薄膜与小尺度材料及力学性能研究组

Recovery of elastic constant of ultrathin Cu films by low temperature annealing

N. Nakamura, H. Ogi, T. Shagawa, and M. Hirao

Graduate School of Engineering Science, Osaka University, Machikaneyama 1-3, Toyonaka, Osaka 560-8531, Japan

A.K. Ghosh^{a, b}

^aDepartment of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109-2136, USA
^bDepartment of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109-2136, USA

Received 23 January 2007;  revised 9 January 2008;  accepted 14 January 2008.  Available online 6 April 2008.

Abstract

In recent literature related to mechanical testing of small-volume metal specimens, plastic strain bursts during apparent elastic loading have been reported for materials commonly known to exhibit smooth yielding. Interpretation of the observed plastic yielding effects in these tests have ignored a significant part of the actual experimental findings, and produced conclusions regarding dislocation structure that these tests do not unequivocally support. It is pointed out that the heterogeneity of dislocation debris left in the microstructure does not clearly represent deformation resistance, nor give a clear indication of strain within the specimen. The measured high rate of strain hardening and stability of plastic flow in the small-volume specimens are dependent on stress-state, and are shown to be not correlated with dislocation debris or dislocation-starvation concepts; rather the reason for the observed strengthening is related to the resistance to slip propagation through the specimen surface to form surface steps, viewed as an atomic-scale shear fracture process, elaborated in a companion paper. In a compression test the surface is closed under high compressive stress, thus repeatedly blocking the process, but in a tension test the surface separates more easily, causing loss of plastic stability.

Keywords: Mechanical properties; Metals; Slip surfaces; Dislocations

Interface Structure and Radiation Damage Resistance in Cu-Nb Multilayer Nanocomposites

M. J. Demkowicz, R. G. Hoagland, and J. P. Hirth

Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA(Received 13 November 2007; published 1 April 2008)

We use atomistic simulations to show that upon removal or insertion of atoms, misfit dislocations in Cu-Nb interfaces shift between two adjacent planes, forming pairs of extended jogs. Different jog combinations give rise to interface structures with unlike densities but nearly degenerate energies, making Cu-Nb interfaces virtually inexhaustible sinks for radiation-induced point defects and catalysts for efficient Frenkel pair recombination.

Buckling behavior of metal film/substrate structure under pure bending

Ying Li,¹ Xi-Shu Wang,¹ and Xiang-Kang Meng²

¹Department of Engineering Mechanics, Tsinghua University, Beijing, 100084, People's Republic of China
²National Laboratory of Solid State Microstructures and Department of Materials Science and Engineering, Nanjing University, Nanjing 210093, People's Republic of China

Determining mechanical properties of thin films from the loading curve of nanoindentation testing

Manhong Zhao^a, Yong Xiang^b, Jessica Xu^c, Nagahisa Ogasawara^d, Norimasa Chiba^d and Xi Chen^a

^aDepartment of Civil Engineering and Engineering Mechanics, Columbia University, New York, NY 10027-6699, USA
^bIntel Corporation, Materials Technology Department, 3065 Bowers Avenue, MS SC2-24, Santa Clara, CA 95054, USA
^cIntel Corporation, Logical Technology Development, 2501 NW 229th Avenue, MS RA3-402, Hillsboro, OR 97124, USA
^dDepartment of Mechanical Engineering, National Defense Academy, Hashirimizu, Yokosuka 239-8686, Japan
Received 14 August 2007;  revised 11 March 2008;  accepted 12 March 2008.  Available online 21 March 2008.

Signature of martensite transformation on conductivity noise in thin films of NiTi shape memory alloys

Chandni U,¹ Arindam Ghosh,¹ H. S. Vijaya,² and S. Mohan²

¹Department of Physics, Indian Institute of Science, Bangalore 560 012, India
²Department of Instrumentation, Indian Institute of Science, Bangalore 560 012, India

Slow time-dependent fluctuations, or noise, in the electrical resistance of dc magnetron sputtered thin films of nickel-titanium shape memory alloys have been measured. Even in equilibrium, the noise was several orders of magnitude larger than that in simple diffusive metallic films and was found to be nonmonotonic around the martensitic transformation regime. The results are discussed in terms of the dynamics of structural defects, which also lay the foundation to a new noise-based characterization scheme of martensite transformation. ©2008 American Institute of Physics