Search

Copyright of Enfermería Clínica is the property of Elsevier B.V. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A foil metallurgy processing technique has been developed to prepare fine-grained laminates based on a two-phase Mg-9Li alloy and fine-grained particulate composites based on hard B4C powders embedded in the two-phase Mg-9Li alloy. The processing steps involve principally cold-rolling and low-temperature recovery processing for preparation of foils, and low-temperature press-bonding for preparation of laminates and composites. In this manner, contamination of the highly reactive alloy is minimized. Good tensile strength and ductility were achieved at room temperature with specific stiffness values of about 3.1 × 106 m3. Both the fine-grained laminates and the particulate composite are superplastic at 200 ° C, exhibiting a strain-rate-sensitivity exponent,m, of 0.5.

The microtexture and grain boundary misorientation distributions (i.e., mesotexture) of the superplastic alloy Al-5 pct Ca-5 pct Zn have been investigated in the as-processed condition, after annealing at 520 °C (for times ranging from 7 minutes to 90 hours) and after tensile straining in the transverse direction (TD). Three different superplastic straining conditions were considered: 550 °C/10−2s−1, 550 °C/10−1s−1, and 400 °C/10−2s−1. Microtexture data were obtained by means of computer-aided electron backscatter diffraction analysis methods. The retention of the deformation texture of the as-received material and the development of an increasingly bimodal grain boundary misorientation distribution following static annealing are consistent with the occurrence of recovery and continuous recrystallization. During superplastic straining, deformation texture components are also retained, but with a change in the grain boundary misorientation distribution toward random, indicating that grain switching occurs during grain boundary sliding (GBS). At the midlayer, however, a change from an initial texture component near the Cu-type texture component toward the Brass texture component, {011}〈211〉, was observed even as the misorientation distribution became more random. This change in texture component is associated with the occurrence of single slip during superplastic flow.

The present work is part of an investigation into the use of rapid solidification and powder metallurgy techniques to obtain iron-boron alloys with good mechanical properties. Two Fe-B binary alloys and two ultrahigh boron tool steels were gas atomized and consolidated by hot isostatic pressing (HIP) at temperatures ranging from 700 °C to 1100 °C to have a fine microstructure. Optimum properties were achieved for the binary alloys at low consolidation temperatures, since the solidification mi-crostructure from the original powders is eliminated and, at the same time, fine microstructures and low porosity are obtained in the alloys. At high temperatures and low strain rates, three of the four alloys exhibited low stress exponents, but only the Fe-2.2 pct B alloy showed tensile elongations higher than 100 pct. At low temperatures, only the Fe-2.2 pct B alloy deformed plastically. This alloy showed values of tensile elongation and ultimate tensile strength that were strongly dependent on testing and consolidation temperatures.

The high-temperature deformation behavior of two ultrahigh boron steels containing 2.2 pct and 4.9 pct B was investigated. Both alloys were processedviapowder metallurgy involving gas atomization and hot isostatic pressing (hipping) at various temperatures. After hipping at 700 °C, the Fe-2.2 pct B alloy showed a fine microstructure consisting of l-µm grains and small elongated borides (less than 1µm) . At 1100 °C, a coarser microstructure with rounded borides was formed. This alloy was superplastic at 850 °C with stress exponents of about two and tensile elongations as high as 435 pct. The microstructure of the Fe-4.9 pct B alloy was similar to that of the Fe-2.2 pct B alloy showing, in addition, coarse borides. This alloy also showed low stress exponent values but lacked high tensile elongation (less than 65 pct), which was attributed to the presence of stress accumulation at the interface between the matrix and the large borides. A change in the activation energy value at theα-γtransformation temperature was seen in the Fe-2.2 pct B alloy. The plastic flow data were in agreement with grain boundary sliding and slip creep models.