新型亞穩(wěn)態(tài)β鈦合金ti5al5v5mo3cr0.5fe循環(huán)變形機(jī)理及疲勞斷裂性能研究

1、合肥工業(yè)大學(xué)博士學(xué)位論文新型亞穩(wěn)態(tài)β鈦合金Ti-5Al-5V-5Mo-3Cr-0.5Fe循環(huán)變形機(jī)理及疲勞斷裂性能研究姓名：黃俊申請(qǐng)學(xué)位級(jí)別：博士專業(yè)：材料加工工程指導(dǎo)教師：薛克敏；周杰；王執(zhí)銳2011-06ABSTRACT The improved hardenability and reduced sensitivity to forming variables of Ti-5Al-5V-5Mo-3Cr-0.5Fe

2、 (Ti-5553) alloy has made it a candidate to replace Ti-10V-2Fe-3Al and Ti-6Al-4V for landing gear manufacturing in Boeing-787 and Airbus-A380. Systematic work on the fatigue and cyclic deformation behavior of Ti-5553 is

3、meaningful for the damage tolerance designing. In the present study, the cyclic deformation response and the corresponding micromechanical mechanism is thoroughly investigated. In general, it includes two major parts. Th

4、e first part is about the cyclic deformation response and fatigue damage mechanism of the BCC Ti-5553 with β-annealed treatment, for fundamental understanding this new material for future applications. The second part sy

5、stematically investigates the cyclic hardening/softening response and corresponding dislocation configuration of the Ti-5553 alloy with bimodal microstructure. The main contribution of this dissertation can be discussed

6、 as follows. 1. Mechanical deformation response of the β-annealed metastable Ti-5Al-5V-5Mo-3Cr-0.5Fe alloy under the condition of pure compressive fatigue stress has been initiated to investigate. This BCC Ti-5553 materi

7、al demonstrates the initial cyclic softening followed by saturation mechanism irrespective of the employed compressive peak stress level. Dislocation movement upon cycling has been initially studied for better understand

8、ing the cyclic deformation behavior of the β-annealed metastable Ti-5Al-5V-5Mo-3Cr-0.5Fe alloy. TEM investigation reveals dislocation annihilation and detwinning process in the total strain cycling specimens. Such activi

9、ties, together with the intersection of coherent omega precipitates by moving dislocations, are considered to be responsible for the initial softening; whereas the dislocation dipole flip-flop mechanism is presumably res

10、ponsible for the cyclic saturation behavior. 2. Attempt has been made for the first time to explain the strain localized planar slip behavior by considering the stacking fault energy (SFE) as well as the free-electron-t

11、o-atom (e/a) ratio. The progressive observation of surface morphology evolution reveals typical planar slip behavior and early formation of strain localization-induced fatigue microcracks. Using the new criterion: relati

12、onship between the SFE and e/a, with consideration of the shearing process of nano-scaled omega precipitates, as well as the as-received microstructure, to analyze the strain localization phenomenon and planar-slip mode

13、in the material. 3. Cyclic deformation response of Ti-5553 alloy with β-α bimodal structure is systematically investigated through total strain controlled fatigue tests. The cyclic hardening/softening behavior was found