Characterization of ultrafine La x Sr1−x MnO3 powder prepared by spray pyrolysis

The characterization of La _x Sr_1−x MnO₃ powders produced by spray pyrolysis using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observation, specific surface area (Brunauer-Emett-Teller), and particle size distribution measurements shows that the resultant large particles are loose agglomerates consisting of many small particles. However, the sintered tiny particles can form hard agglomerates, and the particle size increases remarkably. The structures of the powders before and after sintering were identified by x-ray diffraction (XRD). The study of the electrical property of the powder shows that the powder is a metallic conductor. In a reducing atmosphere, the powder can be decomposed. When the powder is cofired with yttria-stabilized zirconia 5% (YSZ) powder at 1200 °C for 5 h, no new phase is produced, and the powder remains a single provskite hexagonal-rhombohedral structure.     

Effect of the zone of plastic deformation of the fractal properties of a fracture surface

In order to determine the effect of the plastic zone on the fractal properties of a fracture surface, specimens of medium-carbon steels are studied after tough and brittle fracture. A fractal analysis is conducted for each specimen by the method of vertical sections. The sizes of the determining parameters of the fractures and plastic zones under the fracture surfaces are determined by measuring the Knoop microhardness. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 7, pp. 21–25, July, 1997.     

Calculated hardenability for improved consistency of properties in heat treatable engineering steels

Hardenability is one of the most important parameters controlling the heat treated properties of engineering steels. It affects the consistency of response for microstructure, hardness, strength, toughness, and dimensional change (distortion). This study illustrates that a major benefit of controlling hardenability is improving the consistency of dimensional distortion resulting from heat treatment. To facilitate the supply of steels to hardenability limits, especially restricted hardenability, a new technique was developed for the prediction of Jominy hardenability from chemical composition. The technique, termed the “Database Method,” uses measured Jominy hardenability and chemical composition data, contained in a database, to calculate the hardenability for a query composition. Using up to ten known steels, selected from the database with compositions closely matching that of the query steel, a small adjustment is made to the measured hardenability of each known steel allowing for the small difference in composition between the query and chosen steel. The final calculated result for the query steel is taken as the average of the various estimates. The basis of the Database Method is explained, and the advantages are illustrated for selecting engineering grades.     

Regular features of wear in heterogeneous structures of high-strength coatings

High-strength coatings on alloys of various morphology prepared by methods of surface impregnation are effective (wear resistant) in operation and economical in production. The requisite structure, wear resistance, and antifriction properties can be provided by a proper choice of the production technology of the coating and the quality parameters of the triboengineering layers, which determine the operating capacity, namely, the geometric (thickness of the coating and depth of the diffusion zone), structural (porosity, phase composition, substructural components), and physical and mechanical (macro- and microstresses, microhardness) parameters and the strength of cohesion with the substrate.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 6, pp. 21 – 25, June, 1996.     

The Oxidation Behavior of Y2O3-Dispersed β-NiAl

Y₂O₃-dispersed NiAl was produced by a powder-metallurgy process. By adding Y as an oxide dispersion (OD), problems with NiY_x formation and internal oxidation were avoided. Short-term isothermal and cyclic-oxidation performance at 1200°–1500° C was compared to cast NiAl alloys with and without Zr. Results indicate that the Y₂O₃ addition was beneficial to scale adhesion and significantly modified the α-Al₂O₃ scale microstructure, similar to a Zr alloy addition. However, at 1400 and 1500° C, neither the Y₂O₃ or Zr additions changed the scale-growth rate, eliminated the formation of voids at the metal-scale interface or prevented scale spallation. These similarities in performance suggest that similar mechanisms occur when the reactive element is added as either an OD or an alloy addition.     

The Fe-Ni (iron-nickel) system

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