On the structural unit model of grain boundary structure

Abstract

A critique of the structural unit model is presented. It is shown that the predictive capacity of the model is severely limited when it is applied to boundaries with relatively-high-index rotation axes. Recent computer simulations suggest that ‘high index’ means 〈221〉 and above. A new approach to grain boundary structure is needed for mixed tilt and twist boundaries.     

Formation of Cu precipitates and vacancy clusters in neutron-irradiated Fe–Cu alloys

Two Fe–Cu binary model alloys, Fe–0.3Cu and Fe–0.6Cu, were irradiated with fission neutrons at doses ranging from 4?×?10^?6 to 0.16 dpa (displacements per atom) at ～573 K to investigate the formation of Cu precipitates and microstructural evolution. The Cu content only affected the formation of Cu precipitates and microvoids at low doses. In Fe–0.3Cu, the formation of microvoids and Cu precipitates initiated at doses of 1.2?×?10^?4 and 4?×?10^?5 dpa, respectively. On the other hand, the formation of microvoids started at a dose of 4?×?10^?4 dpa in Fe–0.6Cu, and Cu precipitates were formed even after irradiation to 4?×?10^?6 dpa. On further irradiation, the difference in the formation of Cu precipitates and microvoids was small. Microvoids grew with increasing irradiation dose up to 3?×?10^?3 dpa in both alloys. Prominent aggregation of Cu atoms occurred upon irradiation from 3?×?10^?3 to 1.6?×?10^?2 dpa and the microvoids shrank. The Cu precipitates no longer grew, and microvoids nucleated and grew in the matrix above a dose of 1.6?×?10^?2 dpa in both alloys. The present studies clearly reveal the relationships between the formation and growth of Cu precipitates and microvoids with irradiation dose.     

Thermal aging effects on magnetisation reversals in a pre-deformed Fe-1wt%Cu alloy studied via first-order reversal curves

Abstract

The ability of amorphous metallic alloys to resist irradiation-induced structural changes will depend on the composition of the alloy and the particle fluences used. In this paper we show that a fast neutron fluence of 10²⁰ cm^?2 can induce local crystallization in a refractory NiTi glass. For specimens irradiated with lower fluences, the mode of crystallization of the amorphous matrix is changed from that of a primary process to a eutectic mechanism.     

The crystal structure of Al20.6Ta22.4 and its relation to Frank–Kasper phases

The monoclinic phase in the Al–Ta system has been identified by means of X-ray single-crystal structure analysis as Al_{19+ x} Ta_{24? x} (x?=?1.6), Pearson symbol mP86. Al_20.58Ta_22.42 crystallizes in the space group P2₁/n, with a?=?987.86?pm, b?=?990.12?pm, c?=?1489.45?pm and β?=?99.958°. Twinned crystals of the title compound can be obtained by iodine-promoted reactions of the elements. In the experiments described here, the reactions took place in sealed tantalum ampoules at 1400°C. Single-phase samples were obtained by a metallurgical powder method, which minimizes aluminium loss by incongruent vapourization. The composition was found to span the range 0.51?≤?x _Ta?≤?0.53. Al_{19+ x} Ta_{24? x} decomposes in the solid state at 1450°C into Al₆₉Ta₃₉ and σ-AlTa₂. The crystal structure is analyzed in relation to tetrahedral close-packed structures. The kinship with Cr₃Si-type and H-type structures is accentuated.     

A RESPONSE TO CARL HELRICH: THE LIMITATIONS AND PROMISE OF QUANTUM THEORY

Abstract. I respond to Carl Helrich's criticism of my proposition that the emergence of complex order in the universe is from Virtual State Actualization (VSA). The question is discussed as to whether quantum theory is able to afford any kind of quantum ontology or whether it merely allows an epistemological view. I point out that, even though many contradictory interpretations of quantum theory are currently possible, the concept of VSA is based on molecular properties that are so simple and factual that they are beyond interpretation. Helrich's appeal for caution in proceeding from physical reality to Divine Reality is wholeheartedly supported and a detailed discussion is given.     

Professional learning as ‘diffractive’ practice: rhizomatic peer coaching

Acknowledging an abundance of technicist models for teacher continuing professional development (CPD), the authors draw from Deleuzoguattarian theory to frame peer coaching as rhizomatic practice. Rhizome theory enables engagement with the creative breaks and departures in peer coaching assemblages. Agentic and innovative teacher learning can occur when teachers can take lines of flight to think differently about their teaching practices. Deleuzoguattarian notions of rupturous lines signal teacher-generated possibilities for new initiatives. Located in an Aotearoa/New Zealand facilitated inquiry CPD context, the article explores how nine teachers engaged in a formal process of collaborative dialogue. A rhizomatic approach to dialogue encompasses a dynamic view of teacher learning. Openness to emergence can enable educators to theorise pedagogy creatively to potentiate a multiplicity of pathways forward.     

Vacancy-mediated structural changes in Au–Cu nanoparticles

We report the formation of new phases in bimetallic Au–Cu nanoparticles. These phases were observed in nanoparticle synthesised by adopting a three-step protocol in a single pot. Nanoparticles at 180°C for 1?h led to the formation of single-phase solid solution of Cu in Au. Subsequent heat treatment at 290°C for 2?h of these Au–Cu nanoparticles revealed three new phases. One of them relates to the modification of occupancy of Cu in an ordered AuCu tetragonal phase (tP4). This cell although retains tetragonal symmetry but displays metrical properties akin to that of a cube. The other two relates to vacancy ordering along <111> directions in the {111} planes of an ordered AuCu3 cubic phase (cP4). On the one hand, statistical occupancy of vacancy on Cu site in this cell leads to the reduction of cell size from ～3.75?Å to ～3.5?Å whereas ordering of vacant layer on the other hand gives rise to symmetry breaking. Former continues to display cubic symmetry whereas latter transforms to a trigonal cell.     

The state of order in Fe–Al studied by precession electron diffraction

Precession electron diffraction (PED) has been carried out on a fully ordered Fe–40at.%Al solid solution in order to explore its suitability for determining the state of order. The integrated intensity ratio of a superlattice reflection with respect to a fundamental reflection was measured as a function of the sample thickness and the results are well fitted by dynamical simulations. It is proposed that, in addition to conventional X-ray diffraction, PED may provide access to the state of order at microscopic and nanoscopic scales.