| Coating is the material carrier of thermal spraying technology which is one of the key technologies in the field of surface engineering.As an important index to evaluate the quality of the coating,bonding strength is key factors that affect the coating service security.With the wide application of thermal spraying technology,it is urgent to develop a kind of field tester which is simple,convenient and efficient to measure the bonding strength of coating.Coating damage behavior study and mechanism analysis under the effect of surface indentation is the foundation to realize the rapid and accurate measuring bonding strength of coating.In this paper,two different principle of bonding strength instruments of static load and impact were autonomously developed by using acoustic emission technology in combination with surface indentation.Through the instruments,the coating failure mechanism was studied,the distribution of acoustic emission signals in the process of failure of coating was analyzed and the statistical model between acoustic emission signal and coating bonding strength was established.The results showed that:(1)Through the process optimizing,bonding strength differences of three kinds of coating of alloy coating,ceramic coating with transition coating and ceramic coating without transition coating were prepared by the high-effect supersonic plasma spraying technique.The compositions and basic properties of surface coatings were characterized and tested.The results showed the coatings were uniform and dense with low porosity,hardness and bonding strength were significant differences,the performance of coating met the experimental requirements.(2)Two different principle of bonding strength instruments of static load and impact were autonomously developed.The process of static load type bonding strength tester could be precise control because the load and depth could be adjust.Field tests of coating bonding strength could be implemented by impingement bonding strength tester,which was easy processing,easy to carry,simple operation and impact strength can be adjusted.(3)The parameter of bonding strength tester was optimization.The regularities of distribution of acoustic emission signal in the loading process were analyzed.AE amplitude was very sensitive to material micro deformation,energy count and waveform voltage were more sensitive to fracture failure of the coatings.Type and thickness of coating on the influence of the acoustic emission signal was ed,head shape and impact kinetic energy were optimized.Comparison of two different principles of bonding strength tester,static load type bonding strength tester was difficult to effectively induce coating failure and easy generation pseudo acoustic emission signal because its loading process was relatively slow,which partly affected the reliability of the coating bond strength test.Impingement bonding strength tester effectively avoided the generation of wrong acoustic emission signal and ensured the reliability of the coating bonding strength test results because it was easy to induce coating failure.(4)Substrate and three kinds of coating were tested by impingement bonding strength tester.The surface morphology of indentation,the combination failure mechanism of coating and the regularities of distribution of acoustic emission signal were analyzed.The main influence of indentation morphology was the coating bonding strength,the coating bonding strength was greater,the size and crack or flake of the indentation was smaller.The combination failure mechanism of different coatings was difference,alloy coating was given priority to interface crack,ceramic coating without transition coating was given priority to coating fracture and with a certain interface craze,ceramic coating with transition coating between the transition coating and substrate was given priority to interface crack,between the ceramic layer and transition coating was given priority to coating fracture and with a certain interface craze.Acoustic emission signals were relatively sensitive to coating combination failure,the coating bonding strength was greater,the acoustic emission signal was smaller.Acoustic emission energy count was suitable for representation the coating bonding strength,acoustic emission amplitude and waveform voltage were suitable for checking result.(5)Acoustic emission signal of all coatings was cluster by k-means clustering algorithm,which clearly distinguished the different bonding strength three kinds of coating and substrate and proved that the coating bonding strength and the acoustic emission signal occurring in the process of impact had a close inner link.Mathematical relation models of bonding strength-energy count,bonding strength-amplitude and bonding strength-waveform voltage were established by regression analysis.y=exp(2225÷x+2.7)was the mathematical expressions of bonding strength-energy count,which could be used to calculate the coating bond strength.y=exp(740÷x-4.5)was the mathematical expressions of bonding strength–amplitude,which could be used to inspection results.y=exp(1.868÷x+3)was the mathematical expressions of bonding strength-waveform voltage,which could be used to further inspection results. |
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