Effect of stacking fault energy on the dynamic recrystallization during hot working of FCC metals: A study using processing maps

The influence of stacking fault energy (SFE) on the mechanism of dynamic recrystallization (DRX) during hot deformation of FCC metals is examined in the light of results from the power dissipation maps. The DRX domain for high SFE metals like Al and Ni occurred at homologous temperature below 0·7 and strain rates of 0·001 s−1 while for low SFE metals like Cu and Pb the corresponding values are higher than 0·8 and 100 s−1. The peak efficiencies of power dissipation are 50% and below 40% respectively. A simple model which considers the rate of interface formation (nucleation) involving dislocation generation and simultaneous recovery and the rate of interface migration (growth) occurring with the reduction in interface energy as the driving force, has been proposed to account for the effect of SFE on DRX. The calculations reveal that in high SFE metals, interface migration controls DRX while the interface formation is the controlling factor in low SFE metals. In the latter case, the occurrence of flow softening and oscillations could be accounted for by this model.

Thiomalates of alkaline earth metals

Solid state 1:1 complexes of divalent Mg, Ca, Sr and Ba with thiomalic acid(tma) have been isolated and characterised by elemental analysis, IR spectra and thermal studies. It is shown that tma coordinates to the metal ions through carboxylic oxygen atoms. Thermal studies of these complexes show that desulphurisation preceeds decarbonylation reaction leading to the formation of metal carbonates in all the cases except Mg where MgO is the end product. Thermal stability of the anhydrous thiomaltes follows the order Mg not, vert, similar Ca > Sr > Ba. Structures have been proposed based on the information obtained from these studies.

Coexistence of para and ferromagnetic phases of Fe3+ in undoped CdZnTe (Zn similar to 4%) crystals

The signatures of the coexistence of para and ferromagnetic phases for the Fe3+ charge state of iron have been identified in the low temperature electron spin resonance (ESR) spectra in undoped CdZnTe (Zn similar to 4%) crystals and independently verified by superconducting quantum interference device (SQUID) and AC susceptibility measurements. In the paramagnetic phase the inverse of AC susceptibility follows the Curie-Weiss law. In the ferromagnetic phase the thermal evolution of magnetization follows the well-known Bloch T-3/2 law. This is further supported by the appearance of hysteresis in the SQUID measurements at 2 K below T-c which is expected to lie in between 2 and 2.5 K. (C) 2010 Elsevier Ltd. All rights reserved.

Rapid synthesis of room temperature ferromagnetic Ag-doped LaMnO3 perovskite phases by the solution combustion method

We report the rapid solution combustion synthesis and characterization of Ag-substituted LaMnO3 phases at relatively low temperature using oxalyl dihydrazide, as fuel. Structural parameters were refined by the Rietveld method using powder X-ray diffraction data. While the parent LaMnO3 crystallizes in the orthorhombic structure, the Ag-substituted compounds crystallize in the rhombohedral symmetry. On increasing Ag-content, unit cell volume and Mn-O-Mn bond angle decreases. The Fourier transform infra red spectrum shows two absorption bands corresponding to Mn-O stretching vibration (v(s) mode) and Mn-O-Mn deformation vibration (v(b) mode) around 600 cm(-1) and 400 cm(-1) for the compositions x = 0.0, 0.05 and 0.10, respectively. Electrical resistivity measurements reveal that composition-controlled metal to insulator transition, with the maximum metal to insulator being 280 K for the composition La0.75Ag0.25MnO3. Increase in magnetic moment was observed with increase in Ag-content. The maximum magnetic moment of 35 emu/g was observed for the composition La0.80Ag0.20MnO3. (C) 2010 Elsevier Ltd. All rights reserved.

A Photoelectron Spectroscopic Study Of The Interaction Of Oxygen, Nitrogen And Transition-Metals With C-60 Films

Evidence is presented for the strong interaction of oxygen and nitrogen with solid films of buckminsterfullerene based on core-level spectroscopic studies. Cr, Ni and Cu deposited on C60 films interact strongly giving rise to large changes in the C(Is) and C(2p) binding energies as well as the (2p) binding energies of the transition metals.

Concentrations and loads of some metals and fluorine in the River Kokemäenjoki in 1975 and 1977

Tiivistelmä: Metallien ja fluorin pitoisuuksista ja määristä Kokemäenjoessa vuosina 1975—1977

A ferromagnetic resonance study of La1-xCaxMnO3

Ferromagnetic resonance spectra of La1-xCaxMnO3 powders (0.1 less than or equal to x 0.9) have been investigated over a range of temperatures. The spectra could be fitted to a sum of two Lorentzians for all the compositions. The intense line with a nearly constant g shows a linear decrease in linewidth with increase in temperature, while the weaker line with a variable g shows a maximum in linewidth in the T-c region. The latter is also associated with a g(eff) which depends on the composition. Copyright (C) 1996 Elsevier Science Ltd

Joining of dissimilar metals: issues and modelling techniques

Joining of dissimilar metals involves a number of scientific issues, the modelling of which offers unique challenges. This review discusses the complexities in different joining processes and dissimilar combinations, and the corresponding computational techniques that have the potential to address the same. Future directions in modelling at both macroscopic and microscopic scales are also suggested.

