117,601 research outputs found
DRY SLIDING BEHAVIOUR OF PEO (PLASMA ELECTROLYTIC OXIDATION) TREATED AA 2618/20 % Al2O3P COMPOSITE
No full textThe present study focuses on the influence of the PEO (Plasma Electrolytic Oxidation) treatment on the tribological behaviour of the AA2618/20 % vol. Al2O3p composite, dry sliding against induction hardened UNI C55 steel. Particle-reinforced Al based composites offer a higher wear resistance by comparison with the corresponding unreinforced alloys, however, the presence of critical loads and/or velocities which lead to transition towards severe wear regime, was often observed. In such conditions, the composite can show higher wear rates than those of unreinforced alloys. For this reason, surface modifications, such as PEO, might contribute to improve wear resistance. In this paper, topography, microstructure, phase constitution and surface hardness of the PEO-treated composite were investigated and its tribological behaviour was studied by dry sliding tests using a block-on-ring tribometer. The results were compared with those from the uncoated composite, demonstrating a very positive effect of the PEO treatment, which moved transitions from mild to severe wear towards more severe test conditions, in terms of both load and velocity
CEMENTAZIONE A BASSA TEMPERATURA DI ACCIAI INOSSIDABILI AUSTENITICI: STUDIO DELLA RESISTENZA A CORROSIONE E AD USURA
No full textIl progetto propone attività di ricerca indirizzate allo studio della resistenza a corrosione e ad usura dell'acciaio inossidabile austenitico AISI316L dopo cementazione a bassa temperatura, effettuata sia con un processo impiegato industrialmente, che trattato mediante cementazione a bassa temperatura assistita da plasma, in condizioni di laboratorio messe a punto dall'Unità di Ricerca (UR) dell'Università di Roma Tor Vergata
High strain rate superplasticity in aluminum matrix composites
No full textRecently, several studies have demonstrated that a variety of metallic materials, including aluminium-based composites, can exhibit superplasticity at relatively high strain rates (≥10-2s-1). High strain rate superplasticity (HSRS) is very attractive for commercial applications, mainly for materials difficult to shape or machine with conventional techniques, such as metal matrix composites. In this work, the possibility of achieving HSRS in a recently developed composite with an AA6013 matrix reinforced with about 20 vol % of SiC particles (AA6013/20/SiCp) was studied. Uniaxial tensile tests were carried out at high strain rates (1 x 10-1s-1 and 1 x 10-2s-1) and in a temperature range between 520 and 590°C. A maximum elongation-to-failure of 370 per cent was obtained at 560°C with a strain rate of 1 x 10-1s-1. This temperature is very close to the temperature at which melting of the composite starts. Scanning electron microscopy (SEM) analyses of fracture surfaces in the optimum superplastic condition showed the presence of filaments, the formation of which generally related to the presence of a liquid phase at the grain boundaries and/or at the interfaces
Aspetti metallurgici nella superplasticità
No full text"Micrograined" or "structural" superplasticity is the ability of policrystalline materials (metals, ceramics, composites) with very fine grain size (d 0.4 T m, where T m is the absolute melting point) and low strain rates (ε̇ = 10 -5 to 10 -1 s -1). The main microstructural requirements for the observation of superplastic behaviour in high strength materials (the aluminum alloys AA7012, AA7075 and AA7475, the precipitation hardening stainless steel 17- 4 PH [AISI 630] and the nickel-based superalloy IN- 718) are presented and discussed. The chemical compositions of the tested materials are reported in tables 1, 2, and 3, while the microstructures of the as-received alloys are shown in fig. 1. Taking into account the main deformation mechanism (grain boundary sliding), an important role is played not only by the presence of a fine-grained microstructure (stable at high deformation te..
