China Science

We have studied the nanoindentation structures achieved at room temperature (RT) on (0 0 1) GaAs with either n or p doping. Elastic–plastic nanoindentations were made over a wide range of loads (between 0.2 and 50 mN) at RT with a Berkovich indenter using two different orientations. Transmission electron microscopy was used to observe systematically the nanoindentation structures (central zone and rosette arms) and to investigate changes in dislocation activity. The mechanical response of both types of samples is relatively similar in terms of hardness, critical shear stress or pop-in load amplitude. In contrast, the indentation rosette structure appears to be sensitive to both doping and indenter orientation. Perfect dislocations show long screw segments only in n-doped specimens, a finding that is attributed to mobility effects. Moreover, p-doped specimens show no partial dislocations while n-doped specimens show partial dislocations in both rosette arms.

E. Le Bourhisa Email:eric.le.bourhis@univ-poitiers.fr?G. Patriarcheb
[a]Université de Poitiers, Laboratoire de Métallurgie Physique, UMR 6630 CNRS, SP2MI-Téléport 2-Bd Marie et Pierre Curie, BP 30179, 86962 Futuroscope-Chasseneuil Cedex, France;[b]Laboratoire de Photonique et de Nanostructures, UPR 20 CNRS, Route de Nozay, 91460 Marcoussis, France

Although it is well known that thin films exhibit mechanical properties very different from those of their bulk counterparts, knowledge of the underlying mechanisms is incomplete. Single-crystalline films have a favorable microstructure for investigating the scaling behavior of mechanical properties. We present a novel experimental route for preparing single-crystalline Au films on a compliant polyimide substrate. For such single-crystals, we have developed a synchrotron-based tensile testing technique to measure the isothermal stress–strain curves and average peak widths. The analysis of Laue diffraction patterns as well as a parallel transmission electron microscopy study give new insight in the initial and evolving microstructure of the films. Complex novel deformation mechanisms are found, including a transition of the dominant deformation mechanism from full to partial dislocations in films thinner than 160 nm. The scaling behavior is described in view of the coexistence of different deformation mechanisms where the nucleation stress for single dislocations very likely governs the behavior.

Patric A. Grubera?Christian Solenthalerb?Eduard Arzta?Ralph Spolenakb Email:ralph.spolenak@mat.ethz.ch
[a]Universitt Stuttgart, Institute of Physical Metallurgy, Heisenbergstrasse 3, D-70569 Stuttgart, Germany;[b]Laboratory for Nanometallurgy, Department of Materials, ETH Zurich, Wolfgang-Pauli-Strasse 10, 8093 Zurich, Switzerland;[c]Max Planck Institute for Metals Research, Heisenbergstrasse 3, D-70569 Stuttgart, Germany

Thin gold films can be strengthened by the incorporation, during reactive sputtering, of nanosized dispersions of monoclinic zirconia. Micron-thick films containing 2 vol.% zirconia particles having a particle size of 1–3 nm are found to have an indentation hardness of 3.8 GPa after annealing for 60 h at 500 °C in air. Sputtered gold films of the same thickness and annealed under the same conditions had a hardness of 2.3 GPa. The nanoparticles of zirconia resist coarsening with no change in diameter between deposition and after 60 h at 500 °C. They also suppress grain growth of the gold grains. The electrical resistivity of the strengthened gold films was 4.5 ?? cm, about 55% higher than gold films. The temperature coefficient of resistivity was unaffected.

Jesse R. Williamsa?David R. Clarke aEmail:clarke@engineering.ucsb.edu
[a]Materials Department, College of Engineering, University of California, Santa Barbara, CA 93106-5050, USA

Micron-sized aluminum pillars, fabricated by focused-ion beam milling, were subjected to compression in a nanoindenter using a flat-ended tip to examine their deformation behavior. The deformation was jerky and the statistical distributions of the sizes of the bursts, their occurrence frequency, as well as the stresses at which they occurred were analyzed. The burst size was found to increase with stress in an approximately exponential manner. Post-mortem transmission electron microscopy investigation of the dislocation structures revealed that the dislocation density of the micro-pillars did not grow significantly after severe deformation. Based on the experimental observations, a Monte Carlo model was developed to describe the stochastic nature of deformation of these micro-pillars.

