Oxide dispersion in high-entropy alloy (HEA) improves mechanical properties, corrosion resistance, and high-temperature oxidation. Several studies have been reported on oxide-dispersed high-entropy alloys prepared by Spark plasma sintering and hot pressing, but only a few on coating. This study aims to investigate a novel Fe-free Co1.7 Cr0.4Ni2.5Al2.4 Nb0.23 HEA dispersed with oxide (1 wt % Y2O3) for bond coat application in the thermal barrier coatings (TBC) System. The elemental powders in desired stoichiometry along with yttria were milled for 5 h in a planetary ball mill with a ball-to-powder ratio of 10:1 at a speed of 300 rpm followed by heat treatment at 1050 C for 1 h in argon. ODHEA bond coat and yttria-stabilized zirconia (YSZ) topcoat was coated by high-velocity oxygen fuel (HVOF) and air plasma spray on a nickel superalloy substrate, respectively. The coating shows the formation of FCC, BCC and Laves phase. The hardness and Young's modulus for the coating were approximately 610 HV and 172 GPa. Good oxidation resistance with an average TGO layer thickness of less than 7 μm was observed after 100 h of isothermal oxidation.

Solid oxide fuel cells (SOFCs) receive significant attention due to theirs high efficiency, environmental advantages, and fuel flexibility. The interconnect is a crucial part that connects each cell in the SOFC stack. The High Entropy Alloy (HEA) of FeCoCrNiMn0.5 is a promising candidate for an interconnect material at intermediate temperatures (600 °C to 800 °C) in Solid Oxide Fuel Cells (SOFC) due to its good thermal stability and electrical conductivity. However, FeCoCrNiMn0.5 HEA has a higher coefficient of thermal expansion (CTE) than the other interconnect materials (SUS 430, Crofer 22 APU) in SOFCs such as LSM (Lanthanum Strontium Manganite) cathode and NiO-YSZ anode. The high CTE in an HEA is undesirable as it mismatches with the CTE of cathodes and anodes in SOFC. The present study investigates the thermophysical properties and oxidation behavior of an Nb-contained HEA (Cr21Co21Fe21Ni21Mn11Nb5) to achieve reduced CTE and improved oxidation properties than the existing interconnect HEAs. The novel Cr21Co21Fe21Ni21Mn11Nb5 HEA was produced by the vacuum arc melting technique. The structure, chemical composition, mechanical properties, CTE, and thermal stability of the HEA were investigated. The oxidation study was also carried out by oxidizing the as-cast HEA at 800 °C for 25, 50, 100, and 200 hours. The study revealed that the presence of Nb reduces the CTE, increases oxidation resistance, and improves the mechanical properties of the HEA. The harmful Chromium oxide layer does not appear on the top of the thermally grown oxide layer during oxidation of the HEA. This passivation of the Chromium oxide layer will significantly reduce the Cr-poisoning in SOFC.

The present study aims at investigating the effect of pre-milling nickel (Ni) and aluminium (Al) powders on the sintering behaviour of NiAlFeCoCr high entropy alloys (HEA). As-milled NiAlFeCoCr HEA was prepared by mixing the Ni, Al, Fe, Co and Cr powders (in equiatomic ratio) for 10 h in a planetary ball mill. In case of pre-milled (NiAl)FeCoCr HEA, Ni and Al powders were initially milled for 5 h and this mixture was then further milled with Fe, Co and Cr powders for another 10 h. XRD, SEM-EDS, TG-DSC and Dilatometric analysis were performed for the characterization of these HEAs. The formation of FCC and BCC phases was observed in both, as-milled and pre-milled HEAs. The sintering behaviour (at 1000–1200 °C) of the HEAs was compared and observed that as-milled HEA sintered by viscous flow mechanism, which was absent in case of pre-milled HEA. An exothermic reaction observed in the as-milled HEA at 518 °C representing Ni and Al reaction, was absent in the pre-milled HEA, indicating that Ni and Al had reacted during the pre-milling process. The micro-Vickers hardness of as-milled HEA also increased from 638 ± 8.73 HV to 662 ± 12.24 HV upon pre-milling.

This study aims at using Fly Ash (FA) particles as reinforcement particles in the Mg matrix and studying the thermal properties of the novel Mg-3Ca/FA composites produced via liquid processing route. About 3, 6 and 9 wt.% of FA was added to these composites. SEM micrographs of composites show the presence of Mg2Ca at grain boundaries of α-Mg, as well as micropores and agglomerates of FA particles. Mg reacts with Fly Ash constituents such as SiO2 and Al2O3 to form MgO, CaO, Mg2Si, CaMgSi and MgAl2O4, which have lower thermal conductivity than the Mg-3Ca alloy. The in situ formed phases created large number of interfaces, which increased with an increase in FA concentration in Mg composites. Decomposition of oxides increases the number of solute elements (Al, Si, etc.) in Mg that induces lattice distortions and reduction in heat flow (HF), Cp and CTE of composites. Evidently, HF, Cp and CTE of FA-reinforced composites are due to lower thermal conductivity of FA and in situ formed metal oxides when compared to that of Mg-3Ca alloy. Addition of 9 wt.% FA to the alloy reduced the Cp (at 100 °C) from 0.4033 to 0.2842 J/g °C (i.e., by 29.53%) and CTE (at 200 °C) from 26.0 to 21.9 (× 10−6)/°C (i.e., by 15.57%).

