Structural, Wear and Corrosion Properties of Nitrided, PVD and Electroless Ni-B Coated EN-GJS-700-2 Cast Iron

Abstract

The structural properties, surface hardness, wear and corrosion behaviors of plasma- and gas-nitrided, PVD TiN coated and electroless Ni-B coated EN-GJS-700-2 (GGG-70) grade ductile cast iron (DI) were investigated in detail. The structural properties were examined with an optical microscope, a scanning electron microscope and x-ray diffraction. The surface hardness was tested with Vickers microhardness tests; the wear behavior was investigated by ball-on-flat linear reciprocating abrasion/friction tests and the corrosion behavior was studied by electrochemical tests. The 1.95 & micro;m PVD TiN coating had the hardest surface hardness with 2782 HV0.001 value. All nitrided and coated specimens exhibited better wear and corrosion resistance than the DI-substrate. The PVD TiN coating demonstrated the best wear resistance with the lowest wear loss (0.231x10(-3) mm(3)) and the lowest friction coefficient value (0.16). Corrosion tests revealed that electroless Ni-B-coated specimens (0.002 mm/year corrosion rate) and nitrided specimens (0.002 mm/year for plasma- and 0.076 mm/year corrosion rate for gas-nitrided) showed excellent corrosion resistance, while the PVD TiN-coated specimen (0.673 mm/year corrosion rate) showed moderate corrosion protection0020.