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This study aims to develop Ni-P coatings with high P content (≥11 wt.%) reinforced with WC nanoparticles on F22 steel substrates. The introduction of conductive WC in the plating solution dramatically increases reactivity of the plating solution, and consequently a tuning of deposition parameters, in terms of temperature and WC concentration, is required to obtain nanocomposite coatings with improved mechanical properties. The coatings' porosity and incorporation and dispersion of the reinforcing phase as a function of temperature and WC concentration were analyzed by quantitative image analysis from Scanning Electron Microscopy (SEM) micrographs. Increasing the temperature and concentration of nanoparticles leads to a faster plating rate and a dramatic increase in both porosity and agglomeration of the reinforcing phase, with detrimental effects on the coatings' microhardness. The best compromise between coating parameters was obtained by deposition at 70 °C and 6.5 g/L of WC, with a plating rate ≈ 12 μm/h, porosity lower than 1.5%, and a good combination between particle incorporation and agglomeration. In these conditions, a hardness increase by 34% is achieved in comparison to standard Ni-P. Coatings were then heat treated in air at 200 °C for 2 h, to induce growing stress relaxation, or 400 °C for 1 h, to study effects of crystallization and precipitation. X-Ray Diffraction (XRD) analysis demonstrated that WC introduction does not alter the microstructure of Ni-P coatings, but delays grain growth coarsening of precipitates. Hardness improvement by 6.5% and 45% is registered after treatment at 200 °C and 400 °C, respectively. An increase in elastic modulus, measured by instrumented indentation, was found in WC-reinforced coatings compared with Ni-P. Potentiodynamic polarization tests revealed that both introduction of WC nanoparticles and heat treatment also enhance corrosion resistance. [ABSTRACT FROM AUTHOR]

Unalloyed copper objects were produced in the Chalcolithic Southern Levant in a two‐step process. Copper ore was smelted in pit furnaces, and the mechanically extracted copper prills melt in crucibles and cast into objects. However, the air supply remained unknown, and practical considerations shed doubt on the validity of some of the reconstructed practices. To refine the reconstruction, the metallurgical material from Abu Matar was reassessed. Most importantly, several previously unreported fragments suggest the use of bellows and covering the furnace with large pottery fragments. Our results provide probably the earliest evidence for the use of bellows. [ABSTRACT FROM AUTHOR]

Shape memory effect (SME) and the relation with corrosion behavior of Cu-Zn-Al Smart Memory Alloys (SMAs) were investigated using different techniques: Scanning Electron Microscopy equipped with an Energy Dispersive System, X-Ray Diffraction analysis, Electrochemical Test in NaCl solutions with different concentrations (0.035%, 0.35% and 3.5%), which simulate coastal conditions, mechanical characterization through tensile test and guided bend test. SMAs are an important class of smart materials able to recover after deformation a pre-imposed shape through a temperature modification. These alloys show great potential, finding several applications in medicine and in different types of industry sectors (aerospace, architecture, automotive etc.). Cu-based SMAs, including Cu-Zn-Al alloys, have lower production costs with respect to Ni-Ti alloys as well as good possibility in seismic and architectural applications. A Cu-Zn-Al alloy with a theoretical composition of 25 wt.% Zn and 4 wt.% Al was produced by casting method. The aim of this study is to characterize the microstructure, the mechanical properties and the corrosion behavior through different kind of standard corrosion tests of this alloy and to evaluate the effect of corrosion damage on the shape memory recovery capability through a combination of corrosion and thermo-mechanical cyclic test and SEM observations. [ABSTRACT FROM AUTHOR]

The aim of this work is to design a lightweight, creep-resistant blade for an axial single-stage micro-gas turbine. The selected process was casting of an intermetallic titanium/aluminum alloy. All the project phases are described, from the preliminary thermodynamic and geometric stage design, to its three-dimensional (3D) modeling and the subsequent finite element method-computational fluid dynamics (FEM-CFD) analysis, to the manufacturing process of the single rotor blade. The blade making (height 7 cm and chord 5 cm, approximately) consisted in a prototyping phase in which a fully 3D version was realized by means of fused deposition modeling and then in the actual production of a full-scale set of blades by investment casting in an induction furnace. The produced items showed acceptable characteristics in terms of shape and soundness. Metallographic investigations and preliminary mechanical tests were performed on the blade specimens. The geometry was then refined by a CFD study, and a slightly modified shape was obtained whose final testing under operative conditions is though left for a later study. This paper describes the spec-to-final product procedure and discusses some critical aspects of this manufacturing process, such as the considerable reactivity between the molten metal and the mold material, the resistance of the ceramic shell to the molten metal impact at high temperatures, and the maximal acceptable mold porosity for the specified surface finish. The CFD results that led to the modification of the original commercial shape are also discussed, and a preliminary performance assessment of the turbine stage is presented and discussed. [ABSTRACT FROM AUTHOR]

