Al-TiB2纳米晶薄膜中的反Hall-Petch效应

多种微结构因素作用的相互交织使纳米晶合金中是否存在与纯金属类似的反Hall-Petch现象难以得到实验证实。选用Al-TiB_2体系,采用二维结构纳米多层膜的方法,实现了对晶粒尺寸因素的孤立和使其独立地改变,研究了晶粒尺寸对薄膜力学性能的作用规律。结果表明:Al-TiB_2过饱和固溶纳米晶薄膜也与纳米晶纯金属Al一样,存在硬度随晶粒尺寸减小从遵从Hall-Petch关系提高转变为偏离Hall-Petch关系,并进一步出现反Hall-Petch效应的3个阶段,实验得到了偏离Hall-Petch关系为32 nm,产生反Hall-Petch现象的临界晶粒尺寸为8 nm,这2个临界晶粒尺寸与分子动力学方法对纳米晶纯金属A1计算的结果相当。

The Experiment Confirmation of the Inverse Hall-Petch Effect in Al-TiB2 Nanocrytalline Films

The effect of grain size in nanocrystalline alloys is difficult to reveal experimentally because challenges of controlling a number of other microstructure factors. This paper designed and prepared a series of multilayered films with Al-TiB2 crystalline layers of different thickness but with amorphous layers of identical thickness. In these multilayered films, the heights of columnar crystals in crystalline layers were controlled from 8 to 128nm and their diameters kept at ~15 nm, independent of their heights. This design achieved the control of grain size, independent from other microstructure factors. The analysis of mechanical properties of these multilayered films showed that the inverse Hall-Petch phenomenon also exists in Al-TiB2 nanocrystalline alloys , as nanorystalline pure Al. The critical grain sizes of deviation from the Hall-Petch relationship and the inverse Hall-Petch phenomenon are approximately 32 nm and 8 nm respectively. These critical grain sizes are similar to those reports in nanorystalline pure Al by molecular dynamic simulations.