Application of the positron annihilation method for structural characterization of metal matrix composites
Jerzy Dryzek*, Ewa Dryzek*, Jezry Sobczak**, Paweł Darłak** *Instytut Fizyki Jądrowej, ul. Radzikowskiego 152, 31-342 Kraków **Instytut Odlewnictwa, ul. Zakopiańska 73, 30-418 Kraków
Quarterly No. 2, 2005 pages 74-80
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abstract The work presents the preliminary results of application of the positron annihilation method for characterization of MMCs microstructure using as an example the aluminum matrix composites reinforced with short alumina-based fibers. The detailed analysis of methodological aspects of applied innovative experimental method has been done taking into account the known and relatively simple techniques used for the detection of gamma radiation (Figs 1, 2). The obtained results of the process of positron annihilation have been discussed on an example of monolithic pure copper and aluminum alloys (Tab. 1, Fig. 3). The investigation has been done on the samples taken from the composite piston, produced from near eutectic alloy AlSi12CuNiMg and locally reinforced with a MORGAN porous ceramic preform by squeeze infiltration and further solidification under a pressure of 230 MPa (Fig. 4). The as-received preform had 22 ±2 vol.% short alumina-based fibers (96% Al2O3, 4% SiO2). The comparison measurements of the positron life time have been done in both monolithic part of the piston as well as in its reinforced par (Fig. 5, Tab. 2 and 3). The spectrum corresponding to the monolithic part shows one value for the positron life time while the spectrum taken from the reinforced part and presenting the composite AlSi12CuNiMg/22% Al2O3 indicates the well distinguished fraction of the three positron lifetime components. These measurements have been done on the samples in as-cast condition and after heat treatment (precipitate hardening). The results obtained have been analyzed from viewpoint of the effects of such structural defects as discontinuities noted by SEM characterization (Fig. 6). The proposed method can be recommended for the characterization of structural defects, particularly those, which are difficult to be identified by other methods. The authors express their gratitude to the Committee of Scientifics Research (Poland) which has supported this work within grant. Key words: annihilation of positrons, structural investigations, metal matrix composites