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In the context of developing an innovative seismic dissipation system, which aims to compromise on the steadiness of friction and processes costs, this work deals with the tribological characterization of an S355JR structural steel, whose surface has been preliminarily treated by different mechanical and galvanic processes. Tribological tests were performed in a pin-on-disk configuration and in reciprocating motion, using values of 1 Hz and 2 Hz as the motion inversion frequency, a constant normal load of 50 N, and variable test duration, according to the most frequent seismic events. The tribological system was composed of S355JR structural steel pins and disks of the same steel, which were alternatively treated by electrolytic nickel plating, electrolytic zinc plating, and two different shot peening processes. The results highlight that while electrolytic nickel increments the overall steadiness of the coefficient of friction (COF), electrolytic zinc plating guarantees the longest first steady-state stage and a COF lower than the one guaranteed by the coupling of untreated pins and disk.

The present work focuses on the evolution of hardness and impact toughness after thermal exposure at high temperatures of the AlSi10Mg alloy produced by selective laser melting. The thermal exposure simulated the vapor deposition of coatings on aluminum alloys. The aim is to assess the possibility of combining the ageing step of heat treatments and the deposition treatment. The alloy was aged at 160 and 180 °C for up to 4 hours, both directly and after an innovative rapid solution treatment. Direct ageing had no significant effects on the microstructure, showing an almost constant hardness trend. These results accord with the impact properties, which showed a negligible difference in the impact toughness of the direct aged and the as-built samples. The same ageing treatments performed after rapid solution treatment induced age hardening in the alloy. The hardness values were lower by 38% than those of the directly aged samples. The innovative solution treatment positively affected impact toughness, which increased by 185% compared to the directly aged material. These results highlight that the ageing step can be integrated with the vapor deposition process. Moreover, the heat treatment is suitable for components requiring high impact strength after coating.

The performance improvement in engineering components during operation is a challenging issue and surface engineering methods have been attracting considerable interest in both research and industrial fields [...]

Surface material loss due to erosive wear is responsible for the increased cost of maintenance and downtime in industries. Hence, hardfacing is one of the most valuable and effective techniques employed to improve the wear resistance of heavy-duty components. The present paper investigates the microstructural and erosive wear characteristics of a hypereutectic high-chromium cast iron, considering the erosion resistance, resulting from the impact of micro-sized particles, of both as-received and heat-treated conditions. Micro-sized particles involve the erosion-resistant characteristics of carbide and matrix, contemporary. Due to this, the enhancement of the matrix strength could improve the mechanical support to withstand cracking deformation and spalling. Accordingly, the effect of a destabilization heat treatment on the microstructure was firstly investigated by hardness tests, X-ray diffraction analyses, optical and scanning electron microscopy. Specifically designed erosive tests were carried out using a raw meal powder at an impingement angle of 90°. The resulting superior wear resistance of the heat-treated samples was relayed on the improved matrix microstructure: consistent with the observed eroded surfaces, the reduced matrix/carbides hardness difference of the heat-treated material is pivotal in enhancing the erosion resistance of the hardfacing. The present results contribute to a better understanding of the microstructure–property relationships concerning the erosive wear resistance.

Due to the high complexity of the Additive Manufacturing processes, the effect of individual deposition parameters on integrity and mechanical performance of the 3D-printed part is not easily assessable. An energy density-based approach is often adopted to overcome such complexity, being the Volumetric Energy Density (VED) one of the widely used parameters. However, previous works on the AlSi10Mg alloy suggest that fully dense parts could be achieved with a well defined VED range. This study investigates different combinations of deposition parameters to reproduce part of this range and assess its effect on porosity, microstructure and tensile properties of the AlSi10Mg alloy. It was found that different combinations of deposition parameters in the employed VED range did not alter the microstructural features significantly. Conversely, they severely affected porosity, showing that VED is not a reliable parameter to predict the final density of the additively manufactured components. Moreover, specimens produced with a similar VED but different hatch spacing exhibit significantly different tensile properties. This fact suggests that the effect of deposition parameters should not be solely related to the amount of energy imparted to the material. Finally, systematically higher tensile properties characterise our specimens compared to results available in the literature, due to the microstructure obtained with the adopted combination of deposition parameters. The energy density-based approach lacks in considering the effect of process parameters on the microstructural features other than porosity, which could identify their actual proper combination misleadingly. Our results suggest that new approaches to define the optimum choice of process parameters need to be evaluated to maximise the final performance of AM components.

