Influence of self-lubricating non-metal phase on the erosion and wear behavior of Ni-based abradable coatings

In this study, the influence of self-lubricating hexagonal boron nitride (hBN) on the erosion and abradability of Ni-based abradable coatings was investigated. Two coatings of same metallic content, one with and one without hBN, were deposited by means of plasma spray to different densities and consequently hardness values. Subsequently, the coatings were subjected to erosion and abradability testing at room temperature in order to evaluate their performance. In addition, to capture the characteristics of the wear process, a detailed chemical and structural analysis was performed within the near-surface region of the worn specimens (i.e. abradable and blade) by means of Scanning Electron Microscopy (SEM), Transmission Electron Microscopy, and micro-Raman spectrometry.

The erosion resistance of the coatings increased with increasing the density as well as with the addition of hBN, which correlated well with the hardness results. The abradability of the coatings without hBN showed a reverse correlation with erosion capability where the less erosion resistant coatings were more abradable as manifested by the lower blade wear. Similarly, the high density hBN content coatings caused higher blade wear compared to the lower density coatings with hBN. However, the coatings with hBN showed overall better abradability compared to the ones without, which correlated well with slightly lower interface temperatures (i.e. measured by means of thermocouples and IR thermometer) and was attributed to the difference in the particle pull-out mechanism.