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• 1. Fleury, E.
Fe-based amorphous alloys as bipolar plates for PEM fuel cell2006In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 159, no 1, p. 34-37Article in journal (Refereed)

Two compositions of Fe-based Fe50Cr18Mo8Al2Y2C14B6 and Fe44Cr15Mo14Y2C15B6N4 amorphous alloys were developed as alternative bipolar plate material for polymer electrolyte membrane fuel cell (PEMFC). In this paper, we present results of an investigation on the electrical, mechanical, corrosion properties and processing ability of these amorphous alloys. The combination of excellent properties indicated that Fe-based amorphous alloys could be potential candidate materials as bipolar plates in PEMFC.

• 2. Haribabu, S.
Effect of Al Addition on the Microstructure and Phase Stability of P91 Ferritic-Martensitic Steel2019In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 50, no 3, p. 1421-1436Article in journal (Refereed)

This paper presents the results of an experimental and computational study carried out to elucidate the effect of Al on the microstructure and phase stability of P91 F/M steel in as-cast, homogenized and normalized conditions. Al-added steels followed ‘Ferritic-Austenitic’ mode of solidification and the as-cast microstructures consisted of δ-ferrite + α′-martensite, the volume fraction of ferrite and hardness of martensite increased with Al concentration. Heat treatments and DSC experiments confirmed increased stability for δ-ferrite with Al addition. Systematic change in the phase transformations temperatures and volume fraction of equilibrium phases due to Al addition was estimated with the help of Thermo-Calc®. Al addition promoted the formation of AlN which was confirmed through electron microscopy-based investigations. AlN dissolution temperature was always above γ-loop which made it impossible to dissolve during austenization. With the help of Scheil and equilibrium simulations using Thermo-Calc®, elemental partitioning between δ-ferrite and α′ phases was found to be the reason for higher hardness of martensite. Based on experimental evidences, it is concluded that except in the case of 0.48 wt pct Al-added steel it is impossible to obtain single phase γ-field (without ferrite) at high temperature thereby a fully martensite structure on cooling.

• 3. Jayamani, Jayaraj
Synthesis and characterization of nanometer-sized Ti-based amorphous powders2007In: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326, Vol. 22, no 6Article in journal (Refereed)

We present a simple method for preparing nanometer-sized, Ti-based amorphous powders from the Y28Ti28Al24Co20and Y36Ti20Al24Co20two-phase amorphous alloys. The initial microstructure of these rapidly quenched alloys is composed of Ti-based, amorphous, spherical, nanometer-sized particles embedded in a Y-based amorphous matrix, with particle size dependent on the alloy composition. The Ti-based powders were extracted from the two-phase amorphous alloys through selective dissolution of the Y-rich matrix in a 0.1 M HNO3solution. The powders of size ranging between 20 and 200 nm have smooth and spherical morphology, and exhibit different magnetic behavior than the bulk alloy of identical composition.

• 4. Jayamani, Jayaraj
Globulization mechanism of the primary Al of Al−15Cu alloy during slurry preparation for rheoforming2005In: Metals and Materials International, ISSN 1598-9623, E-ISSN 2005-4149, Vol. 11, no 3Article in journal (Refereed)

Semisolid slurries of Al-15Cu alloy were produced for rheoforming by a low temperature pouring technique. To investigate the morphological change of the slurry in terms of the particle mean diameter and the roundness factor, samples were extracted during the continuous cooling and the isothermal holding stage of the slurry by a simple technique of interrupt quenching. Results demonstrated that the fine-grained equiaxed dendritic structure, which formed during low temperature pouring, is changed to a globular structure when held at a semisolid temperature for sufficiently long holding time. With regard to the globulization mechanism of the primary α-phase, local melting is considered to take place at the neck of equiaxed dendrites, leading to the separation of small new particles during continuous cooling. These newly formed particles eventually grow during isothermal holding in the semisolid temperature by obeying theD3=Kt kinetic law, which suggests coarsening by Ostwald ripening.

