Mechanical properties and deformation modes of grade 1 commercially pure titanium at cryogenic temperature

Abstract

In this study, we have investigated the deformation behaviour of Grade 1 commercially pure titanium at 20°C, -100°C and -170°C. Optical microscope and electron backscatter diffraction were applied to characterise the twins activated during tensile testing and the crystal orientations of the sample, and further to analyse the orientation dependent slip activity. The higher density of twins was exhibited at lower deformation temperature. The twinning activity was also higher in the parallel loading (RD) than transverse loading (TD) to rolling direction. According to the Schmid factor analysis, the grains were most favourable for <a>-prism slip in the RD sample, whilst the large fraction of grains was favourable for <a>-basal slip in the TD samples. The activation of slip systems is anticipated to be changed with decreasing temperature due to the different effect of temperature on critical resolved shear stress between slip systems. The work-hardening was affected by twinning- and dislocation-induced hardening depending on the temperature and crystal texture. Consequently, the high work-hardening capacity increased or maintained the total elongation (EL) with decreasing temperature (EL: 66% vs. 70% (RD) and 55% vs. 51% (TD) between 20°C and -170°C).