基于正电子湮没寿命谱研究Fe-6.5wt.%Si合金中热空位的生成

Formation of thermal vacancies in Fe-6.5wt.%Si alloy studied by positron annihilation lifetime spectra

正电子湮没技术(PAT)是一种无损伤的材料探测技术,它可以反映正电子所在处电子密度或电子动量分布的信息.由于正电子对原子尺度的缺陷非常敏感,所以正电子湮没技术(PAT)是研究纯金属及金属间化合物中热空位生成的有效工具.基于正电子寿命谱技术对金属间化合物Fe-6.5wt.%Si合金热轧板在不同温度退火后缺陷变化进行研究,发现了正电子平均寿命在673K左右迅速增加,673至1073K温度范围内平均正电子寿命的温度曲线为明显的S形状,1073K以上平均正电子寿命趋于常数,通过分析正电子平均寿命的温度变化曲线,得到了Fe-6.5wt.%Si合金中热空位生成的临界温度值,并计算得到了该合金的空位生成激活焓为HVF=0.54eV.

Thermal atomic defects play an important role in deformation behavior of intermetallic compounds. Posi- tron annihilation technology （PAT） is a non-destructive testing technology for investigation on the thermal vacancy formation in pure metals as well as in intermetallic phases. The positron lifetime can reflect the information of elec- tronic density and momentum, therefore this technique is very sensitive to the vacancies. The formation of thermal vacancies in intermetallic compounds Fe-6.5wt. %Si alloy was studied based on the positron lifetime spectrometry. Fe-6.5wt. %Si alloy ribbons was annealed at temperatures from 373 to 1 073 K. The results indicated that the defects of thermal vacancy exist in the hot-rolled ribbons of Fe-6.5wt. %Si alloy after quenching from a high tempera- ture. Below 673 K, the mean positron lifetime is approximately a constant 112 ps. There is a characteristic Sshaped increase in the mean positron lifetime between 673 and 1 073 K. This is due to the appearance of an additional posi- tron lifetime component. This is attributed to the annihilation of positrons trapped at thermal vacancies. Above 1 073 K, positron trapping saturates giving rise to an approximate constant value of the mean positron lifetime. By studying the temperature curve of the mean positron lifetime, we determine the formation temperature of thermal va- cancies, and calculate the vacancy formation enthalpies Hv =0.54 eV in Fe-6.5wt.%Si alloy.