• 5. Jayamani, Jayaraj
Passivation behaviour of structurally relaxed Zr48Cu36Ag8Al8 metallic glass2009In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 479, no 1, p. 257-261Article in journal (Refereed)

The electrochemical corrosion behaviour of as-prepared and structurally relaxed Zr48Cu36Ag8Al8 glassy alloy samples was investigated in 1M H2SO4. Results show that the active–passive transition behaviour of Zr48Cu36Ag8Al8 glassy alloy depends on the amount of free volume (FV) present in the metallic glassy alloy. Poor passivation due to active dissolution of Cu was displayed by the Zr48Cu36Ag8Al8 glassy alloy when it was in a high energy metastable state with relative high amount of FV. It is shown that by reducing the amount of FV in the glass, the passivation behaviour is significantly improved.

• 6.
Korea Institute of Science and Technology, South Korea.
Potential of Cr2AlC Ternary Carbide as Material for Bipolar Plate in PEMFC2007In: Solid State Phenomena, ISSN 1012-0394, E-ISSN 1662-9779, Vol. 124-126, p. 927-930Article in journal (Refereed)

In this paper, we present results of an investigation on the physical, mechanical, chemical properties and processing ability of the Cr2AlC ternary carbide bulk material synthesized by hot pressing technique. The combination of excellent properties indicated that Cr2AlC ternary carbide alloy could be potential candidate materials as bipolar plates in polymer membrane fuel cell (PEMFC).

• 7. Jayamani, Jayaraj
Corrosion mechanism of N-containing Fe–Cr–Mo–Y–C–B bulk amorphous alloys in highly concentrated HCl solution2007In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 449-451, p. 517-520Article in journal (Refereed)

The Fe49Cr15.3Mo15Y2C15B3.4N0.3 (numbers indicate at.%) amorphous alloy in concentrated HCl solution was found to have a corrosion resistance of at least one order of magnitude higher than the N-free Fe-base amorphous alloy. X-ray photoelectron spectroscopy analyses were performed to understand the corrosion mechanism. It was found that the enrichment of Cr oxide and the presence of MoN nitrides on the surface in the passive layer were at the origin of the high corrosion resistance of the N-containing Fe-base amorphous alloy.

• 8. Jayamani, Jayaraj
Corrosion behaviors of Fe45−xCr18Mo14C15B6Y2Mx (M=Al, Co, Ni, N and x=0, 2) bulk metallic glasses under conditions simulating fuel cell environment2007In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 434-435, p. 237-239Article in journal (Refereed)

The corrosion properties of the Fe45−xCr18Mo14C15B6Y2Mx (with M=Al, Co, Ni, N and x=0, 2) bulk metallic glasses have been investigated in a 1M H2SO4+2ppm F− solution at 80°C with H2 and air bubbling, which simulate environments of the polymer electrolyte membrane fuel cell. The partial replacement of 2at.% Fe led to significant modification of the corrosion behavior and resulted in corrosion resistances superior to that of stainless steel.

• 9. Jayamani, Jayaraj
Corrosion studies on Fe-based amorphous alloys in simulated PEM fuel cell environment2005In: Science and Technology of Advanced Materials, ISSN 1468-6996, E-ISSN 1878-5514, Vol. 6, no 3-4, p. 282-289Article in journal (Refereed)
• 10. Jayamani, Jayaraj
Development of metallic glasses for bipolar plate application2007In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 449-451, p. 30-33Article in journal (Refereed)

Fe- and Ni-base amorphous alloys were developed and characterized as alternative bipolar plate materials for polymer electrolyte membrane fuel cell (PEMFC). Lower interfacial contact resistances were obtained for the Fe-base in comparison with Ni-base alloys and particularly the N-containing Fe-base amorphous composition exhibited values almost comparable to that of stainless steel upon high compaction load. Under conditions simulating the anodic and cathodic PEMFC environments, both the Fe- and Ni-base amorphous alloys displayed higher corrosion resistance than stainless steel.

