Surface nanodeformation of discontinuously reinforced Ti composite by in situ atomic force microscope observation
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J.-M. Yang Department of Materials Science and Engineering, University of California, Los Angeles, California 90095-1595
Y.F. Liu Research Center for Advanced Science and Technology, The University of Tokyo, Meguro-ku, Tokyo 153-8505, Japan
Y. Kagawa National Institute of Materials Science, Tsukuba, Ibaraki 305-0047, Japan; and Research Center for Advanced Science and Technology, The University of Tokyo, Meguro-ku, Tokyo 153-8505, Japan (Received 29 March 2007; accepted 27 June 2007)
The surface nanodeformation of a discontinuously reinforced Ti–6Al–4V composite during tensile loading was investigated by in situ atomic force microscope (AFM) observation. The material used was a TiB whisker and TiC particle reinforced Ti–6Al–4V composite. The evolution of surface roughness and slip band spacing was quantified as a function of applied strain. The microstructural damage during tensile loading was also studied. The formation of slip bands within a grain of the Ti–6Al–4V matrix was clearly observed when the applied strain above was 1.3%. The amount of slip bands and surface roughness increase with increasing applied strain. The rupture of TiC particle and multiple cracking of TiB whiskers were also observed at the applied strain above 1.3%. The interaction of slip bands with the reinforcements and mechanisms of deformation and fracture of the composite were elucidated.
I. INTRODUCTION
Discontinuously reinforced titanium composites containing TiB and/or TiC are emerging as promising materials for advanced aerospace and automobile applications.1–5 The composite has been shown to have attractive combinations of strength, Young’s modulus, fracture toughness, and excellent creep and fatigue resistance.4,5 It is very widely recognized that the matrix properties and the reinforcement volume fraction, shape, size, spatial distribution, and so forth, play an important role in determining the composite strength and ductility. Gorsse and Miracle4 showed that the strength and ductility of TiB whisker reinforced titanium composite (TiB/Ti) were associated with the microstructure and the reinforcement distribution. Damage occurred from largesized or clustered whiskers at low strain levels and propagated through the whiskers rather than at the reinforcement/matrix interface. Soboyejo et al.5 showed that
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0383 3098 J. Mater. Res., Vol. 22, No. 11, Nov 2007 http://journals.cambridge.org Downloaded: 31 Mar 2015
predominant fatigue crack growth mechanism of TiB/Ti composite was the onset of transverse cracking across the TiB whiskers and the TiB whisker bridging, which operated behind the crack tip. Ma et al.6 described the higher creep resistance in TiB whisker and TiC particulate reinforced titanium composite due to the load transfer mechanism with high aspect ratio TiB whiskers. The damage and fracture processes in discontinuously reinforced composites have been studied by various experimental techniques, such as in situ scann
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