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The present study is focused on the wear behavior of an innovative AlMgScZr alloy manufactured using the laser powder bed fusion process. This material, commercially known as Scalmalloy®, exhibits high strength and ductility, together with low anisotropy, which instead represents a strong limitation for other alloys produced by additive manufacturing processes. The typical heat treatment for this alloy is an annealing treatment at 325 °C, which leads to a further increase in mechanical performances as a result of precipitation of intermetallic particles containing Sc and Zr. These precipitates usually exhibit good thermal stability, as shown by studies of alloys with similar chemical composition but manufactured via conventional processes. This ensures good performance of the alloy also at high temperatures, in the range 100-250 °C. Among the mechanical properties of this innovative alloy, wear resistance has rarely been studied so far, especially as a function of temperature. However, its evaluation can provide valid ideas for new applications, not only in the aerospace industry, but also in the automotive field. For this reason, the wear behavior of AlMgScZr alloy at high temperatures has been studied in this work. Pin-on-disk tests were performed at different temperatures on samples produced by additive manufacturing followed by annealing at 325 °C for 4 h. The coefficient of friction was monitored during the tests and the wear rate was calculated from the measurement of the track profile. Furthermore, the damaging mechanisms were accurately studied by observations of the morphology of the sample surface after progressive testing. These analyses, performed by using a scanning electron microscope, allowed the identification of the evolution of the wear mechanism with temperature. These results can be used for the determination of optimum ranges for application of this alloy for components that can experience high temperature exposure during their service.

The application of an innovative high-pressure T6 treatment (HPT6) to additively manufactured AlSi10Mg alloy is reported in this paper. The aim of this treatment is to obtain the effective densification of the material together with the hardening effects typical of T6 heat treatment in one step. For comparison, a two-step treatment consisting of hot isostatic pressing followed by conventional T6 treatment was applied. Standard annealing and T6 treatment alone were also considered. The microstructural and mechanical properties of alloys treated under all the studied conditions were analyzed and their density was measured to quantify their densification. Although the application of high pressure hindered the diffusion mechanisms, and thus could limit the hardening effect of heat treatment, HPT6 treatment was found to ensure suitable mechanical properties and high densification. Furthermore, it required less time; therefore, it can be considered as a time-efficient process for high-performance applications.

A series of commercial and non-conventional heat treatments was performed to modify the initial as-cast microstructure of two high-chromium (14 wt% and 18 wt% Cr) white cast irons and a low chromium nickel-bearing grade (Ni-Hard 2) for slurry pumping applications. The effect of each heat treatment on the microstructure of the alloys was carefully investigated by optical and scanning electron microscope and X-ray diffraction analysis. Samples were tested for impact erosion resistance in flowing slurry by using a modified-Coriolis apparatus and their weight losses were related to microstructure and hardness. The analysis showed that the erosion resistance of these alloys is related to the carbides volume fraction and hardness, in combination with the matrix microstructure. In case of high-chromium white irons, the destabilization heat treatment (950°C-2h) produced a hard martensitic matrix with secondary carbides that gave superior erosion resistance compared to all other conditions. Excellent performances were obtained also for Ni-Hard 2 in as-cast condition, indicating that this alloy could be an economic alternative to high chromium irons in applications where good erosion resistance is required.

Electric arc furnace (EAF) slags were investigated by micro-Raman spectroscopy. A slag sample characterised by well-developed crystalline phases was obtained. The EDXS elemental composition made it possible to recognize the grains corresponding to the brownmillerite, larnite and magnesioferrite phases, as identified by XRD in the same powdered sample. The grains were collected and analysed by &micro, Raman spectra, and the results showed good reproducibility in each grain and good agreement with spectra of the phases reported in the literature. A Raman database devoted to crystalline phases of EAF slag identification was created to be used by portable Raman instruments, allowing the phase characterisation of the slag directly during steel production.

