Volume 106, Issue 3

The phase equilibria in the “MnO”–Al 2 O 3 –SiO 2 system in equilibrium with metallic alloy have been determined. This paper is the second of two papers presenting research undertaken as part of a broader study on the phase equilibria in the Al 2 O 3 –CaO–Li 2 O–“MnO”–SiO 2 multi-component system, representing the major components of the lithium ion battery recycling slag. The experimental procedures involve equilibration of high purity powder mixtures at high temperatures, rapid quenching, and accurate measurement of phase compositions using electron probe micro-analysis. The liquidus surface is determined at temperatures between 1373 K and 1523 K in the tridymite, rhodonite, tephroite, galaxite, spessartine, corundum and Mn-anorthite primary phase fields resulting in an accurate representation of the phase diagram. The system is found to contain three binary peritectics and four binary eutectics, six ternary peritectics and three ternary eutectics.

A technique to measure the stress from an imperfect Debye–Scherrer ring is reported. In a previous work, the authors reported a technique to calculate the stress from the Fourier series of a normal strain of a Debye–Scherrer ring and suggested that it is possible to calculate the stress from an imperfect Debye–Scherrer ring if the Fourier series is obtained. The present work presents a technique to calculate the Fourier series of an imperfect Debye–Scherrer ring. Industrially, this is important because the object of interest is often covered by other objects or engraved. The aim of this work is to develop a technique that extends the application range of the X-ray stress measurement.

The effect of heat treatment on the microstructure and tensile properties of Ti-5Al-3Zr-4Mo-3V alloy are investigated in this paper. The results showed that the microstructural evolution with temperature could be classified into three stages in terms of the variation in β matrix. At stage I (670–790°C), some acicular primary α phase was retained and coarsened in β matrix; at stage II (790–830°C), the acicular primary α phase almost completely dissolved and no secondary α phase formed in β matrix during the following air cooling, and stress-induced martensitic transformation during tensile testing at room temperature occurred which caused the “double yield” phenomenon; at stage III (830–910°C), the secondary α phase precipitated in β matrix during the cooling, which led to a significant increase in the tensile strength.

The present study introduces a new method to characterise and evaluate the roping behaviour of aluminium sheet alloys of the AA 6 xxx series for car body applications. The new approach combines two known methods into a novel powerful tool, (i) the measurement of a 3D surface topography with a white-light interferometer and (ii) the subsequent data analysis by means of Fourier analysis. Use of the white-light interferometer allows analysing roping of deformed samples without the need of additional surface preparation steps, e.g. inking, stoning, etc., which may falsify the surface appearance. The use of data analysis by means of fast Fourier transform allows differentiating between different surface phenomena, e.g. unidirectional component versus isotropic components. It was found that the new approach is capable of giving reliable and reproducible data, which qualifies this method to study roping in aluminium car body sheets in an objective manner.

In this paper, the effects of process parameters, such as the tool rotational and traverse speeds, on temperature evolution and the microstructural and mechanical properties of dissimilar friction stir welding between 3 mm thick AA 7075 aluminum alloy and polycarbonate (PC) plates were investigated. The tool rotational and traverse speeds were varied from 3000 to 3500 rpm and 50 to 150 mm min −1 , respectively. The joint fabricated at 3250 rpm and 100 mm min −1 yielded a highest tensile load of 586 N. Microstructural analysis of the stir zone revealed an interlock phenomenon, the transportation of AA 7075 in polycarbonate, and the absence of ceramic-type (carbide, hydride or oxide) compounds. Microhardness (HV) measurement on the weld zone showed an uneven distribution due to the complicated microstructure of the welded joint. The maximum temperatures of 164°C and 66°C were obtained at 3250 rpm and 100 mm min −1 at a distance of 5 mm away from the welding centerline in the AA 7075 and PC side, respectively.

Plasma nitriding at 500°C for 14 h was applied to austenitic 304 stainless steel for surface hardening. The effect of surface treatment on the corrosion resistance of the material was investigated in naturally-aerated 0.5 M NaCl solution for 30 days using linear potentiodynamic polarization and electrochemical impedance spectroscopy methods. Both as-cast and plasma nitrided stainless steel samples underwent spontaneous passivation, though the nitrided sample exhibited more positive zero current potential, higher breakdown potential, and lower anodic current densities than the as-cast material. Impedance spectra were interpreted in terms of a duplex passive film, corrosion resistance mainly arising from a thin inner compact layer, whereas the outer layer was more porous and less sealing. Capacitive behaviour and high corrosion resistance were observed in the low and medium frequency ranges for the nitrided samples.

In this study, the corrosion susceptibility of aluminium matrix composites reinforced with sol–gel TiO 2 -coated silicon carbide particles has been investigated. The corrosion of the composite, fabricated by means of a liquid metal infiltration technique, was established in chloride-containing alkaline environments using the potentiodynamic polarisation technique. Microstructural and interfacial characterisation of the composite was carried out by using an optical microscope, scanning electron microscope, energy dispersion spectroscopy and X-ray diffractometer. The corrosion performance and its effect on the composite microstructure are discussed in relation to previous observations.