Silver and its alloys undergo tarnishing with time, which is a black stain on the surface due to the formation of Ag2S. Developing a tarnish resistant Ag alloy was attempted by alloying Ag with elements that form a passive oxide layer on the surface. Germanium is proven to provide better tarnish resistance to sterling Silver alloy (92.5 wt% pure) which is available under the trade name of Argentium©. The present work investigates the tarnish resistance behavior of sterling silver alloy (92.5 wt% pure) containing various additions of Copper, Zinc, and Germanium. The alloys were prepared by melting and casting route, followed by Passivation Heat Treatment (PHT) to create a stable and continuous oxide layer. The temperature for PHT was optimized using thermogravimetry analysis (TGA) of the alloys prepared. Accelerated tarnish test was carried out to investigate the tarnishing behavior of alloy samples obtained before and after PHT. The samples were characterized using XRD, SEM-EDX, and micro-Raman Spectroscopy. The change in reflectance of the samples after tarnish test is determined using UV–Visible reflectance spectroscopy. The mechanism behind the tarnish resistance was derived using Density Functional Theory (DFT) by comparing sulphur (S2) and Oxygen (O2) adsorption energies (BE) of the alloying elements. The lower value of S2 (BE)/O2 (BE) indicates better oxidation and tarnish resistance. The ratio ranges between 222 % (Pure Ag) and 132 % (for Ag-4.2Cu-2.8Zn-1.4Ge) and the p-p between Ge and O has contributed to the reduction in the ratio.

Investigation of Solid Oxide Fuel Cells (SOFCs) is receiving great attention due to its higher efficiency and zero environmental pollution during operation. Interconnects are a critical part of the SOFC stack which connects the cells in series and combines the electricity produced. The present study aims to investigate High Entropy Alloys (HEAs) for interconnect application in intermediate temperature SOFC. Towards this, FeCoCrNi, FeCoCrNiMn0.1, FeCoCrNiMn0.5, and FeCoCrNiMn HEAs are prepared by vacuum arc melting and examined for its phase evaluation. Thermal stability, thermal expansion, resistivity, oxidation, and Area Specific Resistance (ASR) are investigated up to 800 °C. Oxidation studies show the formation of multicomponent oxide in the HEAs which suppresses the growth of Cr2O3 layer. FeCoCrNiMn0.1, FeCoCrNiMn0.5, and FeCoCrNiMn HEAs possess ASR values less than 100 mΩ.cm2 in the temperature range of 600–800 °C which ensure the superior performance of the SOFC stack.

The present work reports the effect of increasing concentration of antiferromagnetic element Cr in FeCoCrxNi2Al (x = 0.5, 1.5) high entropy alloy (HEA) on their magnetic properties. We find that the structure and composition of different phases present in HEA significantly affects its magnetic properties. Interestingly, the sample with Cr concentration x = 1.5 showed two times larger saturation magnetisation as compared to x = 0.5. Furthermore, the magnetisation versus temperature response shows multi-phase character and exhibits distinct behaviour in low temperature and high temperature regime in both the samples. The obtained soft ferromagnetic behaviour of these HEA is crucial for the development of a new class of HEA for various applications.

The effect of Ti0.1 and Ti0.1Si0.1 addition on the high temperature isothermal oxidation behavior of dense FeCoCrNiAl and FeCoCrNi2Al high entropy alloy (HEA) consolidated by vacuum hot pressing were investigated by X-ray diffraction, Scanning Electron Microscopy and Raman Spectroscopy. Mechanical properties such as hardness, Young's modulus, and thermal properties such as differential scanning calorimetry (DSC) and coefficient of thermal expansion (CTE) were also investigated. The weight gain recorded after isothermal oxidation for 5,25,50 and 100 h at 1050 °C was found to be parabolic in nature. X-ray diffraction analysis (XRD), as well as Raman spectroscopy analysis of HEA's oxidized at 1050 °C for 100 h, shows the formation of the Al2O3 phase. A homogeneous thin oxide scale without any discontinuity was observed throughout the cross-section. Ti and Si addition in 0.1 at. % improves mechanical properties, oxidation resistance, and reduces waviness of the oxide scale.

The present study aims to investigate non-stoichiometric Al1.4Co2.1Cr0.7Ni2.45Si0.2Ti0.14 high entropy alloy (HEA) as a bond coat material for the TBC (Thermal Barrier Coating) system. The mechanical activated synthesized HEA was sprayed on a Ni-based superalloy substrate by High-velocity oxy-fuel (HVOF) spraying, and 8 mol% Yttria Stabilized Zirconia (YSZ) was deposited on HEA by Air Plasma Spray (APS). X-Ray Diffraction (XRD) analysis and Scanning Electron Microscopy (SEM) were used to investigate the phases and microstructure of the as-synthesized HEA powder, Ni superalloy/HEA-bond coat, and Ni superalloy/HEA-bond coat/YSZ topcoat. The mechanical properties of the coating like microhardness, Young's modulus and residual stress between bond coat and YSZ top coat was evaluated using the Nano-Hardness Tester (NHT). The TBC system was investigated for cyclic oxidation at 1050 ℃ for 100 cycles, and its cross-sections were analyzed for TGO (Thermally grown oxides) layer composition, thickness and interdiffusion of elements. The properties of the TBC system containing HEA as a bond coat were compared with those of the conventional TBC system comprising of MCrAlY (AMDRY 365–4) as a bond coat. It was observed that HEA containing TBC displayed exceptional high temperature properties and were comparable to MCrAlY.