In the present work, the effect of Cr and Mn addition on corrosion resistance was investigated on AlSi3Mg alloy. Potentiondynamic corrosion tests in a 3.5 wt. % NaCl solution were performed on samples in different heat-treated conditions, and corrosion current density and potential were determined by Tafel method. Brinnel hardness measurements were also carried out in order to couple corrosion resistance with mechanical properties. It was interestingly found that Cr presence enhanced mechanical properties and corrosion resistance in comparison with the base alloy.

Heavy-section ductile iron castings solidify under low cooling rates, giving the risk to form defects like non-metallic inclusions, microporosities and degenerated shapes of graphite that have a negative effect on fatigue resistance, favoring the crack nucleation. The aim of this work is to precisely identify the defects that most affect the fatigue behavior in heavy-section castings, in order to guide the foundry to take the proper countermeasures. For this purpose, fatigue rotating bending tests were carried out on specimens machined from small-scale samples opportunely cast to reproduce long solidification times. The fracture surface of broken samples were investigated by means of Scanning Electron Microscopy in order to identify crack initiation points and fracture mechanisms. Shrinkage porosities and spiky graphite were found to play the most important effect on crack nucleation, lowering the fatigue resistance of the castings, while chunky graphite just behaved as a preferential path for crack propagation.

The goal of this paper is to investigate the failure of a mandrel pin mounted on a rolling contact test bench. For this purpose, different methods of analysis were conducted, including metallography and stress analysis. The stress values in the failed pin were determined by Finite Elements. The high notch effect and the incorrect mounting of the specimens were identified as the failure causes. A pin design change is proposed to reduce the maximum stress even in the case of incorrect specimen mounting.

The influence of chunky graphite on mechanical properties, especially on fatigue resistance, of an EN-GJS-400 ferritic ductile iron, was investigated by tensile and rotating-bending tests. The samples for the experiments were machined from two heavy section castings. The first one was cast with the addition of a Ce-containing inoculant to promote chunky formation and the second one by using a standard Ce-free inoculant. The presence of chunky graphite in the samples decreased tensile strength and elongation at break, while no significant effect on the hardness and yield strength was measured. Also fatigue strength was negatively affected, with a decrease of fatigue limit of about 12%. This value was calculated also taking into account the different amount of microporosity in the two sets of samples and its effect on the fatigue strength by using the Murakami approach.Fracture analysis showed that chunky graphite has a limited influence on fatigue crack nucleation if compared to micro-shrinkages, while it behaves as a preferential path for crack propagation. A simple way to consider the presence of chunky graphite in the fatigue design of heavy section ductile irons is proposed on the basis of the present results and taking into consideration the published data too. Keywords: Ductile cast iron, Chunky graphite, Fatigue limit, Microporosity, Analysis of statistics of extremes, Fracture analysis

A solution, quenching and ageing heat treatment is often performed on additive manufactured AlSi10Mg parts to dissolve the anisotropy due to the layer-by-layer building. This study investigates the influence of temperature and duration of solution and ageing treatment on microstructure, hardness and density of AlSi10Mg alloy produced by direct metal laser sintering. A parallel investigation is carried out on AlSi10Mg samples produced by gravity casting to analyse the different response to the same heat treatment conditions. The highest hardness, combined with an acceptable increase of porosity, is reached after selected heat treatment parameters. It was also found that, compared to the as-produced condition, this treatment leads to a decrease of ultimate tensile strength, without affecting the yield strength of additive manufactured samples, and reduces the difference in properties along the two building directions. The high properties of the as-produced samples are related to the finer microstructure and, as proved by the differential scanning calorimetric measurements, to the self-quenching phenomenon.

30NiCrMoV12 quenched and tempered samples were coated with 4 μm of CrN produced by cathodic arc deposition technique. Micro-blasting treatment was performed on the coated samples, after the deposition, to remove defects like droplets from the surface. The fatigue limit was assessed and compared to that of the bare steel. A basic characterization of the coating/substrate was performed (hardness, roughness and adhesion). The residual stress distribution next to the surface of the samples was measured and its effect on the fatigue limit was evaluated. The micro-blasting treatment does not adversely affect the hardness and the adhesion of the coating nor the fatigue resistance of the coated samples.

