Macroscopic 2D Design of Micro/Nano Grain Architectures by Laser Interference Metallurgy
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Macroscopic 2D Design of Micro/Nano Grain Architectures by Laser Interference Metallurgy Frank Muecklich1, Carsten Gachot1, Rodolphe Catrin1, Ulrich Schmid2, and Andrés Lasagni1,3 1 Functional Materials, Saarland University, Saarbruecken, Germany 2 Chair of Micromechanics, Microfluidics/Microactuators, Saarland University, Saarbruecken, Germany 3 W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, 30332-0405 ABSTRACT Tailoring of micro/nano structures and surface functionalization are key goals in surface processing of materials. A new technology for a unique geometric precise 2D micro/nano design of grain architectures is presented. By means of super lateral grain growth crystalline lattice patterns such as line-, dot- and cross-like patterns were generated. The grain dimensions may be selected between a few nanometers and about 10 micrometers. The phase and grain formation was characterized by Electron Backscatter Diffraction with regard to orientation distribution and texture formation. Furthermore, dynamic aspects of this laser induced recrystallization process are studied, such as the heat transport in the films, comparing the vertical with the lateral solidification velocities by two-dimensional finite element method (FEM) simulations. Finally, the mechanical properties of the tailored thin films have been determined using nanoindentation experiments. INTRODUCTION Laser Interference Metallurgy [1] is a rather new surface processing technology, allowing quick, well defined periodic and long range ordered microstructures on macroscopic areas. In this technique, the high power nanosecond laser pulse is split into several coherent sub beams which interfere on the surface of the sample. The shape and the dimensions of the interference pattern as well as its period P (repetitive distance between features) can be controlled by the angle (α), intensity arrangement of the individual sub laser beams, and laser wavelength (λ) [2]. As an example, two overlapping laser beams produce a line-like interference pattern with period P=λ /(2 sinα)[2]. This technique facilitates various metallurgical processes such as melting, recrystallization, recovery and the formation of intermetallic phases for example on the lateral scale of the microstructure but also topography effects in metals, ceramics or polymers [1]. Thin metallic films are mainly characterized by a logarithmic normal grain size distribution with randomly oriented grains, independent of the deposition technique used (i.e. sputtering or e-beam evaporation) [3]. As far as technical applications are concerned, microstructural randomness leads to highly inhomogeneous and non-optimized device characteristics [4]. Consequently, circumventing the random grain alignment by a laserinterference induced localized recrystallization with specified threshold energies results in a control of nucleation sites and grain orientations and is therefore of basic importance [5].
In this work, we report about the microstructural tailor
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