Band 109, Heft 11

Fracture properties of materials are strongly influenced by initial microstructure/texture, loading conditions, environment, notch geometry and phase transformations. The notch geometry effect on fracture properties of materials is very sensitive to the geometry of structure, scale effects and loading mode. A critical literature review is performed to understand several consensuses about the complexity of notch geometry in the deformation and fracture responses of materials. It is still not clear in these circumstances which variable is the most important to determine the mechanical properties of materials. This article deals with the quantitative methods for designing specimen geometry for different applications. However, microstructure alone is not a sufficient parameter for designing new alloys. In this work, the effect of notch geometry and temperature on the tensile properties of titanium alloys has been determined through a Bayesian computational framework under an artificial intelligence paradigm. The dataset considered for computation is essentially obtained from the elegant experimental research of Jenkins and Willard. Their analysis was performed on a physical basis and gives very clear indications to designers about the influence of temperature and specimen geometry on the mechanical properties of the alloys. The engineering significance of both the results is compared comprehensively. The present models have been applied to corroborate that the calculations are reasonable in the context of established solid mechanics and metallurgical theories. It has also been possible to gauge the isolated influence of particular variables such as elastic stress concentration factor, which exactly cannot in practice be varied independently. This highlights the ability of the technique to examine the new phenomena in cases where information cannot be accessed experimentally. This model will be instrumental for mechanical engineers to design critical industrial components.

This paper presents the results of an investigation on the oxidation damage mechanisms of the intermetallic alloy Ti-46Al-7Nb-0.7Cr-0.1Si-0.2Ni. The oxidation was carried out in air at two temperatures: 900 °C and 925 °C. The effects of temperature and cooling rate were taken into consideration. It is also determined that the mass gain of the oxidized alloy is slightly higher when cooling is performed at a higher rate.

A high Al 2 O 3 content (40 wt.%) reinforced Al coating was deposited on AZ91D magnesium alloy through the low-pressure cold spraying technique. It was found that the low-pressure cold spraying method could deposit a high quality aluminium coating on AZ91D magnesium alloy with bonding strength ranging from 17.7 MPa to 25.2 MPa. The average porosity in this case is about 2.6 %, and the alumina particles are distributed uniformly. Electrochemical tests revealed that the low-pressure cold sprayed Al + 40 % Al 2 O 3 coating has better corrosion resistance than magnesium in neutral 3.5 wt.% sodium chloride solution. Low-pressure cold sprayed aluminium coating can separate the magnesium substrate from a corrosive electrolyte, which can significantly improve the anticorrosion performance of the AZ91D magnesium alloy.

Aluminum metal matrix composites are the fastest developing materials for structural applications due to their superior properties. In this study, Al(Zn)/Al 2 O 3 nanocomposite and also Al(Zn) solid solution were fabricated successfully using mechanochemical synthesis and spark plasma sintering. The structural evolution of the powder particles after different milling times was studied by X-ray diffraction analysis. Also, the corrosion behavior of Al(Zn)/Al 2 O 3 metal matrix nanocomposite was evaluated and compared with that of nanocrystalline Al(Zn) alloy. The nanocomposite had been prepared via mechanochemical reaction between zinc oxide and aluminum powder mixture derived from a high-energy ball milling process. The results showed that the Al(Zn)/Al 2 O 3 nanocomposite is formed after 40 h of milling time. Also, it was found that the polarization resistance of the sample containing Al 2 O 3 is significantly higher (more than 67 times) than that of nanocrystalline Al(Zn) alloy (sample without Al 2 O 3 ).

The effects of Zr content on the existence forms of Zr and as-cast structure of high purity aluminium were investigated under a certain solidification condition. Results show that the existence forms of Zr depend on the Zr content. Zr can completely dissolve in the matrix when Zr content is lower than 0.15 wt.%. Certain agglomeration Al 3 Zr phases with complex morphology were formed in the aluminium matrix as the Zr content increased up to 0.2 wt.%. The amount and size of the agglomeration which is primary Al 3 Zr crystals increased when the Zr content increased further to 0.3 wt.%. The effects of Zr content on the grain size of high purity aluminium were limited, as the Zr content increased from 0.05 wt.% to 0.15 wt.%. The average grain size decreased from 492 μm to 159 μm, as the Zr content increased from 0.15 to 0.25 wt.%. The electrical conductivity of aluminium linearly decreased from 62.2% IACS to 58.2% IACS, when the Zr content increased from 0.05 wt.% to 0.15 wt.%. While it remained almost constant at approximately 56.5% IACS for Zr content between 0.25 and 0.3 wt.%.

