Laser Cladding of Stellite Alloys

Abstract

Metal components often operate in a corrosion and wear combined environment, which results in surface-initiated failure. Therefore, any approach that improves surface performance can extend the service life of the components. Laser cladding (LC) as an advanced surface modification technique has been widely employed in surface engineering. Stellite alloys are cobalt-based superalloys, displaying exceptional properties such as high-temperature strength, corrosion/oxidation, and wear/erosion resistance. They have a wide range of applications, for example, Stellite 6 a common material for the seat surface enhancement of various control valves, and Stellite 21 is often used for valve trims under high-pressure steam. In this chapter, the wear and corrosion performances of conventional and novel Stellite alloy hardfacings, which are prepared via laser cladding, are studied. The microstructures of the hardfacings are characterized using scanning electron microscopy (SEM) with an EDAX energy-dispersive X-ray (EDX) spectroscopy and X-ray diffraction (XRD). The wear properties of the hardfacings are evaluated on a pin-on-disk tribometer in dry-sliding mode. The corrosion performance of the hardfacings is investigated under electrochemical tests in various corrosive media such as morpholine solution with pH 9.5, to simulate the amine environment of boiler feedwater in power generation industry, 3.5 wt% NaCl solution, which is a common corrosive solution used to rank materials for corrosion resistance, and Green Death solution, representing the typical industry corrosive environment. It is demonstrated that novel Stellite alloy mixture (70 wt% Stellite 3 and 30 wt% Stellite 21) hardfacings, Stellite 22 and Stellite 728, are all superior to corresponding conventional Stellite 6 and Stellite 21 hardfacings, respectively, with respect to hardness, wear, and corrosion resistance.