Thermal spray coating of Al-Cu-Fe quasicrystals: Dynamic observations and surface properties

In this study, we prepared Al-Cu-Fe quasicrystals (QCs) via thermal spray coating after optimizing the process parameters. Both in-situ XRD and in-situ TEM were used to investigate the thermal stability of QC phase. These dynamic techniques uniquely allow for a direct observation of QC growth upon heating and cooling. We show that the cubic β-Al-Cu-Fe is the dominant phase at room temperature (initial stage), but with an increase in temperature, the QC takes over at 650 °C, consistent with thermodynamic calculations. Further increasing the temperature to 800 °C, the QC phase transforms into cubic β-Al-Cu-Fe such that the β-Al-Cu-Fe phase is the only phase in existence at 870 °C. Based on this result, we annealed the sample after thermal spray deposition for one hour at 650 °C, which yielded an almost pure QC coating. The contact angle (against water) before annealing was 50°±4° but improved dramatically to 130°±5° after annealing at 650 °C for 1 h. This study provides a better understanding of QC formation during heat treatment as well as that of other secondary phases. Furthermore, these results can be used to manufacture QC coatings with enhanced interfacial properties that are central to technological applications.