1,721,268 research outputs found
Design of high performance structural alloys using second phases
No full textDevelopment of high performance structural alloys is not an easy task since the improvement in one property (e.g., strength) often results in the degradation of other properties (e.g., ductility, toughness). One of the ways of overcoming the obstacle is to utilize the beneficial effects of second phases. This paper presents some examples to show how such approach has enabled us to develop structural alloys for specified properties. Examples are drawn from our research programs on high-temperature Mg alloys, and wrought Mg alloys, and bulk amorphous alloys. (c) 2006 Elsevier B.V All rights reserved.X1113sciescopu
STRUCTURE AND PROPERTIES OF RAPIDLY SOLIDIFIED AL-LI-CU-MG-ZR ALLOYS WITH A HIGH ZIRCONIUM CONTENT
No full textA study has been made of the structure and mechanical properties of rapidly solidified alloys with a high zirconium content (0.5 wt.%). The addition of 0.5 wt.% Zr to Al-Li alloys enables the alloys to have optimum combinations of mechanical properties without post-solution treatment stretching. The microstructure of the alloys mainly consists of a "composite precipitate", with delta' surrounding the beta' core. This composite precipitate is highly resistant to dislocation shear, making the overall deformation mode quite homogeneous. The improved deformation mode of the high zirconium content Al-Li alloys results in good combinations of mechanical properties in underaged condition. However, in peak-aged and over-aged conditions, the beneficial effect of the composite precipitates is outweighed mainly by the detrimental effect of the precipitate-free zone, which controls the deformation and fracture behavior of the peak-aged and overaged specimens. Additions of copper and magnesium do not promote the precipitation of T1 or S' phases in the microstructure because of the absence of stretching. However, copper and magnesium give substantial solid solution strengthening, increasing the ultimate tensile strength of the alloys to a much larger degree than in conventional ingot metallurgy Al-Li alloys.X119sciescopu
Critical Assessment 6: Magnesium sheet alloys: viable alternatives to steels?
No full textIncreasing global demands for energy conservation and environmental protection have prompted automotive manufactures to develop lightweight automobiles. As the lightest of structural alloys, Mg alloys offer significant potential for weight reduction, but have yet to see significant application in automobiles, particularly in sheet form. The current technical issues preventing the widespread application of Mg sheet alloys in automobiles (cost, mechanical properties and formability, joining, corrosion resistance) are assessed and future research needs to develop viable Mg sheet alloys for these applications are identified.X113834sciescopu
MODELING OF CRYSTALLIZATION KINETICS OF BULK AMORPHOUS ALLOYS DURING COOLING
No full textClassical heterogeneous nucleation theory coupled with DTA data has been used to analyze the crystallization behavior of continuously cooled bulk amorphous alloys. Continuous cooling transformation and time temperature transformation diagrams of several bulk amorphous alloys with a wide range of critical cooling rates R-c have been calculated. The calculated results are in good agreement with the experimental results, suggesting that our approach is quite appropriate for analyzing the crystallization kinetics of bulk amorphous alloys with a wide range of R-c. A new parameter for GFA is also suggested based on the thermal analyses data obtained during cooling.111sciescopu
EFFECT OF T1 PRECIPITATE ON THE ANISOTROPY OF AL-LI ALLOY-2090
No full textA study has been made of the effect of T1 precipitate on the anisotropy of an Al-Li alloy 2090. The critical role of T, precipitates has been identified by comparing the behavior of the alloy with various microstructures. These include (1) T8E41 tempered specimen with T1, theta' and delta', (2) reverted specimen with T1, (3) re-solutionized specimen with very fine delta', and (4) under-aged specimen with fine delta' and theta'. It has been shown that the {110} [112] crystallographic texture developed during thermomechanical treatment has a direct effect on the anisotropy. It also has an indirect effect by causing an inhomogeneous distribution of nucleation sites for T1 among four {111} habit planes during stretching and accordingly inhomogeneous distribution of T1 precipitates among four possible {111} planes during aging. Such inhomogeneously distributed T1 precipitates in both T8E41 tempered and reverted specimens affect the variation of tensile properties, particularly elongation with specimen orientation.X1146sciescopu
Crystallisation kinetics of Zr(41.2)Ti(13.8)Cu(12.5)Ni(10)Be(22.5)BMG alloy during heating
No full textThe crystallisation behaviour of Zr41.2Ti13.8Cu12.5Ni10.0Be22.5, bulk metallic glass (BMG) alloy during heating front the amorphous state has been investigated. Upon heating. the nucleation process was not consistent with classical nucleation theory. This problem can be overcome by substituting the nucleation density with the number density Of nuclei. N. for growth of the crystalline phase, which is estimated from the length scale of the microstructure. The growth of crystalline phase is the governing process for crystallisation of the Zr41.2Ti13.8Cu12.5Ni10Be22.5 alloy upon heating. The growth process is more important than the nucleation process for analysing the crystallisation mechanisms of the amorphous state. Non-isothermal heating DSC data have been analysed with a modified crystallisation kinetics model based on the nonisothermal transformation theory. Using this model. the onset crystallisation temperatures at various heating rates have been calculated. The calculated critical heating rate to avoid crystallisation is 190 K s(-1) which matches well with the experimental value. The onset crystallisation times for isothermal annealing conditions have also been calculated and compared with the isothermal DSC data. Time temperature transformation (TTT) and continuous heating transformation (CHT) diagrams have been constructed quantitatively. The crystallisation kinetics of BMG alloys call be more reliably analysed with our modified crystallisation kinetics model than with several nucleation models.X117sciescopu
Role of interface boundaries in the deformation behavior of TiAl polysynthetically twinned crystal: In situ transmission electron microscopy deformation study
No full textTo understand the role of boundaries in the deformation behavior of TiAl, in situ straining experiments in transmission electron microscopy have been performed on thin foils of polysynthetically twinned (PST) crystal of Ti-49.3 at.% Al. The deformation behavior of PST TiAl is anisotropic, depending on the angle between the lamellar boundaries and the straining axes. For L-orientation, deformation twins and ordinary dislocations transmit across the true-twin (TT) boundaries but are reflected at the pseudo-twin (PT) and rotational order-fault (RO) boundaries. For transverse (T) orientation, deformation twins are transmitted across all TT, PT, and RO boundaries. For I-orientation, shear deformation occurs parallel to the lamellar boundaries. There is a transmission of deformation across the interphase (IP) boundary in longitudinal orientation, but deformation is blocked and reflected at the IP boundary in T-orientation. The role of the various types of boundaries in localized deformation behavior was evaluated by considering Schmid factors and geometric compatibility factors.X118sciescopu
Analysis and prevention of cracking phenomena during bending of cold-rolled 430 stainless steel
No full textX111sciescopu
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