Processing and characterization of dual phase steel foam

Porous materials featuring cellular structures are known to have many interesting combinations of physical and mechanical properties. Some of them have been extensively used in the transportation field (i.e. balsa wood). Steel foams presented promising theoretical properties for both functional and structural applications in transportation, but processing of such a kind of foams is complex due to their high melting point. Recently a technique for processing Cu-based alloys open-cell foams through the molten metal infiltration of a leachable bed of amorphous SiO2 particles was proposed. A variation of the proposed technique that uses SiC particles as space holder is now presented and was recently successfully applied for dual phase steel foam processing. Results from a processing of dual phase DP500 steel foams, including some morphological, micro-structural and mechanical characterization, are here presented

Characterization and Comparison of Single VAR-Remelted and Double VAR-Remelted Ingots of INCOLOY ® Alloy 925

Alloy 925 is a nickel-based superalloy usually produced by Electric Arc Furnace (EAF), followed by Argon Oxygen Decarburization (AOD) and Vacuum Arc Remelting (VAR). It can undergo to one VAR remelting (EAF-AOD-VAR) or, if necessary due to process instabilities, two VAR remelting (EAF-AOD-VAR-VAR). The characterization of A925 ingots remelted one or two times after forging and aging was carried out to enhance differences. The VAR remelting rate of single- or double-remelted samples was correlated to metallurgical and mechanical properties. The microstructure observation revealed a higher quantity of MC, M23C6 and TiN precipitates (both inter- and intragranular) in single-remelted samples: the intergranular ones increase in quantity going from the ingot center position to the external one where cluster of titanium nitrides were detected. The higher presence of intergranular precipitates causes a high deterioration of impact toughness (71.1 ± 12.7 vs 90.5 ± 7.1 J) and lateral expansion (0.91 ± 0.18 vs 1.14 ± 0.07 mm). On the other hand, the number of remelting does not affect other tensile properties and hardness. Therefore, the different behavior of forged ingots at single and double remelting are not related to the number of remelting and remelting rate. On the other hand, the slightly lower toughness of single-remelted forged ingots can be corelated to defects derived from casting

Mechanical and tribo-metallurgical behavior of 17-4 precipitation hardening stainless steel affected by severe cold plastic deformation: a comprehensive review article

This article comprehensively reviews the mechanical properties and tribo-metallurgical behavior of 17-4 precipitation hardening stainless steel (17-4PH SS) during and after cold plastic deformation. Referring to the scientific literature, stainless steels are one of the few types of ferrous alloys which could be appropriately set up through cold working processes in the forms of sheets or other shapes. Likewise, some other metal alloys such as mild low-carbon-based steels, copper and its alloys, aluminum alloys, and some others are the few types of metal alloys which have this capability. On the other hand, in engineering applications, there are several types of mechanical failures, which must be taken into account to investigate the mechanical behavior and tribo-metallurgical properties of any targeted materials. For example, corrosion resistance, wear resistance, and fatigue failure are investigated according to the microstructural studies, comprising of the grain size, grain boundaries, orientations, dislocations, and so on. Based on the published results, focusing on 17-4PH SS, one of the most main effective factors on mechanical and tribo-metallurgical performance is the grain size. Also, the favorable balance of two mechanical properties of strength and ductility has been reported as a dilemma in the materials science, and the problem delineates upon the limitations of numerous structural materials potentials. Following the failure analysis of the materials, in order to diminish the damages caused by fretting fatigue some methods such as ultrasonic processes are applied for the treatment of 17-4PH SS via changing the microstructure, residual stress, and other parameters. Also, through the other cold deformation technologies, the nanostructured surface layer with highly upgraded mechanical properties of several ultrasonic surface rolling process-treated 17-4PH SS has been obtained. To this end, such cold working processes on 17-4PH SS and their subsequent results are elaborated in this review paper. Graphical abstract: [Figure not available: see fulltext.

A study on the stability of carbon nanoforms–polyimidazolium network hybrids in the conversion of co2 into cyclic carbonates: Increase in catalytic activity after reuse

Three different carbon nanoforms (CNFs), single-walled and multi-walled carbon nanotubes (SWCNTs, MWCNTs) and carbon nanohorns (CNHs), have been used as supports for the direct polymerization of variable amounts of a bis-vinylimidazolium salt. Transmission electron microscopy confirmed that all CNFs act as templates on the growth of the polymeric network, which perfectly covers the nanocarbons forming a cylindrical (SWCNTs, MWCNTs) or spherical (CNHs) coating. The stability of these hybrid materials was investigated in the conversion of CO2 into cyclic carbonate under high temperature and CO2 pressure. Compared with the homopolymerized monomer, nanotube-based materials display an improved catalytic activity. Beside the low catalytic loading (0.05–0.09 mol%) and the absence of Lewis acid co-catalysts, all the materials showed high TON values (up to 1154 for epichlorohydrin with SW-1:2). Interestingly, despite the loss of part of the polymeric coating for crumbling or peeling, the activity increases upon recycling of the materials, and this behaviour was ascribed to their change in morphology, which led to materials with higher surface areas and with more accessible catalytic sites. Transmission electron microscopy analysis, along with different experiments, have been carried out in order to elucidate these findings

