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Strain rate sensitivity behaviour of the thin films of Al, Al-Si and nanocomposite Al-Si-N: A comparative study
No full textA comparative study on the strain rate sensitivity behaviour of magnetron sputtered Al, Al-Si and Al-Si-N thin film deposited on stainless steel 304 substrate was carried out. Strain rate sensitivity and activation volume can provide a clear picture regarding the time dependent deformation mechanisms taking place in a material. The variation of the two key parameters, strain rate sensitivity and activation volume were investigated for the films of metal Al, metal alloy Al-Si and Al-Si-N nanocomposite coatings. As strain rate have a significant impact on the creep phenomenon and different materials respond differently when subjected to varying strain rates, a brief study on the creep behaviour is also presented here. The mechanical behaviour of the three different coatings was correlated with their structural properties for a deeper insight into the microstructural dependent dynamic mechanical behaviour
A brief review on the development of self-healing, hydrophobic and antifouling epoxy coating
No full textEpoxy coatings are the most used industrial coating system. While corrosion resistance through the
barrier performance of the coating is well tested, the addition of multifunctionality is the new research objective. The responsiveness of the epoxy coating to the mechanical damage will not only add to its barrier performance but also delay the corrosion of the underlying metal. Such responsiveness of the coating is desired to manage the maintenance schedule. Various methods tested to add the “self-healing” attribute to the epoxy coatings are
discussed. Surface modification to add hydrophobic character to the epoxy coating is also another functionality for value addition and is useful in many applications. For marine applications, fouling resistance is very important. Attempts made to develop anti-fouling epoxy coating are also reviewed. The brief review, giving a broad overview of the research trend, is intended to give a way forward in the development of the epoxy coating
Effect of dual crosslinking on physico-chemical properties of hydrogels prepared from chitosan and alginate
No full textHydrogels have established their utility in the field of biomedical science and technology including drug delivery and tissue engineering, among other applications. Crosslinking density critically affects the resultant
physical property of the hydrogels. Here, we have successfully synthesized carboxymethylchitosan (CMC) and
oxidized alginate (AA) from chitosan and sodium alginate, respectively. CMC and AA were used to fabricate
CMC-AA-single network (CMC-AA-SNH) and CMC-AA-double network (CMC-AA-DNH) hydrogels. Crosslinking of CMC-AA-SNH was done by dynamic covalent bonding, that is, imine bond formation, whereas CMC-AA-DNH was crosslinked via covalent imine bond and Ca2+ mediated ionic interactions. Fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (1H NMR) studies were employed to
characterize the components of the hydrogels. Effect of dual crosslinking over the single crosslinked hydrogel
was extensively analyzed by rheological studies. Scanning electron microscopy revealed that the CMC-AA-DNH
was more densely packed with interconnected structure than CMC-AA-SNH. Swelling study demonstrated that
the degree of swelling of CMC-AA-DNH was significantly less than CMC-AA-SNH due to more crosslinking density. Compressive mechanical test of the hydrogels further indicated that CMC-AA-DNH exhibits fracture stress of 79.5 kPa. These results indicate how the physical and mechanical properties of a polymeric hydrogel system can be tuned through control of crosslinking, which have important implications for the use of these gels for biomedical applications
Microstructure–Property Correlation in High-Strength Formable Steel with Varying Nb-Si Content
No full textHigh-strength formable quality (HSFQ) steel grades, steel A (0.038Nb, 0.031Si), steel B (0.034 Nb, 0.27Si),
and steel C (0.044Nb, 0.26Si), with varying Nb and Si content has been investigated. The microstructure,
texture, precipitation, mechanical properties and corrosion behavior of these steel grades have been explored.
Very fine grain size in the range of 2.7-3.6 lm was obtained in all these steel grades through
controlled hot rolling. However, a significant variation in the crystallographic texture and precipitation
behavior in these steels was observed. A higher volume fraction of gamma fiber texture components and uniformly
distributed fine Nb(C, N) precipitates were obtained in steel B as compared to steel A and C. This
resulted in better properties in steel B with relatively high PSE (product of strength–elongation), high
uniform elongation, and high hole expansion ratio. The corrosion properties of the steels were also evaluated,
and steel B showed better corrosion resistance among the three grades. Considering the overall
performance and properties of these steel grades, steel B with an optimum Nb and Si content is found to
have better property and performance among the three grades
CSIR-NML NEWSLETTER JUNE- 2021
Get PDFSummary of significant activities
For the period June, 2021,
CSIR-National Metallurgical Laborator
A comprehensive review on recycling methods for cemented tungsten carbide scraps highlighting the electrochemical techniques
No full textThe scraped and end-of-life tungsten carbide materials demand innovative recycling methods to recover valuable refractory and strategic metals like tungsten, cobalt, nickel etc. The efficient treatment of this material significantly benefits to economics as compared to its ore. Several methods based on pyrometallurgy or hydrometallurgy or their suitable combination have been explored. These methods encompass several unit operations tested at the laboratory as well as on the pilot scale. Some of the methods also matured into technology on a commercial scale. However, the demonstration at the pilot plant scale is towards the validation of the developed process. Each of the methods tested so far has its own pros and cons. For instance, the combination of pyro-hydrometallurgical process has some advantages over hydrometallurgical processes such as higher efficiency, lower costs, and a few industrial requirements, but it is energy-intensive and requires high capex. Besides, considerable attempts have been put into the development of the electrodissolution processes, recently. Several studies available through reports, research articles, and patents recommend a selective electro-dissolution process, which is flexible enough to recycle different varieties of WC scraps. Various electrolytes based on acidic (H2SO4, HCl, H3PO4, HNO3) and alkaline (NaOH and NH3) media worked well to dissolve the refractory metal. Several additives are often added as supporting agents to obviate the most common constraint in electrodissolution, i.e., passivation of the anode. This review particularly highlights the electrochemical methods for the recycling of WC materials along with other recycling methods in brief
