Faculty Publications
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Item Corrosion aspects of Al and Mg based composites(Elsevier, 2025) Bhole, K.B.; Arya, S.B.; Nayak, J.Corrosion is a significant concern in various industries, particularly in applications where metal components are exposed to aggressive environments. Aluminum (Al) and magnesium (Mg) are lightweight metals that find extensive use in aerospace, automotive, and structural applications. However, their susceptibility to corrosion limits their widespread adoption in certain conditions. Metal matrix composites (MMCs) have emerged as a promising solution to enhance the corrosion resistance of these metals while maintaining their desirable mechanical properties. The corrosion resistance of pure Al and Mg is often compromised in harsh environments due to galvanic coupling, electrolyte exposure, and chemical reactions. MMCs, where metal works as a matrix while reinforced by ceramic or hard metallic phases, offer a unique property to tailor a required mechanical property along with suitable corrosion resistance. However, it is challenging to control as well as enhance resistance to corrosion in various corrosive environments. The development of advanced metal matrix composites with tailored corrosion resistance profiles holds the key to expanding the application range of Al and Mg in diverse industries, ensuring their longevity and reliability in corrosive environments. A range of electrochemical techniques, including open circuit potential, electrochemical impedance spectroscopy, and polarization resistance test, highlighting their applications are discussed. © 2026 Elsevier Inc. All rights reserved..Item Identification of voice disorders using speech samples(2003) Nayak, J.; Subbanna Bhat, P.This paper attempts to identify pathological disorders of larynx using Wavelet Analysis. Speech samples carry symptoms of disorder in the place of their origin. The speech signal is subjected to wavelet analysis, and the coefficients are used to identify disorders such as Vocal Fold Paralysis. Multilayer Artificial Neural Network is used for classification of normal and affected signals.Item AR modeling of heart rate signals(Institute of Electrical and Electronics Engineers Inc., 2004) Nayak, J.; Subbanna Bhat, P.; Acharya, A.U.; Niranjan, U.C.; Sing, O.W.The electrocardiogram (ECG) is a representative signal containing information about the condition of the heart. The shape and size of the P-QRS-T wave, the time intervals between its various peaks etc may contain useful information about the nature of disease afflicting the heart. However, the human observer can not directly monitor these subtle details. Besides, since bio-signals are highly subjective, the symptoms may appear at random in the time scale. Therefore, the heart rate variability signal is used as the base signal for the highly useful in diagnostics. This paper deals with the analysis of eight cardiac abnormalities using Auto Regressive (AR), modeling technique. The results are tabulated below for specific example. © 2004 IEEE.Item Reliable and robust transmission and storage of medical images with patient information(2004) Nayak, J.; Subbanna Bhat, P.; Kumar, M.S.; Acharya, A.U.A new method for compact storage and transmission of medical images with concealed patient information in noisy environment is evinced. Digital Watermarking is the technique adapted here for interleaving patient information with medical images. The patient information, which comprises of text data and signal graph, is encrypted to prevent unauthorized access of data. The latest encryption algorithm (Rijndael) is used for encrypting the text information. Signal graphs (ECG, EEG EMG etc.) are compressed using DPCM technique. To enhance the robustness of the embedded information, the patient information is coded by Error Correcting Codes (ECC) such as (7,4) Hamming, Bose-Chaudhuri-Hocquenghem (BCH) and Reed Solomon (RS) codes. The noisy scenario is simulated by adding salt and pepper (S&P) noise to the embedded image. For different Signal to Noise Ratio (SNR) of the image, Bit Error Rate (BER) and Number of Character Altered (NOCA) for text data and percentage distortion (PDIST) for the signal graph are evaluated. The performance comparison based on the above parameters is conducted for three types of ECC. It is elicited that coded systems can perform better than the uncoded systems. © 2004 IEEE.Item Reliable transmission