Volume 113, Issue 7

Development of nanosized nitride particles in the ferrite matrix of steels is known to drastically enhance the mechanical properties. In the present work an attempt is made to utilize an unconventional method to produce the dispersion strengthened material. The gaseous nitriding treatment of Fe-4.6 at.% Al alloy powder was carried at 580 °C to realize the dispersion of aluminium nitride particles in the ferrite matrix of powders. Such nitrided powders were consolidated using spark plasma sintering. Powders and the sintered compacts were characterized using various techniques. Nitrided powders contained iron nitrides as matrix with AlN as dispersed precipitates. Annealing treatment of nitrided powders in Ar atmosphere led to the reduction of the iron nitrides to ferrite while AlN precipitates were still retained. The sintering behavior of nitrided and Ar annealed nitrided powders was studied and discussed with thermodynamic stability of iron nitrides and aluminium nitrides in ferritic matrix.

Environmental barrier coatings (EBCs) have been widely used as protective layers to protect the surface of ceramic components from water vapor degradation and hot corrosion at operating temperature. In this study, ytterbium monosilicate (Yb 2 SiO 5 ) and mullite (3Al 2 O 3 ·2SiO 2 ) powders were synthesized by mechanical alloying to be considered as a new environmental barrier coating. The composite powder was granulated by the spray dryer process and deposited on SiC reinforced by carbon fibers (SiC/C f ) substrate using the atmospheric plasma spray method. Phases in the synthesized composite powders and the deposited EBC were identified using X-ray diffraction. A field emission scanning electron microscope equipped with energy dispersive X-ray spectroscopy was utilized to study the powder morphology and coating microstructure. After the spray dry processing, the powders exhibited a spherical morphology and good-flowability with a mean particle size of 20–40 µm. The coating thickness was measured to be between 100 and 150 μm. In addition, the results of nanoindentation testing exhibited a hardness of about 8 GPa and an elastic modulus of about 111 GPa for the deposited coatings.

Selective coatings are produced with high absorption in the ultraviolet/visible range, composed of ilmenite deposited on stainless steel substrates and aluminum substrates, using the cathodic cage plasma nitriding/deposition technique, for application in solar thermal absorbers. Ilmenite was initially characterized by means of X-ray fluorescence, X-ray diffractometry and thermal analysis. The coatings produced were optically characterized in the UV/Vis range, the microstructural evaluation of coatings was by scanning electron microscopy and data on the roughness parameters of the films produced were obtained by optical profilometry. Uniform selective surfaces with high solar absorbance (87 %) were obtained in the ilmenite samples deposited on stainless steel substrate.

In this research, 1-(2-methoxyphenyl)-3-(4-chlorophenyl) triazene was studied as a compound with high nonlinear optical properties for use in optical devices. For this purpose, the compound was synthesized and its structure was identified by melting point and infrared and nuclear magnetic resonance spectroscopy. Then, the bandgap energy of the title compound was determined to be 2.4 eV using the Tauc relation. Density functional theory and time-dependent methods were used for calculations of magnetic moment, natural band orbital, analysis of frontier molecular orbitals, first and second order hyperpolarizability. The results showed a dipole moment of 2.45 Debye for the molecule. The calculation of the hyperpolarizability showed the values of −109.6, 128.9 and −3694 a.u. for the first, second and third order polarizability respectively. Finally, the experimental and computational results showed that the compound has significant nonlinear optical properties and will be suitable for nonlinear optics studies and applications in optical devices.

Due to the absence of weak-links in grain boundaries, less anisotropy, and high availabilities at reasonable cost, magnesium boride, MgB 2 , has been studied extensively in the past decade. It has relatively high critical temperature, which is correlated to crystallographic and electronic structures. Two topological indices, the electric connectivity index and valence energy level connectivity, are characteristics of compound branching. We develop the Gaussian process regression (GPR) model to shed light on the relationship between topological descriptors and superconducting transition temperature for doped MgB 2 superconductors. The model is highly accurate and stable, which contributes to fast predictions of superconducting transition temperature.

In this study, the microstructure and mechanical properties of a Cu-rich multiple-principal-element alloy with the composition (Cu 50 Ni 20 Cr 20 Mn 10 ) 95 Al 5 (at.%) were investigated. It was found that after 900 °C/1 h annealing process, the as-cast alloy has achieved promising mechanical properties with a yield stress of 510 MPa, an ultimate tensile stress of 820 MPa and tensile elongation of 30 %. These properties are superior to those of traditional nickel–aluminum bronze (NAB) alloys. Moreover, the as-annealed alloy exhibited much better anti-corrosion properties with respect to the NBA alloys. Transmission electron microscopy observations showed that high-number-density nano-scaled L1 2 -type ordered particles have precipitated in the Cu-rich phase after heat treatment and this was regarded as the main mechanism responsible for the enhancement of yield stress.

The microstructural evolution during natural ageing and artificial ageing treatment has been quantified in Al–Cu–Li alloys with Cu/Li ratios of 2.3 and 3.9. Methods including various ageing, hardness testing, transmission electron microscopy and differential scanning calorimetry were employed. The precipitation of T1 (Al 2 CuLi) phase was confirmed for the first time in the high Li content alloy under natural ageing treatment for 5 months, while the Li-lean alloy exhibits barely any precipitation at room temperature. Under artificial ageing, the Li-rich alloy exhibits a significant increase in hardness due to the formation of high density spherical δ′ phase. On the other hand, the increasing Cu/Li ratio promotes the precipitation of the Cu containing precipitates T1 and θ (Al 2 Cu), the high Cu/Li ratio (3.9) alloy shows a recovery of ductility, with a uniform elongation of ∼20 %, which is caused by the strong interactions between the dislocations and the nano-scale T1 and θ precipitates. Meanwhile, as the main strengthening precipitate changes from θ and T1 to T1 alone with prolonged ageing time, the alloy displays a double-peak age hardening behavior. This work sheds light on the design of high strength and ductile Al–Li alloys through the well-controlled T1 phase precipitation.