Barium bismuthate microrods were synthesized by a simple ethylenediamine-assisted hydrothermal route using barium acetate and sodium bismuthate as the source materials. The X-ray diffraction pattern shows that the barium bismuthate microrods are composed of monoclinic BaBiO 2.5 phase. Scanning electron microscopy images show that the length and diameter of the barium bismuthate microrods are about 10–20 μm and 500 nm–1.5 μm, respectively. The formation and growth of the barium bismuthate microrods are closely related to the temperature, processing duration and ethylenediamine concentration. The solid UV–vis diffuse reflectance spectrum shows that the band gap of the barium bismuthate microrods is 1.42 eV which has strong absorption ability in the visible light region. The phtocatalytic activity of the barium bismuthate microrods has been evaluated by the photocatalytic removal of gentian violet under natural solar light irradiation in aqueous solution. Gentian violet with a concentration of 10 mg · L −1 can be totally removed by 10 mg barium bismuthate microrods in 10 mL aqueous solution.

LiNi 0.6 Co 0.2 Mn 0.2 O 2 , an α-NaFeO 2 type layered lithium transition metal oxide, is deemed as one of the most promising cathode materials for lithium-ion batteries. To ascertain the structural evolution and formation mechanism of this compound during high-temperature solid-state synthesis, thermal and structural analysis methods were performed, confirmed with the characterization of morphology and lithium residue. LiOH, used as the lithium source, showed both a lower initial temperature and a lower degree of lithium intercalation compared to Li 2 CO 3 when reacting with the precursor. A higher temperature for Li 2 CO 3 and a longer reaction time for LiOH during sintering would be beneficial to the material synthesis. Furthermore, a pre-heat treatment process in the temperature range of 400–600°C is beneficial for the lithium intercalation reaction.

Magnesium metal matrix composites (MMCs) have generated keen interest in recent times for potential usage in automotive and aerospace industries owing to their superior strength to weight ratio and high temperature resistance. With the concurrent attention to the requirements of high wear resistance and weight reduction, research into magnesium based MMCs has produced significant contributions in the automotive industry in the last few decades. Materials possessing high wear resistance under dry sliding conditions are associated with a stable tribo-layer on the worn surface and the formation of fine equiaxed wear debris. For abrasive wear, the influence of sliding speed, applied load, wearing surface hardness, reinforcement fracture toughness, percentages of reinforcement and morphology are critical parameters in relation to the wear regime encountered by the material. In this review, contemporary wear theories, issues associated with counter-face wear, and wear mechanisms are discussed in detail. Other areas of research relevant to abrasive wear of Al-based Mg alloys and Mg MMCs containing discontinuous reinforcement phases, such as the role of the reinforcement phase, are presented. Major effects such as interfacial transition, agglomerating phenomenon, formation, and distribution of in-situ Mg 2 Si, MgAl 2 O 4 , β-Mg 17 Al 12 and MgO in the metallic matrix, filler–matrix bonding and phase transition are discussed in this article.

In this study, 0.96(K 0 .5 Na 0.5 )NbO 3 -0.04LiNbO 3 (KNLN) + x wt.%CuO piezoelectric ceramics, where x = 0.0, 0.1, 0.2, 0.25, and 0.30, have been successfully fabricated using the conventional solid-state reaction method. The effect of CuO on the sintering behavior, structure, microstructure, and electrical properties of KNLN ceramics was studied. The addition of CuO reduced the sintering temperature of the ceramics from 1 050 °C to 950 °C. The experimental results showed that with CuO doping, the KNLN ceramics can be well sintered at a low temperature and show a dense, pure perovskite structure. At a sintering temperature of 950 °C and CuO content of 0.25 wt.%, the best physical properties of the ceramics, such as density ( ρ ), 4.14 g cm −3 ; electromechanical coupling factors ( k p ), 0.33 and ( k t ), 0.43; dielectric constant ( ∊ ), 349; dielectric loss (tan δ ), 0.008; mechanical quality factor ( Q m ), 133; and piezoelectric constant ( d 33 ), 130 pC N −1 , were obtained.