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Study of mechanical, microstructural and thermal stability properties of friction stir processed aluminum 2024-T3 alloy
No full textFriction Stir Processing (FSP) was applied on AA2024-T3 plates. The hardness and tensile properties of the stir zone were tested, and a microstructure study was conducted. During the FSP the coarse elongated grains of the parent material changed into fine equiaxed ones, refinement of the coarse precipitates detected at the parent material occurred at the same time. The material subjected to FSP was found to be thermally unstable, as revealed by aging experiments at 300◦C and precipitate chemical analysis. TEM study showed that the rolled parent material contained low-angle sub-grains with dislocation network boundaries. During FSP these were replaced by fine equiaxed grains with clear boundaries and no dislocation tangles. This led to the conclusion that the material underwent Dynamic Recovery (DRV) during the rolling process, as opposed to Dynamic Recrystallization (DRX) during FSP. Thus, FSP appears to have the technological potential for improving the microstructure and mechanical properties of AA2024
Microstructure, Thermal Stability during Creep and Fractography Study of Friction-Stir-Processed AA2024-T3 Aluminum Alloy
No full textPlastic Deformation Mechanisms of Base Material and Friction Stir Welded AZ31B-H24 Magnesium Alloy
No full textPlastic deformation mechanisms operating in parent metal and friction stir welded AZ31B magnesium alloy
No full textOxidation Effects on Short-Term Creep Response in Air of Commercially Pure Titanium (CP-2 Ti)
Full text linkThe creep response in the air of commercially pure titanium was investigated at 550, 600, and 650 °C to assess the effect of oxidation on the mechanical response. Experiments demonstrated that prolonged exposures at high temperatures produced a marked reduction in the minimum creep rate under a given applied stress. Microhardness measurements showed that a hardened zone formed in proximity to the surface due to oxygen penetration into the metal. A simplified composite model was then used to describe the creep response. In this model, the sample consisted of two zones, the hard case that was enriched in oxygen and the soft pure-titanium core, both creeping with similar strain rates. Calculations led to an estimation of the dependence of the minimum creep rate on stress and temperature for the hard high-oxygen zone. The simplified composite model presented here provided a good description of the experimental creep data for pure titanium, tested in its air, and a reliable picture of the effect of oxidation on complex Ti alloys
A study of the metallurgical and mechanical properties of friction-stir-processed cu
Full text linkFriction stir processing (FSP), a severe plastic deformation process, was applied on pure Cu to obtain a stir zone with a very fine grain size. Yet, when FSP is used, the stir zone is as wide as the diameter of the shoulder at the upper surface of the weld and markedly narrower near its opposite surface. This property, as well as the differences between the advancing side and the retreating side, makes it impossible to obtain a uniform cross-section as far as the microstructure and mechanical properties are concerned. For these reasons, a new approach is proposed in which the material was processed on both sides, thus yielding a wider, rectangular and more homogenous stir zone from which all the specimens were machined out. Processing the material from both sides eliminated any microstructural difference between the upper and the lower side, at least within the gauge length’s cross-section of the creep specimens. Although grain refinement was detected, the mechanical properties of the friction-stir-processed (FSP’ed) material are inferior relative to those of the parent material. The TEM study reported in the current paper revealed the existence of nanosized grains in the FSP’ed material due to dynamic recrystallization (DRX) occurring during the processing stage. Because both X-ray inspection and fractography showed that the FSP’ed material was free of defects, the material may not comply with the Hall–Petch relation due to lower dislocation density caused by XRD occurring during FSP. The inverse Hall–Petch effect may also be considered as an assistive mechanism in mechanical property deterioration
Deformation mechanisms operating during creep of friction stir welded AZ31B magnesium alloy
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Revisiting copper as a case study of creep in pure metals: Prediction of creep response in pure Cu in half-hard and friction-stir-processed states
Full text linkA physical model was used to obtain a pre-assessment of the dependence of minimum creep rate on stress and temperature for ETP copper under two different initial conditions, i.e., in the R240 half-hardened state and after friction stir processing. Although the R240 samples contained a high dislocation density owing to pre-straining, the material that underwent friction stir processing (FSP) had a much finer grain size and a far lower dislocation density. The original Sandström physically based model developed for copper was modified to take into account the strengthening role of the grain boundaries, and its declining importance with increasing temperature and/or decreasing applied stress. In addition, the grain growth effect was estimated using appropriate empirical equations. The model curves obtained by introducing a few initial information, such as the grain size and the ultimate tensile strength at room temperature, in the resulting set of constitutive equations, largely overlapped. This finding was somewhat in conflict with the traditional view, which assumes that a fine grain size is an ineffective source of creep strengthening, if not detrimental. Subsequent creep experimental testing carried out between 178 and 355 °C substantially confirmed the picture provided by the pre-assessment, and the minimum creep rate values for the two materials largely overlapped on the same curves. Only at 355 °C did the FSP samples exhibit a somewhat higher creep rate, when compared with the R240 samples and the pre-assessment curve. The experimental data obtained for R240 copper at 475 °C were not properly described by the physical model, as expected on the basis of the previous literature reports
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