This study is a detailed failure analysis of galvanized high carbon steel wires, which developed coating cracks during the torsion test performed as a quality control at the end of the manufacturing process. Careful visual inspections showed that the cracks are already present in the coating before the torsion test. In order to explain the origin of these cracks, systematic metallographic investigations were performed by means of optical and scanning electron microscope on both the wires and the rods that have been cold drawn to produce the wire. The chemical composition of the galvanized coatings was evaluated by means of energy dispersive spectroscopy. Micro bidimensional X-ray diffraction experiments were also performed to measure the residual stresses in the galvanized coating. The results showed that the failure is related to two main factors: the relatively high content of silicon in the steel and the unsuitable cooling rate of the rods at the exit from the galvanizing bath. The mechanism proposed to explain the origin of the defects was supported by Finite Elements Methods simulations and verified with in-plant tests. The proper countermeasures were then applied and the problem successfully solved.

In heavy section cast iron components, anomalous microstructures can be formed especially at the core, because of low cooling rate, with a consequent decrease in mechanical properties. The matrix microstructure, the presence of surface defects, such as inclusions and porosities, and the size and morphology of graphite nodules are critical issues to ensure the adequate performance of the component in fatigue applications. Proper design of heavy section ductile iron castings requires a database of information about microstructures and mechanical properties that nowadays is missing or is very poor. In this paper, we presented the mechanical characterization of ductile irons with solidification times up to 20 h, carried out to identify the metallurgical and the process parameters that most affect the improvement in fatigue strength. An innovative production line was designed, aimed at reproducing on a small-scale sample the characteristics of heavy walled components. A standard ferritic ductile cast iron compared to a ferritic cast iron with high silicon content and a fully pearlitic ductile cast iron were studied by tensile, Brinell hardness and rotating bending fatigue tests. Optical microscope analysis and scanning electron microscope observations of the most significant fracture surfaces were also performed. It was concluded that the ferritic cast iron is more suitable for the production of large thickness castings undergoing fatigue loads, because the decrease in ductility and its effect on other properties is less pronounced.

Damaged DLC coatings usually require remanufacturing of the entire coated components starting from an industrial chemical de-coating step. Alternatively, a complete or local coating repair can be considered. To pursue this approach, however, a local coating removal is needed as first operation. In this context, controlled decoating based on laser sources can be a suitable and clean alternative to achieve a pre-fixed decoating depth with high accuracy. In the present study, we investigated a laser-based decoating process executed on multilayered DLC films for advanced tribological applications (deposited via a hybrid PVD/PE-CVD technique). The results were acquired via multifocal optical digital microscopy (MF-ODM), which allowed high-resolution 3D surface reconstruction as well as digital profilometry of the lasered and unlasered surface. The study identifies the most critical process parameters which influence the effective decoating depth and the post-decoating surface roughness. In particular, the role of pulse overlap (decomposed along orthogonal directions), laser fluence, number of lasing passes and assist gas is discussed in text. A first experimental campaign was designed to identify the best conditions to obtain full decoating of the DLC + DLC:Cr layers. It was observed that decreasing the marking speed to 200 mm/s was necessary to obtain a sufficient pulse overlap and a nearly planar ablation profile. By operating with microsecond pulses and 1 J/cm2 (fairly above the ablation threshold), less than 10 passes were needed to obtain full decoating of the lasered area with an etching rate of 1.1 μm/loop. Further experiments were then executed in order to minimise the roughness of the rest surface with the best value found at around 0.2 μm. Limited oxidation but higher R a values were observed in Ar atmosphere.

