高压下铌的强度和状态方程研究

室温下,以氦为传压介质的准静水压环境中加压到41GPa,在两柱全景金刚石对顶砧中加压到70GPa,研究了铌在高压下的强度和状态方程.准静水压下,X射线衍射数据拟合得到的体弹模量和其一阶导数分别为166(2)GPa和3.2(2).铌的差应力与剪切模量的比值(t/G)在超过6GPa后几乎为常数,表明由于塑性形变而发生屈服.结合高压下的剪切模量,发现铌在6GPa时由于塑性形变而发生宏观屈服时受到的差应力约为1.26GPa.差应力从2到6GPa可以表示为t=-0.557(94)+0.306(21)p,其中p是压力,单位是GPa.差应力在30GPa后再次增大,表明铌开始出现强化现象,此时对应的差应力约为1.67GPa.在70GPa时,铌受到的差应力最大,且约为3.96GPa.

Investigation of strength and equation of state in niobium at high pressure

The strength and equation of state of niobium (Nb) have be investigated using quasi-hydrostatic x-ray diffraction with helium as pressure medium up to 41 GPa, as well as radial x-ray diffraction up to 70 GPa in a 2-fold paranomic diamond anvil cell (DAC) at ambient temperature. The quasi-hydrostatic x-ray diffraction data (XRD) yields a bulk modulus and its pressure derivative as K0=166(2) GPa with K0''=3.2(2). The ratio of t/G is found to remain constant above ~6 GPa, indicating that the niobium started to experience yield with plastic deformation at this pressure. Combined with independent constraints on the high-pressure shear modulus, we found that niobium sample could support a differential stress of ~1.26 GPa when it started to yield with plastic deformation at ~6 GPa under uniaxial compression. The differential stress in niobium ranges from 0.03 GPa to 1.26 GPa with pressure increasing from 2 GPa to 6 GPa and can be described as t=-0.557(94)+0.306(21)P, where P is the pressure in GPa. The second increasing of t values occurs after ~30 GPa, suggesting that strengthen of Nb with a strength of ~1.67 GPa. A maximum differential stress, as high as ~3.96 GPa can be supported by niobium at the high pressure of ~70 GPa.