高压下铌的强度和状态方程研究

Investigation of strength and equation of state in niobium at highpressure

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.

The strength and equation of state of niobium(Nb)have been 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)yield a bulk modulus and its pressure derivative as K 0=166(2)GPa with K′0=3.2(2).The ratio of differential stress to shear modulus(t/G)is found to remain constant above 6 GPa,indicating that the niobium starts 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 starts to yield with plastic deformation at 6 GPa under uniaxial compression.The differential stress in niobium ranges from 0.03 to 1.26 GPa with pressure increasing from 2 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.