Currently, additive manufacturing (AM) experiences significant attention in nearly all industrial sectors. AM is already well established in fields such as medicine or spare part production. Nevertheless, processing of high-performance nickel-based superalloys and especially single crystalline alloys such as CMSX-4® is challenging due to the difficulty of intense crack formation. Selective electron beam melting (SEBM) takes place at high process temperatures (~ 1000 °C) and under vacuum conditions. Current work has demonstrated processing of CMSX-4® without crack formation. In addition, by using appropriate AM scan strategies, even single crystals (SX SEBM CMSX-4®) develop directly from the powder bed. In this contribution, we investigate the mechanical properties of SX SEBM CMSX-4® prepared by SEBM in the as-built condition and after heat treatment. The focus is on hardness, strength, low cycle fatigue, and creep properties. These properties are compared with conventional cast and heat-treated material.

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Microstructure and Mechanical Properties of CMSX-4 Single Crystals Prepared by Additive Manufacturing

Recent developments on the optical properties of thin films of chalcogenide glasses

Biomineralization of tellurium and selenium-tellurium nanoparticles by the white-rot fungus Phanerochaete chrysosporium

Polycrystalline InSe diode structures, which have been known as a phase-change material, were studied for the first time where the current–voltage characteristics show high potential for data storage application. Highly oriented InSe films were prepared onto heated quartz substrates using the co-evaporation technique with 20% Se over pressure followed by 1 h annealing at the growth temperature. The films were characterized by X-ray diffraction, Raman spectroscopy and atomic force microscopy. InSe films were found to grow in 3-dimension with a roughness of around 400 nm. Diode structures were fabricated for the first time using these InSe films with both Mo bottom and Pt top electrodes that show large change in the electrical characteristics upon fabrication procedures. Thick InSe films (800 nm) showed Schottky characteristics, yielding a barrier height of approximately 1.0 eV.

Structural and Electrical Properties of InSe Polycrystalline Films and Diode Fabrication

We report the electrical and optical studies of thin films of a-GaxSe100−x nanorods (x = 3, 6, 9 and 12). Thin films of a-GaxSe100−x nanorods have been synthesized thermal evaporation technique. DC electrical conductivity of deposited thin films of a-GaxSe100−x nanorods is measured as a function of temperature range from 298 to 383 K. An exponential increase in the dc conductivity is observed with the increase in temperature, suggesting thereby a semiconducting behavior. The estimated value of activation energy decreases on incorporation of dopant (Ga) content in the Se system. The calculated value of pre-exponential factor (σ0) is of the order of 101 Ω−1 cm−1, which suggests that the conduction takes place in the band tails of localized states. It is suggested that the conduction is due to thermally assisted tunneling of the carriers in the localized states near the band edges. On the basis of the optical absorption measurements, an indirect optical band gap is observed in this system, and the value of optical band gap decreases on increasing Ga concentration.

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Effect of Composition on Electrical and Optical Properties of Thin Films of Amorphous Ga(x)Se(100-x) Nanorods.

Se–Te nanostructured thin films were deposited on glass substrates in the presence of oxygen and argon by thermal evaporation. The properties of Se–Te thin films strongly depend on the deposition method. During the process used, the substrate is cooled to a temperature of 77 K employing liquid nitrogen. The nanostructured thin films of Se 100− x Te x (where x =4, 8 and 16) are deposited on glass substrate. The surface morphology of the deposited films was investigated through Scanning Electron Microscopy (SEM). The typical size of these nanostructures is in the range 40–100 nm and the length is of the order of several micrometers. The optical parameters i.e. optical gap ( E g ), absorption coefficient ( α ), and extinction coefficient ( k ) are calculated in the wavelength range 190–1100 nm. It was found that the optical band gap decreased from 3.4 to 2.9 eV when Te concentration was increased in the Se 100− x Te x nanostructured thin films. The large bandgap may be attributed to the decrease in particle size which clearly exhibits a quantum size effect. XRD analysis was performed to confirm glassy nature of the nanostructured thin films.

Optical properties of selenium–tellurium nanostructured thin film grown by thermal evaporation

The crystallization parameters such as glass transition temperature (Tg), onset crystallization temperature (Tc), peak crystallization temperature (Tp) and enthalpy released (ΔHC) of the bulk Se–Te chalcogenide glass has been studied by using Differential Scanning Calorimeter (DSC), under non-isothermal condition at a heating rate of 20 K/min. The values of Tg, Tc, Tp and ΔHC with and without laser irradiation for different exposure time have been studied. The optical absorption of pristine and laser irradiated thermally evaporated Se–Te films has been measured. The films shows indirect allowed interband transition that is influenced by the laser irradiation. The optical energy gap has been found to decrease from 1.61 to 1.38 eV with increasing irradiation time from 5 to 20 min. The results have been analyzed on the basis of laser irradiation-induced defects in the film.

Effect of laser irradiation on thermal and optical properties of selenium–tellurium alloy

The effect of laser irradiation on the optical properties of thermally evaporated Se100−x Te x (x=8, 12, 16) chalcogenide thin films has been studied. The result shows that the irradiation causes a shift in the optical gap. The results have been analyzed on the basis of laser irradiation-induced defects in the film. The width of the tail of localized state in the band gap has been evaluated using the Urbach edge method. As the irradiation time increases, the values of the optical energy gap for all compositions decrease, while tail energy width increases. It is also observed that the optical energy gap decreases with increasing Te content in the alloy. These changes are a consequence of an increment in disorder produced by laser irradiation in the amorphous structure of thin film.

Effects of laser irradiation on optical properties of a-Se100−x Te x thin films

The photoconductive properties such as dark conductivity, steady state and transient characteristics of a-Se85−xTe15Hgx thin films, prepared by thermal vacuum evaporation technique have been studied in the temperature range 312–380 K. Analysis of data shows that the activation energy of dark current is greater as compared to the activation energy of photocurrent. The activation energy increases at higher concentration of Hg which shows that the defect density of states decreases. Analysis of intensity dependent photoconductivity shows that the bimolecular recombination is predominant. The transient photoconductivity shows that the carrier lifetime decreases with the increase in Hg concentration and increases at higher concentration of Hg. This decrease is due to the transition trapping process. Further the photosensitivity and carrier lifetime increases at higher concentration of Hg which also confirms that the density of defect states decreases.

Photoconductivity of Se85−xTe15Hgx thin films

Se100−xHgx bulk samples have been prepared by conventional melt quenching technique. The thin films of the material have been prepared on glass substrate using the thermal evaporation technique. The transmission spectra has been studied to measure the optical constants like absorption coefficient (α), extinction coefficient (K), optical band gap (Eg), Urbach energy (Ee). The DC conductivity (σdc) of Se100−xHgx has been also studied to find the activation energy ( Δ E a ) . The optical band gap increases and Urbach energy first increases then decreases with increase in Hg concentration. DC conductivity and activation energy increases with increase in Hg concentration. These materials are found suitable for the optical disk materials and in optoelectronic devices due to their high absorption coefficient and dependence of reflectance on composition.

Adam A Bahishti

Papers

Optical properties of selenium–tellurium nanostructured thin film grown by thermal evaporation

Effect of laser irradiation on thermal and optical properties of selenium–tellurium alloy

Effects of laser irradiation on optical properties of a-Se100−x Te x thin films

Photoconductivity of Se85−xTe15Hgx thin films

The study of optical parameters and DC conductivity of Se100−xHgx thin films