K.S. Nga?A.H.W. Ngan aEmail:hwngan@hku.hk
[a]Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong, China

In this study, the bainitic microstructure of a furnace-cooled electro-slag-refined 5% Cr steel was studied by the electron backscattered diffraction (EBSD) technique. The pole figures suggest a strong orientation relationship close to the Nishiyama–Wassermann type, i.e. there are 12 variants of the bainite sheaf that emerge from the three Bain correspondences. The microstructure consists of the bainite variants arranged in four sheaf colonies or morphological groups. Each sheaf colony, in turn, is made of one crystallographic group composed of 3 variants of bainite – one from each of the three Bain correspondences. Computations based on the phenomenological theory of martensitic crystallography (PTMC) show that the observed morphology is a product of stress-coupled autocatalytic nucleation. The 1 1 1Austenite 3-variant tension-coupled sheaf group predicted by the computations is the one that is experimentally observed.

V. Pancholia?Madangopal Krishnanb Email:madangk@barc.gov.in?I.S. Samajdarc?V. Yadavc?N.B. Ballalc
[a]Department of Metallurgical; Materials Engineering, IIT-Roorkee, Roorkee-247667, Uttarakhand, India;[b]Materials Science Division, Bhabha Atomic Research Centre, Mumbai-400085, India;[c]Department of Metallurgical Engineering; Materials Science, IIT-Bombay, Powai, Mumbai-400076, India

We have used thermodynamically calculated phase diagrams of Cu–Zr–Ti to identify two low-melting Cu-rich alloys denoted by A and B as bulk amorphous alloys where none were thought to exist. These alloys show greater stability of the glassy phase than previously discovered alloys in the same system, as evidenced by the critical casting diameter of 5 mm. We also calculated a temperature-composition diagram for alloy A as a function of Y using an approximate thermodynamic description of Cu–Zr–Ti–Y. This diagram shows that the liquidus temperature of alloy A decreases with the addition of Y, reaches a minimum, and increases again. Our experiments indeed showed the glass-forming ability of A reaches a maximum diameter of 10 mm when 2 at.% Y was added and then decreases again. We thus propose that the thermodynamically calculated liquidus temperature is an excellent guide to synthesize bulkier glasses, which can be readily obtained from calculated phase diagrams.

Hongbo Caoa?Ye Panb?Ling Dinga?Chuan Zhanga?Jun Zhua?Ker-Chang Hsiehc?Y. Austin Changa Email:chang@engr.wisc.edu
[a]Department of Materials Science; Engineering, University of Wisconsin-Madison, 1509 University Avenue, Madison, WI 53706, USA;[b]School of Materials Science; Engineering, Southeast University, Nanjing 210096, China;[c]Institute of Materials Science; Engineering, Sun Yat Sen University, Kaohsiung 80424, Taiwan

Data on lattice rotations and dislocation structures induced in aluminium by tensile deformation are analysed together in order to extract the active slip systems. The analysis falls in two steps: (i) from the combination of lattice rotation and dislocation structure data, the grain orientation space represented by the stereographic triangle is subdivided into regions with the same active slip systems; and (ii) the active slip systems calculated from the lattice rotations are compared with those known to be active based on the dislocation structure. For the entire stereographic triangle active slip systems which are in good agreement with both lattice rotations and dislocation structures are identified, showing that the grain orientation is the primary factor controlling the slip systems.

Grethe Winther aEmail:grethe.winther@risoe.dk
[a]Center for Fundamental Research: Metal Structures in Four Dimensions, Materials Research Department, Ris DTU – National Laboratory for Sustainable Energy, Technical University of Denmark, DK-4000 Roskilde, Denmark

In 1920 the Shanghai Bankers Association launched an initiative to standardize Chinese bank accounting classification and terminology, which in 1924 led to the first standard terminology that was gradually adopted by all Chinese banks. This paper examines that neglected experience by employing a framework informed by Pierre Bourdieu’s theory of practice. We delineate the relations among foreign banks, Chinese modern banks, and native banks in the field of Chinese banking; explore the habitus of modern bankers that motivated the standardization initiative; and analyze how the initiative accrued cultural capital and social legitimacy to modern bankers and how social actors’ interaction with the state determined the interaction among them, resulting in the domination of modern banks in the field and the domination of the state over the field.

Yin XuaEmail:yxu@odu.edu?Xiaoqun Xub
[a]Department of Accounting, Old Dominion University, Norfolk, VA 23529, USA;[b]Department of History, Christopher Newport University, Newport News, VA 23606, USA