Materials have been very important from the beginning of rocketry. Compared to aircraft gas turbines, rocket engine turbines experience very severe thermal start/stop transients, high operating speeds, and hydrogen environments which result in the following unique requirements for rocket engine turbine blade materials: high thermal strain low-cycle fatigue strength; high mean stress high-cycle fatigue strength; resistance to hydrogen environment embrittlement; thermal shock resistance; and relatively short time stress-rupture/creep strength. Failure of the components potentially operating under severe physically stressed conditions results in burning or explosion, which in turn leads to the catastrophic failures. Although a considerable amount of work has been done in the particular area by coating of the substrate material with different coating compositions such as MCrAlY but a lot is left to be explored. High entropy alloy (HEA) possesses good creep strength, excellent oxidation resistance, hot corrosion and wear resistance, high hardness, superior thermal and chemical stability. The present study deals with the Al0.5CoCuCrFeNi high entropy alloy prepared by mechanical activated synthesis and coated on the substrate material by using HVOF (High Velocity Oxygen Fuel) method in order to enhance the overall performance of the components in comparison with the conventional ones. Presence of the coating is observed to have an increment in the surface hardness by 96% in comparison with the substrate material as measured by the Vicker's hardness apparatus and also an improvement in the hot corrosion resistance of the material. Other properties of the material thus obtained after coating such as chemical stability, wear resistance, density, oxidation etc. can be examined using different testing and experimentation techniques.

Mechanically alloyed high-entropy alloy (HEA) has taken considerable attention due to its ease of fabrication. Recent trend progresses towards the development of non-equiatomic HEAs to enhance the material properties compared to equiatomic alloys. Sintering behaviour of widely investigated equiatomic FeCoCrMnNi HEA has been reported. However, no report exists on the sintering kinetics of non-equiatomic HEA, when the concentration of a particular element is increased in the alloy powder. The present work attempts to study the isothermal and non-isothermal sintering behaviour of mechanically alloyed non-equiatomic Fe2CoCrMnNi HEA over a temperature range of 950–1100°C in an argon atmosphere. Activation energies for sintering and diffusivity parameters of Fe2CoCrMnNi HEA were calculated from dilatometric measurements through the sintering models. The result indicates the grain boundary diffusion as a dominating sintering mechanism for this alloy powder.

Present work reports the thermal stability and thermal expansion behavior of dual-phase FeCoCrNi2Al HEA prepared by Mechanical Activated Synthesis and consolidated by hot pressing. The thermal stability of the phases present in FeCoCrNi2Al HEA has been extensively studied using in-situ high-temperature X-ray diffraction (HT-XRD) in conjunction with dilatometry and differential scanning calorimetry (DSC). The DSC thermogram shows a single endothermic peak at 1430 °C (1703 K) which belongs to the melting point of the alloy. HT-XRD and dilatometry experiments were carried out from room temperature to 1000 °C (1273 K). HT-XRD study has shown that the room temperature FCC + BCC (face-centred cubic + body-centred cubic) phases remains stable up to 1000 °C (1273 K). Although the amount of BCC phase has increased above 800 °C (1073 K), no additional phase formation was observed in HT-XRD. The coefficient of thermal expansion (CTE) curve shows linear increment up to 1000 °C (1273 K) with a slight change in slope beyond 800 °C (1073 K). Theoretical CTE was computed using the lattice parameter of the FCC phase, obtained from HT-XRD, as a function of temperature and compared with experimental CTE. Third-order polynomial equation was fitted to the experimental CTE data and the constants were evaluated which can be used to predict the coefficient of thermal expansion of the alloy.

The current study is focused on the development of a novel nanofluid for efficient thermal management in the automotive sector. For this, novel Cr2AlC-based nanofluids were prepared and its properties were compared with conventional nanofluids prepared under similar condition. h-BN, MoS2, Al2O3, and Cr2AlC powders of <60 nm were prepared by high energy ball mill and were added into the EG fluid in 0.25 and 0.50 wt%. The nanofluids were investigated for viscosity, flash point, fire point, thermal conductivity, stability, and freezing temperature. The flash and fire points of EG increase with the addition of nanocrystalline powders. The viscosity of nanofluids decreases and thermal conductivity increases with increase in temperature. Among all addition, nanofluid containing 0.50 wt% of Cr2AlC shows maximum enhancement in the thermal conductivity and freezing temperature by 57.91% and 42.15%, respectively. It also shows a good stability up to 20 days.

