铝纳米晶的正电子湮没研究

采用自悬浮定向流-真空热压法,在不同压强下制得铝纳米晶材料,并利用X射线衍射(XRD)和正电子湮没寿命谱(PALS)分析手段对铝纳米晶的结构和微观缺陷进行表征.XRD分析表明:所制备的铝纳米晶的晶粒度为48 nm.PALS分析表明:铝纳米晶的微观缺陷主要为类空位以及空位团,而微孔洞很少;短寿命τ1,中间寿命τ2以及其对应的强度I1,I2随压强变化而呈现阶段性变化;压制压强(P)低于0.39 GPa时制得的纳米晶空位团随压强的增加而逐渐转变为类空位;0.39 GPa P 0.72 GPa时,各类缺陷发生消除;P 0.72 GPa时,各类缺陷进一步发生消除.随压强的提高,铝纳米晶的密度增加,其显微硬度也明显增高.

Nanocrystalline aluminum studied by positron annihilation lifetime spectroscopy

Aluminum nanoparticles with an average diameter of about 48 nm are compressed in a cemented-carbide mold under different pressures to produce nanocrystalline aluminum by the hot-pressing technology in a high vacuum condition. The X-ray diffraction and the positron annihilation lifetime spectroscopy (PALS) are used to characterize the microscopic structures of nanocrystalline aluminum. The PALS experimental results indicate that there are three types of defects in nanocrystalline aluminum, i.e., vacancy-like defects, vacancy clusters, and microvoids, which are corresponding to three lifetime components of positrons. The pressure for compaction has a great influence on the positron annihilating behavior. The vacancy clusters transform into the vacancy-like defects with increasing the pressure when it is below 0.39 GPa. The three types of defects tend to be rapidly eliminated in a pressure range from 0.39 GPa to 0.72 GPa. When pressure is above 0.72 GPa, the defects are further eliminated in nanocrystalline aluminum. The density and microhardness of nanocrystalline aluminum increase significantly with increasing the pressure for compaction.
Keywords： the flow-levitation method the hot-pressing technology aluminum nanocrystalline positron lifetime spectroscopy