Effect of temperature on the strength and conductivity of a deformation processed Cu-20%Fe composite

The high temperature (22–600 °C) properties were evaluated for a Cu-20%Fe composite deformation processed from a powder metallurgy compact. The ultimate tensile strengths decreased with increasing temperature but were appreciably better than those of similarly processed Cu at temperatures up to 450 °C. At 600 °C, the strength of Cu-20%Fe was only slightly better than that of Cu as a result of the pronounced coarsening of the Fe filaments. However, at temperatures of 300 and 450 °C, the strength of Cu-20%Fe is about seven and six times greater, respectively, than that of Cu, as compared to about a two fold advantage at room temperature. Therefore, Cu-20%Fe composites made by deformation processing of powder metallurgy compacts have mechanical properties much superior to those of similarly processed Cu at room temperature and at temperatures up to 450 °C. The pronounced decrease in electrical conductivity of deformation processed Cu-20%Fe as compared to Cu is attributed to the appreciable dissolution of Fe into the Cu matrix which occurred during the fabrication of the starting compacts where temperatures up to 675 °C were used. While the powder metallurgy compacts used for the starting material for deformation processing in this study did not lead to a high conductivity composite, the powder metallurgy approach should still be a viable one if processing temperatures can be reduced further to prevent the dissolution of Fe into the Cu matrix.     

The Residual Stress Relaxation Behavior of Weldments During Cyclic Loading

Accurate measurement of residual stress is necessary to obtain reliable predictions of fatigue lifetime and enable estimation of time-to-facture for any given stress level. In this article, relaxation of welding residual stresses as a function of cyclic loading was documented on three common steels: AISI 1008, ASTM A572, and AISI 4142. Welded specimens were subjected to cyclic bending (R = 0.1) at different applied stresses, and the residual stress relaxation existing near the welds was measured as a function of cycles. The steels exhibited very different stress relaxation behaviors during cyclic loadings, which can be related to the differences in the microstructures of the specimens. A phenomenological model, which treats dislocation motion during cyclic loading as being analogous to creep of dislocations, is proposed for estimation of the residual stress relaxation.     

A comparison of strengthening mechanisms in rolled and axisymmetrically deformed Ti-20Y composites

Two Ti-20%Y metal-metal composites were deformation processed: one axisymmetrically and the other by rolling. The microstructures, preferred crystallographic orientations, and tensile strengths of each were measured periodically as the deformation progressed. The axisymmetrically deformed Ti matrix developed a [10 0] fiber texture, and the rolled composite acquired a texture with the <0001> tilted 31° from the sheet normal toward the transverse direction with [10 0] parallel to the rolling direction. The orientations of the {10 0}<11 0> and (0002)<11 0> slip systems in Ti with these textures were used in conjunction with the maximum possible slip distances for dislocation travel in each specimen to demonstrate that the axisymmetrically deformed material should be stronger than the rolled material for composites of equal phase thickness and spacing. The strengths of the two composites measured in this study were compared at similar microstructural phase sizes and spacings, and the axisymmetrically deformed composite was indeed found to be somewhat stronger, although the difference in strengths was not large.     

Characterization of strength and microstructure in deformation processed Al-Mg composites

The microstructures, mechanical properties and electrical resistivity have been evaluated for deformation processed Al-20 vol%Mg and Al-13 vol%Mg composites. The Mg second phase adopts a convoluted, ribbon shape filamentary morphology after deformation. Both the size and spacing of these filaments decreases with deformation. The strength of these composites increases exponentially with reduced spacing of Mg filaments. The electrical resistivity of these Al-Mg composites is slightly higher than that of pure Al.     

The roles of typicality, instance dominance, and category dominance in verifying category membership.

