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Co28Cr6Mo alloy is one of the most widespread biomaterials used for the fabrication of permanent implants that nowadays can be processed by Additive Manufacturing (AM) techniques. In fact, the biomedical field takes great advantages from additive technologies, specifically Selective Laser Melting (SLM), due to the possibility of realizing tailored devices, based on the actual patience needs. Conventional processing routes of this alloy are complex and often require a heat treatment aimed at improving, for example, wear resistance. However, by considering the very fine and peculiar SLM microstructure, heat treatment parameters should be specifically optimized. The present work focused on the investigation of the effects induced by aging treatments in the microstructure of SLM Co28Cr6Mo alloy. The analyses allowed to delineate the evolution occurred in the microstructure as a consequence of thermal exposure and to identify the conditions which determine the complete modification of the as-built microstructure.

The Co28Cr6Mo alloy is a well-established metallic biomaterial, widely used for the fabrication of orthopaedic permanent implants for joint replacement. Nowadays the manufacturing of Co28Cr6Mo medical devices is expensive and time consuming in the reason of high melting point, high hardness and low machinability of this alloy. The Additive Manufacturing (AM) technologies, such as Selective Laser Melting (SLM), allow to simplify the manufacturing route and, noteworthy, to realize customized implants based on patient-specific needs. However, many concerns remain to obtain high quality and reliable components; in particular, the relationship between the different process parameters and the final microstructure needs a deeper investigation. In the present work a wide range of process parameters have been considered for the production of SLM specimens and the corresponding final microstructure has been fully characterized. The experimental investigation allowed to define the best processing window of energy density values for producing near full-density and defect-free components.

The fatigue behavior of Al-Si-Mg castingalloys is affected by the solidificationmicrostructure and especially by defects suchas gas pores, shrinkage pores and oxidefilms. This paper reports the microstructuralcharacterization of a die cast engine headmade of the A356 (G-AlSi7Mg0.3) alloy andthe long-life fatigue strength determinationusing specimens extracted from the cast. Themicrostructural characterization wasachieved by optical microscopy and digitalimage analysis to identify the different classesof solidification defects and to evaluate thecorrelation between local SDAS and the sizeand shape of the defects. Fatigue testing wasperformed under rotating bending and thestress amplitude vs cycles to failuredependence showed a large scatter. Thereason for this is related to local stressconcentration induced by the pores, whichwas analyzed by the finite element method,developing models of a material volumecontaining solidification pores characterizedby 2D and 3D techniques (i.e. opticalmicroscopy with image analysis and X-raytomography, respectively).

The aim of the present research was to study the effect of the Friction Stir Welding process on the microstructure and impact toughness of the composites W6A20A (AA6061 reinforced with 20vol.% of Al2O3 particles) and W7A10A (AA7005 reinforced with 10vol.% of Al2O3 particles). FSW, because of the concurrent effect of severe plastic deformation and frictional heating during welding, had effects both on the reinforcing particles and the aluminium matrix. It induced a significant reduction in the reinforcement particles size and their better distribution in the welded zone as well as a grain refinement of the aluminium alloy matrix in the nugget due to dynamic recrystalizzation. The frictional heating, moreover, had effects on the growth, dissolution and re-precipitation of hardening precipitates. The impact tests showed that the total impact energies increased in the FSW composites, respect to the corresponding base materials.

This study focuses on components for a pressing device involved in a sliding contact. In particular, the tribosystem consists of a pin (AISI A2 tool steel) and a guide plate (UNS C95500 aluminium bronze) coupled under a counterformal line contact. Firstly, the main wear mechanisms in the pin/guide plate contact were identified by failure analysis on real components after field operation, in order to define the conditions for lab-scale dry sliding tests (block-on-ring). Adhesive wear of bronze (leading to material transfer on steel) and two-body abrasion due to hard carbides from tool steel were the main wear mechanisms in field operation. Secondly, lab-scale tests were carried out for studying the influence of (i) applied load, (ii) sliding speed and (iii) bronze microstructure (as-cast condition or precipitation hardened) on tribological behavior. Tribological laboratory tests showed that the coefficient of friction of the bronze/steel couple was more influenced by applied load and sliding speed than by bronze heat treatment conditions. The wear behavior of bronze is mainly influenced by its work hardening capacity as well as by its ability to form a stable and protective copper oxide surface layer.

This study detected and investigated the degradation effects and dynamics of the tin amalgam reflective layer of ancient mirrors. The experimental results have been obtained by different spectroscopic techniques: Light Microscopy, Scanning Electron Microscopy with Energy Dispersive X-ray Microanalysis (SEM–EDS), Atomic Force Microscopy (AFM) and μ-Raman Spectroscopy. The latter two were applied for the first time to characterize the amalgam of ancient mirrors. Amalgam alteration products in form of concentric rings with alternate different compositions of tin oxides have been studied on both the amalgam reflective layer inner surface and on its cross-sections. For the first time SEM images of micro-cross-sections of different amalgam degradation products, such as amalgam “drops” and craters, have been obtained. The size of the nano-particles of tin oxides, as amalgam degradation products, was estimated around 3–8 nm by AFM and micro-Raman, as already previously detected through TEM. Micro-Raman showed the presence of both cassiterite and romarkite nano-crystals forming the concentric rings, as only previously hypothesized. This investigation allowed to obtain further experimental evidence and a more advanced comprehension about the structure and formation phases of the amalgam decay products, giving further support to some statements by previous authors and suggesting some assertions different from the ones of previous studies.

Al-Si-Cu alloys with high Fe content are widely employed in high pressure die casting (HPDC). Even if Fe is usually considered an impurity in secondary aluminum alloys, leading to the formation of harmful intermetallic compounds, it helps in mitigating or eliminating the problem of die soldering. As a result, secondary Al alloys with Fe content of about 1 wt% are commonly employed for the production of HPDC castings. Aiming to change the morphology of harmful Fe-bearing phases towards less detrimental morphologies, proper alloying elements may be added to the alloys. Mn and Cr (both present in the aluminum scrap), as instance, are reported to prevent from the formation of the acicular β-Al5FeSi phase, leading to the formation of more compact and polygonal intermetallics. Such phases are usually referred to as “sludge” particles. The influence of sludge particles on mechanical properties of Al-Si-Cu castings is still under investigation. The present work aims at evaluating the effect of impurities (Fe, Mn and Cr) typically present in secondary Al alloys on the microstructure and mechanical properties of the A380 (Al-Si-Cu) alloy. Samples with different Fe, Mn and Cr content were produced and processed through a directional solidification equipment to obtain specimens with controlled SDAS (~10 μm). Hardness and rotating bending fatigue tests were carried out at room temperature. Mechanical properties of the alloys were then related to the microstructure, analyzed by optical and scanning electron microscopy.

This research activity was focused on the microstructural and mechanical characterization of an innovative rare earth rich magnesium alloy, EV31A (Elektron 21®), in the sand cast and standard T6 conditions. Microstructural analyses were carried out by means of optical and scanning electron microscopy, in order to highlight the microstructural evolution induced by the heat treatment. The results show different intermetallic particles and eutectic compounds which, depending on their composition, may dissolve or not during solution treatment. Specific yield and ultimate strength of the investigated alloy were reported to be higher if compared to the more common AZ91 magnesium alloys and comparable to that of the widely used A356 cast aluminum alloy.