Studies On Stress Corrosion Behaviour Of Ultra-fine Grain Cu-Cr-Zr Alloys

Cu-Cr-Zr alloy are widely used in various fields of national production for their excellent electrical conductivity and corrosion resistance.In the process of application,materials often beared the corrosive liquid environment and the action of stress causing stress corrosion and fracture easily.The improvement of strength by grain refinement and heat-treatment is to adapt different using requirements of Cu-Cr-Zr alloy.The corrosion properties effection of grain refinement and aging heat-treatment of Cu-Cr-Zr alloy has to be studied.Therefore,in these paper,the electrochemical corrosion by means of polarization curve and impedance analyses the corrosion resistance involving coarse and Ultra-fine grain(UFG),aging and solution,and different corrosive media.The slow strain rate testing(SSRT)through scanning electron microscope and optical microscope analyses the corrosion resistance and the fracture mechanism in different media environments of Cu-Cr-Zr alloy.The main research results are as follows:(1)The electrochemical experiment of Cu-Cr-Zr alloy in 0.5 M and 1 M and 5 M solution containing chloride ion showed that with the increase of Cl~-concentration,the increased of current density of Cu-Cr-Zr alloys,and the reduced of corrosion resistance of aging UFG and coarse grain Cu-Cr-Zr alloys.The corrosion resistance of aging coarse crystals was better than that UFG Cu-Cr-Zr alloy in 1M sodium chloride solution.The coarse crystal samples of aging treatment have better corrosion resistance than that un-aging heat-treatment.while the corrosion resistance of un-aging UFG Cu-Cr-Zr alloy is better than that aging samples.(2)The slow tensile curves under different strain rates showed that the yield strength and tensile strength decreased and the elongation increased of Cu-Cr-Zr alloy of coarse crystal and superfine crystal with the decrease of strain rate.The SSRT in the 1 M sodium chloride solution showed that the relative plastic damage(I_?)and relative strength loss(I_?)in sodium chloride solution was greater than 0.5 M sodium chloride solution.With the increase of Cl~-concentration,the membrane rupture and repair process in 1 M sodium chloride solution caused the reduced of stability of the membrane and the membrane rupture seriously.These progress formed spot corrosion pit easily and the pit under the action of tensile stress forming a larger stress concentration,reducing material plasticity and strength.(3)The results of electrochemical corrosion studied in sodium nitrite solution showed that the corrosion resistance of coarse crystals is better than that of ultrafine crystals,and the corrosion resistance of ultrafine crystals decreasing after aging treatment.The results of SSRT in sodium nitrite solution showed that stress corrosion occurred in coarse crystals in sodium nitrite solution.The stress corrosion cracking sensitivity(SCC)was greater than that of ultrafine crystals.The stress corrosion sensitivity of un-aged superfine crystal is greater than that of aged superfine crystal.(4)The results of electrochemical corrosion study in MS solution showed that the corrosion resistance decreased in MS solution without DHP of aging UFG Cu-Cr-Zr alloy.In MS solution containing DHP,with the increase of DHP concentration,the increases of corrosion resistance.The DHP could build a protective coating films on the metal surface to inhibit anodic dissolution.In the SSRT of MS solution,UFG Cu-Cr-Zr alloy are not easy to undergo stress corrosion in MS solution.In MS solution,due to the addition of DHP into MS solution enhanced the stress corrosion resistance of UFG Cu-Cr-Zr alloy,the increase of plasticity with the increase of DHP content.(5)The results of electrochemical study under three corrosion solution environments showed that the corrosion resistance of UFG Cu-Cr-Zr alloy in sodium nitrite solution is better than that of MS solution and NaCl solution.The results of SSRT showed that it is difficult to cause stress corrosion in the three solutions of the aging UFG Cu-Cr-Zr alloy.