The Research On Corrosion Resistant Of Ni-Cr-Mo-Cu Alloy

As one of three kinds of failure modes of the mechanical components, corrosion of metals connects with all regions of economy directly. Therefore, based on the APF factor method and referencing to nowadays advance corrosion resistant alloys, seven schemes versatile Ni-Cr-Mo-Cu corrosion resistant alloys were designed and prepared by manual electro- arc furnaces in this thesis. Alloys were solution-treated at 1140℃ for 2.5h. Corrosion resistance and mechanisms of these alloys were researched through erosion, electrochemical corrosion and high temperature oxidation.Erosion test of alloys was performed in the solutions of 80% sulphuric acid, 30% hydrochloric acid, mixtural acid (15%HCl+15%H)₂SO₄+10%H3PO4+10%HNO₃) and 15% FeCl₃. Referring to the best versatile alloy, APF equals to 2.875, the influences of type, concentration and temperature of acid were studied, the activation energy of corrosion in solutions of acids were calculated and corrosion products were observed and analyzed by SEM, optical microscopy and EDS respectively. The results show that corrosion rates of alloys rise with the increasing of concentration and temperature of acid;Corrosion activation energy of alloys in the solutions of 80% sulphuric acid, 30% hydrochloric acid, mixtural acid are 75.389KJ/mol, 75.114KJ/mol and 114.517KJ/mol respectively;Alloys have the best corrosion resistant property in these three kinds of acids at room temperature;The erosion behavior of alloy in sulphuric acid belongs to general corrosion, pitting corrosion happened when alloy was put in hydrochloric acid, and the content of Mo decreases in these places.The anodic polarization curves in different electrolyte solutions were measured by the experiments of electrochemical corrosion. The actions of all elements in alloy were analyzed by discovering the changes of corrosion potentials, corrosion current density, passivation potentials and passivation retaining current density in different of alloys and in different electrolyte solutions. The result shows that in 80% sulphuric acid, with the rising of Cr content, the corrosion current density, critical passivation current density and passivation retaining current decrease, it shows that the corrosion resistance of Ni-Cr-Mo-Cu alloy increases with the rising of Cr content;Interaction of Mo and Cr makes the alloy with more Mo passives first and the passivation retaining current density is lower, the passive film prolongs the happening of pitting corrosion in hydrochloric acid;Corrosion potentials of alloy in 80% sulphuric acid is higher than that in 30% hydrochloric acid, while passivation potentials is lower, which shows thatthe corrosion phenomena of alloy in 30% hydrochloric acid solution is more serious than that in 80% sulphuric acid. There is no transpassivation in mixtural acid.The anti-oxidation behaviors of Ni-Cr-Mo-Cu alloy were studied by thermogravimetric method at 600 "C, 800 °C and 1000°C respectively. The profile morphologies and phase structure of oxidation layers were observed and analyzed by SEM and XRD, and oxidation curves was fit the by least-square method. The result shows that the oxidation curves of Ni-Cr-Mo-Cu alloy show cubic parabola type and oxidation activation energy is 200.25KJ/mol, the main oxiding products are NiCK Cr2C>3 and NiC^O^ Cr2O3 was formed at the beginning, then NiO and NiCr2C>4 were formed slowly, C^Ch and NiC^O* prevent the diffusion of metal ions effectively, So that Ni-Cr-Mo-Cu alloy shows excellent anti-oxidation in high temperature for long times.