Aluminum segregation in zinc alloys is a well-known problem during melting and casting. In molten Zn alloys, in fact, Al tends to float on the surface of the bath because of its lower density than zinc. The same problem also occurs during casting solidification, causing chemical gradients along part thickness and soundness problems. As a consequence, the use of high aluminum content zinc alloys, such as ZA27, can be limited.In this paper the effectiveness of rheocasting method on decreasing Al-segregation phenomenon in ZA27 was investigated. The slurry was obtained by using the ultrasound technique, starting from the fully liquid down to different solid fraction percentages. The metal was then cast into a permanent steel mold. The produced samples were completely characterized by metallographic analysis (optical and scanning electron microscope), to assess the microstructure modification induced by the treatment. Hardness tests were also performed to evaluate mechanical properties. For comparison, the same tests were performed on conventionally cast samples.The analyses show that the use of a semisolid alloy increases the homogeneity of the part in terms of hardness, chemical composition and microstructure; furthermore casting’s shrinkage porosity is significantly reduced.

Zinc alloys are known for their low melting point, high castability, and useful wear resistance in certain applications, and at a relatively low cost. In the recent years, many attempts have been made to substitute more expensive copper alloys for zinc-based materials in wear-critical parts. In this regard, the most investigated zinc alloy is ZA27, but good wear resistance can be also achieved by using an alloy with lower aluminium content, like Zamak2. In this paper, the sliding wear behavior of a novel zinc alloy ZnAl15Cu1 was compared to that of ZA27 and Zamak2 in order to assess its relative suitability for applications where sliding wear resistance is required. Pin-on-disk tests were carried out using both bearing steel and a leaded brass sliding partners under three loads and various sliding distances. Friction coefficient and wear rates were compared. Analyses of the worn surfaces was done to identify the damage mechanisms and to understand the friction coefficient behaviour. The ZnAl15Cu1 alloy exhibited wear resistance that is comparable to or better than that for ZA27 and Zamak2.

Lamellar gray cast iron, with a mainly pearlitic microstructure, is widely used in the automotive industry, mostly in the manufacturing of brake disks. This work analyzes in depth the effects of small variations of titanium content on the microstructure and mechanical properties of cast iron brake disks. For this purpose, eight different heats of EN-GJL-250 cast iron were selected, with a similar chemical composition but with different titanium contents, varying from 0.013 to 0.031%. The drops in mechanical strength and hardness values measured on the high-Ti samples were correlated to microstructural variations quantitatively observed by means of optical and scanning electron microscope. It was found that titanium combines to form titanium nitrides, suppressing the beneficial microstructural effects of nitrogen at solidification. Residual nitrogen, if present in sufficient quantity, promotes the nucleation of primary austenite from the liquid and the formation of a fine microstructure, with small eutectic cells and lower graphite content. Such a microstructure provides brake disks with better mechanical properties. The interpretation of results was further supported by thermal analysis and thermodynamic calculations.

The application of semisolid process was investigated on Pb-Sb alloys that are normally used for metallic parts in car batteries, in order to increase their mechanical properties and corrosion resistance. The semisolid behaviour of a Pb-4%Sb alloy was analysed by means of rheological and calorimetry differential scanning experiments. The alloy was melted, treated by ultrasound to obtain the semisolid state and then poured into permanent moulds. Some of these samples were also heated in semisolid temperature range and injected in thixo-casting apparatus. Both poured and injected samples were characterized by metallographic analysis, mechanical test and electrochemical corrosion experiments. The results show an improvement of mechanical and corrosion resistance

The application of power ultrasound to liquid alloys can be a simple and cost effective method to induce both degassing and grain refinement in a single step, without the need of inert gas or inoculants additions. In this paper, the treatment of liquid hypoeutectic AlSi5 alloy by ultrasound waves and its effects on microstructure were investigated. The corrosion behavior of ultrasound treated samples was compared to that of the non-treated ones by means of immersion and electrochemical tests. It was observed that the ultrasound treated alloy offers better quality, higher mechanical properties and improved corrosion resistance, as a consequence of a more uniform distribution of the solute.

