Effect of thermal degradation on the properties and wear behavior of Cr-V-C composite coatings grown on ductile iron

The thermal fatigue behavior of chromium vanadium carbide (Cr - V - C) coatings and the wear of the coatings after thermal fatigue cycling was studied. The Cr - V - C coatings were grown on the surface of a ductile iron using thermo-reactive diffusion (TRD) and subjected to thermal fatigue in the temperature range of 25 to 750 degrees C for up to 500 cycles. Characterizations were made using scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, microhardness measurements and wear tests. The Cr - V - C coated samples displayed superior thermal fatigue and wear resistance compared to the untreated ductile iron, mainly due to the dissolution of graphite nodules in the vicinity of the surface during TRD. The dissolution of graphite reduced the possibility of failure initiating from graphite nodules and graphite-matrix interfaces. Increasing the number of cycles resulted in increased flaking and decreased wear resistance in both the Cr - V - C coatings as well as the untreated ductile iron. Although much of the Cr V C coating was lost (due to flaking) after thermal cycling, the absence of graphite near the surface still provided improved resistance to wear in the TRD-treated samples. The results of this study indicate that TRD coatings hold great promise for use in the industrial applications.