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 (1wt % Y2O3) for bond coat application in the thermal barrier coatings (TBC) System. The elemental powders in desired stoichiometry along with yttria were milled for 5h in a planetary ball mill with a ball-to-powder ratio of 10:1 at a speed of 300rpm followed by heat treatment at 1050°C for 1h 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 172GPa. Good oxidation resistance with an average TGO layer thickness of less than 7µm was observed after 100h of isothermal oxidation.

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.

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, FeCoCrNiMn 0.1, FeCoCrNiMn 0.5, 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 Cr 2 O 3 layer. FeCoCrNiMn 0.1, FeCoCrNiMn 0.5, and FeCoCrNiMn HEAs possess ASR values less than 100 m?.cm 2 in the temperature range of 600–800 °C which ensure the superior performance of the SOFC stack.

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 MgCa at grain boundaries of ?-Mg, as well as micropores and agglomerates of FA particles. Mg reacts with Fly Ash constituents such as SiO and AlO to form MgO, CaO, MgSi, CaMgSi and MgAlO, 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)/°C (i.e., by 15.57%).

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The present work reports the effect of increasing concentration of antiferromagnetic element Cr in FeCoCrNiAl (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 Ti 0.1 and Ti 0.1 Si 0.1 addition on the high temperature isothermal oxidation behavior of dense FeCoCrNiAl and FeCoCrNi 2 Al 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 Al 2 O 3 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 Al 1.4 Co 2.1 Cr 0.7 Ni 2.45 Si 0.2 Ti 0.14 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.

Present work reports the thermal stability and thermal expansion behavior of dual-phase FeCoCrNi 2 Al HEA prepared by Mechanical Activated Synthesis and consolidated by hot pressing. The thermal stability of the phases present in FeCoCrNi 2 Al 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.

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 FeCoCrMnNi HEA over a temperature range of 950–1100°C in an argon atmosphere. Activation energies for sintering and diffusivity parameters of FeCoCrMnNi 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.

The present study focuses on the influence of solid lubricants (MoS 2, h-BN, Cr 2 AlC, and Cr 2 AlCAg) 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% MoS 2, h-BN, Cr 2 AlC, and Cr 2 AlCAg 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 Ni 3 S 2, Cr 7 C 3, and Ag 2 MoO 4 act as a friction modifier and reduces the COF. NiMoAl-20 wt% Cr 2 AlC 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-CrAlC MAX phase composite coatings on stainless steel substrate have been investigated. NiMoAl with different amounts of CrAlC (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 CrAlC MAX phase in NiMoAl enhances the mechanical properties and reduces the surface roughness and porosity. NiMoAl-20 wt.% CrAlC and CrAlC 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 CrAlC 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 present investigation is focused on the enhancement of tribological properties of 5W-30 engine oil by the addition of Cr 2 AlC 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 MoS 2 nanoparticles incorporated 5W-30 engine oils. Cr 2 AlC 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, Cr 2 AlC nanolamella additivated engine oil shows low coefficient of friction (COF) and wear, as compared to that of h-BN and MoS 2 modified oils. Cr 2 AlC modified oil yields least iron content in the oil after the tribo-test. This could be attributed to the high aspect ratio of Cr 2 AlC crystals than that of MoS 2 and h-BN crystals, and the formation of relatively high strength tribofilms. Among all the prepared lubricating oil, Cr 2 AlC nanolamella additivated engine oil possesses higher stability.

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.