论文标题
通过两步烧结的超均匀纳米晶体材料
Ultra-uniform Nanocrystalline Materials via Two-Step Sintering
论文作者
论文摘要
纳米晶金属和谷物尺寸<100 nm的纳米晶金属和陶瓷（例如机械强度，硬度，断裂韧性和储存的介电能）引起了极大的兴趣。关于实现纳米颗粒的讨论已经很多，但是关于保持物质可靠性至关重要的晶粒尺寸均匀性知之甚少。一个特别有趣的问题是，是否可以比Hillert [1]在正常谷物生长的理论上预测的尺寸分布更窄，这是一种有可能通过Lifshitz，Slyozov，Wagner（Wagner（LSW）[3,4]和Hillert在实践中实现的均值增长指数[2]的可能性。我们证明，这可以在散装材料中以适当设计的两步烧结途径来实现，该路线（a）利用中间烧结阶段的大型生长指数，尽管剩余孔隙率剩下孔隙率，但仍会形成最均匀的微观结构，并且（b）在其上冻结谷物的生长，同时继续致密，以达到全密度。所得密度的散装AL2O3陶瓷的平均晶粒尺寸为34 nm，并且尺寸分布较窄，而尺寸分布却较窄。 Bulk Al2O3 with a grain-size distribution narrower than the particle-size distribution of starting powders was also demonstrated using this strategy, as were highly uniform bulk engineering metals and ceramics of either high purity and high melting points (Mo and W-Re) or highly complex compositions (core-shell BaTiO3 and 0.87BATIO3-0.13BI（Zn2/3（NB0.85TA0.15）1/3）O3）。
Nanocrystalline metals and ceramics with <100 nm grain sizes and superior properties (e.g., mechanical strength, hardness, fracture toughness and stored dielectric energy) are of great interest. Much has been discussed about achieving nano grains, but little is known about maintaining grain-size uniformity that is critical for material reliability. An especially intriguing question is whether it is possible to achieve a size distribution narrower than what Hillert[1] theoretically predicted for normal grain growth, a possibility suggested, for growth with a higher growth exponent, by the generalized mean-field theory[2] of Lifshitz, Slyozov, Wagner (LSW)[3,4] and Hillert but never realized in practice. We demonstrate that this can be achieved in bulk materials with an appropriately designed two-step sintering route that (a) takes advantage of the large growth exponent in the intermediate sintering stage to form a most uniform microstructure despite porosity remaining, and (b) freezes the grain growth thereon while continuing densification to reach full density. The resultant dense bulk Al2O3 ceramic has an average grain size of 34 nm and a much narrower size distribution than Hillert's prediction. Bulk Al2O3 with a grain-size distribution narrower than the particle-size distribution of starting powders was also demonstrated using this strategy, as were highly uniform bulk engineering metals and ceramics of either high purity and high melting points (Mo and W-Re) or highly complex compositions (core-shell BaTiO3 and 0.87BaTiO3-0.13Bi(Zn2/3(Nb0.85Ta0.15)1/3)O3).
