材料期刊网

计算了有应力和无应力状态下产生非球对称应变的氢原于的化学位之差,μ_σ-μ_0=-VΣσ_iε_(ii)~′,其中U就是氢应变场和外应力场的互作用能.对纯剪应力τ,则U=-0.55133Vτ(ε_(11)-ε_(22)),因而当氢在α-Fe中引起四方畸变时,它和剪应力就有互作用,从而可导致氢在45°面上富集,这就可解释充氢的无裂纹扭转试样以及III型裂纹试样能沿45°面产生氢致滞后断裂的实验事实.当非球对称应变的氢择优分布时,在拉伸和压缩条件下的氢浓度公式并不相同,分别为C_t=C_0exp[(0.70089ε_(11)+0.29911ε_(22))Vo/RT],C_0exp[(0.14956ε_(11)+0.85044ε_(22))Vσ/RT].因此,根据氢渗透实验所获得的C_t/C_0和C_p/C_0,就可定出ε_(11)/ε_(22).例如,用Bockris的数据可得ε_(11)/ε_(22)=1.27.这表明氢在α-Fe中的应变是非球对称的.

The difference between the chemical potential,μ_σ,of hydrogen atoms produ-cing a non-spherical symmetry strain in a solid sample under stress and that,μ_0corresponding to the state without stress has been studied.It is shown that μ_σ-μ_0=■=U,where σ_1——principal stress,■——strain component along thedirection of the principal stress,V——volume and U——interaction energy betweenthe strain field and external stress field.The hydrogen atoms producing the tetragonally symmetric strain are preferen-tially ordered in samples under stress.As a result,the variation of hydrogenconcentration with tensile stress σ will be different from that with compressive stressσ.For a general polycrystal the formulas are respectively■where C_t,C_p,C_0——hydrogen concentraiton under tensile stress,compressive stressand without stress respectively.Hence,ε_(11)/ε_(22)may be determined in terms of C_t/C_pwhich can be obtained by hydrogen permeation measurement.For example,according to Bockris's data,ε_(11)/ε_(22)=1.27 at temperature of 27℃ which impliesthat the strain field of hydrogen atoms in α-Fe is non-spherical symmetry.For a torsional stress τ,U=-0.55133Vτ(ε_(11)-ε_(22)).The interaction can resultin the enrichment of hydrogen atoms and hydrogen induced delayed crackingalong the planes inclined at an angle of α=45°to torsional axis,which was ob-served in pre-charged smooth torsional or type Ⅲ cracked specimens made of ultra-high strength steel.