The main challenge when preparing powder metallurgy parts for metallographic analysis is revealing the true porosity of the material after grinding and polishing. Learn how to prepare powder metallurgy parts for analysis quickly and with reproducible results.
Download the full application note
Fig. 1: Experimental powder metallurgy stainless steel, color etched
The density of a compacted and sintered component influences its strength, ductility and hardness. Therefore, metallography of powder metallurgy parts usually includes checking for specific porosity.
In process control, metallography of powder metallurgy parts is used to check porosity, non-metallic inclusions and cross-contamination. The metallography of powder metallurgy parts also plays an important role when developing new products or improving manufacturing processes.
Fig. 2: Powder metallurgy steel with 0.5 % C, diffusion alloyed with Ni, Cu and Mo. Etched in picral, showing areas of fine pearlite surrounded by ferrite, martensite, bainite and Ni-rich austenite
Fig. 3: Powder metallurgy steel with 0.8 % C, pre-alloyed with 1.5 % Mo. Etched with Nital, showing dense bainite
The further sections on this page briefly describe how to overcome these challenges. The procedures have been used successfully in practical laboratory applications and have proven to give reproducible results.
For a more detailed description of the procedures outlined here, download the full application note.
Fig. 5: Same specimen as Fig.1 after 8 minutes of diamond polishing (3 μm)
Fig. 7: Sintered tungsten carbide (WC/Co), etched with Murakami’s reagent 1500x
Fig. 8: Carbide distribution in conventionally produced steel
Fig. 9: Carbide distribution in powder metallurgically produced steel
Common chemical etching solutions for the relevant metal or alloys can be used. When working with chemicals the standard safety precautions must be observed.
| Etchants for copper powder metals and copper powder alloys | |
| 100 ml water 20 ml hydrochloric acid 5 g Iron-III-chloride |
Etch for 10-20 seconds Rinse with water followed by isopropanol |
| 100 ml water 10 g ammonium persulfate (use fresh only) |
Rinse with water followed by isopropanol |
| Etchants for steel powder metals | |
| 1-3% Nital for iron-carbon alloys, iron-carbon-copper alloys and pre-alloyed iron-molybdenum: 100 ml ethanol 1-3 ml nitric acid |
Etch for 10-60 seconds depending on carbon content Rinse with isopropanol |
| Etchants for stainless steel powder metals | |
| Vilella’s reagent: 45 ml glycerol 15 ml nitric acid 30 ml hydrochloric acid |
Etch for 30 seconds to 5 minutes Rinse thoroughly with water followed by isopropanol |
| Etchants for tungsten carbide powder metals | |
| Murakami‘s reagent: 100 ml water 10 g potassium or sodium hydroxide 10 g potassium ferricyanide |
Etch by immersion or swab etch Rinse thoroughly with water followed by isopropanol |
All images by Birgitte Nielsen, Applications specialist, Denmark
For specific information about the metallographic preparation of powder metallurgy parts, contact our application specialists.
