Multilayer Composites Based on PTFE Films and Fiberglass

Fibre Chemistry - The article is devoted to the development of two-layer composites with a fluoroplastic matrix and fiberglass reinforcing elements. The fluoroplastic matrix acts as a protective...     

Investment casting of NiAl single-crystal alloys

Significant progress has been made in the understanding of solidification conditions, microstructure evolution, and defect formation during investment casting of NiAl single crystals. The high liquidus temperatures of NiAl alloys result in a larger dendrite arm spacing than is found in superalloy René N5. Because of their higher thermal conductivities, NiAl alloys have higher cooling rates and lower temperature gradients during solidification than René N5. These differences give NiAl alloys a lower tendency to form freckles and a higher tendency to form equiaxed grains. However, with the aid of process modeling, single crystals of various shapes of NiAl alloys have been produced.     

Properties of maraging steels after high-temperature treatment

Conclusions For the optimal structure of austenite in maraging steels they should be subjected to rolling with a final rolling temperature not over 900°, rapid heating to Ac₃+30°, and rapid cooling.Institute of Solid State Physics, Academy of Sciences of the USSR. I. P. Bardin Central Scientific-Research Institute of Ferrous Metallurgy. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 4, pp. 31–33, April, 1981.     

Partial Electrode Processes at AC-Polarized Copper in Chloride and Nitrate Media

The dissolution of a copper electrode by passing a rectangular alternating current of an infralow frequency (1/6 Hz) was studied by chronopotentiometric method. The near-electrode concentrations of copper oxidation products were calculated by the numerical solution of the boundary problem of transient diffusion. In concentrated chloride electrolytes, the shape of the E vs. t plot was found to be determined by transient mass transfer. The ratio of the copper reduced during the cathodic half-period to its amount dissolved in the anodic half-period was estimated experimentally. This ratio was used to determine the distribution of faradaic charges between different partial electrode processes. In nitrate electrolytes, cathodic process significantly affects the anodic dissolution of copper.     

Grain Size Variation in Coatings

An increase in grain size during deposition occurs in physical vapor deposition. Columnar grain structures result as the coating thickens beyond the point of constant grain size (>25 μm). As the deposition is taking place, the grain size of the Ti coating increases from that on the order of 0.01 (Jim to that greater than 1.0 μm. At a certain critical thickness during deposition, t_c, the grain size stabilizes. This study examines the minimum coating thickness required to produce the ultimate grain size. Then this investigation relates the critical thickness to the texture of the coating.     

Shell-element formulations in LS-DYNA3D: their use in the modelling of sheet-metal forming

Recent developments in finite-element (FE) analysis include the generation of an increasing number of element formulations. With the burgeoning use of FE simulations for sheet-metal forming, these elements are being applied to finite-strain problems.

This paper examines the cost-benefit relationship of the seven four-noded shell elements currently included in the LS-DYNA3D element library for sheet-metal forming. In order to assess the relative merits of the shell formulations, the Numisheet 93 square benchmark problem was solved using each of the shell formulations. Strain predictions, drawing force, and the relative cpu times are presented. Conclusions are drawn about the cpu cost-effectiveness of the available shell elements.     

Characterizing the deformation of cold-rolled copper sheet

An advanced x-ray diffraction technique allows the development of texture components to be monitored and provides supplementary information about the cold work and residual stresses in cold-rolled copper sheet. The new technique confirms the results of an ultrasonic test, except for the ultrasonic test’s sensitivity to grain size. The new x-ray diffraction technique could be adapted to provide in-process, nondestructive evaluation of thin copper sheet, even for material moving at high speeds.     

Initial stages of the high-temperature corrosion of commercial Fe-Cr-Ni alloys in a carburizing atmosphere of low oxygen partial pressure

The early stages of corrosion of AISI 314, HK 40, and Alloy 800H have been studied in a strongly carburizing (a_C=0.8), weakly oxidizing atmosphere at 1098 K. Samples with electropolished and cold-worked surfaces were exposed for up to 400 min. at temperature, in a conventional corrosion rig or in a reaction vessel which was installed within an X-ray photoelectron spectrometer. The latter facility allowed the effects of the specimen heating rate and the rat of gas flow to be investigated. Examination of the corrosion products was accomplished with the aid of XPS, SEM, TEM, and conventional metallography. Initially, surface layers comprised of -Cr₂O₃, (Mn, Cr)₃O₄, and SiO₂ formed, with layer structure, microstructure, and composition being functions of alloy composition and surface condition. Only on the cold-worked surfaces did a well-developed duplex oxide, consisting of an outer, Cr-rich oxide layer and an inner, SiO₂ layer, form. In good agreement with the predicted value of 1.9 wt.%, between 1.4 and 2 wt.% Si in the alloy was required to form a complete SiO₂ layer. After an incubation period, -Cr₂O₃ became unstable and transformed to M₇C₃; the carbides then grew by diffusion of metal from the alloy substrate. The presence of manganese, as (Mn, Cr)₃O₄, in the surface oxide influenced the mode of carbide growth, whereas the rate of carbide growth was severely suppressed by a continuous SiO₂ layer which acted as a diffusion barrier both to metal and to carbon. It is argued that the SiO₂ layer is most effective in reducing carburization when it is free from or contains very few structural defects.     

Structure and Properties of Amorphous-Crystalline Alloys of the Nd – Fe – B System

A novel x-ray technology is used for studying the phase composition and the sizes of crystallites in amorphous-crystalline alloys of the Nd – Fe – B system obtained by the method of centrifugal sputtering for manufacturing permanent magnets.     

Effect of fine structure of Pb-In solid solutions on their deformation-induced strengthening at low temperatures

The specific features of low-temperature deformation-induced strengthening of Pb-In single crystals have been studied in a wide range of impurity concentrations. It was shown that a change in the strain-rate sensitivity of flow stress in the concentrated solid solution is connected with the inhomogeneous distribution of impurities. Based on the X-ray diffuse-scattering data, it was found that the short-range order of separation type was formed in these alloys; i.e., the lead atoms were randomly arranged and the indium atoms formed clusters whose characteristic size increased with concentration in a range of 1.0–1.9 nm. In the concentrated alloy, the appearance of coarse impurity clusters as strong obstacles for mobile dislocations in comparison with the impurity atoms and forest dislocations causes not only a sharp increase in the flow stress but also a change in the energy of dislocation-dislocation interaction.