Reseach On Microstructure And Properties Of Pure Zirconium By Friction Stir Processing

Pure zirconium,a key structural materials in chemical industry,beacause of its good mechanical properties and high corrosion resistance.In this paper,pure zirconium was prepared to gain fine-grained microstructure by friction stir processing(FSP);the microstructure was charactered by OM,EBSD and XRD,including grain size and texture.In addition,the mechanical properties(microhardness,tensile properties)and corrosion properties were examined.The main conclusion was as follows:The sound and non-defect surface was obtained by FSP,with rotation rate of 300 r/min and traverse speed of 118 mm/min.The grain size was refined from 21 ?m to 3.7 ?m after FSP.The c axis of(0002)texture was rotated to PD(Processing direction,PD)of ~40°,and the texture strength was raised from 6.31 to 50.9.Moreover,the high angle grainbouderies were increased after FSP.The average microhardness of SZ(Stir zone,SZ)was obviously increased by 58.6%,compraring to BM(Base materials,BM).In addition,the strength of PD was higher than that of TD(Tranverse direction,TD).This anisotropy phenomenon was caused by the difference of grian orientation or texture.Prism slip was the main deformation mechanism at room temperature.Comparing to BM,the yeiled strength along PD was increased by 153.4% after FSP;this may be attributed by grain refinment and strong basal texture.Electrochemical corrosion properties were characterized in CH3 COOH and H2SO4 solution.The passive phenomenon was both observed in anode,however,the difference was found in cathode,mainly for oxygen reduction reaction in CH3 COOH solution and for hydrogen evolution reaction in H2SO4 solution.Corrosion current density was decreased by 23.3% and 13.4% for BM and FG samples,respectively.The immersion corrosion properties were also characterized in CH3 COOH and H2SO4 solution.The FG samples show the tiny pittings in CH3 COOH solution,and a less degree corrosion morphology in H2SO4 solution.The corrosion rate of FG samples was dropped by 56.8% and 30.4% in CH3 COOH and H2SO4 solution.The corrosion products were consisted of ZrO2,ZrH2 and ZrH in both solutions.In addition,the main corrosion mechanism was pitting and comprehensive corrosion,resipectively.The elevated corrosion resistance was mainly contributed by grain refinement and strong basal texture.