The role of strain rate response in plane strain abrasion of metals

Titanium flats were scribed by silicon carbide wedges over ranges of temperatures and applied strains and with lubrication. The response of the material to scribing was noted by recording the coefficient of friction, the surface morphology of track and the subsurface deformation. Additional data were obtained from (1) uniaxial compression of titanium, (2) scribing of oxygen-free high conductivity copper and (3) scribing of aluminium under dry and lubricated conditions to analyse and explain the observed variation in response of titanium to scribing with strain, temperature and lubrication.

Influence of the ferromagnetic layer on the pair breaking and low alternating current field magnetic response in superconductor/ferromagnet bilayer

We investigate the influence of the ferromagnetic layer on the magnetic and transport properties of YBa2Cu3O7-delta in YBa2Cu3O7-delta (YBCO)/La0.7Sr0.3MnO3 (LSMO) bilayers. The temperature dependent dc magnetization study reveals the presence of magnetic anisotropy in YBCO/LSMO bilayer as compared to the pure YBCO layer. The ac susceptibility study on YBCO/LSMO bilayers reveals stronger pinning and the temperature dependent critical current is found to be less prone to temperature. Besides, the current (I) dependent electrical transport studies on YBCO/LSMO exhibit a significant reduction in the superconducting T-c with increase in I and it follows I-2/3 dependence in accord with the pair breaking effect. The higher reduction of superconducting T-c in YBCO/LSMO is believed to be due to the enhanced pair-breaking induced by the spin polarized carriers being injected into the superconductor. (C) 2011 American Institute of Physics. doi: 10.1063/1.3560029]

Roughness generated in surface grinding of metals

When a metal is surface ground the roughness generated is the summation of a function of the wheel roughness and the roughness due to wheel attrition and damage to the workpiece. We identify this function here as a maximum em,elope profile, which is fractal within certain cut off wavelengths determined by the dressing conditions of the wheel. Estimating the global displacement of the binder-grit-workpiece system from the maximum envelope power spectra, we determine the plastic indentation of the workpiece at characteristic length scales using simple contact-mechanical calculation. The estimated roughness corresponds well with that recorded experimentally for hard steel, copper; titanium and aluminium.

Assessing formability of sheet metals through advanced tensile and LASER speckle analysis

The ability of a metal to resist strain localisation and hence reduction in local thickness, is a most important forming property upon stretching. The uniform strain represents in this regard a critical factor to describe stretching ability - especially when the material under consideration exhibits negative strain rate sensitivity and dynamic strain ageing (DSA). A newly developed Laser Speckle Technique (LST), e.g. see [1], was used in-situ during tensile testing with two extensometers. The applied technique facilitates quantitative information on the propagating plasticity (i.e. the so-called PLC bands) known to take place during deformation where DSA is active. The band velocity (V-band), and the bandwidth (W-band) were monitored upon increasing accumulated strain. The knowledge obtained with the LST was useful for understanding the underlying mechanisms for the formability limit when DSA and negative strain rate sensitivity operate. The goal was to understand the relationship between PLC/DSA phenomena and the formability limit physically manifested as shear band formation. Two principally different alloys were used to discover alloying effects.

Electrochemical processing of ocean manganese nodules with microbial enhancement to recover valuable metals

In this paper, electroleaching and electrobioleaching of ocean manganese nodules are discussed along with the role of galvanic interactions in bioleaching. Polarization studies using a manganese nodule slurry electrode system indicated that the maximum dissolution of iron and manganese due to electrochemical reduction occurred at negative DC potentials of -600 and -1,400 mV(SCE). Electroleaching and electrobioleaching of ocean manganese nodules in the presence of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans at the above negative applied DC potentials resulted insignificant dissolution of copper, nickel and cobalt in 1 M H2SO4 and in sulfuric acid solution at pH 0.5 and 2.0. Mechanisms involved in electrobioleaching of ocean manganese nodules are discussed. Galvanic leaching of ocean manganese nodules in the presence of externally added pyrite and pyrolusite for enhancement of dissolution was also studied. Various electrochemical and biochemical parameters were optimized, and the electroleaching and galvanic processes thus developed are shown to yield almost complete dissolution of all metal values. This electrobioleaching process developed in the laboratory may be cost effective, energy efficient and environmentally friendly.