Effects of low-temperature coating process on mechanical behaviors of ADI

Austempered ductile iron (ADI) is an austemper-treated ductile iron with acicular ferrite and high-carbon austenite as the matrix of microstructure. In general, the austempering is isothermally treated about in the temperature range from Ms to 450 °C, thus the traditional case hardening of high temperature cannot be available to treat ADI. In recent years, physical vapor deposition (PVD) technique using lower processing temperature has been widely adopted to coat various films, such as diamond-like carbon (DLC), CrN, TiN and so on, on the engineering material for surface modification. In particular, DLC film possesses excellent mechanical properties such as high hardness and low friction coefficient. Electroless nickel (EN), another lower temperature coating process, has also a wide field of application such as the industrial components and machine parts. Thus, the purpose of this study is to investigate the effect of EN and PVD–DLC surface coatings on mechanical behaviors of ADI, especially the tensile and fatigue properties. Analyses of the resulting films were also performed for correlating the mechanical properties attained to the coating characteristics.