The evolution of microstructure in relation to dating and nationality of origin was investigated in twenty-four cast iron objects of street furniture produced between XIX and XX centuries in United Kingdom, France, and Italy. Chemical composition of the metalworks was evaluated by glow-discharge optical emission spectrometry. Fragments from the cast irons were analyzed by optical microscopy and scanning electron microscopy with energy-dispersive spectroscopy. Form, distribution, and size of graphite were evaluated in the microstructure according to standard EN ISO 945-1:2008. An image analysis software was employed to quantify the area fraction of graphite in the matrix, major axis, and shape factor of graphite lamellae, area fraction of manganese sulfides (ψ S), area fraction of steadite, and number of eutectic cells per area unit. All data were grouped and linear discrimination analysis (LDA) was applied to assess the group assignment and the probability of correct classification for each metalwork. The results showed that the microstructural features were compatible with those of cast irons produced in the XIX and XX centuries. Values of ψ S also suggested re-melting of cast irons, associated with recycling of cast iron and/or steel scraps. The high values of steadite found in the metalworks are probably due to the excellent castability required for complex shape castings in these centuries. The LDA multivariate analysis allowed to discriminate cast irons based on the year of manufacturing and the nationality of origin.

The purpose of the study is to assess the influence of SiC particles and heat treatment on the wear behaviour of Ni–P coatings when in contact with a 100Cr6 steel. Addition of reinforcing particles and heat treatment are two common methods to increase Ni–P hardness. Ball-on-disc wear tests coupled with SEM investigations were used to compare as-plated and heat-treated coatings, both pure and composite ones, and to evaluate the wear mechanisms. In the as-plated coatings, the presence of SiC particles determined higher friction coefficient and wear rate than the pure Ni–P coatings, despite the limited increase in hardness, of about 15%. The effect of SiC particles was shown in combination with heat treatment. The maximum hardness in pure Ni–P coating was achieved by heating at 400 °C for 1 h while for composite coatings heating for 2 h at 360 °C was sufficient to obtain the maximum hardness. The difference between the friction coefficient of composite and pure coatings was disclosed by heating at 300 °C for 2 h. In other cases, the coefficient of friction (COF) stabilised at similar values. The wear mechanisms involved were mainly abrasion and tribo-oxidation, with the formation of lubricant Fe oxides produced at the counterpart.

In the present paper, microstructural and mechanical properties of an innovative AlSi3Mg alloy were studied. Particularly, the effect of the addition of Cr and Mn on tensile strength and impact toughness was evaluated. In fact, the presence of these elements leads to the formation of an intermetallic phase with a globular or polyhedral morphology. It was therefore investigated the role played by Cr-Mn containing particles in the failure mechanism and the influence of the heat treatment parameters. Moreover, tensile and impact tests were performed on A356 samples in T6 condition, whose results were compared with the performance of the innovative alloy. Considering the static properties, the innovative alloy showed remarkable values of tensile strength, while ductility was improved only after heat treatment optimization. Poor impact toughness values were measured and the microstructural analysis confirmed the presence of coarse intermetallics, acting as crack initiation and propagation particles, on the fracture surfaces.

The request of even more stringent restrictions, regarding efficiency and environmental impact of industrial components, determines an optimized use of primary energy but also entails the design of more lightweight, smart and flexible devices, able to adapt their operation as a function of several different inputs. In this framework, the use of a fascinating class of metallic materials, called Shape Memory Alloys (SMAs), could represent a valid support for the designers. The capability of these materials to react to an external stimulus, without continuing to supply energy to external actuators, represents, especially in the aerospace engineering field, a technological breakthrough. The present paper reports the basic ideas and summarizes the important aspects related to the development of SMA-based actuators in relation to the present state of the art. A case study of morphing blades, equipped with embedded SMA strips, for an automotive cooling fan is reported. Finally, some hints, regarding the design process of SMA-based actuators, are proposed.

