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Laser beam welding of C–Mn steel plates with Ni powder filler metal has been performed. Metallography samples of the welded cross-section have been observed by scanning electron microscopy (SEM) and submitted to energy dispersive spectroscopy to obtain Ni concentration profiles. On the basis of the experimental results, neural networks have been carried out. These networks were first validated and then utilized to foresee Ni concentration along the welded thickness. The objective of obtaining the best Ni penetration and minimizing powder loss was reached optimizing, by numerical simulation, process parameters, such as powder rate and joint geometry.

The effects of nitrogen and oxygen absorption on lattice expansion of Ti–6Al–4V have been investigated by high-temperature X-ray diffractometry. Experiments have been performed on stress-free powder for its high surface–volume ratio and to avoid possible effects on diffraction patterns due to texture change and recovery of defective structures induced by the measurement cycle at temperature. Cell parameters a and c , measured at increasing temperatures up to 600 °C, show linear trends with different slopes. As temperature increases, the cell volume expands and the c / a ratio changes. This is due to both lattice thermal expansion and absorption of oxygen and nitrogen. Part of the gas remains entrapped in the metal after cooling to room temperature causing a residual lattice distortion. Results have been compared with literature data obtained in analogous tests performed on bulk Ti–6Al–4V alloy both in vacuum and in inert gas atmosphere.

Effects on metal targets after an explosion include the following: fracture, plastic deformation, surface modifications, and microstructural crystallographic alterations with ensuing mechanical properties changes. In the case of small charge explosions, macroscopic effects are restricted to small charge-to-target distances, whereas crystal alterations can still be observed at moderate distances. Microstructural variations, induced on gold-alloy disk samples, as compared to previous results on AISI 304Cu steel samples, are illustrated. The samples were subjected to blast-wave overpressures in the range of 0.5 to 195 MPa. Minimum distances and peak pressures, which could still yield observable alterations, were especially investigated. Blast-related microstructural features were observed on the explosion-exposed surface and on perpendicular cross sections. Analyses using X-ray diffraction (XRD) were performed to identify modifications of phase, texture, dislocation density, and frequency of mechanical twins, before and after the explosions. Optical metallography (OM) and scanning electron microscopy (SEM) observations evidenced partial surface melting, zones with recrystallization phenomena, and crystal plastic deformation marks. The latter marks are attributed to mechanical twinning in the stainless steel and to cross-slip (prevalent) and mechanical twinning (possibly) in the gold alloy.

An indirect method for the evaluation of cooling rate of a squeeze cast aluminum alloy is proposed. Cooling rate is inferred by simple local mechanical tests such as microhardness or indentation. A predictive model is used to correlate cooling rate and mechanical properties. An aluminum alloy (EN-AB46000) was squeeze cast. Four cylindrical samples were fabricated at different values of the squeezing pressure (from 0 to 100 MPa). Samples were cut longitudinally at the middle height and microhardness was measured along the sample radius as well as dendrite size. Moreover yielding stress was evaluated by means of FIMEC test in the centre of the sample section. Mechanical properties can be related to dendrite size and used for cooling rate inference.

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This paper proposes a new technique based on artificial neural network useful for the characterization of superplastic behaviour, in particular for PbSn60 alloy. A three-layer neural network with back propagation (BP) algorithm is employed to train the network. The network input parameters are: alloy grain size, strain and strain rate. Just one is the output: the flow stress. Experiments are performed to evaluate the behaviour of PbSn60 alloy, subject to uniaxial tensile test, when the cross speed is kept constant. The strain rate sensitivity value (m) has been estimated analyzing the slope of the log σ – log e ˙ curve. It is shown that BP artificial neural network can predict the flow stress and, consequently, the m index during superplastic deformation with considerable efficiency and accuracy.

AISI 304 steel with a biphasic structure (α′+γ), induced by plastic deformation at room temperature, shows an anomalous evolution of martensite content when heated at 400 °C. High-temperature X-ray diffraction has been used to investigate the phenomenon. Isothermal measurements at 400 °C for times up to 2.0 × 10 4 s show that martensite progressively transforms to austenite but an increase of martensite content is observed after cooling to room temperature. The result confirms that the heat treatment causes composition inhomogeneities and a local increase of M S (martensite start temperature) in the zones depleted of alloying elements so that a certain amount of martensite can form during cooling to room temperature. The temperature range of martensitic transformation is 240–190 °C and was determined by dynamic modulus measurements.

