This book includes a plain text version that is designed for high accessibility. To use this version please follow this link.
11-08 :: August 2011


nanotimes News in Brief


Aluminum Alloys // The Nanoscale Secret to Stronger Alloys


© Text: LBL


69


S


cientists and their colleagues at Lawrence Ber- keley National Laboratory (Berkeley Lab) have


combined atomic-scale observations with the po- werful TEAM microscope at Berkeley Lab’s Natio- nal Center for Electron Microscopy (NCEM) with atom-probe tomography and other experimental techniques, and with theoretical calculations, to reveal how nanoparticles consisting of cores rich in scandium and surrounded by lithium-rich shells can disperse in remarkably uniform sizes throughout a pure aluminum matrix.


“With the TEAM microscope we were able to study the core-shell structure of these nanoprecipitates and how they form spheres that are nearly the same in diameter,” says U. Dahmen, the director of NCEM and an author of the Nature Materials paper descri- bing the new studies. “What’s more, these particles don’t change size over time, as most precipitates do. Typically, small particles get smaller and large parti- cles get larger, a process called ripening or coarse- ning, which eventually weakens the alloys. But these uniform core-shell nanoprecipitates resist change.”


In the aluminum-scandium-lithium system the resear- chers found that, after the initial melt, a simple two- step heating process creates first the scandium-rich cores and then the lithium-rich shells of the spherical


particles. The spheres self-limit their growth to achie- ve the same outer dimensions, yielding a lightweight, potentially heat- and corrosion-resistant, superstrong alloy.


“Scandium is the most potent strengthener for alu- minum,” says NCEM’s V. Radmilović, who is also a professor of metallurgy at the University of Belgrade, Serbia, and an author of the paper. “Adding less than one percent scandium can make a dramatic diffe- rence in mechanical strength, fracture resistance, corrosion resistance – all kinds of properties.” Becau- se scandium diffuses very slowly through the solid aluminum matrix, the solid mix must be heated to a high temperature (short of melting) before scandium will precipitate.


Lithium is the lightest of all metals (only hydrogen and helium are lighter) and brings not only lightness to an aluminum alloy but, potentially, strength as well. Lithium diffuses much more rapidly than scan- dium, at much lower temperature.


“The problem is that, by itself, lithium may not live up to its promise,” says U. Dahmen, a long-time col- laborator with Radmilović. “The trick is to convince the lithium to take on a useful crystalline structure, namely L12.”


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92  |  Page 93  |  Page 94  |  Page 95  |  Page 96  |  Page 97  |  Page 98  |  Page 99  |  Page 100  |  Page 101  |  Page 102  |  Page 103