Microstructural and Tribological Behavior of Pack-Borided Ni-Based Hastelloy C-276 Superalloy

Abstract

Although the toughness and corrosion resistance of Ni-based superalloys are high due to their face-centered-cubic structure, their surface hardness and, thus, wear resistance are not satisfactory. The boriding process is an attempt to overcome the limitation of Ni-based superalloys in tribological applications. In this study, the boride layer was grown on Hastelloy C-276 Ni-based superalloy at 975 & DEG;C for 5 and 7 hours by powder-pack boriding to improve wear resistance. Formed boride layers were characterized using a scanning electron microscope (SEM) equipped with energy-dispersive spectroscopy (EDS), X-ray diffractometry (XRD), and nanoindentation. To investigate the effect of boride layers on the wear resistance, untreated and borided surfaces were reciprocated against an alumina ball using a pin-on-disk tribometer, at a velocity of 60 mms(-1), a stroke of 15 mm, a sliding distance of 300 m under loads of 5, 10, and 20 N. The results showed that the thickness of the boride layer increased at the boriding temperature elevated, which was in the range of 86.5 to 132.7 mu m. The hardness of the coatings was observed to be 2016 to 2210 HV0.1. The boriding process caused a decrease in friction coefficients by 13 to 27 pct and an increase in wear resistance by 44 to 67 times at different applied loads. As dominant wear mechanisms, untreated C-276 found abrasive wear and plastic deformation, while in the borided samples, the wear mechanisms changed to oxidation-assisted delamination. In conclusion, the boriding process improved the hardness, modulus of elasticity, and wear performance and, therefore, the service life of Hastelloy C-276.