Properties of HVOF-sprayed Stellite-6 coatings

Abstract

Stellite-6 coatings were deposited onto AISI 304 stainless steel substrate by gas-fueled HVOF spraying, systematically varying the process parameter settings. By operating the HVOF torch with a fuel-rich mixture, dense coatings (<1% porosity) are produced, containing up to ≈3 vol.% oxide inclusions. A substantial amount of a Cr-rich f.c.c. phase is found, mainly produced by quenching of molten lamellae, and distinct from the equilibrium, Co-based f.c.c. solid solution retained in unmelted particles. These coatings exhibit pseudo-passive behavior and survive 5 cycles (100 h) of the Corrodkote test (ASTM B380-97) with no substrate corrosion. Coatings obtained from oxygen-rich mixtures, on the other hand, contain fewer oxide inclusions but also greater porosity, and do not protect the substrate against corrosion. The wear behavior of the coatings is less influenced by deposition conditions. In ball-on-disk dry sliding tests, all coatings exhibit wear rates of 2-3 × 10-5 mm 3 /(N•m), higher than those reported for bulk or clad Stellite, because of interlamellar delamination. Strain-induced, "martensitic" phase transformation from the f.c.c. structure to a h.c.p. one is observed over a 1-2 µm depth below the contact surface. Additional tribo-oxidation is onset when frictional heat dissipation has heated the wear debris enough to trigger its reaction with the environment. Correspondingly, a transition to a regime of higher friction occurs (from ≈0.6 to ≈0.8). At 400 °C, lamellar delamination is suppressed but wear rates rise to 5-8 × 10-5 mm 3 /(N•m) because of abrasive and adhesive wear. At 800 °C, a dense "glaze" tribofilm is formed by sintered debris particles, firmly bonded to a thermally grown oxide scale on the underlying metal surface. The "glaze" protects the coating, lowering the wear rate to ≈1×10-5 mm 3 /(N•m) and the friction coefficient to <0.45. Under high-stress particle abrasion conditions, wear rates of ≈1×10-3 mm 3 /(N•m) are found.

Sliding Wear Behavior of Fe-Al Coatings at High Temperatures

“…Zhu et al [41] reported a decrease of wear rate of undoped Fe-40Al with increasing temperature up to °C. Other authors have reported that more rapid oxidation at 800 °C than at 400 °C may stabilize the adhesion of the oxide layer reducing friction [42]. °C.…”

Effects of Cobalt Content on the Microstructure, Mechanical Properties and Cavitation Erosion Resistance of HVOF Sprayed Coatings

“…The obtained hardness value of cobalt-based alloy coating was 553 HV 0.3 , which was attributed to the coating with the dense structure and the Co-based fcc-phase, as shown in Figure 8. The Cr-rich M 7 C 3 phase was visible in the coating XRD patterns [19,20]. The hardness of the WC-12Co and WC-17Co coatings were found to be higher than that of the cobalt-based alloy coating, which was due to the distribution of the WC particles in the matrix friction that acted as a hardness reinforcement [21][22][23][24].…”

Effects of lateral and vertical ultrasonic vibrations on the microstructure and microhardness of Stellite-6 coating deposited on Inconel 718 superalloy through laser metal deposition

“…Wear-resistant Stellite coatings are applied by various methods such as thermal spraying [9], gas tungsten arc welding (GTAW) [10], plasma transferred arc (PTA) [11], flame spraying [12], and laser metal deposition (LMD) [13]. LMD is a laser cladding approach which can be used to fabricate functional, three-dimensional components.…”