Kim Dasom, Hirayama Yusuke, Liu Zheng, Kwon Hansang, Kobashi Makoto, Takagi Kenta
Department of Materials Process Engineering, Nagoya University, 1 Furocho, Chikusa, Nagoya 464-8603, Japan.
Magnetic Powder Metallurgy Research Center, National Institute of Advanced Industrial Science and Technology, 2266-98 Anagahora, Shimoshidami, Moriyama, Nagoya 463-8560, Japan.
Nanomaterials (Basel). 2021 Apr 30;11(5):1182. doi: 10.3390/nano11051182.
The low oxygen powder metallurgy technique makes it possible to prepare full-dense ultrafine-grained (UFG) Al compacts with an average grain size of 160 nm by local surface bonding at a substantially lower temperature of 423 K from an Al nanopowder prepared by a low oxygen induction thermal plasma process. By atomic level analysis using transmission electron microscopy, it was found that there was almost no oxide layer at the Al/Al interfaces (grain boundaries) in UFG Al compact. The electrical conductivity of the UFG Al compact reached 3.5 × 10 S/m, which is the same level as that of the cast Al bulk. The Vickers hardness of the UFG Al compact of 1078 MPa, which is 8 times that of the cast Al bulk, could be explained by the Hall-Petch law. In addition, fracture behavior was analyzed by conducting a small punch test. The as-sintered UFG Al compact initially fractured before reaching its ultimate strength due to its large number of grain boundaries with a high misorientation angle. Ultimate strength and elongation were enhanced to 175 MPa and 24%, respectively, by reduction of grain boundaries after annealing, indicating that high compatibility of strength and elongation can be realized by appropriate microstructure control.
低氧粉末冶金技术使得通过在423K的较低温度下进行局部表面键合，由通过低氧感应热等离子体工艺制备的铝纳米粉末制备平均晶粒尺寸为160nm的全致密超细晶粒（UFG）铝坯块成为可能。通过使用透射电子显微镜进行原子水平分析，发现在UFG铝坯块的Al/Al界面（晶界）几乎没有氧化层。UFG铝坯块的电导率达到3.5×10 S/m，与铸造铝块体处于同一水平。UFG铝坯块的维氏硬度为1078MPa，是铸造铝块体的8倍，这可以用霍尔-佩奇定律来解释。此外，通过进行小冲孔试验分析了断裂行为。由于大量具有高取向差角的晶界，烧结态的UFG铝坯块在达到其极限强度之前就开始断裂。退火后通过减少晶界，极限强度和伸长率分别提高到175MPa和24%，这表明通过适当的微观结构控制可以实现强度和伸长率的高兼容性。
