In order to guide a reasonable application of the bulk ultrafine-grained industrial pure iron, a serious of ultrafine-grained pure iron samples with different microstructures were fabricated by multi-passes ECAP and heat-treatment, and their microstructures and pitting corrosion behaviour were investigated by transmission electron microscopy (TEM), electrochemical polarization and impedance spectroscopy (EIS) techniques, respectively. Results show that:with the increase of ECAP passes, lath-shaped structure with high dislocation density transforms into equiaxed grains with low dislocation density; the dislocation density decreases and the high-angle grain boundaries increase, after the annealing treatment. ECAP passes have less effect on the self-passivation of pure iron, and its open circuit potential (OCP) and polarization resistance are less changed; the pitting corrosion resistance of the ECAPed pure iron is related to the ECAP passes:the pitting potential first decreases and then increases with the increase of ECAP passes; the self-passivation property and pitting corrosion resistance of the ECAPed pure iron are improved after the annealing heat-treatment, the OCP, polarization resistance and pitting potential values increase obviously.
VALIEV R , ALEXANDROV I , ZHU Y T , et al. Paradox of strength and ductility in metals processed by severe plastic deformation[J]. Journal of Materials Research, 2002, 17 (1): 5- 8.
WANG Y , CHEN M , ZHOU F , et al. High tensile ductility in a nanostructured metal[J]. Nature, 2002, 419 (6910): 912- 915.
VALIEV R . The new trends in fabrication of bulk nanostructured materials by SPD processing[J]. Journal of Materials Science, 2007, 42 (5): 1483- 1490.
STOLYROV V V , ZHU Y T , ALEXANDROV I V , et al. Influence of ECAP routes on the microstructure and properties of pure Ti[J]. Materials Science and Engineering: A, 2001, 299 (1): 59- 67.
WANG J F , BAI P C , ZHANG X Y , et al. Investigation of effect of tensile property and fracture behavior of pure aluminum during ECAP[J]. Journal of Aeronautical Materials, 2009, 29 (3): 33- 38.
RALSTON K D , BIRBILIS N . Effect of grain size on corrosion: a review[J]. Corrosion, 2010, 66 (7): 7500501- 7500513.
RALSTON K D , BIRBILIS N , DAVIES C H J . Revealing the relationship between grain size and corrosion rate of metals[J]. Scripta Material, 2010, 63, 1201- 1204.
LIU L , LI Y , WANG F H . Electrochemical corrosion behavior of nanocrystalline materials-a review[J]. Journal of Materials Science & Technology, 2010, 26 (1): 1- 14.
OGUZIE E , WANG S , LI Y , et al. Corrosion and corrosion inhibition characteristics of bulk nanocrystalline ingot iron in sulphuric acid[J]. Journal of Solid State Electrochemistry, 2008, 12 (6): 721- 728.
WANG S , SHEN C , LONG K , et al. Preparation and electrochemical corrosion behavior of bulk nanocrystalline ingot iron in HCl acid solution[J]. The Journal of Physical Chemistry B, 2005, 109 (7): 2499- 2503.
ZHANG L Y , MA A B , JIANG J H , et al. Sulphuric acid corrosion of ultrafine-grained mild steel processed by equal-channel angular pressing[J]. Corrosion Science, 2013, 75, 434- 442.
WANG H , ZUO Y , MAO J P . Metastable pitting and related morphology of pure iron in NaNO2+NaCl solution[J]. Journal of Beijing University of Chemical Technology, 2004, 31 (5): 41- 44.
JIANG J H , MA A B , SONG D , et al. Anticorrosion behaviour of ultrafine-grained Al-26 wt% Si alloy fabricated by ECAP[J]. Journal of Materials Science, 2012, 47 (22): 7744- 7750.
ZEIGER W , SCHNEIDER M , WORCH H . Passivity and pitting corrosion of a nanocrystalline FeAl8-alloy[J]. Materials Science Forum, 1998, 269-272, 833- 836.
ZIDOUNE M , GROSJEAN M H , ROUE L , et al. Comparative study on the corrosion behavior of milled and unmilled magnesium by electrochemical impedance spectroscopy[J]. Corrosion Science, 2004, 46 (12): 3041- 3055.
LOPEZ-HIRATE V M , ARCE-ESTRADA E M . Characterization of Co-Cu mechanical alloys by linear sweep voltammetry[J]. Electrochimica Acta, 1997, 42 (1): 61- 65.