1,721,097 research outputs found
Aluminum matrix composites reinforced with alumina nanoparticles
No full textThis book describes the latest efforts to develop aluminum nanocomposites with enhanced damping and mechanical properties and good workability. The nanocomposites exhibited high strength, improved damping behavior and good ductility, making them suitable for use as wires. Since the production of metal matrix nanocomposites by conventional melting processes is considered extremely problematic (because of the poor wettability of the nanoparticles), different powder metallurgy routes were investigated, including high-energy ball milling and unconventional compaction methods. Special attention was paid to the structural characterization at the micro- and nanoscale, as uniform nanoparticle dispersion in metal matrix is of prime importance. The aluminum nanocomposites displayed an ultrafine microstructure reinforced with alumina nanoparticles produced in situ or added ex situ. The physical, mechanical and functional characteristics of the materials produced were evaluated using different mechanical tests and microstructure investigation techniques. The book presents and discusses the experimental results in detail, and offers suggestions for future research directions
Laser shape setting of thin NiTi wires
No full textAn unconventional method for shape setting of NiTi shape memory alloy wires is proposed. A laser beam was used to induce straight shape, superelasticity and shape memory effects to thin NiTi wires. Laser treatment revealed to be a suitable and reliable alternative to the conventional final thermal treatment of NiTi wires, which is normally carried out in annealing furnaces. Thermo-mechanical and calorimetric tests showed that the laser heat treatment confers optimal functional properties, analogous to those of commercially available NiTi wires
Thermal cycling of stress-induced martensite for high-performance shape memory effect
Full text linkA novel approach to achieve an extraordinary high stress recovery shape memory effect based on thermal cycling of stressinduced
martensite is proposed. An alternative thermodynamic path is considered in order to achieve outstanding functional properties
of Ni-rich NiTi alloys, which are commonly used at room or body temperature as superelastic materials. Fatigue tests revealed
excellent stability of the material subjected to the novel thermomechanical path, confirming its suitability for employment in highperformance
shape memory actuators
Microstructure and Fracture Behavior of 316L Austenitic Stainless Steel Produced by Selective Laser Melting
No full textSelective laser melting is an additive manufacturing method based on local melting of a metal powder bed by a high power laser beam. Fast laser scans are responsible for severe thermal gradients and high cooling rates which produce complex hydrodynamic fluid flow. These phenomena affect crystal growth and orientation and are believed to be the cause of material spattering and microstructural defects, e.g. pores and incompletely melted particles. In this work, the microstructure and texture of 316L bars built along two different orientations and the effect of different distribution of defects on their mechanical response and failure mechanisms were investigated. Partially molten powder particles are believed to be responsible for the scattering in elongation to failure, reduced strength, and premature failure of vertical samples
Microstructural and Mechanical Properties of As Built, Solution treated and Aged 18Ni (300 grade) Maraging Steel Produced by Selective Laser Melting
No full textMechanical and microstructural properties of 18-Ni (300 grade) maraging steel processed by selective laser melting were investigat-
ed to evaluate the effect of the peculiar processing conditions and of the subsequent heat treatment. No need of solution treatment
prior to aging revealed necessary owing to the rapid cooling rate experienced by the material during selective laser melting. Iso-
thermal aging temperature and time played a main role in promoting austenite reversion. Aging also induced a dramatic increase in
strength with respect to the as-built condition and a decrease in fracture elongation. It is proposed that tensile strength and ductility
are mainly governed by the effects brought by the strengthening precipitates, whereas the concurrent reversion of martensite into
austenite is likely to play a minor role. Analysis of defects induced by selective laser melting process and on fracture behavior of the
tensile specimens allowed to improve the understanding of materials performance and to draw guideline for process improvement
Damping behavior of 316L lattice structures produced by Selective Laser Melting
Full text linkSelective Laser Melting is a powder-bed additive manufacturing technology that allows producing fully-dense metal objects with complex shapes and high mechanical properties. In this work, Selective Laser Melting was used to produce 316L specimens including lattice structures with the aim of exploring the possibility given by additive manufacturing technologies to produce parts with increased damping capacity, especially in relation to their weight. The internal friction of bulk and lattice specimens was measured in terms of delay between stress and deformation (i.e. tanδ) for different applied loads and frequencies. A finite element model was used to design the test and microstructure investigations were performed to support the results obtained by dynamo-mechanical tests
Effect of electrical heating conditions on functional fatigue of thin NiTi wire for shape memory actuators
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