• 11. Jayamani, Jayaraj
Corrosion investigations on zircaloy-4 and titanium dissolver materials for MOX fuel dissolution in concentrated nitric acid containing fluoride ions2016In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 473, p. 157-166Article in journal (Refereed)

Aqueous reprocessing of plutonium-rich mixed oxide fuels require fluoride as a dissolution catalyst in boiling nitric acid for an effective dissolution of the spent fuel. High corrosion rates were obtained for the candidate dissolver materials zircaloy-4 (Zr-4) and commercial pure titanium (CP-Ti grade 2) in boiling 11.5 M HNO3 + 0.05 M NaF. Complexing the fluoride ions either with Al(NO3)3 or ZrO(NO3)2 aided in decreasing the corrosion rates of Zr-4 and CP-Ti. From the obtained corrosion rates it is concluded that CP-Ti is a better dissolver material than Zr-4 for extended service life in boiling 11.5 M HNO3+0.05 M NaF, when complexed with 0.15 M ZrO(NO3)2. XPS analysis confirmed the presence of TiO2 and absence of fluoride on the surface of CP-Ti samples, indicating that effective complexation had occurred in solution leading to passivation of the metal and imparting high corrosion resistance.

• 12. Jayamani, Jayaraj
Enhanced precipitation hardening of Mg–Ca alloy by Al addition2010In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 63, no 8, p. 831-834Article in journal (Refereed)

We report the enhanced precipitation-hardening response of Mg–0.5Ca (wt.%) alloy by microalloying with Al. The peak hardness of 50 HV for the binary alloy was enhanced to 72 HV in a ternary Mg–0.5Ca–0.3Al alloy. Transmission electron microscopy and 3D atom probe analyses confirmed that the improvement in the peak hardness is associated with the dense precipitation of ordered monolayer Guinier–Preston zones and the subsequent formation of Al2Ca causes the over-aging.

• 13. Jayamani, Jayaraj
Electrochemical Activity at the Interface of Dissimilar Explosive Joint of Stainless Steel with Zircaloy by Scanning Electrochemical Microscopy2012In: Journal of Advanced Microscopy Research, ISSN 2156-7573, E-ISSN 2156-7581, Vol. 7, no 3, p. 214-217Article in journal (Refereed)

Electrochemical activity at the interface of dissimilar explosive joint of stainless steel with Zircaloy has been studied in 11.5 M nitric acid using scanning electrochemical microscopy. The reduction of nitric acid and oxidation of nitrous acid in the tip-substrate gap is proposed as a mechanism for the electron transfer reaction. Due to this reaction increase in tip current was observed, indicating that the positive feedback mode of SECM is under operation. The difference in tip current was correlated with the microstructure and the electrochemical activity of the dissimilar weld interface.

• 14. Jayamani, Jayaraj
Electrochemical Studies and XPS Analysis of the Surface of Zirconium-702 in Concentrated Nitric Acid With and Without Fluoride Ions2018In: Transactions of the Indian Institute of Metals, ISSN 0972-2815, E-ISSN 0975-1645, Vol. 71, no 3, p. 521-531Article in journal (Refereed)

Zirconium exhibited pseudo-passive behavior in fluorinated nitric acid (11.5 M HNO3 + 0.05 M NaF) as the current density measured from the electrochemical studies was several orders higher than the value in fluoride free nitric acid. Impedance studies on zirconium sample exposed in 11.5 M HNO3 for 240 h confirmed the formation of the passive film with high polarization resistance value and the calculated thickness of the film based on the capacitance value was about ~4.5 nm. On the other hand, in fluorinated nitric acid, the charge transfer resistance value associated with the zirconium dissolution process was dominant when compared to that of the film formation. Results of X-ray photoelectron spectroscopic investigations upheld the presence of ZrOF2 and ZrF4 and indicated that the protective oxide layer growth was restricted by the presence of fluoride ions.

