Micropillar Compression of MoSi 2 Single Crystals
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Micropillar Compression of MoSi2 Single Crystals Satoshi Nakatsuka, Kyosuke Kishida, and Haruyuki Inui Department of Materials Science and Engineering, Kyoto University Sakyo-ku, Kyoto 606-8501, Japan ABSTRACT Deformation behavior of MoSi2 has been studied by micropillar compressions of single crystalline specimens prepared by focused ion beam (FIB) technique as a function of crystal orientation at room temperature. Activation of the {011} and {013} slip systems were observed in the micropillars compressed along [110] and [0 15 1], respectively. The CRSS values for each slip system exhibit an approximate power law relationship with the edge length of micropillar. The {013} slip exhibit much stronger size-dependence than the {011} slip system.
INTRODUCTION MoSi2 with the tetragonal C11b structure has been recognized as a promising material for structural applications at very high temperatures because of its high melting point (2020°C) and excellent oxidation resistance (figure 1a) [1, 2]. Extensive studies on the mechanical properties have revealed that MoSi2 single crystals with the loading axis orientations away from [001] exhibit significant plastic flow at temperatures as low as room temperature, whereas those close to [001] can be plastically deformed only above 900°C. Five slip systems on {110}, {011}, {010}, {023} and {013} have been confirmed to be operative depending on the loading axis orientation and test temperature [2]. Among these five slip systems, two slip systems of {011} and {013} are operative at room temperature, when the single crystals are compressed along [110] and [0 15 1], respectively. Recently, we have studied microstructures and mechanical properties of MoSi2/Mo5Si3 eutectic composites with ternary additions in order to improve poor fracture toughness and insufficient high temperature strength of single phase MoSi2 [3-5]. Directionally solidified MoSi2/Mo5Si3 eutectic composites possess fine microstructure of a script-lamellar type [3], in which average thicknesses of MoSi2 and Mo5Si3 are in a micrometer order. In order to understand mechanical properties, deformation behavior and fracture behavior of the DS MoSi2/Mo5Si3 eutectic composites, it is helpful to investigate deformation behavior of both
Figure 1. (a) Crystal structure of MoSi2 and (b,c) schematic illustrations of two operative slip systems in MoSi2, (b) {011} slip, (c) (013)[331] slip. component phases in a micrometer scale. Micropillar compression tests have been attracted a new method to investigate the mechanical behavior of crystalline materials at a micron scale. Extensive studies have been carried out mainly for single crystals of fcc and bcc metals and revealed size-scale effects on flow stress and deformation behavior [6,7]. In the present study, micropillar compression tests were carried out for MoSi2 single crystals in order to investigate their deformation behavior at a micrometer scale.
EXPERIMENTAL PROCEDURE Rod ingots were prepared by Ar arc-melting of high purity Mo and Si. Single crystals of MoSi2 were grown
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