Laha et al. [25], the carbide formation in this flame spray system
would be less. In addition, by comparing the standard X-ray peaks of
carbides of iron, nickel, and chromium, there were no high-intensity
peaks in those patterns which would match the possible peak near
2θ–36°. The closest match found seemed to be either oxide of Cr or Fe,
which from SEM micrographs, these phases were also present. Hence,
at the moment, it could be concluded that carbide formation was
possible but only very limited.
Vickers hardness values of stainless steel and SS/CNT composite
coatings are listed in Table 3. The composite coating was harder than
the stainless steel coating by about 58%. Considering the amount of
oxide content in SS coating (~21± 3.4%) and SS/CNT coating (24±
4.5%), these values were not significantly different and this should not
cloud the effect of CNTs on the mechanical properties of stainless
steel. The hardness measurement was also carried out for ten
sampling points and an average value for each sample was obtained.
Hence, the improvement of the SS/CNT coating over the SS coating
was apparent. This superior hardness was therefore mainly caused by
an incorporation of CNTs with only a small influence from oxide
phases. Moreover, CNTs could hold the splats by bridging mechanism
and thus minimized intersplat movement upon an application of load
[20,32]. Apart from this, it has been well understood that the CNTs
have extremely high value of Young's modulus (~1 TPa) and thus
dispersion of CNTs in the stainless steel matrix in this case would
allow elastic recovery of indentation [33] which consequently
improved hardness of the composite coating.
Friction coefficient measured at room temperature of stainless
steel and SS/CNT composite coatings were ~0.6 and ~0.2, respectively.
These values were determined from the average values of the stable
friction period based on the plot of friction coefficient evolution as a
function of sliding distance as shown in Fig. 13. These observed
friction coefficient values were in agreement with their wear
behaviors. Topologies of wear tracks after 150 m sliding distance are
shown in Fig. 14. The average track width of the stainless steel coating
was ~300 μm which was wider than the track of composite coating
(~260 μm). Microstructural investigation within wear scars revealed a
smoother damage surface of the composite coating compared to a
more severe worn surface of the stainless steel coating as illustrated in
Fig. 15. Wear scar of the stainless steel coating was rather rough,
suggesting an occurrence of oxidative wear type due to thermal
oxidation during the wear test. Since the stainless steel coating did not
Laha et al. [25], the carbide formation in this flame spray systemwould be less. In addition, by comparing the standard X-ray peaks ofcarbides of iron, nickel, and chromium, there were no high-intensitypeaks in those patterns which would match the possible peak near2θ–36°. The closest match found seemed to be either oxide of Cr or Fe,which from SEM micrographs, these phases were also present. Hence,at the moment, it could be concluded that carbide formation waspossible but only very limited.Vickers hardness values of stainless steel and SS/CNT compositecoatings are listed in Table 3. The composite coating was harder thanthe stainless steel coating by about 58%. Considering the amount ofoxide content in SS coating (~21± 3.4%) and SS/CNT coating (24±4.5%), these values were not significantly different and this should notcloud the effect of CNTs on the mechanical properties of stainlesssteel. The hardness measurement was also carried out for tensampling points and an average value for each sample was obtained.Hence, the improvement of the SS/CNT coating over the SS coatingwas apparent. This superior hardness was therefore mainly caused byan incorporation of CNTs with only a small influence from oxidephases. Moreover, CNTs could hold the splats by bridging mechanismand thus minimized intersplat movement upon an application of load[20,32]. Apart from this, it has been well understood that the CNTshave extremely high value of Young's modulus (~1 TPa) and thusdispersion of CNTs in the stainless steel matrix in this case wouldallow elastic recovery of indentation [33] which consequentlyimproved hardness of the composite coating.Friction coefficient measured at room temperature of stainlesssteel and SS/CNT composite coatings were ~0.6 and ~0.2, respectively.These values were determined from the average values of the stablefriction period based on the plot of friction coefficient evolution as afunction of sliding distance as shown in Fig. 13. These observedfriction coefficient values were in agreement with their wearbehaviors. Topologies of wear tracks after 150 m sliding distance areshown in Fig. 14. The average track width of the stainless steel coatingwas ~300 μm which was wider than the track of composite coating(~260 μm). Microstructural investigation within wear scars revealed asmoother damage surface of the composite coating compared to amore severe worn surface of the stainless steel coating as illustrated inFig. 15. Wear scar of the stainless steel coating was rather rough,suggesting an occurrence of oxidative wear type due to thermaloxidation during the wear test. Since the stainless steel coating did not
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