1-12. DFT calculations of generalized stacking fault energies and critical shear stresses of alpha-titanium alloys: On the plastic deformation anisotropy and dwell fatigue susceptibility

Qing-Miao Hu1, Hui Yu1,2,3, Shuo Cao1, Sabry S. Youssef1, Ying-Jie Ma1, Jia-Feng Lei1, Yang Qi2,Rui Yang1

1. Institute of Metal Research, Chinese Academy of Sciences 2. Northeastern University
3. Shenyang University of Technology

Abstract: Dwell fatigue of titanium alloys reduces significantly the life-time of the blades and disks of gas turbine engine in a jet aircraft. The dwell fatigue of titanium alloys originates from the plastic deformation anisotropy of the alpha phase with hexagonal close packed crystal structure as the critical resolved shear stress (CRSS) of the pyramidal c+a slip system is 3 to 4 times higher than those of the basal and prismatic a slip systems. Therefore, understanding the anisotropy of the CRSS and plastic deformation of alpha titanium is highly demanded for the rational design of titanium alloys so as to improve the service life-time of the blades and disks. In the present work, the generalized stacking fault energies (GSFE) of a and c+a slip systems of alpha titanium alloys are calculated by using a first-principles method based on density functional theory. The CRSSs of the slip systems are then evaluated with the semi-discrete variational Peierls-Nabarro model. We show that the CRSSs of the basal and prismatic a slips increase with the Al concentration whereas their difference decreases, which explains the variations of yield strength, ultimate strength, fracture toughness of the alloy against the Al concentration. However, Al alloying does not decrease the ratio of the CRSS of the c+a slip to those of the a slips, and, therefore, may not relieve the dwell fatigue susceptibility of the alloy through reducing the plastic deformation anisotropy.

DFT 计算 GSFE 及 CRSS 研究钛合金的塑性变形各向异性及保载疲劳 敏感性

胡青苗 1, 于慧 1,2,3，曹烁 1，Sabry S. Youssef1, 马英杰 1, 雷家峰 1, 祁阳 2, 杨锐 1 

1.中国科学院金属研究所; 2.东北大学; 3.沈阳工业大学 

摘要:钛合金的保载疲劳显著降低航空发动机叶片及叶盘的使用寿命。保载疲劳敏感性源于钛 合金密排六角结构相的塑性变形各向异性:相锥面c+a滑移系的临界剪切应力比基面及柱面 a滑移系高 3~4 倍。因此，研究钛合金相的临界剪切应力(CRSS)及塑性变形各向异性，对合 理设计钛合金、提高航空发动机钛合金部件寿命具有重要意义。在本工作中，我们采用基于密 度泛函立论第一原理方法，计算了钛合金广义层错能(GSFE)随成分的变化，进而采用半离散-变分 Peierls-Nabarro 模型，计算了合金各滑移系的临界剪切应力(Peierls 力)。初步研究结果表明， 钛合金相基面及柱面a滑移系临界剪切应力随 Al 含量增加而增加，且二者差异减小，一定程 度上解释了合金屈服强度、抗拉强度、断裂韧性等随 Al 含量的变化。但 Al 合金化不能减小锥 面c+a与基面及柱面a滑移系的临界剪切应力比值，因此，不能通过降低塑性变形各向异性减 小合金的保载疲劳敏感性。