Formation of Expanded Austenite on a Cold-Sprayed AISI 316L Coating by Low-Temperature Plasma Nitriding
- PDF / 1,927,935 Bytes
- 9 Pages / 593.972 x 792 pts Page_size
- 104 Downloads / 219 Views
Shinichiro Adachi and Nobuhiro Ueda (Submitted April 15, 2015; in revised form June 19, 2015) Low-temperature plasma nitriding at temperatures below 450 °C is commonly applied to austenitic stainless steels to enhance wear resistance, while maintaining corrosion resistance, by forming expanded austenite (known as the S-phase). In this work, low-temperature plasma nitriding of cold-sprayed AISI 316L coatings was examined. A cold-spray technique was developed to produce metal coatings with less oxidation. However, the cold-sprayed AISI 316L coating obtained by use of nitrogen gas as propellant contained many interconnected pores and cracks, and was, consequently, unsuitable as an anticorrosive coating. Therefore, laser post-treatment was used to modify the coating and increase its density to similar to that of bulk steel. The anticorrosive performance of this coating on a carbon steel substrate in NaCl solution was substantially improved. Subsequent low-temperature plasma nitriding enhanced the wear resistance by two orders of magnitude. It is concluded that cold-sprayed AISI 316L coatings treated by laser post-treatment and subsequent low-temperature plasma nitriding could be used as protective coatings under severe wear and corrosion conditions.
Keywords
cold spray, corrosion resistance, laser remelting, plasma nitriding, wear resistance
1. Introduction It has been reported that low-temperature nitriding below 450 C can improve the surface hardness of austenitic stainless steel by producing expanded austenite on its surface. The expanded austenite is usually called the S-phase and is formed by dissolution of a substantial amount of nitrogen in the face-centered cubic (FCC) lattice of austenitic stainless steels, rather than by formation of nitrides. The S-phase is extremely hard, has superior wear resistance, and has excellent corrosion resistance similar to that of ordinary austenitic stainless steel, because the S-phase contains little chromium nitride (Ref 1–13). Thermally sprayed austenitic stainless steel coatings have superior corrosion resistance and are used as corrosion-protective coatings (Ref 14). However, the hardness This article is an invited paper selected from presentations at the 6th Asian Thermal Spray Conference (ATSC 2014) and has been expanded from the original presentation. ATSC 2014 was held in Hyderabad, India, November 24–26, 2014, and was organized by the International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI) and the Asian Thermal Spray Society. Shinichiro Adachi and Nobuhiro Ueda, Technology Research Institute of Osaka Prefecture, 2-7-1 Ayumino, Izumi 594-1157, Japan. Contact e-mail: [email protected].
Journal of Thermal Spray Technology
of such coatings is only approximately 300 HV; therefore, they are used under low-friction conditions only. We have previously examined plasma-sprayed austenitic AISI 316L stainless steel coatings and shown that the surface hardness can be enhanced by low-temperature plasma nitriding and carburizing (Ref 15–17). Fo
Data Loading...