• 15. Jayamani, Jayaraj
Passive film properties and corrosion behavior of Ni–Nb and Ni–Nb–Ta amorphous ribbons in nitric acid and fluorinated nitric acid environments2015In: Materials Chemistry and Physics, ISSN 0254-0584, E-ISSN 1879-3312, Vol. 151, p. 318-329Article in journal (Refereed)

Potentiodynamic polarization and electrochemical impedance studies revealed the passivation ability and corrosion resistance of Ni60Nb40 and Ni60Nb30Ta10 amorphous ribbons in 11.5 M HNO3 and 11.5 M HNO3 + 0.05 M NaF media at room temperature. Mott–Schottky analysis indicated the formation of n-type semiconducting passive film on these amorphous ribbon samples. Electrochemical parameters such as corrosion current density, passivation current density and donor density confirmed the passive film property of Ni60Nb30Ta10 amorphous ribbon to be superior to that of Ni60Nb40 amorphous ribbon. Weight loss was insignificant in Ni60Nb30Ta10 ribbon exposed to boiling 11.5 M HNO3 for 240 h. XPS analysis revealed that the origin of passivity of Ni60Nb40 and Ni60Nb30Ta10 amorphous ribbons in boiling 11.5 M HNO3 was due to the formation of a relatively thick passive film of ≈3 nm enriched with Nb2O5 and a thin passive film of ≈1.5 nm enriched with both Nb2O5 and Ta2O5 on the respective ribbon's surface. In boiling fluorinated nitric acid, Ni60Nb40 ribbon underwent severe dissolution owing to the instability of Nb-oxide passive film and the oxide/metal interface.

• 16. Jayamani, Jayaraj
Nanometer-sized porous Ti-based metallic glass2006In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 55, no 11, p. 1063-1066Article in journal (Refereed)

A porous Ti-based metallic glass has been fabricated by applying the principle of dealloying to the Y20Ti36Al24Co20 two-phase amorphous alloy. The initial microstructure of the two-phase glassy alloy consisted of Ti43.3Y3.7Al15.3Co37.7 and Y38.8Ti12.8Al37.1Co11.3 amorphous phases forming an interconnected structure. To fabricate the porous structure, the Y-rich phase has been selectively dissolved from the alloy using both chemical and electrochemical treatments in 0.1M HNO3 solution. The glassy nature of the porous Ti-based alloy was confirmed by transmission electron microscopy analyses.

• 17. Jayamani, Jayaraj
Nano-porous surface states of Ti–Y–Al–Co phase separated metallic glass2009In: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 17, no 12, p. 1120-1123Article in journal (Refereed)

A novel nano-porous state was fabricated at the surface of the Ti-based metallic glass by selective etching technique. By transforming the surface of the Ti45Y11Al24Co20 phase separated alloy from smooth towards rough with nano-pores in an oxidised state, the passivation behaviour of the glassy alloy in simulated body fluid condition was remarkably improved leading to corrosion resistance significantly higher than that of the Ti–6Al–4V alloy, one of the favourite candidate materials for implant applications.

• 18. Jayamani, Jayaraj
Studies on Corrosion of Titanium and Air-Oxidized Titanium in Fluorinated Nitric Acid2019In: Transactions of the Indian Institute of Metals, ISSN 0972-2815, E-ISSN 0975-1645, Vol. 72, no 7, p. 1917-1926Article in journal (Refereed)

Titanium (Ti) is a lustrous transition metal which possesses excellent corrosion resistance in several aggressive environments but is attacked by acidic fluoride media. In this work, the addition of fluoride ion to nitric acid on the corrosion behavior of Ti and air-oxidized Ti was studied. Air oxidation of Ti at 800 °C for 5 h resulted in the formation of an intact rutile TiO2 layer with a thickness of about 35 μm. The corrosion resistance was investigated from the polarization resistance ($$R_{\text{P}}$$RP) values which were obtained from linear polarization and electrochemical impedance spectroscopy (EIS) measurements. A decrease in the $$R_{\text{P}}$$RPvalue of Ti with the addition of fluoride ion in nitric acid was observed, and this indicated the formation of an unstable layer, which resulted in accelerated dissolution. The several order increase in the $$R_{\text{P}}$$RPvalue of air-oxidized Ti in nitric acid containing fluoride ions pointed the improved resistance to corrosion. The diffusivity of species through the air-oxidized TiO2 layer was estimated from the electrochemical equivalent circuit (EEC) analysis of EIS data. Even though the diffusivity increased by several orders with the addition of fluoride ions, air-oxidized Ti provided better protection against nitric acid containing fluoride ions than Ti. The corrosion rates of Ti and air-oxidized Ti in boiling nitric acid containing fluoride ions were also estimated from weight loss experiments. Even in boiling fluorinated nitric acid, air-oxidized Ti provided better corrosion protection, with corrosion rates of about 1000 times less than that of Ti.

