Selection and change in deformation mode to maintain continuity of strains and slip/twinning planes at lamellar boundaries in fatigued TiAl polysynthetically twinned crystals
✍ Scribed by Takayoshi Nakano; Yasuhiro Nakai; Yukichi Umakoshi
- Publisher
- Institute of Physics and National Institute of Materials Science
- Year
- 2002
- Tongue
- English
- Weight
- 848 KB
- Volume
- 3
- Category
- Article
- ISSN
- 1468-6996
No coin nor oath required. For personal study only.
✦ Synopsis
Change in deformation mode in six types of g domain (A M ±C T ) and a 2 plates in TiAl polysynthetically twinned (PST) crystals fatigued at a loading axis parallel to lamellar planes with stress amplitude (Ds ) of 420±450 MPa was examined by the transmission electron microscope focusing on continuity of macroscopic strains and slip/twinning planes at lamellar boundaries. At Ds 420 and 450 MPa, the strain continuity is always maintained at lamellar boundaries by activation of one of the symmetric twinning systems in A-type domain and selection of the dominant deformation mode between ordinary dislocations and twins in (B and C)-type g domain. The (B and C)-type g domains of B M , B T , C M and C T behave as two sets of (B M ,C T ) and (B T ,C M ) because each set selects either the deformation mode of ordinary dislocations or twins as a dominant system in order to keep macroscopic strain continuity. The set (B T ,C M ) which accounts for a larger volume fraction than the set (B M ,C T ) in TiAl-PST crystals used in this study selected a twinning system at Ds 450 MPa, while ordinary dislocations were selected at Ds 420 MPa. At Ds 450 MPa, twinning deformation prevented the further motion of ordinary dislocations with a Burgers vector parallel to lamellar boundaries, and rapid fatigue hardening occurred accompanied by reduction of the accumulative plastic strain energy. Anomalous change in strain energy during fatigue is in¯uenced by the volume fraction of a set of (B and C)-type domain and the anomalous behavior in fatigued TiAl-PST crystals may disappear when each type of g domain is equally distributed.