CoCr alloy processed by Selective Laser Melting (SLM): effect of Laser Energy Density on microstructure, surface morphology, and hardness
Full text linkSelective Laser Melting (SLM) was used to realize Co-28Cr-6Mo samples. Several process parameters were considered, resulting in a wide range of Laser Energy Density (LED). The study was focused on the investigation of both process and material-related aspects, such as surface morphology, laser tracks dimension and defects formation mechanisms. In addition, macro (HRC) and microhardness (HV0.5) was assessed. A correlation between LED value and density, surface quality, microstructural features and hardness of SLM parts was defined. The final goal was to identify, for the biomedical Co-28Cr-6Mo alloy, the optimal LED window to be considered in order to maximize the overall quality of SLM parts
AA5083 (Al–Mg) plates produced by wire-and-arc additive manufacturing: effect of specimen orientation on microstructure and tensile properties
Full text linkAmong various additive manufacturing (AM) technologies, wire-and-arc additive manufacturing (WAAM) is one of the most suitable for the production of large-scale metallic components, also suggesting possible applications in the construction field. Several research activities have been devoted to the WAAM of steels and titanium alloys and, recently, the application of WAAM to aluminum alloys has also been explored. This paper presents the microstructural and mechanical characterization of WAAM plates produced using a commercial ER 5183 aluminum welding wire. The aim is to evaluate the possible anisotropic behavior under tensile stress of planar elements, considering three different extraction directions in relation to the deposition layer: longitudinal (L), transversal (T) and diagonal (D). Compositional, morphological, microstructural and fractographic analyses were carried out to relate the specific microstructural features induced by WAAM to the tensile properties. An anisotropic behavior was found in regard to the specimen orientation, with the lowest strength and ductility found on T specimens. Reasoning to this was found in the presence of microstructural discontinuities unfavorably oriented with regard to the tensile direction. The results of tensile tests also highlighted an overall good mechanical behavior, comparable to that of conventional AA5083-O sheets, suggesting future use in the realization of very complex geometries and optimized shapes for lightweight structural applications
Influence of Ni-P + DLC multilayer coatings on the tensile properties of the AlSi10Mg alloy produced by Laser-based Powder Bed Fusion
Full text linkThe peculiar microstructure of the AlSi10Mg alloy produced by the laser-based powder bed fusion (L-PBF) process requires the development of specific heat treatments and coatings to exploit its potential fully. The study aims to evaluate the effect of the deposition of an anti-friction/wear Ni-9%P + DLC (hydrogenated amorphous carbon, a-C:H) multilayer coating produced in an industrial environment by the electroless process followed by Arc-Evaporation Physical Vapor Deposition (PVD), on the mechanical properties of the L-PBF AlSi10Mg alloy. In the processing sequence, the DLC deposition phase replaces the artificial aging step in the T5 (direct aging) and T6R (solution treatment, quenching, and aging) heat treatments to reduce industrial costs thanks to comparable temperatures and soaking times. Therefore, the coated samples undergo the following post-production cycles: (i) Ni-P + DLC deposition (T5-like heat treatment) and (ii) rapid solution (SHTR) (10 min at 510°C) + Ni-P + DLC deposition (T6R-like heat treatment). Tensile tests highlight a significant reduction in ductility for T6R-like and T5-like specimens due to the different mechanical responses under static load between the multilayer coating and the substrate. At the same time, no significant differences are found in terms of strength properties. In conclusion, the variation in the static mechanical property trade-off of L-PBF AlSi10Mg induced by this processing cycle reveals critical points to be taken into account when applying a multilayer coating to structural components
Relationship between microstructure, mechanical and magnetic properties of pure iron produced by laser powder bed fusion (L-PBF) in the as-built and stress relieved conditions
No full textIn the present work, the mechanical and magnetic properties of pure iron manufactured by laser-powder bed fusion (L-PBF) were investigated both in the as-built (AB) and stress relieved (HT) conditions, with the aim of elucidating their relationship with the microstructure and evaluating whether and to what extent it can be suitable for industrial applications. The L-PBF process was optimized to obtain high density, crack-free components. Specimens for microstructural analyses, tensile and magnetic tests were manufactured under the optimized conditions and tested both in the as-built and annealed (850 °C for 1 h, to relieve the residual stresses) conditions. Tensile tests showed high tensile strength in both AB and HT conditions (larger than those of conventionally produced pure iron), with higher ductility and lower strength after stress relieving. The magnetic study indicated a not optimal magnetic softness although the heat treatment enhanced the permeability and reduced the coercivity with respect to the as-built condition. The high mechanical strength and low magnetic softness came from the very fine grain size (about 5 μm) of L-PBF pure iron. Instead, the improvement of magnetic softness and ductility after heat treatment was attributed to the possible reduction of dislocation density and consequent stress relief. The results indicated the possibility to achieve a considerably high mechanical strength, in pure iron manufactured by L-PBF, although the fine grain size limits its magnetic softness
Friction and Wear of Aluminum Alloys and Composites
No full textThe chapter starts with an overview on Al alloys and Al-based composites, presenting their physical and mechanical properties, designation, effects of the main alloying elements, microstructural features of cast and wrought Al alloys, strengthening mechanisms and heat treatments. Subsequently the tribological behavior of Al alloys and Al-based composites is presented and discussed, focusing on the dry sliding wear and discussing the effects of: material-related parameters (silicon content, size and shape; other alloying elements and role of intermetallic particles); main operating conditions (load, sliding speed, temperature). Wear maps for Al-Si alloys and MMCs are also reported
Superplastic behaviour of metal matrix composites
No full textStudi recenti hanno mostrato la possibilità di osservare superplasticità ad elevata velocità di deformazione ( > 10^-2 s^-1 ) in materiali compositi a matrice di alluminio, purché caratterizzati da dimensioni molto fini ( < 5 micron ) sia dei grani della matrice che delle particelle di rinforzo. In questo lavoro è stata valutata la possibilità di indurre un comportamento superplastico nel composito AA6013/20SiCp, ottenuto da metallurgia delle polveri e successivamente laminato a caldo.I risultati delle prove di di trazione consentono di ipotizzare un ruolo importante della fase liquida, come meccanismo di "accomodamento" dello scorrimento a bordo grano (GBS), nel corso della deformazione superplastica
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