In order to prove this thought, the following experiment was carried out. 2 g Ti2AlN (< 25 μm, lab made) was immersed in two etching solutions with magnetic stirring. One solution was 20 ml hydrofluoric acid (HF, ≥ 40.0 wt.%; Yantai Far Eastern Fine Chemical Company, China). The other was 2 g KF (>99 wt.%; Aladdin, China) + 40 ml 6 M HCl (36 ~ 38 wt.%; Yantai Shuangshuang Chemical Company, China). The suspension after etching was further ultrasonically treated at room temperature for 1 h. Thereafter etched powders were separated from the suspensions by centrifuge. The powders were dried under vacuum at 60 °C for 8 h.