Tensile properties of magnetron sputtered aluminum-scandium and aluminum-zirconium thin films: A comparative study

摘要

Micro cold forming processes sometime require thin sheets of high strength materials often with a thickness below 30 μm to manufacture products with good mechanical properties. Due to its high strength and anti-recrystallization properties, aluminum-scandium is a promising material for such processes, but cannot be rolled down to the specified thickness. A suitable alternative to this issue is to produce aluminum-scandium sheets in the form of freestanding films using magnetron sputtering. However, a major limitation to the mass production of these sheets is the high cost of scandium. Zirconium, on the other hand, has been reported to act in a similar way as scandium in aluminum alloys, providing precipitation strengthening and anti-recrystallization properties to the material, but features the advantage to be much cheaper than scandium. The aim of this study is to investigate the influence of the deposition process and post treatment parameters on both aluminum-scandium and aluminum-zirconium magnetron sputtered freestanding thin films and to compare their properties regarding the micro forming process. The sheets were deposited with a dc magnetron sputtering unit using two different targets, aluminum with 1.2. at.% scandium and aluminum with 1.2. at.% zirconium and argon as process gas. An unalloyed steel sheet of 100 μm thickness was used as substrate. After deposition the steel was chemically removed in a concentrated nitric acid solution which results in a freestanding sputtered film. Several sheets were produced, each time with a different combination of target power and substrate temperature. The samples were then heat treated at 573. K for 1. h, and the mechanical properties of both as-deposited and heat treated samples were measured with a tensile tester designed for thin samples. Scanning electron microscopy showed a reduced columnar morphology for both aluminum-scandium and aluminum-zirconium films. It could be shown that the substrate temperature as well as the post heat treatment influences the tensile strength of the sheets. Aluminum-scandium thin sheets reached tensile strengths of more than 400. MPa and aluminum-zirconium thin sheets of more than 500. MPa but differed very much in their ductility.