Growth and structure of a combinatorial array of mixed-phase magnesium-aluminum thin-film alloys

Combinatorial gradient-controlled sputter deposition has been employed to produce a library of 100 separate thin films with a wide range of Mg-Al alloy compositions. We have successfully isolated the beta (Mg17Al12) phase in polycrystalline films for investigation. The importance of understanding the physical properties of the beta phase becomes apparent when one realizes the contrary effects associated with its existence in these alloys. The presence of the beta phase has been found to be desirable for increasing corrosion resistance; however, in structural components under tensile loading and/or at elevated temperatures, the beta phase precipitates undergo coarsening which induces poor creep behavior in several common alloys. We have also synthesized amorphous Mg-Al and mixed-phase compositions as identified by X-ray diffraction measurements. We have observed various degrees of surface oxidation which appear to be correlated with the presence of each particular phase. Details of the growth procedure as well as structural and compositional characterization are presented.