Terahertz non-destructive testing of coating thickness of self-lubricating sliding bearings
[Objective]Self-lubricating sliding bearings have many advantages,such as strong bearing capacity,impact resistance,wear resistance,corrosion resistance and pollution-free.In a number of high-precision fields like aerospace,high-speed transportation,military industry and other advanced fields,self-lubricating bearings play a crucial role.In the course of their service,self-lubricating bearings will face a variety of harsh conditions,which will undoubtedly accelerate the wear of the coatings,ultimately leading to failure.In the event of coating failure,the consequences may be unexpected and serious.Consequently,the accurately testing for the condition of the self-lubricating sliding bearing coatings is a crucial step in optimizing the performance of the bearing and ensuring the safety of the mechanism.[Methods]In view of the low accuracy and insufficient reliability of the current wear failure evaluation technology for bearing self-lubricating coatings,a high-precision nondestructive testing method of self-lubricating sliding bearing coating thickness based on terahertz time-domain spectroscopy is proposed in this study.Firstly,the dielectric response characteristics of polytetrafluoroethylene(PTFE)coating materials in the terahertz frequency band are investigated systematically using a terahertz time-domain spectroscopy system.Subsequently,the model of terahertz waves in the self-lubricating plain bearing coating is constructed based on the propagation theory of terahertz waves in multilayer media.Then,the coating thickness of the self-lubricating bearing sample is precisely quantified,and the wear amount is calculated.Furthermore,the use of a terahertz time-domain spectroscopy system for scanning the coating enables the reconstruction of the coating interface,particularly the reconstruction of the interface morphology within the coating.This allows for a more comprehensive and intuitive observation of the wear state within the coating.[Results]The results demonstrate that the terahertz wave exhibits a high degree of permeability to PTFE-type coating materials,with the coating compositions displaying distinct characteristic responses and minimal dispersion within the terahertz frequency band.On this basis,the propagation model for the terahertz waves in PTFE coating is established,and the thickness of the self-lubricating coating is measured by the reflected signal using the time of flight(ToF).The maximum error is 4.69 μm,while the relative error is 2.35％.Moreover,based on terahertz time-domain spectroscopy technology,the wear amount of 1 μm can be accurately represented theoretically.[Conclusions]In this study,a terahertz nondestructive testing method for coating thickness of self-lubricating sliding bearings is proposed.The response characteristics of terahertz waves in self-lubricating coatings are clarified through experiments.The propagation model of terahertz wave in PTFE coating is established,and the thickness of the self-lubricating coating is measured.Furthermore,the terahertz-based wear testing method exhibits superior measurement accuracy in comparison to existing coating detection technologies.At the same time,the morphology reconstruction by the scanning provides a good comprehensive analysis.The proposed method can meet the actual engineering requirements,and provides a new scheme for developing more suitable non-destructive testing technology for self-lubricating coatings.
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