The native oxide thin scale on magnesium(Mg)surface appears continuous and crack-free,but cannot protect the Mg matrix from further oxidation,especially at elevated temperatures.This thermal oxidation process is witnessed in its entirety using a home-made in-situ heating device inside an environmental electron transmission microscope.We proposed,and verified with real-time experimental evidence,that transforming the native oxide scale into a thin continuous surface layer with high vacancy formation energy(low vacancy concentration),for example MgCO3,can effectively protect Mg from high-temperature oxidation and raise the threshold oxidation temperature by at least two hundred degrees.
Flexible, large area electronics using various organic and inorganic materials are beginning to show great promise. During manufacture and service, large deforma- tion of these hybrid materials will pose significant challenges in terms of high performance and reliability. A deep understanding of the ductility or flexibility of macroelectronics becomes one of the major issues that must be addressed ur- gently. This paper describes the current level of understanding on the thin-film ductility, both free-standing and substrate-supported, and relevant influencing factors.
Mechanical tests on small-volume materials show that in addition to the usual attributes of strength and ductility,the controllability of deformation would be crucial for the purpose of precise plastic shaping.In our present work,a"mechanical controllability index"(MCI)has been proposed to assess the controllability of mechanical deformation quantitatively.The index allows quantitative evaluation of the relative fraction of the controllable plastic strain out of the total strain.MCI=0 means completely uncontrollable plastic deformation,MCI=∞means perfectly controllable plastic shaping.The application of the index is demonstrated here by comparing two example cases:0.273 to 0.429 for single crystal Al nanopillars that exhibit obvious strain bursts,versus 3.17 to 4.2 for polycrystalline Al nanopillars of similar size for which the stress-strain curve is smoother.
Using nanoscale electrical-discharge-induced rapid Joule heating, we developed a method for ultrafast shape change and joining of small-volume materials. Shape change is dominated by surface-tension-driven convection in the transient liquid melt, giving an extremely high strain rate of N106 s-1. In addition, the heat can be dissipated in small volumes within a few microseconds through thermal conduction, quenching the melt back to the solid state with cooling rates up to 108 K.s-1. We demonstrate that this approach can be utilized for the ultrafast welding of small-volume crystalline Mo （a refractory metal） and amorphous Cu49Zr51 without introducing obvious microstructural changes, distinguishing the process from bulk welding.
Cheng-Cai WangQing-Jie LiLiang ChenYong-Hong ChengJun SunZhioWei ShanJu LiEvan Ma
Cu–Al/Al nanostructured metallic multilayers with Al layer thickness hAlvarying from 5 to 100 nm were prepared, and their mechanical properties and deformation behaviors were studied by nanoindentation testing. The results showed that the hardness increased drastically with decreasing hAldown to about 20 nm, whereafter the hardness reached a plateau that approaches the hardness of the alloyed Cu–Al monolithic thin films. The strain rate sensitivity(SRS, m),however, decreased monotonically with reducing hAl. The layer thickness-dependent strengthening mechanisms were discussed, and it was revealed that the alloyed Cu–Al nanolayers dominated at hAlB 20 nm, while the crystalline Al nanolayers dominated at hAl[ 20 nm. The plastic deformation was mainly related to the ductile Al nanolayers, which was responsible for the monotonic evolution of SRS with hAl. In addition, the hAl-dependent hardness and SRS were quantitatively modeled in light of the strengthening mechanisms at different length scales.
Ya-Qiang WangZhao-Qi HouJin-Yu ZhangXiao-Qing LiangGang LiuGuo-Jun ZhangJun Sun
An approach based on film buckling under simple uniaxial tensile testing was utilized in this paper to quantitatively estimate the interfacial energy of the nanostructured multilayer films(NMFs) adherent to flexible substrates. The interfacial energies of polyimide-supported NMFs are determined to be *5.0 J/m2 for Cu/Cr, *4.1 J/m2 for Cu/Ta,*2.8 J/m2 for Cu/Mo, *1.1 J/m2 for Cu/Nb, and *1.2 J/m2 for Cu/Zr NMFs. Furthermore, a linear relationship between the adhesion energy and the interfacial shear strength is clearly demonstrated for the Cu-based NMFs, which is highly indicative of the applicability and reliability of the modified models.
Kai WuJin-Yu ZhangGang LiuJiao LiGuo-Jun ZhangJun Sun
