Influence Of Rare Earths On Electrochemical Corrosion Resistance And Mechanical Property Of Duplex Coatings Fabricated On Stainless Steel Alloyed With Ti

Austenitic stainless steels are extensively used in applications of petroleum, chemical engineering, pharmaceuticals & foods industry and other modern industry due to their high thermal resistance, antioxygenic property as well as their good mechanical properties. Nevertheless, in some severe environment like corrosive medium, stainless steels are vulnerable to various kinds of corrosion when exposed to salt solution, especially solution rich in Cl-. In addition, surface wear in daily application leads to mass loss of stainless steel for their poor wear resistance, then mechanical property and corrosion resistance of stainless steel decline. Therefore, protecting of stainless steel has become an important issue for domestic and foreign researchers.Simple, convenient and cheaper methods may be more acceptable to improve the corrosion and wear resistance of stainless steel in practice. Pack cementation is an in situ self-generated chemical vapor deposition（CVD） process with low cost and simple process. In our research, Cr/Ti duplex coatings was fabricated on 304 stainless steel by two-step pack cementation, in order to improve the property of outer Cr coating, RE were added to the pack process to make RE-Cr/Ti duplex coatings with the purpose of higher corrosion and wear resistance. The surface and section microstructure were investigated by X-ray diffraction（XRD）, scanning electron microscopy（SEM） and energy dispersive spectrometer（EDS）. It is concluded from all the outcomes that, RE-Cr/Ti coatings with different RE seem compact and uniform. Average thickness was 20μm to 30μm. RE modified Cr coating combined with Ti coating closely by interdiffusion.RE-Cr/Ti coatings trended to be more resistive towards corrosion compared to 304 stainless steel and Ti coating in electrochemical tests. Potentiodynamic polarization curves and electrochemical impedance spectrum（EIS） results show that RE-Cr/Ti coatings has higher corresponding corrosion potential(E_corr) and lower corrosion current density(I_corr), which improve the corrosion resistance by preventing Cl- from corroding. Coatings with different RE vary from each other in some ways. The wear surfaces of 304 stainless steel, Ti coating and RE-Cr/Ti coatings were examined by SEM, the wear mechanism revealed that the present of RE-Cr/Ti coatings promote adhesive wear, which improve the wear property significantly by showing superficial grinding crack. The mechanical properties of specimens were detected by method of nanoindentation. It is concluded that process of RE-Cr/Ti treating has decreased the elastic modulus and hardness, therefore, the RE-Cr/Ti coatings show the ability of elastic recovery against applied load, which provide theoretical basis of adhesive wear in wear tests.