and storage of medical images with patient information using error control codes(2004) Nayak, J.; Subbanna Bhat, P.; Kumar, M.S.; Acharya, A.U.A new method for compact storage and transmission of medical Images with concealed patient Information in noisy environment if evinced. Digital Watermarking is the technique adapted here for interleaving patient Information with medical images. The patient information, which comprises of text data and signal graph, is encrypted to prevent unauthorized access of data. The latest encryption algorithm (Rijndael) is used for encrypting the text information. Signal graphs (ECG, EEG EMG etc.) are compressed using DPCM technique. To enhance the robustness of the embedded information, the patient Information Is coded by Error Correcting Codes (ECC) Reed Solomon (RS) codes. The noisy scenario Is simulated by adding salt and pepper (S&P) noise to the embedded Image. For different Signal to Noise Ratio (SNR) of the image, Bit Error Rate (BER) and Number of Character Altered (NOCA) for text data and percentage distortion (PDIST) for the signal graph is evaluated. It Is elicited that coded systems can perform better than the uncoded systems. © 2004 IEEE.Item Oxidation and corrosion resistance of TiAl3 coatings(Indian Institute of Metals, 2008) Udayashankar, N.K.; Rajasekaran, S.; Nayak, J.Titanium aluminides based on TiAl, TiAl3 and Ti3Al are potential materials for high temperature aerospace applications. Their low density, high temperature creep resistance, high temperature strength and high oxidation resistance make them excellent coating materials. However mese coatings are likely to be subjected to high temperature and corrosive environments during service. Hence it is aimed to study the oxidation and corrosion resistance of TiAl3 coatings on various types of substrates. In me present work, TiAl3 is coated on high speed steel, stainless steel 304, stainless steel 316, copper and aluminum substrates by physical vapor deposition technique. X-ray diffraction analysis confirms the presence of TiAl3 phase. The hardness studies reveal that better hardness can be achieved with thick coatings. The oxidation behavior of the coatings is studied by carrying out step stress experiments at elevated temperatures. Coated samples are heated up from 400°C in the steps of 100°C for 1h in each step to 3000°C. The mass gain caused by oxidation was determined. The oxidation curve drawn as a function of mass gain versus temperature reveals that TiAl3 film started to oxidize above 800°C, where as oxidation of me uncoated substrates began at a much lower temperature of 550°C. The excellent oxidation resistance of the coatings can be attributed to the formation of an amorphous Al2O3 film. Scanning electron microscope (SEM) and EDAX analysis confirm the presence of an amorphous Al2O3 film. The corrosion behavior of TiAl3 coatings are investigated by the polarization resistance experiments in NaCl aqueous solution at ambient temperature. According to the Tafel plot analysis, the coatings show lower corrosion rate than the untreated substrates. The major corrosion in the coatings arose from electrolyte penetration into the pores of the coatings. In fact, a dense coating showed a high corrosion resistance in an aqueous medium.Item Corrosion inhibition of T-6 treated 6061 Al-SiC(p) composite in hydrochloric acid(Indian Institute of Metals, 2008) Nayak, J.; Hebbar, K.R.Addition of reinforcements like SiC to aluminium matrix has been reported to decrease the corrosion resistance of the matrix due to several reasons, one of them being the galvanic action between the reinforcement and the matrix. Aging of aluminium alloys can also have similar effects as aging results in precipitation of intermetallics. The work deals with effect of aging (T-6 treatment) on the corrosion behaviour as well as corrosion inhibition of 6061Al-SiC composite. Corrosion behaviour of 6061 Al-SiC(p) composite were determined in HCl by Tafel extrapolation technique in the temperature range of 30°C-50°G. Further, the inhibition studies were made using two inhibitors viz. (i) Allyl Thiourea and (ii) Glycyl Glycine. The results indicate that both the organic compounds act as anodic inhibitors and are moderately effective in inhibiting the corrosion of 6061Al-SiC(p) composite. The inhibition efficiency increases with increase in inhibitor concentration. Similar inhibition studies were made on the aged samples. However, in the case