Friction Stir Surfacing of Stainless Steels

Abstract

Stainless steels are among the most commonly used metals in engineering and construction. However, most types of stainless steels cannot show superiorperformancesin both hardness and corrosion resistance. Friction Stir Surfacing is a novel solid-stated processing technique, which can be applied to stainless steel. Previousstudies show that bothhardness and corrosion resistance of stainless steel canbe improved after friction stir surfacing. Thus, in this project, we mainly focused on fabricate and analyze stainless steel coatings. In particularly, we chose SS316L to be the major type of stainless steel to study. Besides SS316L, SS201, SS420, SS416, and SS630 were also involved in this project. We engaged in finding the optimum parameters to fabricate coatings for each grade. And those stainless steel coatings were analyzed by a variety of instruments, which includes optical microscope (OM), scanning electron microscope (SEM), X-ray diffraction (XRD), and electron backscatter diffraction (EBSD).Besides microstructure analysis, we also conducted Vickers hardness test and corrosion test, which includes open circuit potential (OCP) test, cyclic polarization (CP) test, and electrochemical impedance spectroscopy (EIS) test, for those sample coatings. And the versatile results generated by EBSD data analysis could be used to explain results shown in hardness tests and corrosion tests. Besides that, intermetallic alloy coatings werefabricated by using friction stir alloying technique in this project as well. Titanium Boride were added into steels to form alloyed coatings that contain Fe-Ti and Cr-Bcomposites. Cooper was added into SS316L to form copper-rich alloyed coatings. Moreover, SS630 sticks was inserted into SS316L rods to fabricate duplex stainless steel coatings. Lastly, by inserting stainless steel with high stacking fault energy into SS420 and SS2205 rods, alloyed coatings can also be fabricated successfully, although pure SS420 and SS2205 are not capable to form coatings in friction stir surfacing.Those alloyed coatings were undergone same analysis as those pure coatings.