• 19. Jayamani, Jayaraj
Microstructure and Corrosion Behavior of Hf-40 Wt Pct Ti Alloy in Nitric Acid Medium for Reprocessing Applications2016In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 47, no 9, p. 4393-4403Article in journal (Refereed)

The Hf-40 wt pct Ti (Hf-Ti) alloy was developed for neutron poison application in the spent nuclear fuel reprocessing plant. The furnace-cooled Hf-Ti sample exhibited the microstructure comprising equiaxed-α, lamellar-α, and feathery-α. The water-quenched Hf-Ti sample confirmed the presence of lath and internally twinned martensite. In comparison to the furnace-cooled sample, low corrosion current density and passivation current density values obtained for the water-quenched Hf-Ti in 6 M HNO3 at 298 K (25 °C) indicated better passivation ability. The martensitic structure exhibited high hardness (660 HV) and negligible corrosion rate in 6 M nitric acid at 298 K (25 °C). X-ray photoelectron spectroscopic (XPS) analysis confirmed that passivation behavior of this alloy was due to the protective passive film composed of TiO2 and HfO2.

• 20. Jayamani, Jayaraj
Electrochemical and passive characterization of a beta type Ti45Zr38Al17 cast rod in nitric acid medium2012In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 85, p. 210-219Article in journal (Refereed)

Electrochemical behavior of the recently developed beta-type Ti–38at% Zr–17at% Al (TZA) alloy has been studied in nitric acid medium for applications in nuclear reprocessing plant. Potentiodynamic polarization and electrochemical impedance studies revealed that the passive film formed on the TZA alloy was highly protective in nature. Mott–Schottky analysis of the passive film formed on TZA alloy showed n-type semiconducting properties. The electrochemical data confirmed the superior corrosion resistance of TZA alloy as the passive film formed exhibited better properties than that of the commercial pure Ti. XPS analyses confirmed that the stable passivity of TZA alloy in nitric acid was due to the formation of thick and protective passive layer, predominantly of ZrO2 with TiO2.

• 21. Jayamani, Jayaraj
Corrosion behaviour of Ni–Zr–Ti–Si–Sn amorphous plasma spray coating2006In: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 48, no 4, p. 950-964Article in journal (Refereed)

Ni59Zr20Ti16Si2Sn3 amorphous material was deposited by a vacuum plasma spraying technique onto steel and copper substrates in order to investigate their behaviour in a corrosive environment. For comparison, the same alloy was prepared as amorphous ribbons by melt spinning. The amorphous nature of the coatings and ribbons was characterized by XRD, DSC and TEM, while XPS and AES analyses were performed to understand the origin of passivation and mode of corrosion. The corrosion behaviour of the coating was studied in H2SO4 and HCl solutions open to air at room temperature. Potentiodynamic polarisation and galvanic coupling tests were carried out on the substrate and the coating. It was found that the formation of Zr-, Ti- and Si-rich passive oxide layers provide a high corrosion resistance in H2SO4 solution while the breakdown of the passive layer by chloride ion adsorption was responsible for pitting corrosion of the Ni59Zr20Ti16Si2Sn3 amorphous ribbons in HCl solution. Galvanic corrosion was the dominant corrosion mechanism for the coating/copper hybrid structure, in contrast to the Ni59Zr20Ti16Si2Sn3 amorphous coating, which efficiently protected the steel substrate in the corrosive environment.

