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High-entropy alloys are a new class of material. In recent past, high-entropy alloys have attracted a great deal of attention from researchers due to their unique multi-element solid-solution structures and excellent properties. This paper deals with a new promising class of high entropy alloys synthesized through mechanical alloying for 15 h. The elemental powders are milled in high energy ball milling. The elemental powders are taken out at particular time intervals for the phase analysis through X-ray diffractometer. The particle morphology was scrutinized by Scanning electron microscopy. The phase analysis through X-ray diffractometer reveals the formation of face-centered cubic phase along with some Ni-Si based compounds after 15 h of mechanical alloying. An increase in crystallite size is observed with increase in milling time whereas, a decrement in lattice strain is observed with advancing milling time. To support the lattice strain increment, the dislocation density is also calculated by using the variance method. The high negative mixing enthalpy of Si and Ni results into the formation of Ni-Si based compound.

This paper explores the impact of Si addition on the microstructural evolution and mechanical properties of AlCoCrCuFeNiSix (x = 0.3 and 0.6 at. ratio) alloys synthesised by spark plasma sintering of mixed powders. X-ray diffraction technique is implemented for phase formation analysis of the present high entropy alloys. The AlCoCrCuFeNi HEA with Si = 0.3 content shows the evolution of duplex phase of FCC and BCC whereas, with further increase in Si = 0.6 content, the sigma phase appeared along with the BCC and FCC phases. Increased hardness and wear resistance with increased Si element can be attributed to the development of the BCC and sigma phase along with solid solution strengthening. As Si has smaller atomic radius contrasted with the other constituent components in the blend, it decreases the mobility of dislocations, increment the strain energy, and consequently improve the solid-solution strengthening effect.

In this work, the effect of addition of Si on the phase evolution and mechanical properties of AlCoCrCuFeNiSix alloy system has been studied. The High Entropy Alloys (x = 0 and 0.9) have been synthesised by powder metallurgy route which includes mechanical alloying (MA) and spark plasma sintering. X-ray diffraction technique was performed to understand the alloying behaviour and to investigate the phase formation of the high entropy alloys. The samples after spark plasma sintering comprised mainly of body centered cubic structured phase with a small extent of face centered cubic structured phase. With the addition of silicon, the XRD peak intensity of body centered cubic appears strong compared to the face centered cubic structured phase. Moreover, no intermetallic is observed in AlCoCrCuFeNi high entropy alloy system. However, further accumulation of Silicon results in the evolution of sigma (σ) phase.

Herein Tb3+ (0.1, 0.2, 0.5, 1, 1.5, 2 and 2.5 mol %) doped Y4Al2O9 (monoclinic phase of yttrium aluminium oxide Y/Al 2:1) phosphors have been synthesized by conventional modified solid state reaction method (CMSSRM) using inorganic materials like Yttrium Oxide (Y2O3), Aluminium Oxide (Al2O3), Terbium Oxide (Tb2O3) and boric acid as a flux. The prepared phosphor samples were characterized using X-ray diffraction analysis (XRD), photoluminescence (PL), and thermoluminescence (TL) glow curve. From the XRD data, using the Scherrer formula the calculated average crystallite size of Tb3+ doped Y4Al2O9 phosphor is around 235 nm. Photoluminescence excitation spectra show sharp excitation peak centred at 270 nm and broad excitation peak centred at 300 nm which is due to charge transfer band. Here emission spectra show three distinct peaks centred at 492 nm (5D4 → 7F7), 544 nm (5D4 → 7F6) and 584 nm (5D4 → 7F4). Results indicate that PL intensity increases with increasing the concentration of doping ion i.e. Tb3+ up-to 2 mol % after that due to concentration quenching PL intensity decreases. Commission Internationale de l'Eclairage (CIE) values were calculated as X = 0.24 and Y = 0.56 and it shows intense green emission. TL glow curves were analysed with effect of doping ion concentration and effect of variable UV exposure time. Kinetic parameters were calculated using various methods proposed by Chen and others.