Towards the end of the last century, vacuum heat treatment of high speed steels was increasingly used in the fabrication of precision cutting tools. This study investigates the influence of vacuum heat treatments at different pressures of quenching gas on the microstructure and mechanical properties of taps made of M35 high speed steel. Taps were characterized by optical microscopy, scanning electron microscopy with energy dispersive spectroscopy, X-ray diffraction, apparent grain size and Vickers hardness measurements, and scratch tests. Failure analysis after tapping tests was also performed to determine the main fracture mechanisms. For all taps, the results showed that microstructures and the values of characteristics of secondary carbides, retained austenite, apparent grain size and Vickers hardness were comparable to previously reported ones for vacuum heat treated high speed steels. For taps vacuum heat treated at six bar, the highest plane strain fracture toughness was due to a higher content of finer small secondary carbides. In contrast, the lowest plane strain fracture toughness of taps vacuum heat treated at eight bar may be due to an excessive amount of finer small secondary carbides, which may provide a preferential path for crack propagation. Finally, the predominant fracture mechanism of taps was quasi-cleavage.

Several production processes involve the use of turbomachinery for the transport of gases with high concentrations of solid particles. Centrifugal fans employed in clinker production operate under severe erosive conditions. To limit the erosive wear of specific fan zones, wear-resistant plates are used. This paper presents a numerical investigation of the erosion behavior of a large-sized centrifugal fan operating in a cement factory. A contaminant characterization is carried out to define particle shape, size distribution and physical characteristics (i.e. density) on which the particle model is based. In addition, the surface analysis and microstructural characterization of the weld-deposited hardfacing alloy provide the wear-resistant coating features. Particles are tracked with a Lagrangian approach on the instantaneous flow fields corresponding to different relative impeller-to-volute positions. The particle impact angle is found to have a significant influence on the erosion of fan surfaces. CFD predictions are in close agreement with on-field erosion detections.

In the present study, instrumented impact strength tests were carried out on Charpy AlSi10Mg samples produced using laser additive manufacturing in order to accurately investigate the influence of building directions, heat treatment parameters and also the effect of Hot Isostatic Pressing (HIP) on their impact properties. AlSi10Mg cast samples were also tested for comparison. In addition to metallographic inspections, a deep characterization of the fracture surfaces in all the analysed conditions was performed. Microstructural features were also correlated to the impact properties: absorbed energy, peak force, crack nucleation and propagation energies. It was found that additive manufactured samples in as-produced condition exhibit the best performance due to their peculiar microstructure. HIP, followed by T6 heat treatment, is positive for the alloy properties since it effectively reduces porosities, which are a favourable path for crack propagation. Building direction has a clear effect on the fracture propagation. Samples in as-produced condition display greater unevenness of the fracture surface in the horizontal direction than in the vertical direction. This trend is less evident after heat treatment, but still detectable. The fractal dimension of the fracture surfaces is a quantitative parameter sensitive to the building orientation of samples and to the performed heat treatments.

In recent years, the influence of Ni on high-temperature mechanical properties of casting Al alloys has been extensively examined in the literature. In the present study, room temperature mechanical properties of an A356 alloy with Ni additions from 0.5 to 2 wt % were investigated. The role of Ni-based compounds and eutectic Si particles in reinforcing the Al matrix was studied with image analysis and was then related to tensile properties and microhardness. In the as-cast condition, the formation of the 3D network is not sufficient to determine an increase of mechanical properties of the alloys since fracture propagates by cleavage through eutectic Si particles and Ni aluminides or by the debonding of brittle phases from the aluminum matrix. After T6 heat treatment the increasing amount of Ni aluminides, due to further addition of Ni to the alloy, together with their brittle behavior, leads to a decrease of yield strength, ultimate tensile strength, and Vickers microhardness. Despite the fact that Ni addition up to 2 wt % hinders spheroidization of eutectic Si particles during T6 heat treatment, it also promotes the formation of a higher number of brittle Ni-based compounds that easily promote fracture propagation. © 2018 by the authors. Submitted for possible open access publication under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