Shape memory property characterizes the behavior of many Ti based and Cu based alloys (SMAs). In Cu-Zn-Al SMAs, the original shape recovering is due to a bcc phase that is stable at high temperature. After an appropriate cooling process, this phase (β-phase or austenitic phase) transforms reversibly into a B2 structure (transition phase) and, after a further cooling process or a plastic deformation, it transforms into a DO3 phase (martensitic phase). In β-Cu-Zn-Al SMAs, the martensitic transformation due to plastic deformation is not stable at room temperature: a high temperature "austenitization" process followed by a high speed cooling process allow to obtain a martensitic phase with a higher stability. In this work, a Cu-Zn-Al SMA in "as cast" conditions has been microstructurally and metallographically characterized by means of X-Ray diffraction and Light Optical Microscope (LOM) observations. Fatigue crack propagation resistance and damaging micromechanisms have been investigated corresponding to three different load ratios (R=0.10, 0.50 and 0.75). [ABSTRACT FROM AUTHOR]

Absorption chillers generate chilled water by employing as refrigerant water which is evaporated at low pressure. The steam produced is then absorbed by a concentrated LiBr solution. The materials employed for the construction of this kind of plant are usually copper and stainless steel. Despite their good corrosion resistance, the environment rich of halogen ions can lead in some cases to severe corrosion attacks. This paper describes a complex case of corrosion that produced the failure of an absorption chiller pipelines. The failure involved in different steps both copper and stainless steel pipes. [ABSTRACT FROM AUTHOR]

The present paper describes the failure analysis of an aircraft component subjected to several episodes of in service failure, resulted in loss of the aircraft safety. Modern aircrafts are provided with mechanical systems which have the task to open not pressurized hatches during landing. The components of such systems are subject to considerable mechanical stresses in harsh environment (presence of moisture and pollutants, significant and sudden temperature variations). The system is constituted by a sliding piston, a related nipple and by a locking system consisting of 4 steel spheres which are forced into a countersink machined on the piston when the hatches is open. The whole system is activated by a preloaded spring. The machined parts, nipple and piston, are made of EN3358 steel (X3CrNiMo13-8-2), a precipitation hardening stainless steel with very low content of carbon often used in the aerospace. The samples provided by the manufacturer present different types of damage all referable to phenomena relative to the sliding of the piston inside the nipple. The present paper describes the different damage observed and the microstructure of the material, then are reported the results obtained from the characterization of the material of the samples by means of optical and electronic microscopy, carried out to define the mechanisms involved in the system seizure. In order to define the primary cause of failure and to propose solutions to be adopted, also analyzing the criticality of using this PH stainless steel for this application, the results of different tests were compared with system design and working data. [ABSTRACT FROM AUTHOR]

γ-TiAl has been a hot topic of research for more than a few decades now, since it is a potential candidate for high temperature structural applications. In this paper, dispersion strengthening of γ based TiAl alloy, produced by means of centrifugal casting, has been performed to increase its mechanical properties beyond those of standard TiAl alloys. After a careful selection of the alloy composition based on the desired properties, several samples were produced by means of investment casting. This work focused on the effect of Al2O3 nano- and micro-dispersoids on the mechanical properties of the considered TiAl alloy. Microstructural investigations were carried out to study both the alloy microstructure and the Al2O3 dispersion homogeneity. Samples of the produced alloy were subjected to four-point bending tests at different temperatures for evaluating the effect of dispersed particles on mechanical properties. The results of this study were promising and showed that Al2O3 dispersion determined an increase of the mechanical properties at high temperatures. The Young's modulus was 30% higher than that of the reference alloy in the lower temperature range. Over the temperature range 800–950 °C the dispersion strengthening affected the yield stress by increasing its value of about 20% even at 800 °C. A detailed evaluation of fracture surfaces was carried out to investigate fracture mechanisms. [ABSTRACT FROM AUTHOR]

In this work selective laser melting was successfully utilized to produce 316 stainless steel bulk specimens. Although this technology provides many advantages compared to conventional shaping processes, little residual porosity may be a problem for some applications where high strength is required. The objective of this work was to determine, through data analysis, a mechanical and metallographic comparison between thin sheets made by using different manufacturing technologies: Cold rolling and additive manufacturing. This comparison was useful to understand whether it could be more advantageous to use the prototyping for new mechanical components. The results show that the additive manufactured steel, due to its microstructure, is characterized by a higher yield strength and by a lower elongation and ultimate tensile strength. [ABSTRACT FROM AUTHOR]

The oxidation behaviour of six different TiAl–Cr–Nb–Mo alloys was investigated by thermogravimetric method. Isothermal experiments were carried out at 900 °C and 1000 °C in air. The aim of this work was to evaluate the effect of aluminium and of other alloying elements on the oxidation behaviour of TiAl intermetallic alloys. The alloy's microstructure and composition as well as the composition distribution of the oxide scales were analysed by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and X-Ray Diffractometry (XRD). The study highlighted that the oxidation resistance of the considered TiAl-based alloys is strongly affected by its aluminium content, while it seems that an increase of Cr, Nb and Mo concentrations does not affect the oxidation behaviour of the alloy. Yttrium addition, at least in the tested quantity, has a detrimental effect since it promotes the formation of a TiO2–Al2O3 mixed oxide instead of a compact and thin alumina layer. [ABSTRACT FROM AUTHOR]