I am working on CoCrMo alloy produced by SLM. After polishing, I tried to etch my sample with (HCl:HNO3 = 3:1) for 20 minutes but my sample did not etch. I would like to know what are the most suitable etchants and concentrations for CoCrMo alloy, whose chemical compositions are given below. Also, what should I pay attention to when etching such alloys? Your knowledge and experience are very valuable to me. Thank you.

Chemical Composition (wt%)

Co: Balance

Cr: 28.510 wt%

Mo: 5.720 wt%

Al: 0.003 wt%

W: 0.008 wt%

C: 0.050 wt%

Fe: 0.049 wt%

Mn: 0.00. wt%

N: 0.076 wt%

P: 0.009 wt%

S: 0.002 wt%

Si: 0.630 wt%

Ti: 0.002 wt%

B: 0.001 wt%

Ni: 0.008 wt%

Be: 0.001 wt%

Cd: 0.002 wt%

Pb: 0.001 wt%

O: 0.021 wt%