A Method to Etching Microstructure Suitable for Austenite Grain Size Rating of GH4169 Nickel Alloy

The austenite microstructure and twins can be displayed by etching GH4169 nickel alloy with conventional etching solutions. However, the twins makes it difficult to grade the austenite grain size accurately. By adjusting the composition of etching solution, an etching method which only showing the austenite grain boundary was proposed. The experiment results show that using the potassium permanganate water solution (1.5-2 g KMnO₄+7-10 mL H₂SO₄+90-110 mL H₂O+0.1-0.3 mL HCl) heated to 95℃ in a water bath can clearly display the austenitic grain boundary of GH4169 nickel alloy and not display the twins. The obtained microstructure can be used to assess the grain size of nickel alloy accurately.