Investigation Of Microstructure And Mechanical Properties Of Ti₃Sic₂ Max Materials Under Ion Irradiation

Fusion energy is the ultimate solution to the energy crisis of the human society, the complicated operating environment for fusion reactor puts forward strict requirements for materials in fusion reactors. Thanks to noteworthy mechanical properties, excellent damage tolerance and good thermal stability, Ti3SiC2 MAX phase materials have been considered as the most potential candidate for the structural materials of the first wall/blanket for fusion reactor. This thesis is to investigate radiation damage mechanism of the Ti3SiC2 bulk materials. The dissertation concentrated mainly on the microstructure and mechanical properties analysis of Ti3SiC2 by incident X-ray diffracttion (GIXRD) using synchrotron radiation and nano-indentation. The surface morphology of the sample was analyzed by SEM and the internal structure was analyzed by TEM.The Ti3SiC2 was irradiated with 700 keV C+ ions to investigate change of microstructure and mechanical properties under different doses and temperature. Irradiation damage will produce phase separation, various types of dislocation, defects such as holes, and cause reduction of the material performance. A significant increase of the defects occurs at in the surface layer through synchrotron radiation X- ray diffraction analysis (High resolution transmission electron microscopy images and corresponding electron diffraction patterns also verify this phenomenon), a TiC nanocrystalline phase was also formed under the high dose irradiation. The shift and broadening of the observed diffraction peaks are due to a range of defects ranging from micron scale in size. Irradiation damage increases gradually with the increse of radiation dose under 120℃, thanks to its excellent damage tolerance Ti3SiC2 can still reserve some crystallinity even under high radiation dose. Irradiation damage recovered with the increase of irradiation temperature and there was no TiC nanocrystalline phase when the irradiation temperature exceeded a certain value. A minimum damage of irradiated sample appears around 350℃ in the temperature range, which could be attributed to generation, migration, accumulation and recombination of defects pruduced by ion irradiation under different temperature. The relative change of surface hardness through nano-indentation also verifies this phenomenon. There also exits a minimum damage at a certain temperature under 700 keV Si+ irradiation.The thesis also conducts primary study of the helium behavior of Ti3SiC2, GIXRD shows that irradiation damage increases gradually with the irradiation dose under low energy and high-flux helium ions implantation into the sample surface. And irradiation damage recovered obviously under high temperature or post-annealling.