Borodianska Hanna, Krushinskaya Larisa, Makarenko Galina, Sakka Yoshio, Uvarova Irina, Vasylkiv Oleg
Institute for Materials Science, NASU 3, Krzhizhanivsky, Kiev, 03680, Ukraine.
J Nanosci Nanotechnol. 2009 Nov;9(11):6381-9. doi: 10.1166/jnn.2009.1344.
Homogeneous nanostructured Si3N4-TiN composite powder was obtained by nitration of a TiSi2 powder precursor in a nitrogen flow. Mechanoactivation of titanium disilicide increases the nitration rate and reduces the temperature of formation of the Si3N4 and TiN. The properties of hot pressing (HP) and spark plasma sintering (SPS) of the nanostructured Si3N4-TiN composite with Y2O3 and Al2O3 additives have been studied. In the case of the HP-prepared composite the processing conditions are sufficient to form a stable, equilibrated grain boundary framework. The SPS consolidation is extremely rapid, low-temperature process and the sintering temperature was 300-400 degrees C lower than that of the hot pressing temperature. As a result the grain boundary framework was underdeveloped. Post-sintering anneal of the SPS-prepared samples caused significant improvement of their mechanical properties. The SPS and HP-derived Si3N4-40 mass% TiN-6 mass% Y2O3-2 mass% Al2O3 nano-composite of 98.4% and 98.9% of relative density demonstrate the Vickers hardness values of 13.2 and 13.7 GPa, respectively. The grains of Si3N4 and TiN were much finer in the case of the SPS-derived ceramic composite. However, the better development of the grain boundary framework in the case of the higher temperature HP treatment in comparison to the SPS significantly reduced the advantage of nanocrystallinity. In both cases the fracture toughness was comparable even after the improvement of grain boundary framework during the SPS consolidation. The K(1c), of 7.83 MPax m(1/2) of the sample prepared according to the best SPS regime is also comparable to K(1c) of 8.30 MPa x m(1/2) of much coarser hot pressed ceramic with very similar relative density.
通过在氮气流中对TiSi₂粉末前驱体进行硝化反应，获得了均匀的纳米结构Si₃N₄-TiN复合粉末。二硅化钛的机械活化提高了硝化速率，并降低了Si₃N₄和TiN的形成温度。研究了添加Y₂O₃和Al₂O₃的纳米结构Si₃N₄-TiN复合材料的热压（HP）和放电等离子烧结（SPS）性能。对于HP制备的复合材料，加工条件足以形成稳定、平衡的晶界框架。SPS固结是一个极其快速的低温过程，烧结温度比热压温度低300-400℃。结果，晶界框架发育不良。对SPS制备的样品进行烧结后退火，显著改善了其力学性能。SPS和HP制备的Si₃N₄-40质量%TiN-6质量%Y₂O₃-2质量%Al₂O₃纳米复合材料的相对密度分别为98.4%和98.9%，维氏硬度值分别为13.2和13.7 GPa。在SPS衍生的陶瓷复合材料中，Si₃N₄和TiN的晶粒要细得多。然而，与SPS相比，高温HP处理下晶界框架的更好发育显著降低了纳米晶的优势。在这两种情况下，即使在SPS固结过程中晶界框架得到改善后，断裂韧性也是相当的。根据最佳SPS工艺制备的样品的K(1c)为7.83 MPax m(1/2)，也与相对密度非常相似但晶粒粗得多的热压陶瓷的K(1c) 8.30 MPa x m(1/2)相当。
