On the measurement of the nanohardness of the constitutive phases of TRIP-assisted multiphase steels

The nanohardness of the phases present in the microstructure of two TRIP (for TRansformation Induced Plasticity)-assisted multiphase steels differing by their silicon content was measured by nanoindentation in an atomic force microscope. It is observed that the softest phase in both steels is the ferritic matrix, followed by bainite, austenite and martensite. It is also shown that the silicon content of the steel grades is responsible for an increase of the hardness of the ferritic matrix due to solid solution strengthening. Finally, the influence of the preparation mode of the surface prior to the nanoindentation measurements has been investigated. An electropolishing stage after mechanical polishing is acceptable to allow valuable nanohardness measurements. (C) 2002 Elsevier Science B.V. All rights reserved

Pseudotachylyte in muscovite-bearing quartzite: Coseismic friction-induced melting and plastic deformation of quartz

Thin (0.5\u20132 mm thick) pseudotachylyte veins occur within muscovite-bearing ( 3c10% volume), amphibolite-facies quartzites of the Schneeberg Normal Fault Zone (Austroalpine, Southern Tyrol, Italy). Pseudotachylytes are associated with precursor localized plastic microshear zones (50\u2013150 \u3bcm thick) developed sub-parallel to the host-rock foliation and with conjugate sets oriented at a high angle to the foliation. Such microshear zones are characterized by recrystallization to ultrafine-grained (1\u20132 \u3bcm grain size) mosaic aggregates of quartz showing a transition from a host-controlled to a random crystallographic preferred orientation towards the shear zone interior. Subsequent coseismic slip mainly exploited these microshear zones. Microstructural analysis provides evidence of extensive friction-induced melting of the muscovite-bearing quartzite, producing a bimodal melt composition. First, the host-rock muscovite was completely melted and subsequently crystallized, mainly as K-feldspar. Then, about 60% volume of the ultrafine-grained quartz underwent melting and crystallized as spherulitic rims (mostly consisting of quartz \ub1 Ti \ub1 Fe) around melt-corroded quartz clasts. The two melts show immiscibility structures in the major injection veins exploiting microshear zones at high angles to the quartzite foliation. In contrast, they were mechanically mixed during flow along the main fault veins

Elastic moduli and hardness of c-Zr2.86(N0.88O0.12)4 having Th3P4-type structure

The equation of state of the recently discovered oxygen-bearing cubic zirconium (IV) nitride, c-Zr2.86(N0.88O0.12)4, was measured at room temperature in a diamond anvil cell using x-ray powder diffraction combined with synchrotron radiation. From these studies the bulk modulus B0 = 219(13) GPa and its first pressure derivative B0′ = 4.4(1.0) [or B0 = 223(5) GPa, for B0′ fixed at 4] were obtained. Applying nanoindentation techniques the reduced modulus Er ≈ 220 GPa and hardness H ≈ 18 GPa were measured for porous c-Zr2.86(N0.88O0.12)4. The shear modulus of c-Zr2.86(N0.88O0.12)4 was estimated to be at least G0 = 96(13) GPa using the experimental data of B0 and Er, exclusively

Electroreductive radical cyclization of ethyl 2-bromo-3-allyloxy- and -3-(propargyloxy)propanoates catalyzed by (tetramethylcyclam)nickel(I) electrogenerated at carbon cathodes in dimethylformamide

Prova tipográfica (In Press)Reductive intramolecular cyclization of ethyl 2-bromo-3-(3′,4′-methylenedioxophenyl)-3-(propargyloxy)propanoate (1) and ethyl 2-bromo-3-(3′,4′-dimethoxyphenyl)-3-(allyloxy)propanoate (2) promoted by (1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetra-decane)nickel(I), [Ni(tmc)]+, electrogenerated at glassy carbon cathodes in dimethylformamide containing tetraalkylammonium salts, has been investigated. Cyclic voltammograms for reduction of [Ni(tmc)]2+ in the presence of 1 and 2 reveal that [Ni(tmc)]+ catalytically reduces these two compounds at potentials significantly more positive than those required for direct reduction of the bromoesters. During controlled-potential electrolyses of solutions of [Ni(tmc)]2+ in the presence of 1 and 2, catalytic reduction of each substrate proceeds via one-electron cleavage of the carbon–bromine bond to form a radical intermediate that undergoes cyclization to afford, respectively, 2-(3′,4′-methylenedioxophenyl)-3-ethoxycarbonyl-4-methylenetetrahydrofuran (3) and 2-(3′,4′-dimethoxyphenyl)-3-ethoxycarbonyl-4-methyltetrahydrofuran (6). A mechanistic scheme is proposed to account for the formation of each major product.Fundação Calouste GulbenkianCRUPFundação para a Ciência e Tecnologia (FCT)Government Assistance in Areas of National Need (GAANN)Fellowship awarded by Indiana Universit

Electroreductive intramolecular cyclization of a bromo propargyloxy ester catalyzed by nickel(I) tetramethylcyclam electrogenerated at carbon cathodes in dimethylformamide

Cyclic voltammetry and controlled-potential electrolysis have been employed to investigate and characterize the reductive intramolecular cyclization of ethyl 2-bromo-3-(3′,4′-dimethoxyphenyl)-3-propargyloxy-propanoate (1) promoted by (1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane)nickel(I), [Ni(tmc)]+, electrogenerated at glassy carbon cathodes in dimethylformamide containing tetraalkylammonium salts. Cyclic voltammograms for reduction of [Ni(tmc)]2+ in the presence of 1 reveal that [Ni(tmc)]+ catalytically reduces 1 at potentials more positive than those required for direct reduction of 1. During controlled-potential electrolyses of solutions containing [Ni(tmc)]2+ and 1, catalytic reduction of the latter proceeds via one-electron cleavage of the carbon–bromine bond to form a radical intermediate that undergoes cyclization to afford 2-(3′,4′-dimethoxyphenyl-3-ethoxycarbonyl-4-methylene-tetrahydrofuran (2). In the presence of a base (either electrogenerated or deliberately added as potassium tert-butoxide), 2 rearranges to give 2-(3′,4′-dimethoxyphenyl-3-ethoxycarbonyl-4-methyl-2,5-dihydrofuran (3). A mechanistic scheme is proposed to explain the results obtained by means of cyclic voltammetry and controlled-potential electrolysis.Fundação Calouste Gulbenkian

Interface affected zone for optimal strength and ductility in heterogeneous laminate

Interfaces have been reported to significantly strengthen and toughen metallic materials. However, there has been a long-standing question on whether interface-affected-zone (IAZ) exists, and how it might behave. Here we report in situ high-resolution strain mapping near interfaces in a copper-bronze heterogeneous laminate, which revealed the existence of IAZs. Defined as the zone with strain gradient, the IAZ was found to form by the dislocations emitted from the interface. The IAZ width remained largely constant with a magnitude of a few micrometers with increasing applied strain. Interfaces produced both back stress strengthening and work hardening, which led to both higher strength and higher ductility with decreasing interface spacing until adjacent IAZs started to overlap, after which a tradeoff between strength and ductility occurred, indicating the existence of an optimum interface spacing for the best mechanical properties. These findings are expected to help with designing laminates and other heterogeneous metals and alloys for superior mechanical properties