• 22. Jayamani, Jayaraj
Corrosion behavior and surface film characterization of TaNbHfZrTi high entropy alloy in aggressive nitric acid medium2017In: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 89, p. 123-132Article in journal (Refereed)

Corrosion behavior of TaNbHfZrTi high-entropy alloy (HEA) was investigated in nitric and fluorinated nitric acid at ambient (27 °C) and boiling (120 °C) conditions. The alloy passivated spontaneously during potentiodynamic polarization in 11.5 M HNO3 at ambient condition. The corrosion rate was negligible in boiling 11.5 M HNO3, exposed for 240 h. Scanning electron microscopic (SEM) studies did not show any significant corrosion attack. The high corrosion resistance of TaNbHfZrTi HEA was attributed to its single phase bcc structure. X-ray photoelectron spectroscopic (XPS) analysis revealed that the protective passive film formed in boiling nitric acid was predominantly composed of Ta2O5, in contrast to the presence of ZrO2 and HfO2 in air-formed native film. Potentiodynamic polarization studies indicated a pseudo-passivation behavior of the HEA in 11.5 M HNO3 + 0.05 M NaF at ambient condition. In boiling fluorinated nitric acid, SEM images of TaNbHfZrTi HEA displayed a severely corroded morphology indicating the instability of the metal-oxides of the alloying elements. XPS investigations confirmed the presence of ZrF4, ZrOF2 and HfF4 along with un-protective oxides of Ta, Nb and Ti on the film, resulting in decreased corrosion resistance of TaNbHfZrTi HEA in fluorinated nitric acid.

• 23. Jayamani, Jayaraj
Microstructure, mechanical and thermal oxidation behavior of AlNbTiZr high entropy alloy2018In: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 100, p. 9-19Article in journal (Refereed)

The developed as-cast AlNbTiZr high entropy alloy (HEA) resulted in the formation of solid solution bcc dendrites along with the inter-dendritic Zr2Al intermetallic phase. Due to low-density of 5.74 g/cm3 and high yield strength of about 1650 MPa (under compression testing), the alloy exhibited high specific yield strength of approximately 287 kPa m3/kg. Further, the AlNbTiZr HEA showed high fracture strength of 1950 MPa and substantial plastic strain of approximately 17.9%. During the isothermal thermo-gravimetry analysis in the synthetic air, at 873, 973, 1073, 1173 and 1273 K for 3 h, the mass gain behavior of the alloy was nearly parabolic indicating the formation of the protective oxide layer. Further, the long-term oxidation studies of the AlNbTiZr HEA carried out in open air atmosphere for 50 h at 873, 1073 and 1273 K confirmed that the oxide layers formed were protective, intact, and spallation did not occur. Formation of complex oxides such as AlNbO4 and Ti2ZrO6 along with Al2O3, NbO, ZrO2, and TiO2 as confirmed by X-ray diffraction could have led to the sluggish oxidation kinetics of the AlNbTiZr HEA. In contrast, the HfNbTiZr HEA showed poor oxidation resistance at 873 K.

• 24. Jayamani, Jayaraj
Corrosion Behavior of Zirconium, Titanium, and Their Alloys in Simulated Dissolver Solution of Fast Breeder Reactor Spent Nuclear Fuel Using Zircaloy-4 Mock-Up Dissolver Vessel2015In: Nuclear Technology, ISSN 0029-5450, E-ISSN 1943-7471, Vol. 191, no 1, p. 58-70Article in journal (Refereed)
• 25. Park, J. M.
Tailoring of in situ Ti-based bulk glassy matrix composites with high mechanical performance2010In: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 18, no 10, p. 1908-1911Article in journal (Refereed)

In this study, we developed ductile dendrite-reinforced composites in the Ti–Zr–Ni–Cu–Be–(Nb) system. Although in situ composites have been successfully obtained by optimizing alloy composition and cooling rate, plasticity does not always occur. Only when the size, distribution, and elastic constants of the constituent phases are properly controlled, i.e. by creating homogeneously distributed dendrites with lower shear modulus than the glassy matrix, the composites exhibit large plasticity. By controlling the microstructural length scale and by tuning the intrinsic elastic constants of the constituent phases Ti-based bulk glassy matrix composites with good mechanical performance (high yield strength of ∼1.7GPa and large plasticity of ∼25%) have been achieved.