The present study focuses on the influence of solid lubricants (MoS2, h-BN, Cr2AlC, and Cr2AlCAg) addition on the tribological properties of NiMoAl alloy in the range of 30 °C (Room Temperature, RT) to 400 °C. For this, NiMoAl and NiMoAl with 20 wt% of different solid lubricant powders were prepared and coated on a stainless steel substrate by High-Velocity Oxy-Fuel (HVOF) spraying. The coefficient of friction (COF) of NiMoAl coating at RT and 400 °C is 0.72 ± 0.05 and 0.47 ± 0.03, respectively. The addition of 20 wt% MoS2, h-BN, Cr2AlC, and Cr2AlCAg in NiMoAl reduces the COF by (50% & 30%), (47% & 45%), (37% & 49%) and (64% & 66%), respectively at RT & 400 °C. Characterization of the worn-out surfaces shows that the tribo-chemical by-products such as Ni3S2, Cr7C3, and Ag2MoO4 act as a friction modifier and reduces the COF. NiMoAl-20 wt% Cr2AlC coating shows a large decrease in COF with an increase in temperature.

The present study focused on the development of NiMoAl-based self-lubricating composites using solid lubricants as the second phase by powder metallurgy. For this, Cr2AlC MAX phase, Cr2AlC-Ag, and MoS2 powders were mixed with the NiMoAl-based matrix and subsequently hot pressed to produce bulk composite samples. The average hardness and wear resistance of the matrix were found to be increased with the addition of MoS2, Cr2AlC MAX phase, and Cr2AlC-Ag powder to the NiMoAl matrix. The addition of Cr2AlC to NiMoAl was more effective in improving the wear resistance than MoS2. The addition of Cr2AlC and Cr2AlC-Ag has increased the hardness by about 75% than that with the addition of NiMoAl alloy. A scanning Kelvin probe system was used to study the surface properties of the tribofilm in detail through work function mapping from the edge area to the wear area (groove). Among all the samples, the one with the addition of Cr2AlC-Ag powder to the NiMoAl matrix possesses the best tribo-mechanical properties. Cr2AlC-Ag composite addition to NiMoAl was found to decrease the wear rate by one-third and to reduce the coefficient of friction by one-fourth, compared to the base NiMoAl alloy. This was attributed to the high-sintered density and formation of strong tribofilms consisting of mixed oxides such as Ag2MoO4 and Al2O3, as confirmed by micro Raman spectra.

The tribo-mechanical properties of NiMoAl-Cr2AlC MAX phase composite coatings on stainless steel substrate have been investigated. NiMoAl with different amounts of Cr2AlC (10, 20, 50 and 100 wt.%) were prepared by turbo-mixing and deposited by High-Velocity Oxy-Fuel (HVOF) method on stainless steel substrate. The phase composition, microstructure, chemical composition, tribological and mechanical properties of the coatings were analyzed using x-Ray Diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM), Energy-Dispersive x-ray analysis (EDAX), pin-on-disk wear testing rig and nanohardness tester, respectively. The worn surfaces were analyzed by metallurgical optical microscope, FESEM and three-dimensional surface profiler to understand the wear behavior in detail. The addition of the Cr2AlC MAX phase in NiMoAl enhances the mechanical properties and reduces the surface roughness and porosity. NiMoAl-20 wt.% Cr2AlC and Cr2AlC coatings containing equal amounts of oxygen and carbon in the tribofilm show the low coefficient of friction (COF) and wear rate. The addition of the Cr2AlC MAX phase in the NiMoAl matrix up to 20 wt.% reduces the wear rate by one order of magnitude and enhances the coating life by 7000 twist fatigue cycles.

The paper aims to investigate standalone FeCoCrNi2Al, FeCoCrNiAl0.3, FeCoNiAlTi0.4 and NiCoCrAlSi high entropy alloys (HEA) as a possible bond coat material for thermal barrier coating (TBC) system. For this high entropy alloys prepared by mechanical activated synthesis (MAS) were densified by spark plasma sintering (SPS). MAS HEAs were investigated for phase formation, melting temperature and coefficient of thermal expansion by X-ray diffractometer (XRD), Differential scanning calorimetry (DSC) and Dilatometer respectively. Isothermal oxidation of sintered samples was carried out at 1050 °C for a period of 5, 25, 50, 100, 200 and 300 h in the air. The formation and growth of thermally grown oxides (TGO) were investigated by Raman spectroscopy, X-Ray Diffraction, and Scanning electron microscopy (SEM). The oxidation study shows that FeCoCrNi2Al and FeCoNiAlTi0.4 HEA follow parabolic rate weight gain due to the formation of TGO enriched in Al2O3. Discontinuous weight changes due to the formation of CoAl2O4, NiCrFeO4, and Cr2O3 phases were observed in FeCoCrNiAl0.3 HEA. TGO enriched in Al2O3 and NiAl2O4 were observed in NiCoCrAlSi HEA, whereas FeCoNiAlTi0.4 HEA shows the formation of TGO enriched in Al2O3, NiAl2O4, Ti2O3, and Al2O5Ti. Increase in coefficient of thermal expansion (CTE) with increasing temperature is observed for FeCoCrNi2Al and FeCoNiAlTi0.4 HEA. FeCoCrNi2Al HEA showing average CTE of 15.16 ± 0.25 × 10−6/K, good mechanical properties, and containing α-alumina TGO layer, makes it a potential candidate for a bond coat material.

