Ti-22Al-25Nb合金板条组织高温高周疲劳行为

High Cycle Fatiuge at High Temperatures of the Lamellar Microstructureof Ti-22Al-25Nb Alloy

摘要:

研究了双尺寸板条组织的Ti-22Al-25Nb合金在650 ℃和700 ℃下的高周疲劳行为，采用升降法测试了合金的高温高周疲劳强度极限，当应力比R=-1，循环周次Nf=107次时，650 ℃和700 ℃的疲劳强度极限分别为470 MPa和400 MPa。对于双板条组织的Ti-22Al-25Nb合金，其疲劳裂纹既可萌生于试样表面，也可萌生于次表面，并且高周疲劳裂纹在次表面形核的试样具有更高的疲劳寿命。此外，研究发现双尺寸板条组织在高温高周疲劳损伤过程中以胞状析出的形式发生B2→β+O相变，形成组织中的不均匀区域，促使疲劳裂纹在此优先形核。

Abstract:

The high cycle fatigue (HCF) at high temperatures of bimodar size lamellar O pahse microstructure of Ti-22Al-25Nb alloy is studied. HCF strength limits of bimodar size lamellar O pahse microstructure were mearsured via a method named as small sampling up-and-down method (SSUDM). The HCF strength limits at 650℃ and 700℃ were measured to be 470MPa and 400MPa respectively with the stress ratio of -1 and the controlling cycle of 107. It is found that the samples with HCF cracks initiated at subsurfaces can provide significantly longer HCF life than the samples with HCF crack initiated at surfaces. It is found that transformation B2→β+O occurred in the mode of cellular precipitations at initial B2 grain boundaries during the HCF tests. The transformation resulted in inhomogeneous regions in the microstructure. The inhomogenieous regions are the prior cracking areas.