Quasicrystalline coatings: Thermal evolution of structure and properties

Quasicrystals (QCs) are known to exhibit unique properties as a result of t heir unique quasiperiodic structure. Real quasicrystalline (QC) materials, however, may exhibit complex phase structures, and as a consequence, their properties may differ from expectations. In the present work, QC coatings o f the Al-Cu-Fe, Al-Cu-Fe-Cr, and Al-Pd-Mn systems were prepared by a plasma spray process, followed by heat treatments in the range 500-800 degrees C. The phase structure and evolution of the coatings were evaluated, and ther mal diffusivity, hardness, and friction coefficient were measured. The pres ence of quasicrystalline and crystalline phases and their influence on thes e properties is systematically considered for the first time. Broadly, the coatings exhibit the properties expected of QC materials, low thermal diffu sivity, high hardness, and low coefficients of friction, but it is also sho wn that these properties can be sensitive to the phase structure of the coa tings. This suggests that phase structure may be manipulated by heat treatm ent to optimize the properties of QC coatings.