The dependency of microstructure and properties of nanostructured coatingson plasma spray conditions

In this paper, Al2O3-13 wt.% TiO2 coatings formed via a plasma spray approa ch using reconstituted nanosized Al2O3 and TiO2 powder feeds are described. Effects of various plasma spray conditions on the microstructure, grain si ze, phase content and microhardness of the coatings have been evaluated. It is found that phase transformation of nanosized Al2O3 and TiO2 during heat treating, sintering and thermal spraying is, in general, identical to that of micrometer-sized counterparts. Furthermore, the particle temperature du ring thermal spray could be divided into three regimes, i.e. low, intermedi ate and high temperature regimes, according to the characteristics of the c oating produced from the nanopowder. The hardness and density of the coatin g increase with the spray temperature. The phase content and grain size of the coating also exhibits a strong dependency on the spray temperature. The coating sprayed using nanopowder feed displays a better wear resistance th an the counterpart sprayed using commercial coarse-grained powder feed. The observed phenomena are discussed in terms of physics of thermal spraying, mechanisms of coating growth and phase transformation of the oxides. (C) 20 00 Elsevier Science S.A. All rights reserved.