Synthesis, characterization and physical properties of aluminum-copper-iron quasicrystalline plasma sprayed coatings

The phases and microstructures of Al-Cu-Fe powders and coatings were investigated in this study. Powders were prepared by grinding a chill cast ingot and by high pressure gas atomization. The contrasting solidification rates of these two processes yielded very different solidification structures. The cast ingot was very inhomogeneous and contained icosahedral ({dollar}psi{dollar}), cubic ({dollar}beta{dollar}), monoclinic ({dollar}lambda{dollar}) and tetragonal ({dollar}theta{dollar}) phases. The gas atomized powder had a finer scale of phase segregation and consisted primarily of the {dollar}psi{dollar} and {dollar}beta{dollar} phase; a small fraction of the {dollar}lambda{dollar} phase was present as well.; Plasma arc sprayed (PAS) coatings were formed using the above powders. The chemical uniformity of the starting powder was carried over into the PAS coatings. Evaluation of starting powder size during PAS revealed that small powder particles (e.g., {dollar}<{dollar}45{dollar}mu{dollar}m) tended to lose Al by vaporization. This mass loss brought the composition of the coating into a two-phase region of the Al-Cu-Fe phase diagram and produced less of the desired {dollar}psi{dollar} phase.; Substitution of 1 at. pct. B for Al was done to study the effect on altering the solidification microstructure of Al{dollar}sb{lcub}63{rcub}rm Cusb{lcub}25{rcub}Fesb{lcub}12{rcub}{dollar} chill cast ingots, gas atomized powder and PAS coatings. Boron significantly altered the structure of the chill cast ingot, but had less impact on the solidification of the atomized powders or PAS coatings. Differential thermal analysis and electron microscopy indicated that B was modifying solidification by a solute-drag mechanism.; Oxidation and tribological behaviors of PAS Al{dollar}sb{lcub}63{rcub}rm Cusb{lcub}25{rcub}Fesb{lcub}12{rcub}{dollar} coatings were examined. The coatings were resistant to catastrophic oxidation at 500{dollar}spcirc{dollar} and 700{dollar}spcirc{dollar}C in flowing O{dollar}sb2{dollar} for up to 250 hours. The weight gain of oxidized samples followed parabolic kinetics. Pin-on-disc wear tests with a Al{dollar}sb2rm Osb3{dollar} pm against PAS Al{dollar}sb{lcub}63{rcub}rm Cusb{lcub}25{rcub}Fesb{lcub}12{rcub}{dollar} coatings showed brittle behavior at room temperature and increasing plastic behavior at temperatures up to 600{dollar}spcirc{dollar}C. Initial coefficients of friction between the ceramic pin and the quasicrystal coatings ranged from 0.4 to 0.6 at 25{dollar}spcirc{dollar}C and 600{dollar}spcirc{dollar}C, respectively. These values increased with sliding distance. The increase in frictional force was attributed to increased contact area between the pin and coating as sliding progressed.