递归法研究钛合金应力腐蚀机理

STUDY OF STRESS CORROSION MECHANISM OF Ti ALLOYS BY RECURSION METHOD

利用递归法(Recursion)计算了α-Ti中刃位错及裂纹区的电子结构(Fermi能级、结构能、环境敏感镶嵌能等),计算并分析了合金元素Mo,V对α-Ti与β-Ti相原子结合能的影响．结果表明:氢原子在位错处的环境敏感镶嵌能较低,易于在位错处聚积,形成氢原子气团．裂纹尖端Fermi能级高于裂纹其他区域,电子从裂纹尖端流向裂纹其他区域造成电位差,在电解质作用下裂纹尖端阳极分解腐蚀．拉应力与裂纹处的氢气压使裂纹解理或沿晶延伸,促进应力腐蚀的发展．合金元素Mo,V有利于α-Ti合金中β相的形成,阻止裂纹在α相中扩展,提高合金应力腐蚀抗力．

The electronic structure （Fermi level, structure energy, environment sensitive embedding energies etc） of 1/3（1120） edge dislocation in α-Ti phase and the crack formed by edge dislocation piling up were calculated by using Recursion method. The effect of alloying elements Mo and V on the atomic binding energies of α-Ti and β-Ti phases were calculated and analyzed. The results show that the environment sensitive embedding energy of H at the edge dislocation is smaller than that in α-Ti matrix, so H atoms tend to segregate in the edge dislocation area, forming H atom cluster; Compared with the other area, the Fermi energy of the crack tip is higher, so the electrons move to other areas from the crack tip, which results in the electric potential difference between the crack tip and the other areas. The crack tip, as anode, will be decomposed under the electrolyte. The tensile force and the pressure of H atom cluster at the crack make the crack propagate along grain boundaries, which accelerates the stress corrosion. The alloying elements Mo and V are helpful to form β phase, which stops the crack expanding in α-Ti, so enhanced the stress corrosion resistance of Ti alloys.