• 26. Poddar, C.
Corrosion assessment of Ni60 Nb30Ta10 metallic glass and its partially crystallized alloy in concentrated nitric acid environment2020In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 813Article in journal (Refereed)

The corrosion resistance and passive film properties of Ni60Nb30Ta10 metallic glass and partially crystallized ribbon were investigated in 11.5 M nitric acid. The XRD study confirms the formation of nano-crystalline α-Ni in the amorphous matrix during crystallization at 650 °C under vacuum for 1 h. The electrochemical impedance spectroscopy, potentiodynamic polarization, and Mott-Schottky studies on the metallic glass exhibited higher corrosion resistance compared to the partially crystallized ribbon. XPS confirms the enrichment of Nb2O5 and Ta2O5 in the passive film of the glassy structure, while α-Ni is depleted in a partially crystallized alloy that affected the corrosion resistance.

• 27. Poddar, Chiranjit
Effect of thermally grown amorphous oxide film on the corrosion resistance properties of Ni50Zr25Nb25 metallic glass in nitric acid medium2019In: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 113Article in journal (Refereed)

In the presents work, the effects of the surface oxidation of the Ni50Zr25Nb25 metallic glass on the corrosion behavior in nitric acid environment were investigated. The oxidation kinetics at 200 and 400 °C in air environment followed two-stage rate law. SEM and XPS investigation revealed the surface of thin (106 nm) amorphous oxide film composed of NiO, Ni2O3, ZrO2, and Nb2O5 when sample was oxidized at 200 °C. However, oxidation at 400 °C resulted in a thicker (721 nm) amorphous oxide film, enriched with only ZrO2 and Nb2O5. Potentiodynamic polarization results of the thermally oxidized metallic glass at 400 °C exhibited the wider passive range and significantly higher corrosion resistance in concentrated nitric acid when compared to the as-prepared and oxidized sample at 200 °C. After polarization at 2.2 V (Vs. Ag/AgCl), thermally oxidized sample at 400 °C exhibits smooth surface while the as-prepared MG undergoes a severe dissolution in 11.5 M nitric acid.

• 28. Poddar, Chiranjit
Oxidation behaviour of Ni60Nb30Ta10 metallic glass below its glass transition temperature2017In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 728, p. 1146-1152Article in journal (Refereed)

The oxidation behaviour of Ni60Nb30Ta10 metallic glass in air was investigated below its glass transition temperature (665 °C). The oxidation kinetics followed two-stage parabolic rate law at 450 and 550 °C. The parabolic rate constant increased with increase in the oxidation temperature. At 450 °C, a thin amorphous oxide film consisting predominantly Nb2O5 and Ta2O5, with traces of NiO and Ni2O3 was observed on the surface. At 550 °C, oxidation induced outward diffusion of Ni2+ and Ni3+ ions resulted in a thick oxide layer, containing extensive cubic NiO and monoclinic Ni2O3 with traces of metallic Ni on the surface. Interestingly, at 550 °C the Nb2O5 and Ta2O5 oxides were completely absent on the surface of the oxidised layer.

• 29. Poddar, Chiranjit
Passive film characteristics and corrosion behavior of thermally oxidized Ni60Nb30Ta10 metallic glass in nitric acid medium2019In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 783, p. 680-686Article in journal (Refereed)

X-ray photoelectron spectroscopy (XPS) analyses confirmed the formation of different oxides upon thermal air oxidation (TO) of Ni60Nb30Ta10 metallic glass (MG) below the glass transition temperature. At 450 °C (450 TO-MG), surface of the oxide film was enriched with Nb2O5 (65%) and Ta2O5 (26%). Similarly, at 550 °C (550 TO-MG), the upper oxide layer was composed with NiO (67%), Ni2O3 (28.5%) and small fraction metallic Ni (4.5%). The electrochemical corrosion behavior of the thermally oxidized metallic glass samples was studied in 1, 6 and 11.5 M nitric acid at room temperature. Mott-Schottky analyses in nitric acid solutions confirmed the n-type semiconducting nature of the film for as-spun MG. On the other hand, the films formed on 450 TO-MG, and 550 TO-MG exhibited insulating and p-type, respectively. The donor (n-type) and acceptor (p-type) densities increases as the solution concentration increased. In nitric acid solutions, the current densities values obtained from potentiodynamic polarization studies indicated that 450 TO-MG exhibited higher corrosion resistance than the as-spun and 550 TO-MG samples.

