There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Recent progress in aluminum metal matrix composites: A review on processing, mechanical and wear properties

The metal-matrix composites/nano-composites (MMCs/MMNCs) reinforced with hard ceramic particulates have received a tremendous attention due to their potential improvements in physical and mechanical performances. In the present work, we have comprehensively collected currently available experimental data sets of Al-based MMCs/MMNCs and have carried out thorough analyses to quantitatively address the impacts of the reinforcement volume fractions, reinforcement particle sizes, and metal-matrix grain sizes on their mechanical properties including the yield strength, ultimate strength, and strain to failure of composites. We also performed a quantitative analysis on the strengthening mechanisms of Al MMNCs to reveal that the grain refinement can play a major role in increasing the strength of composites. Al-based MMC or MMNC materials generally exhibited an indirect relationship between the strength increase and strain-to-failure increase. The results include a critical comparison for the mechanical performance of particulate-reinforced composites for both pure and alloyed Al matrices to elucidate the contemporary status of Al MMC and MMNC materials.

Mechanical performance of particulate-reinforced Al metal-matrix composites (MMCs) and Al metal-matrix nano-composites (MMNCs)

Different manufacturing processes can be utilized to fabricate light-weight high-strength materials for their applications in a wide spectrum of industries such as aerospace, automotive and biomedical sectors among which accumulative roll bonding (ARB) is a promising severe plastic deformation (SPD) method capable of creating ultrafine grains (UFG) in the final microstructure. The present review discusses recent advancements in the ARB process starting with the ARB basics, intricacies of the underlying mechanisms and physics, different materials, surface and rolling parameters, and finally its key effects on different properties such as strength, ductility, fatigue, toughness, superplasticity, tribology and thermal characteristics. Moreover, results of recent computational investigations have also been briefed towards the end. It is believed that ARB processing is an emerging area with tremendous opportunities in the industrial sector and ample potential in tailoring microstructures for high-performance materials.

Accumulative Roll Bonding—A Review

Many of the properties of austempered ductile iron depend on the austenite which is retained following the bainite reaction. A neural network model within a Bayesian framework has been created using published data to model the retained austenite content. The model allows the quantity of retained austenite to be estimated as a function of the chemical composition and heat treatment parameters. The computer programs associated with the work have been made freely available ( http //www.msm.cam.ac.uk/map/mapmain.html )

Estimation of the amount of retained austenite in austempered ductile irons using neural networks

Recently accumulative roll bonding has been used as a novel method to produce particle reinforced metal matrix composites. In this study, aluminum matrix composite reinforced by submicron particulate alumina was successfully produced and the effects of number of ARB cycles and the amount of alumina content on the microstructure and mechanical properties of composites were investigated. According to the results of tensile tests, it is shown that the yield and tensile strengths of the composite are increased with the number of ARB cycles. Scanning electron microscopy (SEM) reveals that particles have a random and uniform distribution in the matrix by the ARB cycles and a strong mechanical bonding takes place at the interface of particle-matrix. It is also found that the tensile strength of the composite, as a function of alumina content, has a maximum value at 2 vol.%, which is 5.1 times higher than that of the annealed aluminum.

Production of high strength Al–Al2O3 composite by accumulative roll bonding

Accumulative roll bonding (ARB) was successfully used as a severe plastic deformation method to produce Al-SiC nanocomposite sheets. The effects of process pass and amount of SiC content on microstructure and mechanical properties of the composites are investigated. As expected, production of ultrafine grain structures by the ARB process as well as nanosize particulate reinforcements in the metal matrix composite (MMC) resulted in excellent mechanical properties. According to the results of the tensile tests, it is shown that the yield and tensile strengths of the composite sheet increased with the number of ARB cycles without saturation at the last cycles. Scanning electron microscopy (SEM) revealed that the particles had a random and uniform distribution in the matrix by the last ARB cycles, and strong mechanical bonding takes place at the interface of the particle matrix. Transmission electron microscopy (TEM) and the corresponding selected area diffraction (SAD) demonstrate ultrafine grains with large misorientation in the structure. It is also shown that by increasing the volume fraction of particles up to 3.5 vol pct, the yield and tensile strengths of the composite sheets increased more than 1.3 and 1.4 times the accumulative roll-bonded aluminum sheets, respectively.

Fabrication of High-Strength Al/SiC p Nanocomposite Sheets by Accumulative Roll Bonding

Manganese is an inexpensive element and a potent hardenability promoter in ductile iron, but in this role it has the inherent limitations of severe segregation and carbide formation tendencies. In order to use this material in an actual application, attempts must be made to overcome these limitations. In the present work, the effect of austempering time and austenitising temperature on the impact strength and abrasive wear resistance of 1.5Mn austempered ductile iron (ADI) after austempering at 270°C is investigated. The results show that impact resistance is affected adversely by untransformed austenite volume but this parameter improves the wear resistance of high Mn ADI.

Wear behaviour of 1.5Mn austel11pered ductile iron

Dynamic performance, safety and maintenance costs of railway vehicles strongly depend on wheelset dynamics and particularly on the design of wheelset profile. This paper considers the effect of worn wheel profile on vehicle dynamics and the trend of wear in the wheels as a result of the vehicle movements. ADAMS/RAIL is used to build a multi-body system model of the vehicle. The track model is also configured as an elastic body. Measured new and worn wheel profiles are used to provide boundary conditions for the wheel/rail contacts. The fleet velocity profile taken during its normal braking is also used for the simulation. Wear numbers are calculated for different sets of wheels and the results compared with each other. Outcome of this research can be used for modifying dynamic performance of the vehicle, improving its suspension elements and increasing ride quality. It can also be further processed to reach to a modified wheel profile suitable for the fleet/track combination and for improved maintenance of the wheels. A major advantage of the computer models in this paper is the insertion of the wheel surface properties into the boundary conditions for dynamic modelling of the fleet. This is performed by regularly measuring the worn wheel profiles during their service life and by the calculation of the wear rate for individual wheels.

The effect of worn profile on wear progress of rail vehicle steel wheels over curved tracks

Manganese is known as an inexpensive element and a potent promoter of hardenabilty in ductile iron but it also segregates severely and encourages the formation of carbides in the matrix. Thus, it is suggested that when the Mn content is high, attempts should be made to minimise the Mn segregation. In the present work the effect of solidification rate and homogenisation treatment on the severity of segregation of Mn and Si in several types of wear resistant high Mn ductile iron was investigated. It is demonstrated that increasing the solidification rate, leading to a high nodule count, decreases not only the heterogeneity of these elements but also the carbide content.

Microsegregation of manganese and silicon in high manganese ductile iron

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