The paper aims to investigate the effect of elements addition, its enthalpy of mixing, crystal structure and atomic size difference on the formation of solid solution phase during the synthesis of high entropy alloy (HEA) by mechanical alloying. For this CoCrFeNiX and CoCuFeNiX (where X = Ti, Zn, Si, Al), alloys were prepared by mechanical alloying. The phases formed during mechanical alloying were characterised by X-ray diffraction analysis, transmission electron microscopy and differential scanning calorimetry. Titanium and Aluminium addition facilitate solid solution formation during mechanical alloying. Formation of a BCC and FCC solid solution phase was observed for CoCrFeNiX and CoCuFeNiX system (where X = Ti, Al), respectively. Single solid solution phase was not observed for CoCrFeNiZn, CoCrFeNiSi, CoCuFeNiZn and CoCuFeNiSi HEA up to 20 hours of milling.

The present investigation focuses on the effect of Cr 2 AlC MAX phase addition on erosion and oxidation-induced crack healing behavior of Ni–Mo–Al alloy. For this, Ni–Mo–Al and 20 wt% Cr 2 AlC-blended Ni–Mo–Al powders were coated by Air Plasma Spray (APS). For oxidation-induced crack healing studies, the samples were heat treated at 500, 800, and 1100°C in the air for 5 hours. The heat-treated samples were analyzed by X-Ray Diffraction (XRD) analysis, Scanning Electron Microscopy (SEM), and Energy Dispersive Spectroscopy (EDS) for the phases, morphology, and composition. Erosion behavior studies were carried out at 30, 250, 500, 800, and 1000°C temperatures. The average hardness was obtained to be 400 ± 10 HV for Ni–Mo–Al coating and 580 ± 10 HV for 20 wt% Cr 2 AlC-blended Ni–Mo–Al coating. The addition of Cr 2 AlC MAX into Ni–Mo–Al matrix reduces the overall erosion rate and improved the crack healing ability. This was attributed to the presence of in-situ-formed Cr 7 C 3 and Al 2 O 3 phases.

The present investigation is focused on the enhancement of tribological properties of 5W-30 engine oil by the addition of Cr2AlC MAX phase nanolamella. The anti-wear properties of engine oil were investigated by four-ball test rig, using stainless steel balls. The obtained results were compared with h-BN and MoS2 nanoparticles incorporated 5W-30 engine oils. Cr2AlC added nano-fluid (modified lubricating oil) enhances anti-wear properties significantly and increased oil film strength (OFS) of base oil to almost three times. Among all, Cr2AlC nanolamella additivated engine oil shows low coefficient of friction (COF) and wear, as compared to that of h-BN and MoS2 modified oils. Cr2AlC modified oil yields least iron content in the oil after the tribo-test. This could be attributed to the high aspect ratio of Cr2AlC crystals than that of MoS2 and h-BN crystals, and the formation of relatively high strength tribofilms. Among all the prepared lubricating oil, Cr2AlC nanolamella additivated engine oil possesses higher stability.

The present study aims to develop dense FeCoCrNi2Al high entropy alloy (HEA) coating of thickness ≅ 200 μm by high velocity oxy-fuel (HVOF) process. Studies on the microstructure and mechanical properties like microhardness, erosion resistance of the HVOF coated FeCoCrNi2Al HEA has not been reported by any investigator. An adherent coating has been deposited displaying a lamellar microstructure. The X-ray diffractogram of the coating revealed the formation of a major FCC and a minor BCC phase with small amount of oxide. The oxide phase was confirmed to be Al2O3 using Raman spectroscopy. The microhardness of the coating is found to be 600 ± 30 VHN with no crack formation upto a load of 1 kgf. The erosion resistance of the HEA coated steel was evaluated upto a temperature of 800 °C. The coating displays good erosion resistance and the depth of penetration of the erodent was well within the coating thickness with no delamination of the coating, thereby making it suitable for high temperature applications.

The aim of the present study is to investigate the effect of Cr 2 AlC additions on the tribological properties of Piston Ring coated with Ni-Mo-Al alloy. For this Cr 2 AlC MAX phase was blended with Ni-Mo-Al alloy powder in different proportions (10 wt%, 20 wt% and 50 wt%) and coated on the stainless steel piston ring by Air Plasma Spraying (APS). During coating Cr 2 AlC MAX reacts with air and forms Cr 7 C 3 and Al 2 O 3 phases. The in-situ formation of Cr 7 C 3 and Al 2 O 3 was observed to strengthen the alloy. 20 wt% Cr 2 AlC additions to the Ni-Mo-Al alloy yields a good combination of properties, such as improved adhesion, hardness and wear resistance. Composite coating was found to be stable during the exfoliation test of the coated ring. Coating life cycles were found to be nearly doubled by MAX phase addition, as assessed through the twist-fatigue study. These improved properties could be attributed to the finely distributed oxides (alumina) and chromium carbides (Cr 7 C 3 ) within the coated layer, which were formed in-situ during plasma spraying.

