| MAX phases, especially Ti3SiC2and Ti3AlC2, possess a combination of ceramicand metallic properties due to their unique layered structure, initial irradiationinvestigations also have shown that these two materials are highly tolerant of radiationdamage. This indicates that MAX phases may be a family of candidate fuel claddingmaterials of Generation Ⅳ reactor systems. Another new class of layered carbidesbeyond the MAX phases, namely, Zr-Al(Si)-C ceramics, have attracted increasinginterests in the past decade as promising high-temperature ceramics that display highstrength, toughness, high chemical and thermal stability, as well as superior hightemperature mechanical properties.In this thesis, an additive-free, dense predominantly pure phase Zr3Al3C5materials were obtained by an in situ SPS process at1800℃starting with Zr, Al andgraphite powders. In the synthesis process, phases evolution in the580-1800℃werecharacterized, the formation of ZrAl2, prior the final reaction stage, may play a keyrole in achieving high-purity Zr3Al3C5phase. Moreover, the as-synthesized Zr3Al3C5has an anisotropic microstructure, mainly composed of fine and elongated grains. Dueto the relatively finer microstructure and cleaner grain boundaries, the hardness(Vickershardness of13.3Gpa), stiffness (Young’s modulus of390Gpa) as well astoughness (fracture toughness of4.92±0.68MPam1/2) of the as-synthesizedpolycrystalline Zr3Al3C5are a little bit higher than those of the LPS-Zr3Al3C5. Thethermal conductivity at ambient temperature is extrapolated to be12.2Wm-1K-1.The as-fabricated Zr3Al3C5were irradiated with3MeV Au and1MeV Xe ions atdifferent doses, respectively. After irradiated by Au ions, partially phasedecomposition, the decrease of crystallinity, the changes in microstructure andelectrochemical behavior occurred due to the nuclear collision-induced creation ofmany defects and disorder in the Zr3Al3C5crystal structure. The content of ZrCxincreased with the elevated fluences. Ion irradiation induced anisotropic swelling was estimated to be5.6%for an irradiation dose of15.3dpa at room temperature. Severedecrease of crystallinity occurred at a higher dose of15.3dpa due to the seriouslydisorder at the atomic scale and the accumulation of point defects. Moreover, theelectrochemical impedance spectroscopy analysis indicated a relatively higherresistance in the damage layer after irradiated at a dose of4.9dpa. While at a higherdose of15.3dpa, the increased amount of new ZrCxphase and the modification of themicrostructure might improve the conductivity of the damage layer and the resistancedecreased accordingly. After irradiated by1MeV Xe ions at a dose of about15dpa,the Zr3Al3C5thin film show pronounced decrease of crystallinity due to nuclearcollision induced defects. The formation of ZrCxphase can also be found within theZr3Al3C5substrate. Furthermore, the primary stacking periodicity of the alternatingZr-C and Al-C slabs was seriously disturbed owing to the formation of some extendeddefect clusters or dislocation loops. Fuzzy diffraction spots and poly-crystallinecharacterization trend could be observed in the SAED pattern with some evidence ofthe appearance of amorphization.Zr3Al3C5powders with uniform size distribution were prepared via mechanicallycrushing and grinding process.The influence of pH value and PEI content on thedispersion of Zr3Al3C5particles was studied and it was determined that the suspensionwith1wt.%PEI (pH=3) was the best selection.The cotton blended fabric was finishedwith Zr3Al3C5-containing solution by a soaking-rolling-baking process. Cottonblended fabric was successfully modified by the finish agent with1vol%Zr3Al3C5. |
PDF Full Text Request