In-situ Study On Detwinning Behavior Of Commercial Pure Titanium

Titanium and its alloys have been widely used in the fields of national defense and national economy because of their excellent comprehensive properties.In addition to uniaxial tension/compression,the materials may experience deformation and subsequent damage and failure under fatigue,reciprocating and other complex loading during service.In this work,the as-received commercial pure titanium is compressed to prepare deformation twins.The electropolishing process is used to obtain a specific surface morphology,which can be used for digital image correlation?DIC?calculation and electron back-scatter diffraction?EBSD?measurements simultaneously.In-situ scanning electron microscopy?SEM?and EBSD techniques are used to characterize the microstructure evolution during tension,and the mesoscale strain localization is analyzed with DIC technique.The pre-compressed pure titanium samples are electro-polished in the mixed solution of perchloric acid and methanol to regulate their surface morphology by adjusting the electro-polishing voltage and current.When the electro-polishing voltage and current are 16 V and8.30-9.30 mA·mm^-2,respectively,the micron-sized speckles are evenly distributed,and the EBSD indexing rate is 96%,namely,the optimal electro-polishing parameters are obtained.The in-situ EBSD characterization is used to investigate the detwinning of pure titanium under uniaxial tension.The results show that a large number of{10-12}extension twins are activated when the commercial pure titanium is compressed to a large strain along the rolling direction,exhibiting parallel and cross distributions.The detwinning proportion for the cross distributed twins is lower than the parallel distributed twins during tension.The Schmid factor has a positive correlation with the detwinning proportion,and the proportion for the twins with a Schmid factor greater than 0.4 is the largest given a same tensile deformation.The angle?between the crystallographic c-axis of the twin and the loading axis is inversely proportional to the detwinning proportion.The smaller the?value,the more significant the detwinning phenomenon.As the strain increases,the overall kernel average misorientation increases gradually,and the kernel average misorientation values at the grain boundary and inside the twins are larger than the values around them.The evolution images of speckles of pure titanium surface are acquired with in-situ SEM technique.The distributions of strain fields are calculated by incremental DIC.The amplitudes of the normal strain E_xxx for the detwining regions are 3-4 times that of the average E_xx of the specimen,and the detwining regions show obvious strain localization.With the increase of strain,the standard deviations of strain fields of the detwinning regions decrease,indicating a deformation homogenization.