One way to improve the mechanical properties of Al–Si alloys is to add chemical modifiers that affect the microstructure of the cast components. Small amounts of Sr cause the modification of the eutectic Si particles from a coarse plate-like morphology into a fine fibrous one. This study sets out to analyse the effects of chemical modification on an Al–7%Si–0.3%Mg foundry alloy treated with Sr, ranging from 62 to 820 ppm. Assessment of modification level was evaluated by both thermal analysis technique and quantitative microstructural investigations. Up to now, little attention has been paid to the role played by microstructural characteristics in evaluating the modification level, which is commonly performed by comparison with standard images. In the present investigation, numerical methods proposed in the literature have been considered in an attempt to understand their effectiveness. The correlation between thermal analysis results and geometrical parameters of eutectic Si particles highlighted the impact of microstructural homogeneity on modification-level evaluation. In addition, the presence of Ca in Sr-based intermetallics has been further investigated by means of scanning electron microscopy combined with energy-dispersive X-ray spectroscopy.

This paper discusses the effect of different surface treatments on shape memory alloy wires embedded in PolyEster (PE) and VinylEster (VE) polymeric matrices. In particular, two types of chemical etching and a chemical bonding with a silane coupling agent have been performed on the surfaces of the wires. Pull-out tests have been carried out on samples made from a specifically designed Teflon mould. Considering the best results of the pull-out tests obtained with PE resin, the debonding induced by strain recovery of 4%, 5% and 6% pre-strained NiTi wires has been evaluated with the wires being subjected to different surface treatment conditions and then being embedded in the PE matrix. The results prove that the wires functionalised and embedded in the PE resin show the maximum pull-out forces and the highest interfacial adhesion. Finally, it has been found that debonding induced by strain recovery is strongly related to the propagation towards the radial direction of sharp cracks at the debonding region.

The concept of smart morphing blades, which can control themselves to reduce or eliminate the need for active control systems, is a highly attractive solution in blade technology. In this paper, an innovative passive control system based on Shape Memory Alloys (SMAs) is proposed. On the basis of previous thermal and shape characterization of a single morphing blade for a heavy-duty automotive cooling axial fan, this study deals with the numerical analysis of the aerodynamic loads acting on the fan. By coupling computational fluid dynamics and finite element method approaches, it is possible to analyze the actual blade shape resulting from both the aerodynamic and centrifugal loads. The numerical results indicate that the polymeric blade structure ensures proper resistance and enables shape variation due to the action of the SMA strips.

This work is dedicated to optimization of carbide particle system in a weld bead deposited by PTAW technique over D2 tool steel with high chromium content. The paper reports partial melting of the original carbide grains of the Ni-based filling powder, and growing of the secondary carbide phase (Cr, Ni) $$_3$$ W $$_3$$ C in the form of dendrites with wide branches that enhanced mechanical properties of the weld. The optimization of bead parameters was made with design of experiment methodology complemented by a complex sample characterization including SEM, EDXS, XRD, and nanoindentation measurements. It was shown that the preheat of the substrate to a moderate temperature 523 K (250 $$^\circ $$ C) establishes linear pattern of metal flow in the weld pool, resulting in the most homogeneous distribution of the primary carbides in the microstructure of weld bead.

High-pressure die-cast (HPDC) components are being increasingly used due to good flexibility and high productivity. These aspects make HPDC suitable to produce several mass components, especially for the automotive sector. Due to the rapid filling of the die and high cooling rate, the process generally leads to the formation of a wide variety of defects, such as porosity and oxide films. Such defects might act as starting points for fatigue cracks and thus deteriorating the fatigue behavior of the casting. To this respect, the fatigue behavior of die cast aluminum alloys is an important aspect to consider when assessing the performance of complex castings for automotive applications. In the light of these aspects, the goal of this work is to describe how the microstructure affects the fatigue crack initiation and propagation. Die cast AlSi9Cu3(Fe) specimens were produced by means of a specifically designed die and the microstructure was preliminary characterized. Uniaxial fatigue tests were performed at load control with a stress ratio of R = 0.1 and at a single level of stress amplitude. After the fatigue tests, the samples were investigated to assess the propagation of the fatigue cracks; the starting points of cracks were specifically identified and the obtained data suggested how defects strongly influence the damage mechanism of the material.

