Thermal wave interferometry measurements correlated to microstructural properties and bonding behavior of thermally sprayed coatings

• Published in: Surface & coatings technology 2020-11, Vol.402, p.126298, Article 126298
• Main Authors: Arbogast, Jannik, Schaller, Rolf, Rohde, Magnus, Seifert, Hans Jürgen
• Format: Article
• Language: English
• Subjects: Arc spraying; Automobiles; Automotive engines; Bond testing; Bonding strength; Coatings; Correlation analysis; Cross section microscopy; Cylinders; Diffusivity; Evaluation; Image analysis; Interferometry; Investigations; Linings; Mechanical properties; Microstructural analysis; Microstructure; Morphology; Nondestructive testing; Powertrain; Sprayed coatings; Substrates; Thermal diffusivity; Thermal diffusivity measurements; Thermal wave interferometry; Thermally sprayed coatings; Thermography
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2020.126298

In order to guarantee the life-long functionality of modern combustion engines, the bond strength of thermally sprayed cylinder coatings is one crucial property monitored during the large-scale production of modern power trains. However, since the bond strength between cylinder coating and crankcase substrate can only be measured by destructive off-site testing, a fast and reliable non-destructive method characterizing the bonding behavior of cylinder coatings is highly desired. As the presence of defects in the microstructure lowers the bond strength of cylinder coatings, assessing the defect morphology by non-destructive thermal diffusivity measurements shows promising correlation between thermal and mechanical behavior. Laser-excited lock-in thermography is used to apply thermal wave interferometry (TWI) measurements on wire arc sprayed cylinder coatings of passenger car engines. Measured thermal diffusivity values of these coatings show significant variations along the investigated liners. Further, destructive bonding testing as well as microstructural analysis of the investigated cylinder coatings are acquired to evaluate mechanical and microstructural properties. Investigation of the relationship between thermal diffusivity, bonding behavior and microstructure disclose major correlations between the observed quantities. The application of thermal diffusivity measurements as a non-destructive testing method to evaluate the bond strength of thermally sprayed cylinder coatings is discussed in this work. •Thermal diffusivity of cylinder coatings changes significantly along the liner.•Excessive bonding study reveals major influences of the liner position.•Cross section images are used to evaluate binding defects of coating material.•Quantitative image analysis connects thermal and mechanical properties.•Strong correlation between thermal diffusivity and bonding strength is observed.