Equivalent twinning criteria for FCC alloys under uniaxial tension at high temperatures

Deformation twinning, being an important deformation mechanism which accommodates plastic deformation and at the same time leads to high strain hardening rates, is quantitatively studied at different temperatures and different grain sizes for a range of materials of low and medium stacking fault energy (SFE). A twinning criterion has been developed showing the needed critical dislocation density for twin initiation as a function of grain size at different temperature. A series of tensile tests have been conducted on two initial average grain sizes of about 50 and 250 mu m at four different temperatures (room temperature, 200,400, and 6000 degrees C) for all studied materials (304 stainless steel, 316 stainless steel, 70/30 brass, 80/20 brass and 90/10 brass). The dominant deformation mode at room temperature was found to be slip followed by twining for the majority of these materials. At higher temperatures twinning was diminished in some materials with 50 mu m grain size, however in some cases, these materials with the 250 mu m grain size displayed deformation twins. Microstructure study was also conducted to verify the observation revealed from the strain hardening rate behavior. (c) 2007 Elsevier B.V. All rights reserved.