Examined the relationships between category verification reaction time (RT), exemplar typicality, instance dominance, category selection time (an RT measure of category dominance), and 3 production measures of category dominance in 3 experiments with 122 Ss. The category dominance measures were obtained in Exp I for use in 2 nearly identical category verification experiments. In Exp II, the category name was presented 800 msec before the exemplar name. In Exp III, the exemplar name preceded the category name by 800 msec. Multiple regression analyses of the yes and no category verification RTs indicated that category dominance produced large and highly significant effects in all conditions, whereas instance dominance produced marginally significant and selective effects. Typicality had no effect beyond its shared effect with the dominance measures except as a possible suppressor variable. Category selection time was the best predictor, although all of the category dominance measures were better predictors than typicality or instance dominance. It is concluded that typicality may be an inappropriate independent variable for RT tasks studying the memory representation of natural-world knowledge. (33 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

TEM Examination of Heart-Treated Nanocrystalline ZnS

Monodisperse, spherical, submicrometer-size ZnS particles with nanocrystalline substructure were heated and examined in situ using a Gatan hot stage and a transmission electron microscope (TEM) at temperatures ranging from 500° to 900°C. The goal of this study was to observe the micro-structural changes that occur in these particles during heat treatment. The particles, whose morphology consists of an agglomeration of nanocrystals, showed significant grain growth and sintering at temperatures as low as 600°C, much lower than expected for bulk ZnS crystals. In addition, the particles were seen to develop hollow cores during heat treatment. This hollowing effect appears to be related to the nanocrystalline/nanoporous nature of the particles.     

Microstructure of heavily deformed magnesium-lithium composites containing steel fibers

The microstructure of deformation-processed metal-metal composites (DMMC) of Mg-Li alloys containing steel reinforcing fibers was characterized to correlate the fiber size to the deformation strain and mechanical properties of the composite material. Micrographs taken using scanning and transmission electron microscopy techniques revealed fiber sizes larger than predicted from the deformation applied to the bulk composite. Deformation strain in the fibers, therefore, was less than in the bulk material. Measurements from SEM and TEM micrographs were used to calculate the actual deformation strain present in the fibers. This strain was then used to adjust rule-of-mixture (ROM) predictions of the strength of the composite material. However, the experimental strengths of these materials were still less than the adjusted ROM values, potentially due to the presence of fibers considerably larger than the average size measured stereologically. Of the many models used to describe the strengthening observed in DMMC materials, the Hall-Petch relationship best describes the experimental data. Details of the strengthening models are discussed in relation to these composite materials.     

A deformation processed β-Ti + Y metal–metal composite

A Ti-20V-20Y deformation processed metal–metal composite was deformed axisymmetrically by extrusion and swaging to a true strain of 5.9. Tensile strength, ductility, Y phase thickness and spacing, and preferred crystallographic orientation were examined at several levels of true strain as the deformation progressed. The Ti-V metastable BCC solid solution matrix developed a (110) fiber texture. The Y second phase developed a fiber texture that constrained the Y phase to deform in plane strain. Relatively high tensile ductility was observed at all levels of deformation processing strain.     

Continuous Cooling Transformation in Cast Duplex Stainless Steels CD3MN and CD3MWCuN

The kinetics of brittle phase transformation in cast duplex stainless steels CD3MN and CD3MWCuN was investigated under continuous cooling conditions. Cooling rates slower than 5 °C/min. were obtained using a conventional tube furnace with a programable controller. In order to obtain controlled high cooling rates, a furnace equipped to grow crystals by means of the Bridgman method was used. Samples were soaked at 1100 °C for 30 min and cooled at different rates by changing the furnace position at various velocities. The velocity of the furnace movement was correlated to a continuous-cooling-temperature profile for the samples. Continuous-cooling-transformation (CCT) diagrams were constructed based on experimental observations through metallographic sample preparations and optical microscopy. These are compared to calculated diagrams derived from previously determined isothermal transformation diagrams. The theoretical calculations employed a modified Johnson-Mehl-Avrami (JMA) equation (or Avrami equation) under assumption of the additivity rule. Rockwell hardness tests were made to present the correlation between hardness change and the amount of brittle phases (determined by tint-etching to most likely be a combination of sigma + chi) after cooling.