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摘要: 本文采用高压X光衍射方法在金刚石对顶压砧中在位地（in situ）研究了Fe68Co24Ni8（wt%）合金在室温下的压致bcchcp结构相变和直到40.5 GPa的等温压缩行为。实验结果表明该合金在常压下为bcc结构，晶格常数a0=(0.287 00.000 1) nm，体积V0=(7.1190.007) cm3/mol，密度0=(7.9810.008) g/cm3；在20.9 GPa附近出现bcchcp结构相变，两相共存压力区约10 GPa，在此区域内有晶面间距d(002)hcp=d(110)bcc，且原子平面(002)hcp//(110)bcc，hcp相比bcc相体积减小(0.330.02) cm3/mol；高压相hcp结构的晶格参数比值c/a=1.6080.004；相变后原子配位数的增加使得hcp相(002)平面内及(002)平面间的最近邻原子间距比bcc相最近邻原子间距分别增大约1.6%和0.5%；用Murnaghan状态方程对实验数据进行最小二乘法拟合，得到bcc相B0=(13013) GPa，B0'=12.60.5；hcp相V0=(6.620.04) cm3/mol，B0=(24321) GPa，B0'=6.80.3；对于该合金的bccfcp相变时的结构转变机制做了详细的讨论。
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关键词:
- Fe68Co24Ni8合金 /
- 高压X光衍射 /
- 结构相变 /
- 状态方程
Abstract: The pressure induced bcchcp phase transition and the equation of state for Fe68Co24Ni8 (wt%) alloy have been determined by X-ray powder diffraction in a diamond anvil cell (DAC) at room temperature and high pressure up to 40.5 GPa using Zr-filtered Mo K radiation. The experimental results show that the alloy has bcc structure at normal pressure, the lattice parameter, molar volume and density are (0.287 00.000 1) nm, (7.1190.007) cm3/mol and (7.9810.008) g/cm3, respectively. The bcchcp transition was observed at 20.9 GPa, the pressure region of coexisting phases is about 10 GPa. Within this region, d(002)hcp=d(110)bcc and (002)hcp//(110)bcc are obtained, and the molar volume of the hcp is (0.330.02) cm3/mol smaller than that of the bcc. The c/a ratio for the hcp is 1.6080.004 between 20.9 and 40.5 GPa. As a results of the phase transitions, the interatomic distances in the (002)hcp layer and between (002)hcp layer increase by 1.6% and 0.5%, respectively, due to the increase in coordination number. The Murnaghan equation of state was employed to fit the experimental data with the least square method, B0=(13013) GPa, B0'=12.60.5 for the bcc, and V0=(6.620.04) cm3/mol, B0=(24321) GPa, B0'=6.80.3 for the hcp. The mechanism of crystal structure transition from bcc phase to hcp phase for Fe68Co24Ni8 alloy was discussed in detail.-
Key words:
- Fe68Co24Ni8 alloy /
- high pressure /
- X-ray diffraction /
- structure phase transition
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