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Assessment of the Microstructure Evolution of an Austempered Ductile Iron During Austempering Process Through Strain Hardening Analysis

Riccardo Donnini,Alberto Fabrizi,Franco Bonollo,Franco Zanardi,Giuliano Angella 대한금속·재료학회 2017 METALS AND MATERIALS International Vol.23 No.5
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The aim of this investigation was to determine a procedure based on tensile testing to assess the critical range ofaustempering times for having the best ausferrite produced through austempering. The austempered ductile iron(ADI) 1050 was quenched at different times during austempering and the quenched samples were tested in tension. The dislocation-density-related constitutive equation proposed by Estrin for materials having high density ofgeometrical obstacles to dislocation motion, was used to model the flow curves of the tensile tested samples. Onthe basis of strain hardening theory, the equation parameters were related to the microstructure of the quenchedsamples and were used to assess the ADI microstructure evolution during austempering. The microstructure evolutionwas also analysed through conventional optical microscopy, electron back-scattered diffraction techniqueand transmission electron microscopy. The microstructure observations resulted to be consistent with the assessmentbased on tensile testing, so the dislocation-density-related constitutive equation was found to be a powerfultool to characterise the evolution of the solid state transformations of austempering.
2
Unprecedented Tris-Phosphido-Bridged Triangular Clusters with 42 Valence Electrons. Chemical, Electrochemical and Computational Studies of their Formation and Stability

Funaioli, Tiziana,Leoni, Piero,Marchetti, Lorella,Albinati, Alberto,Rizzato, Silvia,Fabrizi de Biani, Fabrizia,Ienco, Andrea,Manca, Gabriele,Mealli, Carlo American Chemical Society 2013 Inorganic Chemistry Vol.52 No.8
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This paper presents the synthesis and structural characterization of the unprecedented tris-phosphido-bridged compounds Pt3(μ-PBut2)3X3 (X = Cl, Br, I), having only 42 valence electrons, while up to now analogous clusters typically have 44e–. The new species were obtained by an apparent bielectronic oxidation of the 44e– monohalides Pt3(μ-PBut2)3(CO)2X with the corresponding dihalogen X2. Their X-ray structures are close to the D3h symmetry, similarly to the 44e– analogues with three terminal carbonyl ligands. The products were also obtained by electrochemical oxidation of the same monohalides in the presence of the corresponding halide. In a detailed study on the formation of Pt3(μ-PBut2)3I3, the redox potentials indicated that I2 can only perform the first monoelectronic oxidation but is unsuited for the second one. Accordingly, the 43e– intermediate [Pt3(μ-PBut2)3(CO)2I]+ was ascertained to play a key role. Another piece of information is that, together with the fully oxidized product Pt3(μ-PBut2)3I3, the transient 44e– species [Pt3(μ-PBut2)3(CO)3]+ is formed in the early steps of the reaction. In order to extract detailed information on the formation pathway, involving both terminal ligand substitutions and electron transfer processes, a DFT investigation has been performed and all the possible intermediates have been defined together with their associated energy costs. The profile highlights many important aspects, such as the formation of an appropriate couple of 43e– intermediates having different sets of terminal coligands, and suitable redox potentials for the transfer of one electron. Optimizations of 45e– associative intermediates in the ligand substitution reactions indicate their possible involvement in the redox process with reduction of the overall energy cost. Finally, according to MO arguments, the unique stability of the 42e– phosphido-bridged Pt3 clusters can be attributed to the simultaneous presence of three terminal halides.This paper presents the synthesis and structural characterization of the unprecedented tris-phosphido-bridged compounds Pt3(μ-PBut2)3X3 (X = Cl, Br, I), having only 42 valence electrons, while up to now analogous clusters typically have 44e−. The new species were obtained by an apparent bielectronic oxidation of the 44e− monohalides Pt3(μ-PBut2)3(CO)2X with the corresponding dihalogen X2. According to MO arguments, the unique stability of the 42e− phosphido-bridged Pt3 clusters can be attributed to the simultaneous presence of three terminal halides.Graphic Abstract <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/inocaj/2013/inocaj.2013.52.issue-8/ic400251y/production/images/medium/ic-2013-00251y_0014.gif'><A href='http://pubs.acs.org/doi/suppl/10.1021/ic400251y'>ACS Electronic Supporting Info</A>

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