Dissolution patterns caused by chemical etching of Al-Co-Cu and Al-Co-Ni decagonal quasicrystals with a HF-HNO₃-H₂O solution

Dissolution patterns essential for Al-Co-Cu and Al-Co-Ni decagonal quasicrystals (d-QCs) have been investigated in detail by chemical etching using a HF-HNO₃-H₂O solution followed by scanning electron microscopy (SEM) observations. The chemical etching of definite surface areas of the samples, which are either normal or parallel to the tenfold axes, using a solution with HF-HNO₃-H₂O (1:5:4 in volume ratio; 0°C; 5-10min), produces a large number of microfacet pits of decagonal prismatic shape. In addition, the same etching test in combination with SEM observations was carried out on a deformed sample of the Al-Co-Ni d-QC, which had been subjected to concentrated mechanical stress at an elevated temperature of 850°C by means of the Vickers indentation technique. The morphological features of the resulting micropits and their possible origins are discussed on the basis of results obtained by SEM observations.