root of the weld. The weld nuggets in both the welds reveal very fine recrystallized grains and the grain size was found to decrease from surface to root of the joint along the thickness of the weld. TEM studies reveal that the weld nugget suffers from dissolution of precipitates and the HAZ consists of wide precipitate free zones, which are considered responsible for lower hardness in the HAZ. It is concluded that sound welds can be produced on thick plates ofAA7075- T651 and welds made on thicker plates exhibit inferior hardness values. Source

Chander G.S.,Swarna Bharathi Institute of Science and Technology | Reddy G.M.,Defense Metallurgical Research Laboratory | Rao A.V.,Defense Metallurgical Research Laboratory
Journal of Iron and Steel Research International | Year: 2012

Fundamental investigation of continuous drive friction welding of austenitic stainless steel (AISI 304) and low alloy steel (AISI 4140) is described. The emphasis is made on the influence of rotational speed on the microstructure and mechanical properties such as hardness, tensile strength, notch tensile strength and impact toughness of the dissimilar joints. Hardness profiles across the weld show the interface is harder than the respective parent metals. In general, maximum peak hardness is observed on the stainless steel side, while other peak hardness is on the low alloy steel side. A trough in hardness distribution in between the peaks is located on the low alloy steel side. Peak hardness on the stainless steel and low alloy steel side close to the interface increases with a decrease in rotational speed. All transverse tensile joints fractured on stainless steel side near the interface. Notch tensile strength and impact toughness increase with increase in rotational speed up to 1500 r/min and decrease thereafter. The mechanism of influence of rotational speed for the observed trends is discussed in the torque, displacement characteristics, heat generation, microstructure, fractography and mechanical properties. © 2012 Central Iron and Steel Research Institute. Source

Balaram V.,CSIR - Central Electrochemical Research Institute | Roy P.,National Institute of Oceanography of India | Subramanyam K.S.V.,CSIR - Central Electrochemical Research Institute | Durai L.,Defense Metallurgical Research Laboratory | And 5 more authors.
Indian Journal of Geo-Marine Sciences | Year: 2015

REE (Rare Earth Elements) and yttrium in sea water samples, from the Afanasy-Nikitin Seamount (ANS) located around 3° South latitude and 83° East longitude in the north central Indian Ocean were precisely determined by high resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) method. A modified procedure has been designed for determination of REE and yttrium wherein the water samples were subjected to a pre-concentration step using bis-2-ethylhexyl phosphoric acid (HDEHP) complexing agent. Sea water reference materials such as NASS-5 and SLEW-3 were used for calibration as well as to check the accuracy of the procedure adopted. Samples were analyzed for REE and yttrium by HR-ICP-MS. Precisions achieved for various rare earths and yttrium is better than 8% RSD with comparable accuracies. Limit of detection (3σ) were generally in the range of 0.02-1.2 pg/ml range for all these elements. This method facilitates rapid and interference-free determination of REE and yttrium from relatively small volume of sea water (10 ml). Recoveries for different REE and Y were better than 5%, and accuracy and precision of the determinations are within 8% RSD. The Ce-negative anomalies with smooth normalized-REE patterns obtained for both certified reference materials and samples further substantiate that the procedure adopted and the data generated are extremely accurate. A slight enrichment of heavy REE were observed in the central Indian Ocean waters which might be attributed to the river flows containing more dissolved trace elements including REE. A sharp negative Ce-anomaly in the normalized REE distribution patterns indicates that the source of REE in particular Ce in marine sediments is seawater. Results of the variation in REE concentrations with depth indicated that the physico-chemical conditions of bottom ocean water follow a very complex mechanism. © 2015, National Institute of Science Communication and Information Resources (NISCAIR). All rights reserved. Source

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