Microstructure and tribological properties of plasma sprayed Al–Cu–Fe quasicrystalline coatings after laser post-treatment processing

Abstract

This paper presents the results of the study on the effect of laser melting–solidification processing on the structure and tribological properties of plasma spray Al–Cu–Fe quasicrystalline alloy coatings. Dense and hard coatings were obtained by the laser post-treatment processing and the volume fraction of the icosahedral (i) phase was found to be dependent on the laser power and scanning velocity conditions. Using a parameter δ, defined as the ratio of the laser power P, to the scanning velocity v, i-phase was observed to form for low values of δ as a consequence of the high cooling rates. Furthermore, a correlation was worked out between the microhardness and the parameter δ. Owing to the microstructure modification, the laser post-treatment provided significant improvement to the tribological properties of the plasma sprayed Al–Cu–Fe QC coatings. The frictional behavior was found to be dependent on the constituent phases formed in the laser post-treated coatings. In particular, low values of the friction coefficient were recorded in the early stage of the test for coatings containing a high volume fraction of i-phase. However, owing to the brittleness of the i-phase, the difference of the frictional behavior was reduced after 150 cycles, and the friction coefficient for all laser post-treated coatings stabilized at a value which was approximately half that of the as-received plasma sprayed coatings. After laser post-treatment, the wear rate was significantly improved only for the coatings containing a high content of i-phase.