Research On The Effect Of The Initial State On Rolling Deformation Mechanism Of Pure Zr

Due to the wide application of zirconium and its alloys in nuclear industry, thedevelopment and research of zirconium alloys has become very important. With thedevelopment of nuclear reactor technology, the demand for the service properties ofzirconium based material increased. The properties are largely determined by themicrostructure which strongly dependent on the deformation mechanism duringfabrication. The plastic deformation of the zirconium rely mainly on slip and twinning,the activation of these deformation modes related to a large number of factors. Forexample, the internal conditions including the arrangement of the atoms, the stackingfault energy, the impurity element, grain size, the second phase particles; as well as theexternal factors like deformation temperature, strain rate, strain, loading method and soon.In this paper, the annealed commercially pure zirconium sheets with typicalbimodal base texture were used to investigate the rolling temperature, initial texture andgrain size effect on the rolling deformation mechanism of zirconium. First, the purezirconium sheet with initial average grain size of10μm was rolled at liquid nitrogen androom temperature respectively. And then the40μm sheet was used for rolling at liquidnitrogen temperature. The metallographical microscope, ECC, EBSD and XRD wereemployed for the microstructure and texture observation. In addition, the twining areafraction and twinning Schmid factor were calculated, the twinning variants selectionlaw was discussed. And then the effect of initial state on the rolling deformationmechanism of pure zirconium was analyzed. Following conclusions can be drawn:1. The {1122} compression twinning,{1012} and {1121} tensile twining aremore activated during rolling at liquid nitrogen temperature compared to that at roomtemperature. And for the samples with initial average grain size of40μm, the number ofthe three kinds of twinning was much larger than10μm samples.2. For the samples with initial average grain size of10μm and40μm rolled atliquid nitrogen temperature, the overall twinning area fraction, the area fraction of{1122} twinning and {1012} twinning increased approximate linearly with increasingstrain, while that of {1121} tensile twinning was always at a low level. When the initialaverage grain size was10μm, the twins mainly generated between10%and20%strain.But a large number of twining activated at5%strain for40μm samples. 3. Slip was the dominant deformation modes of pure zirconium rolled at roomtemperature. When rolled at liquid nitrogen temperature, for small grain size sheet, slipwas prior to twinning at low strain, then the contribution of twinning enhanced withstrain increas; for large grain size sheet, twinning was prior to slip as the dominantdeformation modes at low strain, then slip converted to the dominant deformationmodes with strain increase.4. The texture intensity of specimens rolled at room temperature and liquidnitrogen temperature decreases with strain. The texture type didn’t change significantly,still kept the bimodal distribution. Nevertheless, the evolution prismatic texture wassimilar at the two different temperature, i.e. from <1120>//RD to1010//RD. If theinitial sheet was <1010>//RD, the texture remain unchanged. However, the bimodaldistribution texture of room temperature samples centralize to ND gradually withincreasing strain, while that of liquid nitrogen temperature samples remained thebimodal distribution of inclining30○toward TD.5. For samples rolled at liquid nitrogen temperature, twinning preferentiallyformed in the grain with large Schmid factor, but the activated {1122} twinning variantwas not just V1with the maximum Schmid factor. So that the Schmid law was followed.However, the Schmid factor of activated twinning variant was close to the maximumSchmid factor. And with strain increasing, the larger the Schmid factor of the variant,the more the number.