The role of chloride in the electrochemical behaviour of AZ31B Mg alloy in 0.05 M NaOH was investigated by means of potentiodynamic polarization, Mott–Schottky analysis, electrochemical impedance spectroscopy and scanning electron microscopy. Potentiodynamic polarization curves indicated that chloride concentration increase leads to a narrower passivation region of AZ31B Mg alloy. Also, the polarization curves revealed that increasing chloride concentration leads to higher corrosion current density in AZ31B Mg alloy. The micrographs clearly showed that the number and depth of pits increased with increasing chloride concentration. The Mott–Schottky analysis showed that the passive films have n-type semiconductive characteristics, where the number of oxygen vacancies and interstitials predominate over the cation vacancies. Moreover, Mott–Schottky results showed that the donor densities are in the range of 10 21 cm −3 and increase with increasing chloride concentration.

The role of vaporisation in the evolution of surface micro-structural instability has been investigated in Ni-base superalloys during heat treatment below the solvus temperature. Initial nucleation of beta (β) grains at the surface with random orientations arose from vaporisation of Ni, Co and Cr with subsequent de-stabilisation of gamma (γ) phase. Further vaporisation and inter-diffusion resulted in a discontinuous reaction (secondary reaction zone – gamma prime (γ′) matrix + topologically close packed phases with needle-like morphology). On the other hand, advancement of the secondary reaction zone grain boundary was shown to be dependent only on the solute supersaturation ahead of the boundary. The driving force for growth of the secondary reaction zone was calculated from the Gibbs energy change and nearly all of this force was available to pull the grain boundary.

The rapid synthesis of Mn 3 O 4 powders by a two-step process of pyro-synthesis of ethylene glycol–metal nitrate precursor assisted by nitric acid is reported. A new strategy that accelerates the synthesis and allows obtaining highly pure crystalline Mn 3 O 4 is discussed. The structural and morphological characteristics of the Mn 3 O 4 powders are presented and discussed. The mechanism of formation of the Mn 3 O 4 is also discussed. In comparison with other synthesis methods, the present method shows that the proposed route of synthesis has the main advantage of high production of the powder material in a very short time.

In the present study porous bioactive scaffolds were produced by mixing citric acid porogen and sol–gel derived bioactive glass powder, followed by sintering at 1200, 1250 and 1300°C. Bioglass powder and scaffolds were characterized by means of thermogravimetry, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Total porosity and compressive strength of scaffolds sintered at 1250°C were 70% and 0.8 MPa, respectively. Also, X-ray diffraction analysis of these scaffolds showed calcium pyrophosphate, pseudowollastonite and cristobalite were the main phases found in the composition of the scaffolds at all three temperatures. After immersion of scaffolds in simulated body fluid, remarkable calcium phosphate precipitation was observed under scanning electron microscopy. This scaffold can be a suitable candidate for bone tissue engineering.

The microstructure and age hardening response of deformed Mg-1.5Mn- x Sn ( x = 1 and 5, wt.%) alloys under three different aging temperatures (100°C, 150°C, 200°C) have been investigated. The aging behavior and the mechanical properties are improved by increasing Sn content. On ther other hand, the pre-rolling process is an effective method to improve the age hardening response, and therefore the mechanical properties of ERA (extruded + rolled + aging treatment) state alloys are improved compared with those of EA (extrusion + aging treatment) state samples. The improved mechanical properties of ERA alloys are mainly related to the extensive twins and dislocations formed during the extrusion/rolling processes and Mg 2 Sn precipitates formed in the aging treatment.

Magnesium dititanate, MgTi 2 O 5 was obtained via a microwave synthesis method. Powder X-ray diffraction, infrared spectroscopy and thermogravimetric/differantial thermal analysis measurements have been used to characterize the sample.

In the present study, thin films of Bi 2 S 3 with hollow morphology were deposited by chemical bath deposition at room temperature. The structural, morphological and optical properties of Bi 2 S 3 films were investigated as a function of deposition time. To study the photovoltaic properties, sensitization of SnO 2 photoanode with Bi 2 S 3 was achieved successfully via chemical bath deposition. The solar cell fabricated using SnO 2 –Bi 2 S 3 photoanode showed an open circuit voltage ( V OC ) of 357 mV, short circuit current density of ( J SC ) 740.16 μA cm −2 and fill factor (F.F.) of 31%.

Cobalt-doped CdS nanocrystals (CdS:Co NCs) were synthesized using a rapid microwave activated method. CdSO 4 and Na 2 S 2 O 3 were used as the precursors and Co(NO 3 ) 2 was the source of impurity. Thioglycolic acid was used as the capping agent and the catalyst of the reaction. The structure and optical properties of the NCs were characterized by means of X-ray diffraction, transmission electron microscopy, UV–visible and photoluminescence analyses. NCs had a hexagonal structure, forming round particles with a size of mostly about 3 nm. The band gap of NCs was obtained as about 3.18 eV. Synthesized NCs exhibited white emission between 400–750 nm with a peak located at about 505 nm.