Metal foams by molten metal infiltration of a ceramic particles bed

E' stato messo a punto un processo tecnologico volto a ottenere schiume metalliche a pori aperti adatto per leghe e metalli ad alto punto di fusione. Questo processo si basa sull'infiltrazione di leghe e metalli – portate allo stato liquido - fra le intercapedini presenti tra le particelle ceramiche -allo stato solido. Le particelle ceramiche, successivamente alla solidificazione e al raffreddamento della massa metallica, vengono rimosse per dissoluzione in un agente chimico appropriato. Attraverso questo metodo si riescono ad ottenere schiume metalliche particolarmente omogenee caratterizzate da una densità apparente pari 25-30% della densità propria della lega di partenza, a cui è associata una significativa regolarità nella morfologia dei pori, nonché un'elevata isotropia delle proprietà fisiche e meccaniche. Il processo si basa sull'utilizzo di materiali di basso costo e su tecnologia fusoria facilmente reperibile e questi aspetti rendono elevato il rapporto costi-benefici del processo che è brevettato

Determination of CTOD C in Fibre Metal Laminates by ASTM and Schwalbe Methods

Fibre Metal Laminates (FMLs) have arisen as a demand of the aeronautical industry to use thin sheets with high resistance to fatigue crack growth, high damage tolerance, corrosion resistance and high specific strength. Considering these requirements, FMLs are an advantageous choice when compared to metal alloys currently used. In order to employ FMLs in aircraft structures, designers must hold a deep knowledge of a wide set of their properties including fracture toughness. The aim of this work was to evaluate the available methodologies to measure fracture toughness at instability (CTOD C) in unidirectional fibre metal laminates reinforced with aramid fibres (ARALL®). To achieve this, tests were performed to obtain traditional and Schwalbe CTODs by using experimental ASTM based techniques, especially adapted to these laminates. Results achieved point out that Schwalbe method is more appropriate and also that there are differences between both CTOD parameters

Microstructural characterization and mechanical behaviourof duplex stainless steel 2205 (UNS32305) foams featured bydifferent pore distribution

Metal foams know a good success in all the applications needing low bulk density and attitude in lowering the vibration transmission. In such a context the realization of foams constituted by duplex stainless steels can open new perspectives in order to substitute light alloys in several applications needing corrosion resistance. The foams in steel are rare products for the difficulties in producing them, due to the high melting points featuring these alloys. The metal foams used in this study have been produced through an infiltration procedure licensed by Politecnico di Milano and they have been designed using different porosity distributions and through different thermal patterns. The heat treatment provided has been a solubilisation quenching to control the composition of biphasic microstructure characterizing a duplex steel. Such route has permitted to obtain foams characterized by a combination of different morphologies of porosities and of microstructural organization, i. e. different fraction of ferrite and austenite, whose mechanical behaviour has been studied through compression tests

Production of 17CrMoV5-11 steel sponges utilising powder metallurgical replication technique with SiC as space holder

Porous materials, characterised by their cellular structure, have interesting combinations of physical and mechanical properties. In such a context, steel sponges could be employed as an alternative to light alloys in several applications needing a good compromise between weight and mechanical properties. In this work, a new approach is presented that uses a powder metallurgical replication technique to produce steel foams while using SiC spheres as a space holder. The processed sponges were characterised from a morphological, microstructural and mechanical point of view. The results of the characterisation demonstrated the feasibility and the repeatability of the proposed production route

Performance of stainless steel foams produced by infiltration casting techniques

Ferritic (AISI 430) and austenitic (AISI 304) stainless steel foams were produced exploiting a process based on molten metal infiltration on ceramic model. In particular, SiC foundry filter was used as space holder and, after the solidification, it has been removed by hydrofluoric acid. The produced foams are featured by three different porosity grades (10, 20 and 30 PPI) and by constant relative density (0.60). The morphology, the mechanical properties and the corrosion resistance were studied and the results were correlated to the material, the porosity, the size and the distribution of the voids. Morphologically, the structure is arboreous open-cell foam featured by interconnected cavities. This aspect, combined with the high relative density, assures high compressive plateau stress, structural integrity and good deformability. The corrosive tests, according to the ASTM A262-Met.B and NACE TM-0284, permitted to identify possible application fields for these products

Processing of shape memory CuZnAl open-cell foam by molten infiltration

Foams and other highly porous materials with a cellular structure are known to have many interesting combinations of physical and mechanical properties. In addition, foaming of shape memory alloys (SMA) greatly improves the set of application possibilities. In this work an open-cell metal foam of a CuZnAl SMA is presented. This foam was produced through a recently proposed process, which consists mainly in molten metal infiltration of a bed of silica-gel particles and the subsequent use of hydrofluoric acid (HF) as solvent. The results showed that very regular open-cell foams could be obtained, having an almost spherical cell morphology and relative densities of approximately 0.3. Microstructural and compositional analyses on foamed specimens showed uniform microstructure of ligaments and the absence of SiO2 interaction with the metal. In this way the possibility of foaming CuZnAl system through the proposed low-cost process was clearly demonstrated

Effect of displacement rate and subcritical crack growth on J-R curves of API X65 steels in sour environment

Fracture tests in sour solution of an API X65 steel for J-R curves determination were performed at different displacement rates. The results indicated a strong dependence of J-R curves on the displacement rate. At low displacement rates the J-R curves were affected by subcritical crack growth. Above a certain displacement rate, incubation time prior to subcritical crack growth was observed, being the experimental J-R curves not affected by this mechanism. A procedure to evaluate the contribution or not of subcritical crack growth to J-R curves of carbon steels in aggressive environments, verified for that specific steel-environment combination, is being proposed.Fil: Finamore, C.. Universidade Federal do Rio de Janeiro; BrasilFil: Castrodeza, E.M.. Universidade Federal do Rio de Janeiro; BrasilFil: Perez Ipiña, Juan Elias. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Universidad Nacional del Comahue; ArgentinaFil: Cristea, M.E.. TenarisDalmine; ItaliaFil: Chekchaki, M.. Instituto Nacional de Tecnologia; Brasi

Mechanical properties of martensitic Cu–Zn–Al foams in the pseudoelastic regime

The mechanical properties of martensitic Cu–Zn–Al foams produced through molten metal infiltration of a leachable bed of silica gel were investigated. The novel porous shape memory alloy almost reversibly absorbs compression deformations up to 4%. Intergranular fracture occurs in the material along the test, similar to what is observed in polycrystalline solid samples. Despite its tendency to fracture at localized regions, the material is highly resilient, being able to stand several compression cycles. The Cu–Zn–Al foams showed excellent shape recovery after deformation (95%). This previous fact establishes it as a very promising candidate for interesting applications