Effect of continuous annealing process on various structure parameters of martensite of dual-phase steels
No full textIndustrial continuous annealing process routes for dual-phase steels are mostly found to be non-isothermal in nature. The present study is an effort to understand the importance of non-isothermal annealing process parameters and their impact on the various metallurgical phenomena; such as recrystallisation and phase transformation behaviours of duel-phase steel. These, in turn, are expected to influence various structure parameters of martensite phase which are critical in determining the strength of duel-phase steel. A dual-phase steel sheet in 67% cold rolled full hard condition was subjected to non-isothermal annealing treatment with varying heating rate and inter-critical annealing temperatures. After processing the samples were investigated for structural parameters of martensite phase using a scanning electron microscope, X-ray diffraction, and nanoindentation technique. It was observed that due to non-isothermal nature of continuous annealing process, the hardness of the martensite phase did not follow the hardness trends as determined from conventional carbon concentration. Further, lattice tetragonality of martensite was also affected by increasing its volume fractions. The annealing process apparently influenced the evolution of texture because of the increasing fraction of martensite in dual-phase steel
Creep-fatigue deformation micromechanisms of a directionally solidified nickel-base superalloy at 850 degrees C
No full textIn the present exploration, it was attempted to understand the creep‐fatigue (CF) deformation micromechanisms of alloy CM 247 DS LC by conducting low‐cycle fatigue (LCF) and CF tests employing strain amplitude ranging from 0.6% to 1.0% at T = 850°C in the air and performing extensive electron microscopic examinations. The cyclic life of the alloy lessens for all CF tests conducted at 1 and 5 minute dwell time in comparison to LCF tests. Transmission electron microscopy (TEM) examinations confirmed that during CF tests substructure consists of dislocation loop, mixed dislocations, and γ' rafting, a typical creep deformation signature of nickel‐base superalloys, it also consists of features observed during fatigue deformation such as anti‐phase boundary (APB)‐coupled dislocations inside γ' precipitates and local tangles of dislocations. This confirms that the deformation of CF‐tested specimens is ascribed to the synergistic effect of both creep and fatigue. This fact was further verified by scanning electron microscopic (SEM) examinations
Heat transfer modelling of dropwise condensation behaviour of magnesium vapours in the electrothermal production of magnesium
No full textDuring the extraction of magnesium by the electrothermal process, the condensation of magnesium vapours in the condenser is critical to achieve operational efficiency. In the present work, a mathematical heat transfer model has been developed to predict the growth rate of a single liquid metal drop during dropwise condensation (DWC) of magnesium vapours in the electrothermal process. Homogeneous DWC model has been developed considering negligible thermal resistance at the liquid-vapour interface for a single cycle of liquid magnesium layer formed at vapour-liquid interface. The heterogeneous DWC has been modelled taking into account all possible thermal resistances. The role of constriction resistance on transient droplet growth behaviour has been studied and the parametric sensitivity analysis has been conducted. Parameters i.e. degree of undercooling (Delta T), contact angle (theta), thickness of condenser wall (delta )and constriction effect cause (beta) has been studied for droplet growth behaviour. Heat transfer and specially the constriction resistance was found to be quite significant for heterogeneous DWC of magnesium metal vapours. Alongwith other parameters, the thermally inactive region (beta) on the condenser surface inversely affects the growth. The model-based predicted Mg droplet growth profiles during condensation have been validated with published data on similar DWC studies
Impact of uniaxial stress on soft-magnetic and magneto-impedance properties of vitrified magnetostrictive microwires
No full textThe investigation addresses the impact of stress on soft magnetic and giant magneto-impedance (GMI) of rapidly quenched Fe77.5Si7.5B15, (Co94Fe6)72.5Si12.5B15 and (Co94Fe6)72.5Si12.5B12.5Nb0.5Cr2 microwires. Differential scanning calorimetry revealed interesting phase stability in the later alloys. The vitrified microwires contained dominant Co and a lean Fe content showed much superior soft magnetic properties and high magnetoimpedance. The alloy microwires incorporated with Nb and Cr manifested lowest coercivity value of 0.034 Oe with a high GMImax value of 425% in the as-quenched state. The uniaxial stress applied on the microwires modified the shape of the hysteresis loops and GMI plots. The hysteresis loops showed stress dependence of coercivity based on alloy chemistry, phase stability and consequent magnetostriction. The GMImax revealed sensitive change with respect to the applied stress in all the alloy microwires. In addition to GMImax interesting features were observed in the GMI profile pertaining influence of stress on the anisotropy field. The anisotropy field shifted systematically in one of the alloy microwires which displayed symmetric dual GMI peaks. The stress was also found to modify the asymmetric characteristics in a microwire