Corrosion Behavior Of Cu-10Ni Aolly After Surface Mechanical Attrition Treatment

By means of surface mechanical attrition treatment(SMAT), a nanostructured surface layer was formed on Cu-10Ni plate. And Cu-10Ni alloys with different grain size on nano-surface layer were prepared by SMAT. Microstructure features of nano-surface layer were systematically characterized by using X-ray diffraction (XRD) analysis, Optical microscope (OM) and Micro-hardness tester. Electrochemical polarization curve, electrochemical impedance spectroscopy(EIS) methods and XRD(X-ray diffraction), SEM(scanning electron microscope), EDS (energy-dispersive spectroscopy) technique were used to experimentally investigate the electrochemical corrosion behavior of surface nanocrystallization Cu-10Ni alloy in acid sodium sulfate solution(0.05mol/L Na2SO4+0.05mol/L H2SO4), in aicd solution containing chlorines(0.05mol/L Na2SO4+0.05mol/L H2SO4+0.5mol/L NaCl) and in different acid solution. The influence of annealing on corrosion behavior of surface nanometer Cu-10Ni alloy was also studied. The differences on corrosion properties of surface nanometer Cu-10Ni alloy in aici solution containing chlorines and no-containing chlorines were analysed simply.The results showed that:(1) By means of surface mechanical attrition treatment(SMAT), a nanocrystalline(NC) surface layer was obtained on Cu-10Ni Alloy. The cross-sectional grain size of Cu-10Ni alloy subjected to SMAT increased gradually as the depth increased. When the treatment time was90min, the average grain size on the treated surface of the sample achieved the smallest size of31.03nm. The micro-hardness on the surface was228MPa when the sample was processed for120mins, which was0.52times harder than that of the matrix.(2) In0.05mol/L Na2SO4+0.05mol/L H2SO4aqueous solution, the Cu-10Ni alloy with surface nanometer crystallization had lower corrosive resistance than the coarse Cu-10Ni alloy. And the corrosion rate became faster than the original coarse sample. As the treatment time prolonged, the corrosion property of the Cu-10Ni alloy decreased gradually. XRD showed that there was Cu2O on the corrosive surface of the SMATed Cu-10Ni alloy, but on the corrosive surface of the original coarse sample there wasn’t. EDS showed that the ingredient of the corroded surface of the SMATed samples contained a small amount of S.(3) In the different acid aqueous solution, the corrosion rate of Cu-10Ni alloy after SMATed for60min became faster with the increasing of the concentration of H+, which indicated that the increase of H+prompted the corrosion reaction.(4) In0.05mol/L Na2SO4+0.05mol/L H2SO4aqueous solution, the corrosion property of the SMAT60sample, annealed6hours at200℃, was improved compared to the not annealing sample. But to the original sample, the corrosion behavior of the annealed sample still decreased. It revealed that grain refinement and micro-strain formed during the process had effect on the corrosion property of the Cu-10Ni alloy subjected to SMAT, but maybe the grain refinement was the primary factor which resulted in the speed-up of the corrosion rate.(5) The corrosion behavior of the Cu-10Ni alloy subjected to SMAT decreased in the0.05mol/L Na2SO4+0.05mol/L H2SO4+0.5mol/L NaCl mixture solution compared to the coarse sample. The corrosion products were CuCl and Cu2O and there were more corrosion products on the SMATed samples than the original sample.The corrosion property of Cu-lONi alloy after SMATed for60min was poorer in0.05mol/L Na2SO4+0.05mol/L H2SO4+0.5mol/L NaCl solution than in0.05mol/L Na2SO4+0.05mol/L H2SO4solution. It demonstrated that the Cl-was more destructive to the nanometer surface of the Cu-10Ni alloy.(6) The EIS of the original sample is composed of single capacitive loop, therefore corrosion process was controlled by electrochemical reaction. The EIS of the SMAT60sample was consist of double capacitive loop and had two time constant. The EIS of the SMAT60annealed sample composed of high frequency capacitive loop and low frequency warburg impedance.