Lorenzo Montesano

Influence of ultrasound treatment on cavitation erosion resistance of AlSi7 alloy

Ultrasound treatment of liquid aluminum alloys is known to improve mechanical properties of castings. Aluminum foundry alloys are frequently used for production of parts that undergo severe cavitation erosion phenomena during service. In this paper, the effect of the ultrasound treatment on cavitation erosion resistance of AlSi7 alloy was assessed and compared to that of conventionally cast samples. Cavitation erosion tests were performed according to ASTM G32 standard on as-cast and heat treated castings. The response of the alloy in each condition was investigated by measuring the mass loss as a function of cavitation time and by analyzing the damaged surfaces by means of optical and scanning electron microscope. It was pointed out that the ultrasound treatment increases the cavitation erosion resistance of the alloy, as a consequence of the higher chemical and microstructural homogeneity, the finer grains and primary particles and the refined structure of the eutectic induced by the treatment itself.

Effect of microblasting on cathodic arc evaporation CrN coatings

Abstract Cathodic arc evaporation CrN double layer coatings were deposited onto tool steels in two steps by industrial apparatus. Microblasting was performed on CrN first layer in order to remove metallic droplets and surface defects and to promote the adhesion of the second layer. Surface morphology effects were assessed by a scanning electron microscope coupled with Image analyser software. Nanoindentation and scratch tests were performed to evaluate the changes of coating adhesion and mechanical properties. Structure, microstructure and residual stress were evaluated by X-ray diffraction. In particular, by means of Cu and Cr wavelengths, the residual stresse of both steel substrates and coatings was calculated. The results show that microblasting has no effect on coating hardness and slightly affects the adhesion of the coating to the substrate. On the other hand, microblasting increases coating resistance to cohesive failure and the substrate compressive stress at the coating interface.

Effect of Globular Microstructure on Cavitation Erosion Resistance of Aluminium Alloys

In this paper the effect of globular microstructure on the cavitation erosion resistance was assessed and compared to that of conventional dendritic one. Three different wrought aluminum alloys in as-cast conditions were investigated. The samples were completely characterized by metallographic analyses and microhardness measurements. Cavitation erosion tests were performed according to ASTM G 32 standard. The volume loss was evaluated during the test by periodical interruptions. It was identified the damaging mechanism in case of both dendritic and semisolid microstructure. It was also found that the globular microstructure increases the cavitation erosion resistance only for one of the studied alloys.

Semisolid Processing of Al-Sn-Cu Alloys for Bearing Applications

The aim of this work was to evaluate the advantages in using semisolid processing of Al-Sn alloys in order to improve microstructural homogeneity and, consequently, wear resistance. Different tests were performed on an Al3Sn4Cu by using ultrasound treatments during solidification to obtain an almost globular microstructure. Metallurgical characterizations and pin on disk wear tests were carried out on semisolid as well as on conventionally cast samples in order to assess the benefit of the treatment.

Aluminum Segregation in ZA27 Rheocast Alloy

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.

Corrosion and Wear Behavior of CAE Deposited CrN-PVD Coatings

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.

Investigation of mechanical properties of AlSi3Cr alloy

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.

Investigation on Microblasting Applied to CrN Coatings

A microblasting treatment carried out on CrN coated samples was studied to investigate the induced effect on corrosion and wear resistance. CrN coating was deposited through Cathodic Arc Evaporation technique on quenched and tempered steel. The properties of the coating were studied by hardness measurements, scratch, potentiodynamic, and pin-on-disk tests. The results show that microblasting reduces the corrosion resistance while improving the wear behavior.

Nd:YOV4 laser surface texturing on DLC coating: Effect on morphology, adhesion, and dry wear behavior

The surface of structural components is usually subjected to higher stresses, greater wear or fatigue damage, and more direct environmental exposure than the inner parts. For this reason, the interest to improve superficial properties of items is constantly increasing in different fields as automotive, electronic, biomedical, etc. Different approaches can be used to achieve this goal: case hardening by means of superficial heat treatments like carburizing or nitriding, deposition of thin or thick coatings, roughness modification, etc. Between the available technologies to modify components surface, Laser Surface Texturing (LST) has already been recognized in the last decade as a process, which improves the tribological properties of various parts. Based on these considerations the aim of the present research work was to realize a controlled laser texture on a Diamondlike Carbon (DLC) thin coating (about 3 m thick) without damaging both the coating itself and the substrate. In particular, the effect of laser process parameters as marking speed and loop cycle were investigated in terms of texture features modifications. Both qualitative and quantitative analyses of the texture were executed by using a scanning electron microscope and a laser probe system to select the proper laser parameters. Moreover, the effect of the selected texture on the DLC nanohardness, adhesion and wear behavior was pointed out.

Evaluation of cavitation erosion resistance of Al-Si casting alloys: effect of eutectic and intermetallic phases

In the present paper, the influence of eutectic and intermetallic phases on cavitation resistance of Al-Si alloys was studied. In fact, Al-Si alloys are commonly used for the production of components, such as cylinders, pistons, pumps, valves and combustion chambers, which in service may incur in cavitation phenomenon. Samples of AlSi3, AlSi9 and AlSi9CuFe were characterized from the microstructural point of view. Hardness measurements were also performed. Subsequently, cavitation tests were carried out according to ASTM G32 standard and the erosion mechanism was examined by scanning electron microscope. It was found the both eutectic and intermetallic phases enhance cavitation resistance, expressed in terms of mass loss. Particularly, intermetallic particles with complex morphologies provide a positive contribution, exceeding that of other microstructural features, as grain size. The effect of T6 heat treatment was also evaluated. It was confirmed that the precipitation of fine strengthening particles in the Al matrix successfully hinders the movement of dislocations, resulting in a longer incubation stage and a lower mass loss for heat-treated samples in comparison with as-cast ones. Finally, the relationship between cavitation resistance and material hardness was investigated.