Research On Electrochemical Corrosion Behavior Of Ni₄₇Ti₄₄Nb₉ Shape Memory Alloy

Nitinol-based shape memory alloys are gradually favored by more equipment manufacturing fields because of their stable shape memory functions.Ni47Ti44Nb9 shape memory alloys have been used as pipe joints in aircraft hydraulic systems and undersea oil pipeline systems.The marine environment has higher requirements for the corrosion resistance of metals.The presence of chloride ions and sulfate ions easily penetrate the metal passivation film,destroying the growth of the passivation film and causing different degrees and different forms of corrosion on the metal surface.In this environment,when a pipe joint is connected to a dissimilar metal,the existence of a potential difference due to the different open circuit potentials of the metals will cause galvanic corrosion.At this time,the anode metal with a lower potential loses ions and undergoes an oxidation reaction,causing serious corrosion damage.Therefore,the electrochemical corrosion of Ni47Ti44Nb9 by electrochemical measurement technology,zero resistance galvanometer measurement technology,weight loss method,tow electrode technology,surface analysis technology,etc.,and the coupling between Ni₄₇Ti₄₄Nb₉ and aluminum alloy 3A21 commonly used in aircraft hydraulic pipelines The galvanic corrosion behavior of a pair of Ni₄₇Ti₄₄Nb₉ and X80,a metal commonly used in long oil pipelines,has been studied in depth.The research shows that under the influence of different temperature environments,different chloride ion concentration environments,and different sulfate ion environments,the corrosion performance of Ni₄₇Ti₄₄Nb₉ and its pairs is mainly as follows:?1?The fitting circuit of the electrochemical corrosion process of Ni₄₇Ti₄₄Nb₉ is R?CR?O.The process is affected by the difference between the growth and destruction speed of the passivation film.The main component of the formed which will precipitate on the metal surface under different environmental influences.The unstable massive?Ti,Nb?₂Ni phase is corroded by intergranular corrosion in local corrosion,and the degree of corrosion is slight.The corrosion current density values of Ni₄₇Ti₄₄Nb₉ after the final stabilization in each environment in the experiment are in descending order::60?>Dual ion>3.5%Cl^->40?>1.5%SO₄^2->20?>3.5%SO₄^2->10?>6.5%SO₄^2->6.5%Cl^->1.5%Cl^-.The corrosion current density of Ni₄₇Ti₄₄Nb₉ increased significantly when chloride ion and sulfate ion double ion were mixed,and finally stabilized at about 0.8?A/cm2,which was about 2.5times that of each single ion.?2?For Ni₄₇Ti₄₄Nb₉-3A21,the current density of the galvanic couples in each en vironment is sorted in descending order:6.5%Cl^->60?>40?>3.5%Cl^->1.5%Cl^->1.5%SO₄^2->20?>6.5%SO₄^2->3.5%SO₄^2->10?>Dual ions;Ni₄₇Ti₄₄Nb₉-X80 even pair in each envi ronment The order of galvanic current density between the even pairs is:60?>40?>6.5%Cl^->20?>3.5%Cl^->1.5%Cl^->10?>Dual ions>3.5%SO₄^2->1.5%SO₄^2->6.5%SO₄^2-.Amon g them,pitting is the main form of even-pair anode corrosion,and the surface of ev en-pair cathode Ni₄₇Ti₄₄Nb₉ is relatively intact.?3?With the increase of the cathode area ratio in the pair,the current value of the galvanic current between Ni₄₇Ti₄₄Nb₉-3A21 appears quickly.At this time,the area ratio of the cathode and anode is 1:1.Before this value,the galvanic area increases with the cathode area.The even current density also increases,and the corrosion rate of Ni₄₇Ti₄₄Nb₉ is always small;the pitting zone on the surface of the pair of anodes X80 in Ni47Ti44Nb9-X80 shows the deepening and expansion of pitting spots with the increase of chloride ion concentration,and the development of pitting areas is corroded Product attachment and shedding effects.