Compression, tension and high-velocity plate impact experiments were performed on a typical tough Zr 41.2 Ti 13.8 Cu 10 Ni 12.5 Be 22.5 (Vit 1) bulk metallic glass (BMG) over a wide range of strain rates from $10 À4 to 10 6 s À1 . Surprisingly, fine dimples and periodic corrugations on a nanoscale were also observed on dynamic mode I fracture surfaces of this tough Vit 1. Taking a broad overview of the fracture patterning of specimens, we proposed a criterion to assess whether the fracture of BMGs is essentially brittle or plastic. If the curvature radius of the crack tip is greater than the critical wavelength of meniscus instability [F. Spaepen, Acta Metall. 23 615 (1975); A.S. Argon and M. Salama, Mater. Sci. Eng. 23 219 (1976)], microscale vein patterns and nanoscale dimples appear on crack surfaces. However, in the opposite case, the local quasi-cleavage/separation through local atomic clusters with local softening in the background ahead of the crack tip dominates, producing nanoscale periodic corrugations. At the atomic cluster level, energy dissipation in fracture of BMGs is, therefore, determined by two competing elementary processes, viz. conventional shear transformation zones (STZs) and envisioned tension transformation zones (TTZs) ahead of the crack tip. Finally, the mechanism for the formation of nanoscale periodic corrugation is quantitatively discussed by applying the present energy dissipation mechanism.

The strengthening behavior of particle-reinforced metal±matrix composites (MMCp) is primarily attributed to the dislocation strengthening eect and the load-transfer eect. To account for these two eects in a uni®ed way, a new hybrid approach is developed in this paper by incorporating the geometrically necessary dislocation strengthening eect into the incremental micromechanical scheme. By making use of this hybrid approach, the particle-size-dependent inelastic deformation behavior of MMCp is given. Some comparisons with the available experimental results demonstrate that the present approach is satisfactory.

An experimental device, based on the light-gas gun technology, was set up to realize high speed cutting over a wide range of cutting speeds from 30 m/s to 200 m/s. High-speed cutting experiments were performed on AISI 1045 steels. The investigation of chip morphology, micro-structures, micro-hardness and the finished surface integrity were carried out, focusing on the physical phenomena accompanying the saw-tooth chip formation. The results reveal that, with increasing the cutting speed, the transition of chip morphology from continue to saw-tooth could be attributed to repeated thermoplastic shearbanding rather than periodic cracking. In particular, a severe material flow leading to mass transfer of heat was observed at very high cutting speed. The effect of mass transfer of heat on thermoplastic shear instability was further investigated, which implies that the mass transfer of heat would retard the formation of saw-tooth chip. Finally, the influence of cutting speed and mass transfer on the temperature distribution during high speed machining was briefly discussed.

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We report the observations of a clear fractographic evolution from vein pattern, dimple structure, and then to periodic corrugation structure, followed by microbranching pattern, along the crack propagation direction in the dynamic fracture of a tough Zr 41.2 Ti 13.8 Cu 12.5 Ni 10 Be 22.5 ͑Vit.1͒ bulk metallic glass ͑BMGs͒ under high-velocity plate impact. A model based on fracture surface energy dissipation and void growth is proposed to characterize this fracture pattern transition. We find that once the dynamic crack propagation velocity reaches a critical fraction of Rayleigh wave speed, the crack instability occurs; hence, crack microbranching goes ahead. Furthermore, the correlation between the critical velocity of amorphous materials and their intrinsic strength such as Young's modulus is uncovered. The results may shed new insight into dynamic fracture instability for BMGs.

Nanolaminates of HfO 2 and SiO 2 were prepared using atomic layer deposition (ALD) methods. Successive exposure of substrates maintained at 120 or 160°C to nitrogen flows containing Hf(NO 3 ) 4 and ( t BuO) 3 SiOH led to typical bilayer spacings of 2.1 nm, with the majority of each bilayer being SiO 2 . The density of the SiO 2 layers (measured using X-ray reflectometry (XRR)) was slightly higher than expected for amorphous silica, suggesting that as much as 10 % HfO 2 was incorporated into the silica layers. Based on cross-sectional transmission electron microscopy (TEM) and XRR, oxidation of the silicon substrate was observed during its first exposure to Hf(NO 3 ) 4 , leading to a SiO 2 interfacial layer and the first HfO 2 layer. Combining the ALD of Hf(NO 3 ) 4 /( t BuO) 3 SiOH with ALD cycles involving Hf(NO 3 ) 4 and H 2 O allowed the systematic variation of the HfO 2 thickness within the nanolaminate structure. This provided an approach towards controlling the dielectric constant of the films. The dielectric constant was modeled by treating the nanolaminate as a stack of capacitors wired in series. The nanolaminate structure inhibited the crystallization of the HfO 2 in post-deposition annealing treatments. As the HfO 2 thickness decreased, the preference for the tetragonal HfO 2 phase increased.

Transmission electron microscopy of the amorphization of copper indium diselenide by in situ ion irradiation J. Appl. Phys. 111, 053510 (2012) Diffusion-controlled formation mechanism of dual-phase structure during Al induced crystallization of SiGe Appl. Phys. Lett. 100, 071908 (2012) Local structure of nitrogen in N-doped amorphous and crystalline GeTe Appl. Phys. Lett. 100, 061910 (2012) Facile creation of bio-inspired superhydrophobic Ce-based metallic glass surfaces Appl. Phys. Lett. 99, 261905 (2011) Unexpected short-and medium-range atomic structure of sputtered amorphous silicon upon thermal annealing J. Appl. Phys. 110, 096104 (2011) Additional information on J. Appl. Phys. Specially designed plate-impact experiments have been conducted on a Zr-based amorphous alloy using a single-stage light gas gun. To understand the microdamage nucleation process in the material, the samples are subjected to dynamic tensile loadings of identical amplitude ($ 3.18 GPa) but with different durations (83-201 ns). A cellular pattern with an equiaxed shape is observed on the spallation surface, which shows that spallation in the tested amorphous alloy is a typical ductile fracture and that microvoids have been nucleated during the process. Based on the observed fracture morphologies of the spallation surface and free-volume theory, we propose a microvoid nucleation model of bulk amorphous alloys. It is found that nucleation of microvoids at the early stage of spallation in amorphous alloys results from diffusion and coalescence of free volume, and that high mean tensile stress plays a dominant role in microvoid nucleation.

Structural rejuvenation of glasses not only provides fundamental insights into their complicated dynamics but also extends their practical applications. However, it is formidably challenging to rejuvenate a glass on very short time scales. Here, we present the first experimental evidence that a specially designed shock compression technique can rapidly rejuvenate metallic glasses to extremely high-enthalpy states within a very short time scale of about 365 ± 8 ns. By controlling the shock stress amplitude, the shock-induced rejuvenation is successfully frozen at different degrees. The underlying structural disordering is quantitatively characterized by the anomalous boson heat capacity peak of glasses. A Deborah number, defined as a competition of time scales between the net structural disordering and the applied loading, is introduced to explain the observed ultrafast rejuvenation phenomena of metallic glasses.