Hexagonal KCaGd͑PO 4 ͒ 2 :RE 3+ ͑RE= Ce, Tb, Eu, Tm, Sm͒ were synthesized by coprecipitation method and their vacuum ultraviolet-ultraviolet ͑VUV-UV͒ spectroscopic properties were investigated. The bands at about 165 nm in the VUV excitation spectra are attributed to the host lattice absorptions. For Ce 3+ -doped samples, the bands at 207, 256, 275, and 320 nm are assigned to the 4f-5d transitions of Ce 3+ in KCaGd͑PO 4 ͒ 2 . For Tb 3+ -doped sample, the bands at 203 and 222 nm are related to the 4f-5d spin-allowed transitions. For Eu 3+ -doped sample, the O 2− -Eu 3+ charge-transfer band ͑CTB͒ at 229 nm is observed, and the fine emission spectrum of Eu 3+ indicates that Eu 3+ ions prefer to occupy Gd 3+ or Ca 2+ sites in the host lattice. For Tm 3+ -and Sm 3+ -doped samples, the O 2− -Tm 3+ and O 2− -Sm 3+ CTBs are observed to be at 176 and 186 nm, respectively. From the standpoints of the absorption band, color purity, and luminescent intensity, Tb 3+ -doped KCaGd͑PO 4 ͒ 2 is a potential candidate for 172 nm excited green plasma display phosphors.
Dilute Zn-0.3Al, eutectic Zn-5Al and eutectoid Zn-22Al alloys were processed by multi-pass equal channel angular pressing (ECAP) in order to achieve fine grained (FG) or ultrafine-grained (UFG) microstructure and room temperature (RT) superplasticity. ECAP refined the microstructure of Zn-0.3Al and resulted in a FG Zn-rich η-matrix with an average grain size of 2 µm and homogeneously distributed nano-sized Al-rich α-particles with the grain sizes in the range of 50-200 nm. A bi-modal microstructure was achieved in Zn-5Al alloy with UFG Al-rich α-and FG Zn-rich η-phases having mean grain sizes of 110 nm and 540 nm, respectively. ECAP brought about an agglomerate-free UFG microstructure in Zn-22Al alloy with an average grain size of 200 nm which is the lowest one obtained so far for this alloy after ECAP processing. The maximum RT superplastic elongations of 1000%, 520% and 400% were achieved for Zn-0.3Al, Zn-5Al and Zn-22Al alloys, respectively. Considering the RT superplasticity in Zn-Al alloys, it was found that lower Al content results in higher superplastic elongations even if the alloy has relatively larger grain size. Grain boundary sliding (GBS) was found to be the main deformation mechanism in region-II as the optimum superplastic region during RT deformation for all three Zn-Al alloys with the strain rate sensitivity factor ranging between 0.25-0.31.Keywords: Zn-Al alloys, room temperature superplasticity, ultrafine-grained materials, equal channel angular pressing Влияние химического состава и размера зерен на сверхпластичность при комнатной температуре сплавов Zn-Al, подвергнутых РКУП Низколегированный сплав Zn-0.3Al, эвтектик Zn-5Al и эвтектоидный сплав Zn-22Al были подвергнуты многопро-ходному равноканальному угловому прессованию (РКУП) с целью получения мелкозернистой (МЗ) или ультрамел-козернистой (УМЗ) структуры и достижения сверхпластичности при комнатной температуре. РКУП привело к из-мельчению микроструктуры Zn-0.3Al и формированию МЗ обогащенной Zn η-матрицы со средним размером зерен 2 мкм и однородно распределенных наноразмерных богатых Al α-частиц с размером в интервале 50-200 нм. В сплаве Zn-5Al была получена бимодальная структура с УМЗ богатой Al α-фазой и МЗ богатой Zn η-фазой, имеющими соответственно размеры зерен 110 нм и 540 нм. В сплаве Zn-22Al РКУП привело к формированию не агломериро-ванной УМЗ микроструктуры со средним размером зерен 200 нм, что представляет собой минимальное достигнутое к настоящему времени значение размера зерен, полученное РКУП на данном сплаве. Для сплавов Zn-0.3Al, Zn-5Al и Zn-22Al были получены максимальные сверхпластические удлинения при комнатной температуре, равные соот-ветственно 1000%, 520% и 400%. По отношению к сверхпластичности сплавов Zn-Al показано, что более низкое содержание Al приводит к более высоким сверхпластическим удлинениям, даже если сплав имеет больший размер зерен. Показано, что зернограничное проскальзывание (ЗГП) является основным механизмом деформации в обла-сти II, являющейся оптимальной областью сверхпластической деформации при комн...
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