Caroline Curfs

Precipitation strengthening in high manganese austenitic TWIP steels

Abstract At low strains (∊ 0.3) the work hardening rate decreased slightly. Synchrotron X-ray diffraction analysis suggested that this was due to a reduction in the kinetics of twin formation. The highest strengthening coefficient in cold strips was obtained with Ti additions ≤0.1 wt.% (+1 380 MPa/wt.% Ti) but the effect quickly saturated after an increase of ∼+150 MPa. With Nb additions only modest hardening (+187 MPa/wt.%) could be achieved. The strengthening due to V was >530 MPa/wt.% for V additions ≤ 0.4 wt.% Saturation effects are less critical with V additions and yield stress increases of +375 MPa were demonstrated.

Synthesis and polymorphism of (4-ClpyH)2[CuCl4]: solid–gas and solid–solid reactions

Reaction of blue crystalline solid trans-[CuCl2(4-Clpy)2] 1 (4-Clpy = 4-chloropyridine) with anhydrous HCl gas yields yellow crystalline salt (4-ClpyH)2[CuCl4] 2 with quantitative conversion. The reaction has been followed in situ by synchrotron powder X-ray diffraction using a specially designed gas-handling rig and demonstrates that the initial product is a C-centred monoclinic form of (4-ClpyH)2[CuCl4] (phase II), which then converts in the solid state to a primitive monoclinic form (phase I). The conversion has been quantified at each stage by mixed-phase Rietveld refinement of the powder diffraction data. The two polymorphic forms exhibit different patterns of N–H⋯Cl(Cu) hydrogen bonding and C–Cl⋯Cl(Cu) halogen bonding. Evidence from solution-phase crystallisations of 2 suggests that phase II is a kinetic product and phase I is the thermodynamic product. The salt 2 can also be prepared mechanochemically, by grinding for 2 min green-blue solid CuCl2·2H2O with white solid [4-ClpyH]Cl in a 1 : 2 stoichiometric ratio. The product was identified by powder diffraction as phase I of compound 2 in 97.5% yield, with the remaining material being compound 1.

Thermal expansion of a La-based bulk metallic glass: insight from in situ high-energy x-ray diffraction

Constant-rate heating experiments using a fast x-ray camera (time resolution of 2.7 s) reveal detailed information about the thermal stability of La62Al14(Cu5/6Ag1/6)14Ni5Co5 (at.%) bulk metallic glass. Analyzing diffraction patterns in reciprocal space yields the thermal expansion of the amorphous alloy providing insight into the thermally activated relaxation effects and kinetics of the glass transition. The glass transition appears as a break in the value of the coefficient of volume thermal expansion. Furthermore, real space analysis based on the reduced pair distribution function G(r ) allows one to follow in situ the changes in the local atomic structure of the amorphous material during constant-rate heating. (Some figures in this article are in colour only in the electronic version)

A rational approach to screen for hydrated forms of the pharmaceutical derivative magnesium naproxen using liquid-assisted grinding

Variation of water content in liquid-assisted grinding was utilised to mechanochemically screen for different hydrated forms of magnesium naproxen directly from a mixture of magnesium oxide and naproxen. Structure determination from powder and single crystal X-ray diffraction data, supported by solid-state NMR and synchrotron radiation diffraction experiments, revealed a monohydrate coordination polymer, a discrete tetrahydrate complex, and provided a preliminary structural model for a highly hydrated salt.

Two new arsenides, Eu7Cu44As23 and Sr7Cu44As23, with a new filled variety of the BaHg11 structure.

Two new ternary arsenides, namely, Eu7Cu44As23 and Sr7Cu44As23, were synthesized from elements at 800 °C. Their crystal structure represents a new filled version of the BaHg11 motif with cubic voids alternately occupied by Eu(Sr) and As atoms, resulting in a 2 × 2 × 2 superstructure of the aristotype: space group Fm3̅m, a = 16.6707(2) Å and 16.7467(2) Å, respectively. The Eu derivative exhibits ferromagnetic ordering below 17.5 K. In agreement with band structure calculations both compounds are metals, exhibiting relatively low thermopower, but high electrical and low thermal conductivity.