Recently, an innovative AlSi3Mg alloy with Cr and Mn additions was developed for the production of truck wheels by means of a non-conventional hybrid technique, which combines features of both low pressure die casting and forging processes. The presence of both Cr and Mn leads to the formation of an intermetallic phase rich in Cr, Mn and Fe with a globular or dendritic morphology. Furthermore, proper solution treatments cause the formation of dispersoids in the aluminium matrix. These dispersoids are responsible of enhancing the alloy performance due to dispersion hardening mechanism. In the present work, the tensile properties and the impact toughness of the alloy in as-cast and different heat-treated conditions were studied. Moreover, tensile and impact strength tests were performed on A356 samples in T6 condition machined from traditional LPDC wheels, whose results were compared with the performance of the innovative alloy. Fracture surfaces of tensile and Charpy specimens were observed by Scanning Electron Microscopy (SEM) in order to identify the role of the Cr-Mn containing intermetallic particles in the failure mechanism and the influence of the heat treatment parameters. Considering the static properties, the innovative alloy showed remarkable values of tensile strength, while ductility was improved only after heat treatment optimization. Poor impact toughness values were measured and the microstructural analysis confirmed the presence of coarse intermetallic secondary phases, acting as crack initiation and propagation particles, on the fracture surfaces.

In this investigation, a nickel-base powder mixed with tungsten carbide particles was applied by Plasma Transferred Arc welding (PTA) on the surface of the D2 cold work tool steel to improve surface quality and to extend its lifetime during applications. The Design of Experiment (DoE) method was applied to obtain the appropriate combination of hardfacing parameters and to run the minimum number of tests. Current, travel speed and preheat were considered as variable parameters. These parameters are important to reach a final layer with an appropriate bead geometry accompanied with good metallurgical properties. All samples were prepared for metallurgical investigations and the effect of process parameters on the weld bead geometry was considered. For each experiment run, weld bead geometry parameters were measured including dilution, penetration and reinforcement. Microstructures and the distribution of tungsten carbide particles after welding were analyzed by Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) equipped with an EDS microprobe. In addition, hardness tests were performed to evaluate the mechanical properties of the weld bead layers. Finally, among all the experiments, the best sample with appropriate bead geometry and microstructure was selected. Resumo Nesta investigação, uma mistura de pó a base de níquel com partículas de carboneto de tungstênio foi aplicada por Soldagem a Plasma com Arco Transferido (PTA), na superfície de um aço ferramenta trabalhado a frio D2, para melhorar a qualidade superficial e ampliar o tempo de vida durante as aplicações. Para obter a combinação de parâmetros de aplicação do revestimento apropriada e para executar um número mínimo de testes, foi aplicado o método de Desenho de Experimentos (DoE). Corrente, velocidade de soldagem e pré-aquecimento foram considerados como parâmetros variáveis. Estes parâmetros são importantes para alcançar uma camada final com uma geometria do cordão adequada acompanhada por boas propriedades metalúrgicas. Todas as amostras foram preparadas para investigações metalúrgicas e o efeito dos parâmetros de processo sobre a geometria do cordão de solda foi considerado. Para cada experimento, foram medidos as dimensões da geometria do cordão de solda, incluindo a diluição, penetração e reforço. Microestruturas e a distribuição das partículas de carboneto de tungstênio após a soldagem foram analisadas por Microscopia Óptica (MO) e Microscopia Eletrônica de Varredura equipada com microssonda EDS. Além disso, ensaios de microdureza foram realizados para avaliar as propriedades mecânicas (MEV) das camadas de cordões de solda. Finalmente, entre todos os experimentos, a melhor amostra com microestrutura e geometria do cordão adequada foi selecionada.