Notwithstanding the wide use of PVD coated components, not only in fields where tribological behaviour is important and well assessed, fatigue behaviour is still object of research in applications where enhanced fatigue resistance is required. Aim of this paper is to analyse fatigue crack growth mechanisms and to relate nucleation site to microstructure and residual stress data. Two structural steels were used as substrate (H11 tool steel grade and 2205 duplex stainless steel grade), while a monolayer of CrN 5 mm depth was deposed as coating. Four points bending fatigue tests were carried out in order to obtain the bending fatigue limit. Experimental results obtained by Scanning Electron Microscopy analyses, residual stresses measurements and hardness evaluations carried out using a nanoindenter device were considered to explain the fatigue mechanisms involving a PVD coated part in terms both of nucleation site and crack growth process

Additive manufacturing of metals is a production process developed in the last few years to realize net shape components with complex geometry and high performance. AlSi10Mg is one of the most widely used aluminium alloys, both in this field and in conventional foundry processes, for its significant mechanical properties combined with good corrosion resistance. In this paper the effect of heat treatment on AlSi10Mg alloy was investigated. Solution and ageing treatments were carried out with different temperatures and times on samples obtained by direct metal laser sintering and gravity casting in order to compare their performance. Microstructural analyses and hardness tests were performed to investigate the effectiveness of the heat treatment. The results were correlated to the sample microstructure and porosity, analysed by means of optical microscopy and density measurements. It was found that, in the additive manufactured samples, the heat treatment can reduce significantly the performance of the alloy also because of the increase of porosity due to entrapped gas during the deposition technique and that the higher the solution temperature the higher the increase of such defects. A so remarkable effect was not found in the conventional cast alloy.

Corrosion and wear resistance of Cathodic Arc Evaporation (CAE) CrN coatings deposited on a tool steel were investigated considering the effect of the number of layers (mono or double) and the influence of defects. The CrN coatings were characterized for mechanical (scratch, nanoindentation test), corrosion behavior (polarizarion tests) and tribological properties (pin-on-disk tests). Scanning Electron Microscope analyses on samples before and after the tests were also made in order to identify the type of the defects and the role they play in the coating damage. Monolayer coating shows a good wear behavior with a stable and low friction coefficient, but its corrosion performance is poor. On the contrary, the presence of an interface into the double layer improves the corrosion resistance, but it is a weak point for the coating delamination during wear tests.

This research concerns the study of corrosion effects on different threaded elements to analyse bolted joints working in a saline environment. In particular, this article examines the mechanical behavior of a M8 junction realized by different steels and subjected to different degrees of corrosion. Four materials were investigated: a low-alloyed structural steel in the original condition and the same after zinc-plating; a quenched and tempered steel; and an austenitic stainless steel. For each steel were tested a certain number of threaded rods exposed to a saline water solution, simulating the atmospheric exposure to an aggressive environment. The samples were characterized by different intervals of exposure. During these periods, the threaded elements (threaded rods) were kept in tension applying a tightening torque proportional to the yield strength of the tested steel, to evaluate their susceptibility to stress corrosion cracking. Before and after the different corrosion steps, some metallographic analyses, static tensile and fatigue tests, were carried out to determine, for each sample, the degree of corrosion and its influence on the reduction of the junction resistance. In order to evaluate the stress-intensifying factor and its variation with the imposed degree of corrosion was carried out a FEM analysis.

The aim of this work was to investigate fracture toughness and corrosion resistance of semisolid AlSi5 castings, compared to samples obtained from conventional casting operations. In order to have a semisolid microstructure, the melt alloy was treated by means of ultrasound during solidification and then poured into permanent moulds. Mechanical properties of semisolid and conventional castings were compared by means of ultimate tensile strength (Rm), yield stress (Rp02) and hardness (HV) measurements. Fracture mechanics tests were carried out on Single Edge Notched Bend (SENB) specimens, machined from castings, and pre‐cracked by fatigue. These tests were performed to determine the effect of the microstructure on the J‐Integral resistance (J‐R) behavior and to deeply understand the ductile fracture behaviour of semisolid parts. The J‐Integral versus spaced crack extension (J‐Δa) curves showed an improved resistance of the semisolid microstructure, due to the higher ductility.Finally, the corrosion behavio...

