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

1: Magnetic Particles: Preparation, Properties and Applications: M. Ozaki. 2: Maghemite (gamma-Fe2O3): A Versatile Magnetic Colloidal Material C.J. Serna, M.P. Morales. 3: Dynamics of Adsorption and Oxidation of Organic Molecules on Illuminated Titanium Dioxide Particles Immersed in Water M.A. Blesa, R.J. Candal, S.A. Bilmes. 4: Colloidal Aggregation in Two-Dimensions A. Moncho-Jorda, F. Martinez-Lopez, M.A. Cabrerizo-Vilchez, R. Hidalgo Alvarez, M. Quesada-PMerez. 5: Kinetics of Particle and Protein Adsorption Z. Adamczyk.

Surface and Colloid Science

Metal matrix composites reinforced by nano-particles are very promising materials, suitable for a large number of applications. These composites consist of a metal matrix filled with nano-particles featuring physical and mechanical properties very different from those of the matrix. The nano-particles can improve the base material in terms of wear resistance, damping properties and mechanical strength. Different kinds of metals, predominantly Al, Mg and Cu, have been employed for the production of composites reinforced by nano-ceramic particles such as carbides, nitrides, oxides as well as carbon nanotubes. The main issue of concern for the synthesis of these materials consists in the low wettability of the reinforcement phase by the molten metal, which does not allow the synthesis by conventional casting methods. Several alternative routes have been presented in literature for the production of nano-composites. This work is aimed at reviewing the most important manufacturing techniques used for the synthesis of bulk metal matrix nanocomposites. Moreover, the strengthening mechanisms responsible for the improvement of mechanical properties of nano-reinforced metal matrix composites have been reviewed and the main potential applications of this new class of materials are envisaged.

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Metal Matrix Composites Reinforced by Nano-Particles—A Review

Composites science and technology

This paper presents the complete development and analysis of a soft robotic platform that exhibits peristaltic locomotion. The design principle is based on the antagonistic arrangement of circular and longitudinal muscle groups of Oligochaetes. Sequential antagonistic motion is achieved in a flexible braided mesh-tube structure using a nickel titanium (NiTi) coil actuators wrapped in a spiral pattern around the circumference. An enhanced theoretical model of the NiTi coil spring describes the combination of martensite deformation and spring elasticity as a function of geometry. A numerical model of the mesh structures reveals how peristaltic actuation induces robust locomotion and details the deformation by the contraction of circumferential NiTi actuators. Several peristaltic locomotion modes are modeled, tested, and compared on the basis of speed. Utilizing additional NiTi coils placed longitudinally, steering capabilities are incorporated. Proprioceptive potentiometers sense segment contraction, which enables the development of closed-loop controllers. Several appropriate control algorithms are designed and experimentally compared based on locomotion speed and energy consumption. The entire mechanical structure is made of flexible mesh materials and can withstand significant external impact during operation. This approach allows a completely soft robotic platform by employing a flexible control unit and energy sources.

Meshworm: A Peristaltic Soft Robot With Antagonistic Nickel Titanium Coil Actuators

An 18-Ni 300 grade maraging steel was processed by selective laser melting and an investigation was carried out on microstructural and mechanical behaviour as a function of aging condition. Owing to the rapid cooling rate, the as-built alloy featured a full potential for precipitate strengthening, without the need of a solution treatment prior to aging. The amount of reversed austenite found in the microstructure increased after aging and revealed to depend on aging temperature and time. Similarly to the corresponding wrought counterpart, also in the selective laser-melted 18-Ni 300 alloy, aging promoted a dramatic increase in strength with respect to the as-built condition and a drop in tensile ductility. No systematic changes were found in tensile properties as a function of measured amount of austenite. It is proposed that the submicrometric structure and the phase distribution inherited by the rapid solidification condition brought by selective laser melting are such that changes in tensile strength and ductility are mainly governed by the effects brought by the strengthening precipitates, whereas the concurrent reversion of the γ-Fe phase in different amounts seems to play a minor role.

Aging Behaviour and Mechanical Performance of 18-Ni 300 Steel Processed by Selective Laser Melting

Low temperature annealing dedicated to AlSi10Mg selective laser melting products

Laser welding technology is applied successfully for joining several metallic compounds. Using a Nd-YAG source the process is suitable for precision welding of low thickness metallic sheets. In this work a Nd:YAG laser was used for welding 0.54 mm thick tapes of Ni–49.6at.%Ti shape memory alloy (SMA). Two different microstructural states of the material were chosen (fully recrystallized and partial annealed after 30% cold working) to investigate pseudoelastic and shape recovery behaviours. For the two different metallurgical conditions the mechanical properties of both reference and laser welded samples were tested at several temperatures by stress–strain measurements. A systematic comparison of the results was carried out. Moreover, differential scanning calorimeter (DSC) investigations on samples taken from the heat affected zone and hardness measurements allowed further clarification that the modification was induced by the welding procedure. The results obtained on the fully recrystallized material indicate that the stress-induced martensite and the recovery mechanisms are weakly modified by the presence of the welding zone while the pseudoelastic properties of the partial annealed material are strongly affected.

Effect of Nd-YAG laser welding on the functional properties of the Ni–49.6at.%Ti

Fatigue properties of a pseudoelastic NiTi alloy: Strain ratcheting and hysteresis under cyclic tensile loading

A great effort was performed in order to develop alloys which exhibit transformation temperatures higher than about 150°C. This request has a 2-fold aim: (a) to provide an alloy that can be used in devices in which exercise temperatures as high as 100°C are easily reached (e.g. automotive applications, production plants, etc.); (b) to decrease the reset time by increasing the temperature gap between normal exercise and actuation temperatures. It has been demonstrated that ternary NiTiHf alloys can be a viable option to increase the operating temperature range of SMA. In this work, a NiTiHf alloy has been produced by a plasma arc melting furnace. Plasma technology ensures a good control of alloy composition and contamination, because of its high working pressure (850 mbar) and possibility to melt in a pure gas atmosphere. The produced material has been processed to obtain specimens suitable for calorimetric measurements. The effect of aging and thermal cycling on the thermoelastic martensitic transformation that takes place in the alloy has been evaluated. Specifically, samples taken from plasma melted buttons have been aged at different temperatures. Aging effects and evolution under thermal cycling on martensitic transformation behavior have been investigated by calorimetric measurements. Results obtained allow us to fix the reference framework for the effect of thermal treatments on the transformation properties of the chosen alloy and to compare with similar ones performed on semifinished products, to evaluate the effect of plastic deformation and residual cold work.

Ausonio Tuissi

Papers

Aging Behaviour and Mechanical Performance of 18-Ni 300 Steel Processed by Selective Laser Melting

Low temperature annealing dedicated to AlSi10Mg selective laser melting products

Effect of Nd-YAG laser welding on the functional properties of the Ni–49.6at.%Ti

Fatigue properties of a pseudoelastic NiTi alloy: Strain ratcheting and hysteresis under cyclic tensile loading

NiTiHf shape memory alloy: effect of aging and thermal cycling