The present research aims to investigate the effect of oxide dispersion on the synthesis of High-Entropy (HE) alloy and its properties. For this FeNiCoCrAlMn High-Entropy (HE) alloy dispersed with 2 wt percentage alumina (Al2O3) was synthesized by mechanical activated synthesis. The mechanical activation was carried out by milling the elemental powder mixture of aluminum, cobalt, chromium, iron, nickel and manganese in an equiatomic ratio up to 20 h 2 wt% of Al2O3was added during mechanical alloying to obtain oxide dispersed HE alloy. Upon pyrolysis at high temperature FCC emerged as major phase in both alloys (with and without oxide dispersion). The alumina dispersed HE alloy shows increase in size of AlNi and CrFeMn rich phase after sintering, relatively less thermal expansion coefficient and better oxidation resistance than HE alloy without oxide dispersion. Hardness was found to be doubled after adding 2% alumina. The obtained result indicate that oxide dispersed HE alloy can be useful material for high temperature coating application.

Nanofluids have garnered the attention of material science and heat transfer fraternity across the world for the reported enhancement of their thermal properties and the amenability for a change of their rheological properties under external influence. Of the various nanofluids that have been studied widely, nano-silica fluids comprise a predominant fraction. The alterations in the morphological characteristics of the nano-silica fluids brought about by mechanical treatment of the samples influence their chemical and rheological behaviours. The present work involves the study of milling parameters on the rheological behaviours of silica particles. The micron size silica is reduced to nano size by ball milling, done by 0-20 h at 300 rpm in Fritsch P5 planetary ball mill. This milled powder will be characterized by XRD and SEM for it crystallite size and morphology. Thus prepared silica on treatment with ethylene glycol and water mixture enhances its dispersion in fluids.

The sol-gel technique was used to prepare zinc oxide nanoparticles doped with silver ions. The sample phase and microstructure were characterized by different techniques such as X-ray diffraction, field emission scanning electron microscopy, also absorption and metal composition were finding by UV-visible spectra, EDAX, respectively. In this paper, we tried with ZnO/Ag nanocomposite with pH 9 and varying the composition of silver ions. X-ray diffraction study showed that increasing in intensity of silver with the silver concentration, which indicates the formation of ZnO/Ag composite. The prepared sample maintains the good morphology and microstructure of pure ZnO. Sensing results showing that ZnO/Ag nanocomposite shows better sensing properties. 5 wt % AgNO3 and 0.5 g of ZnO with adding 1 mol NaBH4 in 5 mL of ZnO/Ag composite (pH 9) were giving better sensing output. The fabricated device showed that high sensor response of 72 % at 1000 ppm and the low detection limit is 5 ppm.

The most commonly investigated high entropy alloy, AlCoCrCuFeNi, has been chosen for optimization of its microstructural and mechanical properties by means of compositional changes and heat treatments. Among the different available optimization paths, the decrease of segregating element Cu, the increase of oxidation protective elements Al and Cr and the approach towards a γ-γ' microstructure like in Ni-based superalloys have been probed and compared. Microscopical observations have been made for every optimization step. Vickers microhardness measurements and/or tensile/compression test have been carried out when the alloy was appropriate. Five derived alloys AlCoCrFeNi, Al23Co15Cr23Cu8Fe15Ni16, Al8Co17Cr17Cu8Fe17Ni33, Al8Co17Cr14Cu8Fe17Ni34.8Mo0.1Ti1W0.1 and Al10Co25Cr8Fe15Ni36Ti6 (all at.%) have been compared to the original AlCoCrCuFeNi and the most promising one has been selected for further investigation.

Widely investigated AlCoCrCuFeNi high entropy alloy has been chosen for optimization of the microstructural and mechanical properties. Different paths have been chosen for optimization; namely the decrease of segregating element Cu, the increase of oxidation protective elements Al and Cr and the approach towards a γ-γ' microstructure as in Ni-based superalloys. Microscopical observation has been made for each optimization step and compared with results obtained by Vickers microhardness measurements. Out of five derivate alloys: AlCoCrFeNi, Al23Co15Cr23Cu8Fe15Ni16, Al8Co17Cr17Cu8Fe17Ni33, Al8Co17Cr14Cu8Fe17Ni33Mo1Ti1W1 and Al10Co25Cr8Fe15Ni36Ti6, the most promising one has been chosen for further investigation.

Nanocrystalline pure and Gd3+ doped CoWO4 nanostructures were synthesized by single step chemical precipitation technique. The framework substitution of Gd in CoWO4 nanoparticles was established by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) techniques. XRD pattern reveals the pure and doped CoWO4 nanoparticles belong to the monoclinic structure. The increase in Gd doping enhanced the ‘blue-shift’ in the UV-Vis absorption spectra. Electron microscopy studies clearly evidence the formation of round edged nanocubes with an average particle size of 60–80 nm, emerges in the polycrystalline nature. UV–Visible absorption spectra of Gd doped CoWO4 nanocrystals shows a strong absorption peak at 278nm. Nonlinear optical transmission studies of the nanocomposites is measured using the open aperture Z-scan technique employing 7 nanosecond laser pulses at 532 nm. Experimental results show that both pure CoWO4 and Gd doped nanoparticles exhibit excellent optical limiting performance.

