Static and cyclic oxidation of Nb-Cr-V-W-Ta high entropy alloy in air from 600 to 1400℃

An oxidation resistance study has been made on Nb-Cr-V-W-Ta high entropy alloy in a range of temperature from 600 to 1400℃in air.Static oxidation study has been performed for either(a)12 or 24 h of heating time or(b)3 or 10℃/min heating rates to the desired oxidation temperature.Cyclic oxidation study conducted for three and a half days has been conducted at 600,700,and 800℃using 12 h of heating cycles.The alloy can withstand the cyclic oxidation process with only a reasonable loss of alloy.The identification of oxides indicates crystals of W and Ta oxides in cylindrical form while Nb and Cr oxides show a nodular or granular morphology at both 1000 and 1200℃while and additional of oxide of V in whisker forms at 1200℃.

Fabrication,characterization and optimization of high conductivity and high quality nanocrystalline molybdenum thin films

The present study investigated the influence of substrate temperature(Ts)and working pressure(P(Ar))on tailoring the properties of nanocrystalline(nc)molybdenum(Mo)films fabricated by radio-frequency magnetron sputtering.The structural,morphological,electrical and optical properties of nc-Mo films were evaluated in detail.The Mo films exhibited(110)orientation with average crystallite size varying from 9 to 22(±1)nm on increasing Ts.Corroborating with structural data,the electrical resistivity decreased from 55μΩcm to 10μΩcm,which is the lowest among all the Mo films.For Mo films deposited under variable P(Ar).the(110)peak intensity decrement coupled with peak broadening on increasing P(Ar).Lower deposition pressure yielded densely packed thin films with superior structural properties along with low resistivity of 15μΩcm.Optimum conditions to produce high quality Mo films with excellent structural,morphological,electrical and optical characteristics for utilization in solar cells as back contact layers were identified.

Effects of yttria content on the CMAS infiltration resistance of yttria stabilized thermal barrier coatings system

The effects of YO(1.5)doping in yttria-zirconia based thermal barrier coatings(TBCs)against CMAS interaction/infiltration are discussed.The TBCs with an YO(1.5)content ranging from 43–67 mol.%(balance Zr O2)were produced by electron beam physical vapor deposition(EB-PVD)techniques.The results reveal a trend of higher apatite formation probability with the higher free YO(1.5)available in the yttriazirconia system.Additionally,the infiltration resistance and amount of consumed coating appears to be strongly dependent on the YO(1.5)content in the coating.The thinnest reaction layer and lowest infiltration was found for the highest produced 67 YO(1.5)coating.Complementary XRD experiments with volcanic ash/YO(1.5)powder mixtures with higher yttria contents than in the coatings(80 YO(1.5)and pure YO(1.5))also showed higher apatite formation with respect to increasing yttria content.The threshold composition to promote apatite-based reaction products was found to be around 50 YO(1.5)in zirconia which was proved in the coatings and XRD powder experiments.An YO(1.5)-ZrO2-Fe O-TiO2 bearing zirconolite-type phase was formed as a reaction product for all the coating compositions which implicates that TiO2 in the melt acts as a trigger for zirconolite formation.This phase could be detrimental for CMAS/volcanic ash infiltration resistance since it can be formed alongside with apatite which controls or limits the amount of Y^(3+)available for glass crystallization.The Fe rich garnet phase containing all the possible elements exhibited a slower nucleation compared to apatite and its growth was enhanced with slow cooling rates.The implications of phase stability and heat treatment effects on the reaction products are discussed for tests performed at 1250°C.

Microstructures in a Nb-Cr-V-W-Ta high entropy alloy during annealing

A Nb-Cr-V-W-Ta high entropy alloy has been subjected to annealing treatment at 600,700 and 800℃in air for 6 h.Five different phases have been identified based on their composition in the as received condition.The annealing treatment does not alter the phase analysis and compositions except for the W-rich phase where minor changes in the composition have been observed.This is considered as an experimental evidence of sluggish diffusivity associated with HEAs.Absence of phase transformation during the heating and the minimal changes in observed compositions of the phases is an indication of the resistance to diffusion offered by the elements of the high entropy alloy.Scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS)and color X-ray elemental mapping have been used to conduct this research.

Effect of sintering temperature on the chemical bonding,electronic structure and electrical transport properties of β-Ga_(1.9)Fe_(0.1)O_(3) compounds

A model system,which is based on iron(Fe)doped gallium oxide(Ga_(2)O_(3))(Ga_(1.9)Fe_(0.1)O_(3)),has been considered to elucidate the combined effect of transition-metal ion doping and processing temperature on the chemistry,local structure and chemical bonding,and electrical transport properties of a wide band gap oxide(Ga_(2)O_(3)).The Ga_(1.9)Fe_(0.1)O_(3) compounds were synthesized using standard high-temperature solid state reaction method.The effect of processing conditions in terms of different calcination and sintering environments on the structural and electrical properties of Ga_(1.9)Fe_(0.1)O_(3) compounds is studied in detail.Structural characterization by Raman spectroscopy revealed that Ga_(1.9)Fe_(0.1)O_(3) compounds exhibit monoclinic crystal symmetry,which is quite similar to the intrinsic parental crystal structure,though Fedoping induces lattice strain.Sintering temperature(T_(sint))which was varied in the range of 900-1200℃,has significant impact on the structure,chemical bonding,and electrical properties of Ga_(1.9)Fe_(0.1)O_(3) compounds.Raman spectroscopic measurements indicate the proper densification of the Ga_(1.9)Fe_(0.1)O_(3) compounds achieved through complete Fe diffusion into the parent Ga_(2)O_(3) lattice which is evident at the highest sintering temperature.The X-ray photoelectron spectroscopy validates the chemical states of the constituent elements in Ga_(1.9)Fe_(0.1)O_(3) compounds.The electrical properties of Ga_(1.9)Fe_(0.1)O_(3) fully controlled by T_(sint),which governed the grain size and microstructural evolution.The temperature and frequency dependent electrical measurements demonstrated the salient features of the Fe doped Ga_(2)O_(3) compounds.The activation energy determined from Arrhenius equation is 0.5 e V.The results demonstrate that control over structure,morphology,chemistry and electrical properties of the Ga_(1.9)Fe_(0.1)O_(3) compounds can be achieved by optimizing T_(sint).