International audience; The development of new devices has created needs of precision, conformal at the atomic level deposition of high quality thin film materials. In the last years, Atomic Layer Deposition (ALD) has received much interest as a potential deposition method for advanced thin film structures. ALD presents several advantages: the film is excellently conformal and reproducible; the film thickness depends only on the number of reaction cycles, which makes the thickness control accurate and simple; the film can be deposited onto all kind of substrates. Because of the process slowness, layer thickness is generally less than 100 nm. This makes more difficult to study all characteristics of the coating. Thin layers deposited onto bulk substrates are generally in tensile or compressive stress state, which may significantly affect physical properties and possibly compromise their lifetime. To determine the residual stress it is mandatory to know the elastic constants that may also depend on the microstructure of the layers and thus the deposition process.In this work, 2D X-ray diffraction (XRD2) in combination with in situ tensile testing has been applied for the first time to measure elastic properties of TiO2 anatase films obtained by ALD. Experimental conditions, the tensile stage being installed in a laboratory micro-diffractometer equipped with a 2D image-plate detector, and the information that can be extracted from 2D diffraction patterns will be discussed. Based on these preliminary results, synchrotron radiation beam time has been allocated to study elastic properties of these thin films. The advantages and disadvantages of the proposed laboratory equipment, with respect to the synchrotron beam lines, are discussed.

In cutting operations it is very important to know the surface residual stresses on the final part since they affect functional aspects of the workpiece such as: fatigue life, resistance to corrosion and wear resistance. Recent studies showed that the development of tensile or compressive stresses is mainly influenced by the cutting parameters, tool geometry and the nature of the worked material. This paper reports the results obtained when studying the influence of different types of lubrication and of some process parameters (i.e. the tool nose radius and the feed rate) on the workpiece residual stresses in cutting operation. The experimental tests were carried out turning AISI 1045 steel bars. The maximum and minimum principal residual stresses on the surface were identified measuring the stresses along three different directions (0°/+60°/−60° with respect to the bar axis) using the X-ray diffraction technique. In addition, a 3D FEM model of the process was developed with the aim of proving the ability of such a model in predicting the surface residual stresses.

In order to contribute to a better understanding of the mechanical properties of gold alloys this paper investigates the mechanical behaviour of an 18 carat yellow alloy; the strain hardening behaviour during a tensile test was measured in the annealed as well as in different cold-work conditions. In addition, the contribution of different strengthening mechanisms is discussed on the basis of current results and of data reported in literature. In particular, the contributions of grain size refinement and copper solid solution alloying in improving the mechanical strength of gold alloys were quantified.

A CrN monolithic 5 μm thick was deposited on a substrate of H11 tool steel and was characterised by XRD analysis and nanoindentation measurements. Hardness, elastic modulus, chemical composition, texture and lattice constants were determined along with the through-thickness residual stress distribution. A high level of compressive stress was obtained both at the surface and inside the coating; data always higher than 2 GPa were measured. Low values of compressive stresses were measured in the steel side near the coating/substrate interface. Those results, coupled with a good adhesion of the interface, allow, when cycling loads are applied to the coated component, a nucleation of the fatigue crack inside the substrate material. Therefore, the critical microstructural parameter that strongly affects the fatigue resistance of the CrN coated samples investigated becomes the size of nonmetallic inclusions working as discontinuity inside the steel substrate, close to the location of the coating/substrate interface. Indeed, in such a location the compressive residual stresses induced by the deposition technique are low and, therefore, insufficient to oppose the tensile stress induced by the applied loading condition during four-point bending fatigue tests.

This paper studies the effect of artificial aging on the wear resistance of the recently developed Zn-15Al-1Cu-Mg alloy. Pin-on-disk tests were performed to evaluate the evolution of friction coefficient and wear rate on samples produced via spin casting. Hardness and tensile properties were also monitored as a function of aging time. After the tests, wear scares and fracture surfaces were analyzed by scanning electron microscope, in order to understand the damage and the failure mechanisms. It was found that hardness and tensile strength decrease with the aging time, while both friction coefficients and wear rates increase.