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Fe_(68)Co_(24)·Ni_8(wt％)合金在室温下的压致bcc→hcp结构相变和直到40.5GPa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α0=0.2870±0.0001nm,体积V_0=7.119±0.007cm^3/mo1,密度ρ_0=7.981±0.008g/cm^3;在20.9GPa附近出现bcc→hcp 结构相变,两相共存压力区约10GPa,在此区域内有晶面间距d(002)_(hcp)=_1d(110)_(bcc),且原子平面(002)_(hcp)//(110)_(bcc),hcp相比bcc相体积减小0.33±0.02cm^3/mol;高压相hcp结构的晶格参数比值 c/a=1.608±0.004;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B_0=130±13GPa,B_0’=12.6±0.5;hcp相V_0=6.62±0.04cm^3/mol,B_0=243±21GPa,B’_0=6.8±0.3;对于该合金的bcc→hcp相变时的结构转变机制做了详细的讨论。
The pressure induced bcc-hcp phase transition and the equation of state for Fe68Co21Ni8 (wt%) alloy have been determined by X-ray powder diffraction in a diamond anvil cell (DAC) at room temperature and high pressure up to 40.5GPa using Zr-filtered Mo Ka radiation. The experimental results show that the alloy has bcc structure at normal pressure, the lattice parameter, molar volume and density are 0.2870 ±0.0001 nm, 7.119 ± 0.007cm3/mol and 7.981 ± 0.008 g/cm-1, respectively. The bcc -hep transition was observed at 20.9GPa. the pressure region of coexisting phases is about 10GPa. Within this region, d (002)hep = d(110)hee and (002)hep//(110)het are obtained. and the molar, volume of the hep is 0.33 ± 0.02cm3/mol smaller than that of the bcc. The c/a ratio for the hep is 1.608±0.004 between 20.9 and 10.5GPa . As a results of the phase transitions, the interatomic distances in the (002>hep> layer and between (002)hep 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, Bu = 130 ± 13 GPa. B0' = 12.6 ± 0.5 for the bcc. and Va= 6.62±0.04 cm3/mol. B0= 243 +± 21 GPa. B0' = 6.8 ± 0.3 for the hep. The mechanism of crystal structure transition from bcc phase to hep phase for Fe18Co21Ni8 alloy wasdis-cussed in detail.
出处
《高压物理学报》
CAS
CSCD
北大核心
1991年第2期81-89,共9页
Chinese Journal of High Pressure Physics
基金
国家自然科学基金会的资助
关键词
铁钴镍合金
X光衍射
结构相变
Fe68Co24Nix alloy, high pressure. X-ray diffraction, structure phase transition, equation of state.