Structural properties and phase diagram of the La(Fe1−xRux)AsO system

Structural refinement, lattice micro-strain and spontaneous strain analyses have been carried out on selected members of the La(Fe1-xRux)AsO system using high-resolution neutron and synchrotron powder diffraction data. The obtained results indicate that the character of the tetragonal to orthorhombic structural transition changes from first order for x = 0.10, possibly to tricritical for x = 0.20, up to second order for x = 0.30; for x ≥ 0.40 symmetry breaking is suppressed, even though a notable increase of the lattice micro-strain develops at low temperature. By combining structural findings with previous muon spin rotation data, a phase diagram of the La(Fe1-xRux)AsO system has been drawn. Long-range ordered magnetism occurs within the orthorhombic phase (x ≤ 0.30), whereas short-range magnetism appears to be confined within the lattice strained region of the tetragonal phase up to x < 0.60. Direct comparison between the magnetic and structural properties indicates that the magnetic transition is always associated with structural symmetry breaking, although confined to a local scale at high Ru contents.

Intermetallic germanides with non-centrosymmetric structures derived from the Yb3Rh4Sn13 type.

New germanides with composition RE3Pt4Ge13 (RE = Y, Pr, Sm, Gd, Tb, Tm) have been prepared by high-pressure, high-temperature synthesis. Their crystal structures have been refined, and the relationship of this new rhombohedral and monoclinic structure types with the primitive cubic Yb3Rh4Sn13 prototype is discussed. Band structure calculations within density functional theory confirm the distorted rhombohedral and monoclinic structural arrangements to be energetically more favorable than the simple cubic one. X-ray absorption spectroscopy and magnetic susceptibility measurements indicate that the RE-atoms are in the +3 oxidation state in all studied compounds.

Phase and Structural Behaviour in the NdAlO3-EuAlO3 System

Phase and structural behaviour in the NdAlO3–EuAlO3 system has been studied in the whole concentration range. Depending on x two kinds of solid solutions Nd1‑xEuxAlO3 exist at room temperature: one with rhombohedral (x < 0.15) and one with orthorhombic (x≈ 0.15–0.20, where the co-existence of both phases was observed. First-order structural phase transitions Pbnm↔Rc has been detected in Nd1-xEuxAlO3 with x = 0.3, 0.4, 0.6 at 520 K, 627 K and 988 K, respectively. Based on the experimental and literature data, the phase diagram of the pseudo-binary system NdAlO3–EuAlO3 has been constructed.

Residual Stress Measurements in Australia: Present and Future

The Australian Nuclear Science and Technology Organisation, ANSTO, (http:\\www.ansto.gov.au) has initiated a “Neutrons for Engineering” project to provide an integrated residual stress service to Australian industry and academia. The service is based around measurements of residual stress using neutrons on a newly-refurbished instrument on the HIFAR research reactor. In addition to the neutron measurements there is a range of expertise available on the ANSTO site to solve residual stress problems using other techniques including hole-drilling, strain-gauging, and x-ray diffraction, as well as capabilities for finite element modeling and mechanical testing. In this paper we describe briefly the existing and future facilities at ANSTO for neutron strain scanning and present some benchmark results for the HIFAR strain scanner.

Characterization of the Superelasticity and the Martensitic Transformation from Ti-Nb-(O,N) Biomedical Alloys

In this paper, results concerning newly developed Ti-Nb based superelastic alloys containing interstitial O or N element are presented. These elements were added because of their strong influence on the alpha” martensitic transformation and also because of their solid-solution strengthening effect. Microstructures and mechanical behavior of the alloys were investigated by different methods and compared with a binary Ti-Nb alloy taken as reference. On the other hand, in-situ synchrotron X-ray diffraction analyses during tensile tests have been specifically performed to characterize precisely the stress-induced martensitic transformation in such alloys.