Abstract
Abstract In this work, the substrate, NiCr coating, Al2O3 coating with NiCr undercoating and Al2O3 coating were tested by an impact indentation device equipped with an acoustic emission (AE) detection equipment. The surface morphology, dimension, cross-sectional image, 3D topography of indention and bonding strength of coatings were analyzed. The failure mechanism and AE signal characteristics of the coatings under impact were studied. The results demonstrate that the failure mode of NiCr coating was dominated by interface cracking, and that of Al2O3 coating is fracture and accompanied by a small amount of interface cracking, while Al2O3 coating with NiCr undercoating possesses common characteristics of the first two. The energy counting and wave voltage of AE signal were more sensitive to the bonding strength of coating in the impact process, which can be used to characterize the bonding strength of coating.
Highlights
Thermal spraying technique has been widely used in various mechanical parts as a surface modification technique
The results demonstrate that the failure mode of NiCr coating was dominated by interface cracking, and that of Al2O3 coating is fracture and accompanied by a small amount of interface cracking, while Al2O3 coating with NiCr undercoating possesses common characteristics of the first two
In previous research, which we have carried out, we demonstrated that the process of static load indentation was too moderate to induce the failure of the coating effectively, which led to the extracted signal showing greater dispersion
Summary
Thermal spraying technique has been widely used in various mechanical parts as a surface modification technique. Song [5] proposed that an ideal method to detect the bonding strength of coating needs to meet at least two basic conditions: one is the model that characterizes the failure between the coating and the substrate; the other is the characteristic parameters which can response to the failure of the coating. Based on this idea, we have adopted the approach of "static load indentation + AE detection" to measure the bonding strength of coating, which can provide theoretical basis and experimental support for "indentation method +AE detection "[6,7,8]. Spraying current (A) Spraying voltage (V) Spraying distance (mm) Delivery amount (g/min)
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