Mechanically alloyed in situ nano Al3Ti dispersed Al50Ti40Si10 amorphous matrix alloy powder was consolidated by hot isostatic pressing in the temperature range of 300-600°C with a pressure of 1.2GPa and holed at this temperature for 10min. Microstructural and phase evolution studies of the mechanically alloyed powder and sintered compacts were conducted by X-ray diffraction and transmission electron microscopy. Alloy sintered at 500°C recorded an excellent combination of high hardness (8.61GPa), compressive strength (1212MPa) and Young's modulus (149GPa). Furthermore, these results have been compared with that of earlier studies based on conventional sintering (CCS), and high pressure sintering (HPS). © 2012 Elsevier B.V.

Molybdenum and its alloys are potential materials for high-temperature applications. However, molybdenum is susceptible to embrittlement because of oxygen segregation at the grain boundaries. In order to alleviate the embrittlement small amounts of zirconium were alloyed to a solid solution of Mo-1.5Si alloy. Two Mo-based alloys, namely Mo-1.5Si and Mo-1.5Si-1Zr, were investigated by the complementary high-resolution methods transmission electron microscopy and atom probe tomography. The Mo-15Si alloy shows a polycrystalline structure with two silicon-rich intermetallic phases Mo5Si3 and Mo3Si located at the grain boundaries and within the grains. In addition, small clusters with up to 10 at% Si were found within the molybdenum solid solution. Addition of a small amount of zirconium to Mo-1.5Si leads to the formation of two intermetallic phases Mo2Zr and MoZr2, which are located at the grain boundaries as well as within the interior of the grain. Transmission electron microscopy shows that small spherical Mo-Zr-rich precipitates (<10 nm) decorate the grain boundaries. The stoichiometry of the small precipitates was identified as Mo2Zr by atom probe tomography. No Si-enriched small precipitates were detected in the Mo-1.5Si-1Zr alloy. It is concluded that the presence of zirconium hinders their formation. © 2010 Elsevier B.V.

Splat-quenched, as-cast and aged (2 h at 600 1C after casting) AlCoCrCuFeNi high entropy alloys were investigated by means of transmission electron microscopy and three-dimensional atom probe (3D-AP). 3D-AP revealed anti-correlated fluctuations of the Cr and Fe-Co compositions in Cr-Fe-Co-rich regions of the as-cast alloy. The ferromagnetic behavior of AlCoCrCuFeNi high entropy alloy was correlated with the decomposition of the Cr-Fe-Co-rich regions into ferromagnetic Fe-Co-rich and antiferromagnetic Cr-rich domains, the size of which was determined by statistical analysis of 3D-AP data. The splat-quenched alloy showed a softer magnetic behavior as compared to the as-cast and aged alloys. The aged alloy possessed a higher saturation magnetization and coercivity as compared to the as-cast alloy. © 2010 Elsevier B.V.

The decomposition of an equiatomic AlCoCrCuFeNi high-entropy alloy produced by splat quenching and casting was investigated by the analytical high resolution methods: transmission electron microscopy and three-dimensional atom probe. It could be shown that splat-quenched alloy consisted of an imperfectly ordered body-centred cubic phase with a domain-like structure, whereas normally cast alloy formed several phases of cubic crystal structure. The cast alloy decomposed into both dendrites and interdendrites. A detailed local compositional analysis carried out by atom probe within the dendrites revealed that the alloying elements in the Ni-Al-rich plates and Cr-Fe-rich interplates are not randomly distributed, but segregate and form areas with pronounced compositional fluctuations. Cu-rich precipitates of different morphologies (plate-like, spherical and rhombohedron-shaped) could also be found in the dendrites. The results are discussed in terms of segregation processes governed by the enthalpies of mixing of the binary systems. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

This study reports synthesis of Al65Cu20Ti15 amorphous alloy by mechanical alloying and consolidation of the powder mass by pulsed plasma sintering. During sintering, several intermetallic phases precipitate from the amorphous matrix and cause a significant increase in nano-hardness and elastic modulus. Microstructure in as-milled and sintered conditions was characterized by X-ray diffraction, scanning/transmission electron microscopy and differential scanning calorimetric. Among various conditions of sintering, the composites pulse plasma, sintered at 500C, show the high compression strength (1745 MPa) and high indentation fracture toughness (4.96 MPa m1/2); although, the maximum density (3.73 Mg/in3), nano-hardness (14 GPa) and Young's modulus (208 GPa) in the present alloy have been obtained in the composites pulse plasma sintered at 600C.

This study concerns laser sintering of mechanically alloyed Al50Ti40Si10 powders with partially amorphous and nanocrystalline microstructure. Following laser irradiation with selected parameters, microstructure and mechanical properties on top surface and cross-sectional plane were evaluated by scanning and transmission electron microscopy, X-ray diffraction, hardness measurement and fretting wear testing. Comparison between the thermal profile predicted by a simple analytical model and relevant microstructural parameters including useful depth of sintering suggest that laser assisted sintering could be a useful strategy to consolidate mechanically alloyed powder with novel microstructure into solid components. © 2008 Elsevier B.V. All rights reserved.