In this research, the effect of the addition of nickel powder and the application of a post weld heat treatment (PWHT) on the welding properties of the UNS S32304 lean duplex stainless steel were investigated in order to improve the microstructure and mechanical properties. Nickel powder was directly poured inside the joint gap and mixed with the filler metal during the Gas Tungsten Arc Welding (GTAW) process; moreover, the solution heat treatment was performed at 1100 °C for 10 min. The joints were characterized by optical microscopy (OM) and the evolution of the phase percentages in the different zones was studied by means of the image analysis technique. Tensile and hardness tests were carried out on the joints in order to evaluate the improvement of the mechanical properties. The results showed that both the addition of nickel powder during the welding process and the post weld heat treatment made it possible to improve the mechanical properties of the weld joints. PWHT had the best effect in restoring the equal percentage of ferrite and austenite compared to the addition of nickel powder. Resumo No presente estudo, foi investigado o efeito da adição de pó de níquel e a aplicação de um tratamento térmico pós-soldagem (PWHT) nas propriedades de soldagem do aço inoxidável lean duplex UNS S32304, a fim de melhorar a microestrutura e as propriedades mecânicas. Pó de níquel foi diretamente vertido na abertura da junta e misturado com o metal de adição durante o processo de soldagem a arco com eletrodo de tungsténio e proteção gasosa (GTAW). Além disso, o tratamento térmico foi estabelecido em 1100 °C por 10 min. As juntas foram caracterizadas por microscopia óptica (MO) e a evolução das percentagens de fase nas diferentes zonas foi estudada por meio da técnica de análise de imagem. Os ensaios de tração e de microdureza foram realizados, a fim de avaliar a melhoria das propriedades mecânicas das juntas. Os resultados mostraram que tanto a adição de pó de níquel durante o processo de soldagem e o tratamento térmico pós-soldagem permitiram melhorar as propriedades mecânicas da junta soldada. PWHT mostrou o melhor efeito em restaurar a percentagem igual de ferrita e austenita comparado com a adição de pó de níquel.

The restoration of obliterated serial numbers is a problem of common occurrence in the forensic field. Among several restoration techniques, chemical etching is the most frequently used. The present research is aimed at studying the restoration of serial numbers, stamped on 40NiCrMo4 steel plates, by means of chemical etching. Microstructural characterization was firstly carried out to study the plastically deformed regions surrounding the marks. The obliteration was performed by controlled removals of material at increasing depths of erasure, and five etching reagents were considered to analyze their sensitivity and effectiveness. Experimental results revealed that Fry’s reagent was the most sensitive, able to restore erased marks up to 60 lm under the depth of the imprint. The reagent comprising 25 mL HNO3 and 75 mL H2 O provided good results, recovering the major numbers of characters. A descriptive statistical analysis was conducted to study the operator’s influence on the recovered marks’ identification.

In a traditional automotive cooling system, energy optimization could be achieved by controlling the engine temperature by means of several sensors placed inside the cooling circuit. Nevertheless, in some cases the increasing use of a great number of sensor devices makes the control system too bulky, expensive and not sufficiently robust for the intended application. This paper presents the development of a heavy-duty automotive cooling axial fan with morphing blades activated by Shape Memory Alloy (SMA) strips that work as actuator elements in the polymeric blade structure. The application of smart materials to compact, high-energy density devices as well as the development of modeling and control systems has been of great interest during the last decade. SMAs are frequently combined within monolithic or composite host materials to produce adaptive structures whose properties could be tuned in response to external stimuli. The blade was designed to achieve the activation of the strips (purposely thermo-mechanically treated) by means of an air stream flow. With the aim of studying the morphing capability of the adaptive structure together with the recovery behavior of the NiTi strips, four different polymeric compounds have been compared in a specifically-designed wind tunnel. Digital image analysis techniques have been performed to quantitatively analyze the blade deflections and to evaluate the most suitable polymeric matrix for the intended application. As the airstream flow increases in temperature, the strips recover the memorized bent shape, leading to a camber variation. To study the possibility of employing SMA strips as actuator elements, a comparison with common viscous clutch behavior is proposed. The time range actuator response indicates that the SMA strips provide a lower frequency control that fits well with the engine coolant thermal requirement. The experimental results demonstrate the capability of SMA materials to accommodate the lower power actuators in the automotive field. Finally, the blade tip airfoils, reconstructed using a CAD procedure, were used to study the fluid dynamic behavior of the blade tip airfoil. A CFD numerical simulation was carried out in order to highlight the differences in the airfoil performance due to the different shapes of the blade. The analyses showed that the activated blade tip airfoil led to an increase in the lift coefficient according to the stiffness provided by the polymeric compound. This innovative passive control system results from the selection of (i) the memorized shape of the SMA strips and (ii) the polymeric compound used for the blade structure.