Evidence of exposure of a metal component to a small charge explosion can be detected by observing microstructural modifications; they may be present even if the piece does not show noticeable overall plastic deformations. Particularly, if an austenitic stainless steel (or another metal having a face-centered cubic structure and a low stacking fault energy) is exposed to an explosive shock wave, high-speed deformation induces primarily mechanical twinning, whereas, in nonexplosive events, a lower velocity plastic deformation first induces slip. The occurrence of mechanical twins can be detected even if the surface is damaged or oxidized in successive events. In the present research, optical metallography (OM) and scanning electron microscopy (SEM), and scanning tunneling microscopy (STM) were used to detect microstructural modifications caused on AISI 304Cu steel disks by small-charge explosions. Spherical charges of 54.5 or 109 g TNT equivalent mass were used at explosive-to-target distances from 6.5 to 81.5 cm, achieving peak pressures from 160 to 0.5 MPa. Explosions induced limited or no macro-deformation. Two alloy grain sizes were tested. Surface OM and SEM evidenced partial surface melting, zones with recrystallization phenomena, and intense mechanical twinning, which was also detected by STM and X-ray diffraction. In the samples' interior, only twins were seen, up to some distance from the explosion impinged surface and again, at the shortest charge-to-sample distances, in a thin layer around the reflecting surface. For forensic science locating purposes after explosions, the maximum charge-to-target distance at which the phenomena disappear was singled out for each charge or grain size and related to the critical resolved shear stress for twinning.

Fluidized bed processing is a relatively novel method for coating metal substrates. A detailed study was carried out into surface property and in micro-structure changes induced by fluidized bed processing. In particular, fluidized bed processing of AA 6082 T6 aluminum alloy components using alumina Al2O3 powder was investigated. Firstly, the build up of Al2O3 films was studied and characterized in terms of coating thickness and adhesion. It was found that trends of deposited Al2O3 were consistent with fluidized bed processing time. Secondly, the effect of fluidized bed treatment on surface properties of processed components was examined. Surface morphology was significantly affected and its evolution according to processing time was accounted for. Both compressive residual stresses and increased dislocation density were induced by treatment of external layers of samples, and significant hardening was also detected. Lastly, the ability of fluidized bed processing was tested on 'ad hoc' fatigue samples. Rupture of fluidized bed treated samples as well as untreated samples was also discussed. At any rate, the fatigue behavior of processed components significantly improved. This quite new and unprecedented result is ascribed to the compressive residual stresses and work hardening induced by FB treatment in the outermost surface layers of the aluminum alloy. © 2005 Elsevier B.V. All rights reserved.

Tungsten is a promising armour material for plasma facing components of nuclear fusion reactors because of its low sputter rate and favourable thermo-mechanical properties. Among all the techniques able to realise W armours, plasma spray looks particularly attractive owing to its simplicity and low cost. The present work concerns the optimisation of spraying parameters aimed at 4–5 mm thick W coating on copper–chromium–zirconium (Cu,Cr,Zr) alloy substrates. Characterisation of coatings was performed in order to assess microstructure, impurity content, density, tensile strength, adhesion strength, thermal conductivity and thermal expansion coefficient. The work performed has demonstrated the feasibility of thick W coatings on flat and curved geometries. These coatings appear as a reliable armour for medium heat flux plasma facing component.

Un composito con matrice metallica in lega Ti6Al4V rinforzato con fibre di SiC unidirezionali è stato prodotto mediante compattazione isostatica a caldo (HIP). Misure di diffrazione dei raggi X eseguite a temperature crescenti fino a 600°C in atmosfera di argon ed a temperatura ambiente dopo il ciclo termico hanno permesso di monitorare l’evoluzione delle tensioni residue. Stress bi-assiali di tensione nel piano parallelo a quello contenente le fibre si sviluppano progressivamente man mano che la temperatura cresce e in parte rimangono dopo il raffreddamento. L’origine delle tensioni viene attribuita al vincolo costituito dalle fibre, che ostacola l’espansione del reticolo a seguito dell’assorbimento di azoto ed ossigeno. Questa interpretazione è supportata da osservazioni di microscopia a forza atomica (AFM), che mostrano una sostanziale integrità dell’interfaccia metallo-fibra dopo trattamento di 1 h a 600°C in aria.

Part I of this paper showed that fatigue behaviour of Al-based metal matrix composites (MMCs) can be remarkably improved by means of titanium coatings deposited by sputtering at room temperature. Part II presents the results of finite element (FE) simulations carried out to clarify some aspects of the phenomenon, i.e. the effect of surface cavities. In particular, it was found that the effect of titanium thickness on stress distribution in the substrate is negligible if its surface is smooth. Coatings are effective in improving fatigue life because they seal the cavities present on the surface of MMCs: the better the filling of voids, the higher the stress reduction in the substrate during fatigue tests. After complete filling of cavities, further titanium deposition is useless for reducing stresses and improving fatigue behaviour.