Al-TiB_2纳米晶薄膜中的反Hall-Petch效应

Experiment Confirmation of the Inverse Hall-Petch Effect in Al-TiB_2 Nanocrystalline Films

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 effect of grain size in nanocrystalline alloys is difficult to reveal experimentally because of the interaction between a number of other microstructure factors.A series of multilayered films with Al-TiB2 crystalline layers of different thicknesses were prepared which possessed amorphous layers of identical thickness.The results show that in these multilayered films,the heights of columnar crystals in crystalline layers are controlled from 8 to 128 nm and their diameters are maintained at^15 nm,independent of their heights.This design achieved the control of grain size,independent of other microstructure factors.The analyses of mechanical properties of these multilayered films show that the inverse Hall-Petch phenomenon also exists in Al-TiB2 nanocrystalline alloys,as in nanocrystalline pure Al.The critical grain sizes of deviation from the Hall-Petch relationship and the inverse Hall-Petch phenomenon are approximately 32 and 8 nm,respectively.These critical grain sizes are similar to those of nanocrystalline pure Al by molecular dynamic simulations.