Resistance to wear is an important factor in design and selection of structural components in relative motion against a mating surface. The present work deals with studies on fretting wear behavior of in situ nano-Al3Ti reinforced Al-Ti-Si amorphous/nanocrystalline matrix composite, processed by high pressure (8 GPa) sintering at room temperature, 350, 400 or 450 °C. The wear experiments were carried out in gross slip fretting regime to investigate the performance of this composite against Al2O3 at ambient temperature (22-25 °C) and humidity (50-55%). The highest resistance to fretting wear has been observed in the composites sintered at 400 °C. The fretting wear involves oxidation of Al3Ti particles in the composite. A continuous, smooth and protective tribolayer is formed on the worn surface of the composite sintered at 400 °C, while fragmentation and spallation leads to a rougher surface and greater wear in the composite sintered at 450 °C. © 2009 Elsevier B.V.

Attempts have been made to study the effect of milling energy and type of grinding media on the mechanical activation during the production of MoSi2 from a reaction between Mo and Si3N4. Powder mixtures of Mo and Si3N4 in the molar ratios of 1:1, 1:2 and 1:3 were ball milled using WC, steel, and ZrO2 grinding media for mechanical activation. In order to evaluate the results obtained after high-energy ball milling and pyrolysis of these milled powder mixture, milling parameters have been converted to two energy parameters, namely, impact energy of the ball and total energy of milling. The optimum impact energy of ball required for mechanical activation of Mo + xSi3N4 (x = 3, 2, 1) powder mixtures by WC grinding media was found to be in the range of 0.145-0.173 J, which leads to a reduction of pyrolysis temperature by 100-200 °C. Samples milled with higher impact energy than the optimum range led to formation of undesirable phases, which dilutes the effect of mechanical activation. Samples milled with both steel and ZrO2 grinding media having lower impact energies than the optimum show the presence of enormous contamination during milling and phases like ZrSi2, Fe3Si and Fe5Si3 were observed after pyrolysis without any significant reduction in pyrolysis temperature required for MoSi2 synthesis. © 2008 Elsevier Ltd. All rights reserved.

Si3N4-MoSi2 in situ composite has been synthesized by reacting powders of molybdenum (Mo) and silicon nitride (Si3N4). Mo and Si3N4 powders mixture in a molar ratio of 1:3 were ball milled for 0-100 h. The milled and unmilled powder mixtures were reacted at different temperatures between 1000 and 1600 °C in an argon atmosphere. The effect of mechanical activation (MA) induced by milling has been studied through X-ray diffraction (XRD), differential thermal analysis (DTA), and thermo-gravimetric analysis (TGA). No peaks of Mo in the XRD pattern have been observed after 70 h of milling. The crystallite size of the Mo has been found to be the lowest (41 nm) after milling for 30 h. Similarly, a 100 nm lowest size of crystallite of Si3N4 was observed after milling for 50 h. DTA and TGA results show that the reaction between Mo and Si3N4 enhances with increase in milling time. Milling for 10 h lowers the pyrolysis temperature by 150 °C. Additional milling upto 100 h does not lead to further reduction in the pyrolysis temperature. The intensities of peaks of MoSi2 in the pyrolysed samples increased with increase in milling time. MoSi2 particles of size less than 1 μm were observed to be uniformly distributed through out the Si3N4 matrix. © 2004 Elsevier B.V. All rights reserved.

Mo and Si3N4 powder mixtures in the molar ratio of 1:3 were mechanically activated by high-energy ball milling for 0-100h. No MoSi2 formation was observed during milling. DTA and TGA results showed that the reaction between Mo and Si3N4 enhanced with increase in milling time. The milled powder mixtures were reacted at different temperatures between 1000 and 1400°C for the synthesis of Si 3N4-MoSi2 in situ composite. Complete conversion of Mo in 10-100h milled sample into MoSi2 has been observed after pyrolysis at 1400°C for 1h. In the unmilled (0h) sample lower silicide of Mo i.e., Mo5Si3 has been detected. In the mechanically activated samples, after 10h of milling, no Mo5Si 3 formed after reaction at 1400°C for 1h. The intensities of peaks of MoSi2 in the pyrolysed samples increased with increase in milling time. In the pyrolysed sample both nano- and sub-micron size MoSi 2 particles were observed to be uniformly distributed through out the Si3N4 matrix. © 2004 Elsevier B.V. All rights reserved.

Attempts are made to fabricate Si3N4 - MoSi2 in situ composites by reactive milling and reactive sintering of milled powders. 10 hours of milling Mo and Si3N4 powder mixtures shows the substantive increase in reactivity, which reaches to maximum after 30 hours of milling. The milling however even up to 104 hours does not by itself lead to the formation of MoSi2 phase. The pyrolysis of milled powder mixture with varying amount of sintering aid in the temperature range of 1000-1400 °C indicates that MoSi2 phase forms only at 1400 °C in argon, whereas 1350 °C in vacuum. SEM analysis of milled and pyrolised samples shows uniform distribution of 0.5-1 micron size MoSi2 in Si3N4 matrix. Longer hours of milling often leads to formation of SiC and it also played by large amount of WC contaminations. © 2003 Advanced Study Center Co. Ltd.