The possibility to realize adaptive structures is of great interest in turbomachinery design, owing to the benefits related to enhanced performance and efficiency. To accomplish this, a challenging approach is the employment of shape memory alloys (SMAs), which can recover seemingly permanent strains by solid phase transformations whereby the so-called shape memory effect (SME) takes place. This paper presents the development of a heavy-duty automotive cooling axial fan with morphing blades activated by SMA strips that works as actuator elements in the polymeric blade structure. Concerning the fan performance, this new concept differs from a conventional viscous fan clutch solution especially during the nonstationary operating conditions. The blade design was performed in order to achieve the thermal activation of the strips by means of air stream flow. Two polymeric matrices were chosen to be tested in conjunction with a commercially available NiTi binary alloy, whose phase transformation temperatures (TTRs) were experimentally evaluated by imposing the actual operating thermal gradient. The SMA strips were then thermomechanically treated to memorize a bent shape and embedded in the polymeric blade. In a specifically designed wind tunnel, the different polymeric matrices equipped with the SMA strips were tested to assess the fluid temperature and surface pattern behavior of the blade. Upon heating, they tend to recover the memorized shape and the blade is forced to bend, leading to a camber variation and a trailing edge displacement. The recovery behavior of each composite structure (polymeric matrix with the SMA strips) was evaluated through digital image analysis techniques. The differences between the blade shape at the initial condition and at the maximum bending deformation were considered. According to these results, the best coupling of SMA strips and polymeric structure is assessed and its timewise behavior is compared to the traditional timewise behavior of a viscous fan clutch.

In recent years, a considerable effort has been devoted towards the application of advanced techniques for turbomachinery efficient fluid dynamic control during operations. A novel strategy to dynamically modify and optimize the performance during operations takes advantage of shape memory alloys properties. Experimental and numerical analyses on a morphing polymeric blade for an automotive axial fan are presented. The blade shape change was achieved by shape memory alloys strips, thermomechanically treated, embedded in the blade and thermally activated by hot air stream flow. Measurement of fluid temperature, blade surface temperature pattern and three-dimensional shape change of the blade during activation was performed by means of an innovative image analysis technique in a purpose-built wind tunnel. Computational fluid dynamics numerical simulations were performed to study performance variations and three-dimensional fluid dynamic behavior of the fan originated from the shape memory effect.

This paper deals with the two-way shape memory effect (TWSME) induced on a strip of a nearequiatomic NiTi alloy by means of the shape memory cycling training method. This procedure is based on the deformation in martensite state to reach the desired cold shape followed by cycling the temperature from above Af to below Mf. To this end, the sample was thermally treated to memorise a bent shape, thermomechanical trained as described and thermally cycled in unloaded conditions in order to study the stability of the induced TWSME. Heating to Af was reached by a hot air stream flow whereas cooling to Mf was achieved through natural convection. The evolution of the curvature with the increasing number of cycles was evaluated. The thermomechanical behaviour of the strip undergoing uniform bending was simulated using a one-dimensional phenomenological model based on stress and the temperature as external control variables. Both martensite and austenite volume fractions were chosen as internal parameters and kinetic laws were used in order to describe their evolution during phase transformations. The experimental findings are compared with the model simulation and a numerical prediction based on the approach proposed in [25].

