A TEM investigation of precipitates in high alloy martensitic steels

A TEM investigation of precipitates in high alloy martensitic steels

SCANDEM-90 18! Our group has investigated cell culture contaminants for several years. We have commonly discovered mycoplasmas and yet unknown type ...

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SCANDEM-90

18!

Our group has investigated cell culture contaminants for several years. We have commonly discovered mycoplasmas and yet unknown type of microbial contaminants from cell cultures originating from Finland as well as from several other countries. The novel contaminants are autonomously replicating bacteria-like particles and we have now compared their structure in SEM to that of mycoplasmas. We prepared samples for SEM from cultured mycoplasmas (four strains), from cultured novel contaminants and from 3T6 mouse fibroblast cell cultures, either healthy controls or artificially contaminated by cultured micro-organisms. The cultures were fixed on 14 mm cover slips, dehydrated and critical point dried, or dried without dehydration in dry air. The cover slips were coated with a 20—40 nm gold layer. Cultured mycoplasmas were visualized as coccoid particles with a diameter of 300—600 nm. In 3T6 cultures infected for 24 h, mycoplasmas were harboured on cell walls as large clumps that included elongated long forms. Many of the 3T6 cells were disrupted and vacuolated. The novel contaminants were also coccoid particles with a typical diameter of 100—300 nm. The infected 3T6 cells were again vacuolated and many cells were lysed after 24 h infection. Both mycoplasmas and the novel agent thus have a mild cytopathic effect on 3T6 cells. MATERIAL SCIENCES Microstructures of YBa2Cu3O7~Superconductors. JosÉ A. ALARCO,* EVA OLSSON,*t GORDON DUNLOP,* § HANNES MEDELIUSt and DAVID ROWCLIFFE,t *Division for Microscopy of Materials, Department of Physics, Chalmers University of Technology, S-412 96 Gothenburg, Sweden and tDivision ofCeramics, Royal Institute of Technology, S-100 44 Stockholm, Sweden The microstructures of ceramic YBa2Cu3O7...~,high ‘F~superconducting materials, prepared from freeze dried powders (Medelius and Rowcliffe, 1988), have been characterized using a combination of X-ray diffractometry, optical microscopy, scanning electron microscopy and analytical transmission electron microscopy (TEMSTEM-EDS). Microstructural effects due to either small controlled changes in stoichiometry or different sintering atmospheres (oxygen or air), sintering temperature and annealing time have been examined and related to the superconducting properties. Materials with compositions containing over-stoichiometric quantities of Ba and Cu have been analysed. Special emphasis has been placed upon the interfacial microstructures. Clean boundaries and those containing an amorphous intergranular film between YBa2Cu3O7 grains, interfaces between secondary phases and YBa2Cu3O7 grains, and twin boundaries have all been studied. Superconducting transition temperatures were measured by the real component of the a.c. susceptibility and resistivity. ,~

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Reference Medelius, H. and Rowcliffe, D., 1988. MRS series High 1~Superconductors, part II, Strasbourg, France. ~ Present address: IBM Research Division, T. J. Watson Research Center, Yorktown Heights, New York 10598, U.S.A. § Present address: Department of Mining and Metallurgical Engineering, University of Queensland, St. Lucia. Queensland 4067. Australia.

A TEM Investigation of Precipitates in High Alloy Martensitic Steels. H. 0. ANDREN and G. J. CA!, Department of Physics, Chalmers University of Technology, Goteborg, S-412 96, Sweden This paper presents the results of a TEM investigation of precipitates in matrixes of high speed steels and 12% Cr steel. The specimens of high speed steels were quenched

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from above 1200°Cand tempered at 560°Cthree times and then heated at 600°Cfor 500 h. The specimens of 12% Cr steel were taken from manual arc weld metal that had been immediately heat treated at 750°Cfor 5 h. The investigation shows that in the high speed steels, most secondary precipitates were of the type M2C and MC. M2C precipitated generally along martensitic lath boundaries and inside the laths. The particles of M2C have coarsened during heat treatment. MC precipitated generally inside the martensitic laths and was fine. In 12% Cr steel the precipitate was of the Cr23C6 type situated along the martensitic boundaries and primary austenite boundaries. The precipitates in the investigated steels obeyed certain orientation relationships with the matrix. Surface Coatings of TiN Produced by Gas Evaporation. M. D. BENTZON and F. KRAGH, Laboratory of Applied Physics and Department of Structural Properties of Materials, Technical University of Denmark, 2800 Lyngby, Denmark This work presents a new method for production of surface coatings. The method is based on the extremely high reactivity of ultrafine particles and on the sintering properties of ultrafine TiN particles. Surface coatings of 5-TiN are produced by exposing a tungsten substrate to a flux of ultrafine TiN particles produced by evaporating Ti in an atmosphere of He and N2. The produced TiN particles have fcc structure (5-TiN), are extremely small (5 20 nm) and have a cubic shape with (100) surfaces. The tungsten crucible used as evaporation source was covered by a TiN layer in a quite broad but clearly limited zone between the central part and the water cooled electrode. The TiN coating consists of rectangular 5-TiN grains with a size of 1 10 j.tm; these crystals show up a step-like growing and appear to contain crystal tensions. Ultrafine TiN particles were collected on a vertical tube cooled by liquid nitrogen and studied by TEM. The surface coating and the substrate/coating interface were studied by SEM. Structure Factor Determination from 001 Systematic Row of CBED Patterns in YBa2Cu3O7~Superconductor. NINA BØE and KJERSTI GJØNNES, Department ofPhysics, University of Oslo, Norway The systematic row of reflections (001) in YBa2Cu3O7 superconductor has been studied by the CBED technique in a JEM 2000 FX. Integrated intensities for the 001 lines in wide discs containing several lines were extracted from microdensitometer traces. Theoretical calculations of the structure factor have been carried out in order to refine parameters such as atom positions, thermal parameters, site occupancy and ionicity. The structure factors are sensitive to variations in these parameters in different ranges of 1 (1 meaning the index of reflections in the c* direction, in this case varying from 1 = 1 to 1 = 32). Change in ionicity of Cu and 0 and site occupancy influence the inner structure factors, whereas change in atomic positions has an appreciable effect in high order reflections. Debye Waller factors influence the high order reflections. Reflections up to 0032 have been recorded and compared with calculations based on the published structure. Integrated intensities across the lines are compared with kinematic as well as dynamic calculations. For the high order reflections the kinematic approach is valid; low order intensities are difficult to use in structure factor determination because of strong dynamic interaction. Dynamic calculations of the intensities and theoretical calculation of the structure factors are in good agreement with the observed intensities in the CBED patterns. Observations of Chloride- and Thiosuiphate-induced Pitting in Stainless Steels. ULLA EHRNSTEN, OuTI VARJONEN and TERO HAKKARAINEN, Technical Research Centre of Finland, Metallurgy Laboratory, Espoo, Finland