Effect of Shot Peening on Oxidation and Precipitation in Inconel 718

In this study, the effect of the surface state on the behaviour of Inconel 718 alloy exposed to 640 ∘ C and 700 ∘ C environments for times varying between one and one hundred hours was investigated. In particular, the focus was set on the evolution of oxidation and precipitation phenomena during thermal exposure. Three surface states were considered: two generated through shot peening treatments featuring different coverage levels, while the third condition is a non-peened one. Shot peening treatments modify the surface condition and introduce higher residual stresses and microhardness values than in the non-treated condition. The morphology of the oxides appears to be different depending on the condition observed. Regarding the kinetics, over time the oxidation process follows a parabolic trend and appears to be influenced by the surface state; in particular, severe shot peening treatment is characterized by the highest intensity of the phenomenon. However, the order of magnitude of the weight gains measured suggests that the observed variations can be neglected, and that the positive effect of shot peening can be exploited without introducing oxidation problems. From the point of view of the microstructural evolution, an increase in the coarsening kinetics of γ ” phase was observed in the shot peened layer

First Evidence of Tris(catecholato)silicate Formation from Hydrolysis of an Alkyl Bis(catecholato)silicate

The hydrolysis of 3-ammoniumpropylbis(catecholato)silicate 1, giving two different silica-based materials containing different amounts of tris(catecholato)silicate, is reported. The latter species can be formed through an attack of catechol to the silicon atom in the pentacoordinate complex, in which the silicon-carbon bond is further activated toward electrophilic proton cleavage. The Knoevenagel reaction was used as a probe in order to test the availability of functional groups on the surface of such materials

Microstructural investigation on an Al 6061 T6 alloy subjected to ballistic impact C

Ballistic impact generates significant modifications in the microstructural patterns. High strain rate and local high temperature conditions work together in opposite way: the first causes strain hardening, while the second factor produces softening. Moreover, after the impact, the cooling process is responsible of other local modifications on the arrangement of dislocations and precipitates. Therefore an experimental analysis on Al 6061 T6 cut from the edge of a component subjected to ballistic impact has been carried on in order to investigate on the microstructural modifications. Considerations about the influence on the mechanical behavior and on the fracture propagation are reported. The crystallographic textures and the misorientation featuring the grains play in fact a significant role in the fracture mechanism. The comparison between the texture situation before and after the impact can allow to evaluate the localized straining of the material and to point out its dissipation efficiency as a function of the distance from the damaged surfaces © 2011 Published by Elsevier Ltd. Selection and peer-review under responsibility of ICM1

Highly Functionalized SWCNTs with a Dopamine Derivative as a Support for Pd Nanoparticles: A Recyclable Catalyst for the Reduction of Nitro Compounds and the Heck Reaction

Single-walled carbon nanotubes (SWCNTs) were functionalized with a dopamine derivative in which the amine group was converted to azide (dopamine azide). The direct reaction of SWCNTs and dopamine azide in o-dichlorobenzene at high temperature (160 °C) led to very highly functionalized CNTs (≈60 wt.%). Surprisingly, despite this high degree of functionalization, Raman spectroscopy detected a low disruption of the π-network of the carbonaceous support. This finding was justified by the rehybridization from sp3 to sp2 of the sidewall carbon atoms of CNTs involved in the functionalization process. Further characterization by means of different techniques such as X-ray photoelectron spectroscopy (XPS) analysis and transmission electron microscopy (TEM) allowed to shed some light on the chemical composition and morphology of the obtained material. Moreover, the estimation of the total content of phenolic units and their reducing potential after CNTs functionalization was also assessed using Folin and Ciocalteu and 2,2-diphenyl-1-picryl hydrazide (DPPH) assays. The functionalization of CNTs was exploited to immobilize palladium(II) species that were subsequently reduced with NaBH4 leading to the formation of Pd nanoparticles (NPs). The so obtained hybrid material was used as a recyclable heterogeneous catalyst for the reduction of nitro compounds and the Heck reaction

Templating effect of carbon nanoforms on highly cross-linked imidazolium network: Catalytic activity of the resulting hybrids with Pd nanoparticles

Two different carbon nanoforms (CNFs), namely multi-walled carbon nanotubes (MWCNTs) and carbon nanohorns (CNHs), have been chosen as support for the direct polymerization of a bis-vinylimidazolium salt. Transmission electron microscopy analyses revealed a templating effect of the CNFs on the growth of the polymeric network, which perfectly covers their whole surfaces creating a cylindrical or spherical coating for MWCNTs and CNHs, respectively. Subsequently, the CNFs-polyimidazolium have been used as stabilizers for Pd nanoparticles (Pd NPs), and the obtained materials have been characterized by means of analytical and spectroscopic techniques and then employed as easily recoverable and recyclable catalysts for Suzuki and Heck reactions. Quantitative conversions have been obtained in almost all the explored reactions, even employing low loading of catalyst (down to 0.007 mol%). Suzuki reactions were carried out in pure water under aerobic conditions. Both materials showed excellent activity and recyclability for the investigated C-C coupling reactions, with the CNHs-based material resulting slightly more active than the MWCNTs-based one due to a higher superficial exposure of Pd NPs