A bronze bowl belonging to a private collection, stylistically consistent with the Achaemenid art was investigated to determine the cause of the artwork local fragmentation. The corrosion products were characterised by energy dispersive X-ray fluorescence spectrometry (EDXRF), Raman spectroscopy and scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). The last technique was also used to determine the chemical composition of the alloy. The metallographic analysis showed that the bowl was obtained from a monophasic bronze alloy, containing about 11% tin and other elements in traces. The presence of an inhomogeneous microstructure with both thermal twin bands and slip lines was consistent with multiple hammering steps followed by partial annealing treatments. On the bowl a very limited chloride contamination was observed and chlorides were never detected in proximity to the metal. These findings and the morphological/compositional characteristics of the patinas permitted to classify that on the internal side of the bowl as a modified Type I morphology, while the patina on the external side of the bowl was less compact, so that it was judged borderline between a “noble” patina and a disfiguring one. On this side, a significant intergranular attack was found, reputed responsible for the fragmentation occurred.

The friction and wear behaviour of a carbon steel in sliding contact with a plasma-sprayed ceramic coating (Cr 2 O 3 ) is investigated under different conditions of normal load and relative humidity, through a pin-on-disk equipment. The samples are analysed by means of Optical Emission Spectroscopy (OES), Optical Microscope (OM), Scanning Electron Microscope (SEM) with Energy Dispersive Spectroscopy (EDS), X-ray Diffraction (XRD), surface roughness, fracture toughness and microhardness tester. The friction was continuously monitored during the tests while the wear rate of the coatings was evaluated by measuring the wear scar profiles after the tests. The wear rate of the pins was determined by weighing them before and after the wear tests. For all the normal loads applied in dry conditions, the metallic film transfer onto the ceramic surface was observed. In wet conditions, the metal transfer largely depended on the normal load applied. Microcracks were noticed along the splat and columnar grains boundaries on the Cr 2 O 3 wear scars. The observations of the worn surfaces of the pins indicate a mild-oxidational wear mechanism with the appearance of ploughing and plastic deformation.

In this study the influence of heat input (HI) and heat treatment on submerged arc welded duplex SAF 2205 steel joints has been evaluated. In particular, multi-pass welding operations have been performed on 18 mm thick plates using four different heat inputs; a post-weld solubilizing heat treatment has been carried out in order to reduce the microstructural effects on the structure of the heat affected zone (HAZ). Instrumented impact strength tests have been performed on Charpy samples machined from the welded joints; the total absorbed energy and the two complementary contributions of initiation and propagation energies have been evaluated and correlated to the percentages of ferrite and austenite. The microstructures and the fracture profiles have been observed using an optical microscope (OM) and quantitatively analyzed by means of an image analyzer. A scanning electron microscope (SEM) equipped by energy dispersive X-ray spectroscopy (EDS) has been used to study the fractured surfaces. Hardness profiles have been performed across the joints in order to verify the hardness variations. A total absence of secondary phases has been found on the joints due to the performing of a suitable solubilizing heat treatment after the welding process. The results have shown that the impact properties of the samples have been mostly affected by the different heat inputs; in some cases a partial welding penetration has been found.

Instrumented impact strength tests have been carried out on KV sub-size Charpy samples drawn from A356 aluminium alloy 17-in. wheels, produced by a low-pressure die casting. The wheels show different geometry and thermal treatment. In this paper, the effects of microstructure and defects on the impact properties are studied. The results indicate that the impact energy is lower in as-cast wheel than in T6 heat-treated wheels. A finer microstructure always corresponds to higher impact strength, while a direct correlation between the resistance to crack propagation values and secondary dendrite arm spacing (SDAS) exists. Casting defects, revealed by means of X-ray and density measurements techniques, become critical when concentrated around the V-notch, where they reduce the load bearing area of Charpy specimens. The fracture profile and surface of Charpy specimens have been investigated revealing how the crack crosses the interdendritic eutectic region where a significant fraction of cracked eutectic silicon and intermetallic particles is found. Numerical simulations have been performed to study the filling and solidification behaviour of the alloy of the wheels analysed, in order to predict the final microstructure and shrinkage formation. Solidification times, estimated by means of SDAS measurements and calculated with a numerical simulation approach, show a good correspondence. Critical areas, as concern hot spots and shrinkage porosities, are generally revealed in the zone of the wheels between the spoke and the rim, as well as in the rim area.