of T-6 treated samples, the inhibition efficiency was found to be poor compared to the non-heat treated samples.Item The effect of aging and the protective coating on the oxidation behavior of 6061Al/SiC composite at high temperatures(Trans Tech Publications Ltd ttp@transtec.ch, 2011) Rajasekaran, S.; Udayashankar, N.K.; Nayak, J.This paper analyses the effect of ageing on the oxidation behavior of 6061Al/SiC composite material at temperatures ranging from 500 to 800 K. Also aluminum coating is employed as protective coating in order to improve the oxidation resistance of the composite. SEM, EDAX, XRD and stepped oxidation measurement techniques are used to study the oxidation behavior and to characterize the composite specimens. Oxidation of the composite material without protective coatings is seen to be very rapid during the initial stages of exposure to the high temperatures but subsequently slowed down due to the formation of a protective surface layer of oxide. Among the artificially aged composites, peak aged specimens are more prone to oxidation. The oxidation was especially severe above 600 K. The interface between the matrix and reinforcement particles and the grain boundary regions of the matrix enhance this oxidation process since they provided sites for oxidation initiation. Aluminum coating on the composite obtained by DC magnetron sputtering technique, reduce the oxidation rate effectively since the interface regions between the matrix and reinforcement, grain boundary regions of the matrix are unexposed to the atmosphere. Aluminum coating provides better oxidation resistance for the artificially aged composites. © (2011) Trans Tech Publications.Item Effect of aging and protective coating on the corrosion behavior of 6061 Al / SiCp composite in chloride solutions(Trans Tech Publications Ltd ttp@transtec.ch, 2011) Rajasekaran, S.; Udayashankar, N.K.; Nayak, J.Metal matrix composites considered especially for marine application are typically aluminum-based. Utilization of the composites in marine environments requires adequate corrosion resistance. In this work, the effect of aging and aluminum as resistive coating on the corrosion behavior of 6061 Al / SiC p composite in 1N and 3.5N NaCl solution in the temperature range of 30°C-50°C is studied by means of electrochemical techniques, scanning electron microscope (SEM) and weight loss measurements. Aging results in precipitation of intermetallics in the matrix, this in turn leads to galvanic and pitting corrosion. Pitting initiation and propagation as the main corrosion mechanism was driven by the aging kinetics which is ruled by the reduction in the retained vacancy concentration and at the same time by dislocation density due to the presence of SiCp. Sputtered aluminum coating on the composite effectively resists the pitting initiation and propagation and hence corrosion process. Also the intermetallic precipitates are unexposed to the Chloride solution by the presence of aluminum coating. Hence aluminum coating acts as corrosion resistive coating for the 6061 Al / SiCp aged composites. © (2011) Trans Tech Publications.Item Regression model of oxidation behavior of 6061 Al/SiC composite with and without protective coatings(2011) Priyamvada, B.; Rajasekaran, S.; Udayashankar, N.K.; Nayak, J.This paper analyses the variation of weight gain, Δm, of 6061 Al/SiC composite due to oxidation with time, t, using regression model. Using curve fitting technique, the mathematical equations for the oxidation behavior of the composite are formulated. The generated data according to the mathematical equations are analyzed and compared with the experimental data. More specifically, regression analysis helps in understanding how the typical value of the mass gain (dependent variable) changes when the time of oxidation (independent variable) is varied, while the other independent variable (Temperature) held fixed. Since the oxidation resistance of the 6061Al/SiC composite decreases due to the presence of alloying elements precipitates in the matrix, the effect of aging treatment and protective coatings like Aluminium and AlCrN on the oxidation behavior of the composite is studied. It is observed that the coatings increase the oxidation resistance of the composite. The regression analysis carried out shows a threefold linear variation of weight gain (Dependent variable) with respect to time and temperature of oxidation (Independent variables). © 2011 IEEE.