• 30. Poddar, Chiranjit
Effect of thermal oxidation on the oxide characteristic and corrosion behavior of Ni60Nb40 amorphous ribbon in nitric acid2019In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 479, p. 430-439Article in journal (Refereed)

The air-oxidation is a useful processing treatment to improve the corrosion resistance of Ni60Nb40 amorphous alloy. The oxidation kinetics of Ni60Nb40 amorphous ribbon follow two stage parabolic rate laws at 450 °C and 550 °C. The XPS analysis revealed that the surface of oxidized sample at 450 °C is enriched with Nb2O5, while oxidized sample at 550 °C, comprises of NiO and Ni2O3. The Mott-Schottky analyses confirmed the formation of n-type semiconducting film on the 450 °C oxidized sample in the nitric acid medium, while p-type semiconducting film on the 550 °C oxidized sample. Potentiodynamic polarization and EIS studies show that oxide film on the 450 °C oxidized sample exhibits highly protective barrier to the nitric acid when compared to the oxide film at 550 °C.

• 31. Thirathipviwat, P.
Dalarna University, School of Technology and Business Studies, Materials Technology.
A comparison study of dislocation density, recrystallization and grain growth among nickel, FeNiCo ternary alloy and FeNiCoCrMn high entropy alloy2019In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 790, p. 266-273Article in journal (Refereed)

The microstructural evolutions in terms of dislocation density, annealing twin density as well as with respect to microstructural changes due to recrystallization and grain growth were investigated in pure Ni, equiatomic FeNiCo alloy, and FeNiCoCrMn high entropy alloy (HEA) during the thermomechanical process. All samples were single phase and showed a face-centered cubic (FCC) lattice structure. This was maintained during thermomechanical processing comprising of cold swaging by 85% reduction of cross-sectional area and subsequent annealing at 800 °C. The level of dislocation accumulation during cold swaging increased with the number of constituent elements. The FeNiCoCrMn HEA obtained the highest dislocation density, followed by the FeNiCo and Ni, respectively. After the annealing at 800 °C for 0.5 h, all samples achieved the large fraction of recrystallized grains with minor fraction of substructured grains and no deformed grain. The FeNiCoCrMn HEA obtained the smallest recrystallized grain size (∼5 μm) after the annealing at 800 °C for 0.5 h. This could be a result of the highest dislocation density generated during cold swaging prior to the annealing. The prolonged annealing at 800 °C for up to 24 h led to a grain growth for all the samples, however, at different growth rates. The FeNiCoCrMn HEA revealed the lowest rate of grain growth, but the microstructural changes during the annealing were not significantly different between the FeNiCo and Ni samples. Besides the effect of the number of constituent elements, the type and the combination of constituent elements have an effect on the microstructural evolution during the annealing.

• 32. Vetrivendan, E.
Argon Shrouded Plasma Spraying of Tantalum over Titanium for Corrosion Protection in Fluorinated Nitric Acid Media2018In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 27, no 3, p. 512-523Article in journal (Refereed)

Argon shrouded plasma spraying (ASPS) was used to deposit a Ta coating on commercially pure Ti (CP-Ti) under inert argon, for dissolver vessel application in the aqueous spent fuels reprocessing plant with high plutonium content. Oxidation during plasma spraying was minimized by shrouding argon system. Porosity and oxide content were controlled by optimizing the spraying parameters, to obtain a uniform and dense Ta coating. The Ta particle temperature and velocity were optimized by judiciously controlling the spray parameters, using a spray diagnostic charge-coupled device camera. The corrosion resistance of the Ta coatings developed by ASPS was investigated by electrochemical studies in 11.5 M HNO3 and 11.5 M HNO3 + 0.05 M NaF. Similarly, the durability of the ASPS Ta coating/substrate was evaluated as per ASTM A262 Practice-C test in boiling nitric acid and fluorinated nitric acid for 240 h. The ASPS Ta coating exhibited higher corrosion resistance than the CP-Ti substrate, as evident from electrochemical studies, and low corrosion rate with excellent coating stability in boiling nitric, and fluorinated nitric acid. The results of the present study revealed that tantalum coating by ASPS is a promising strategy for improving the corrosion resistance in the highly corrosive reprocessing environment.

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