METALLOGRAPHY OF POWDER METALLURGY ALLOYS
Powder metallurgy specimens require additional steps to reveal the correct void content and size. Are you forgetting these steps?
Metallographic specimen preparation of powder metallurgy (P/M) materials presents problems when the material is not compacted to full density by hot-isostatic pressing. Some alloys are processed to full density like high-speed steel tool steels, nickel-base superalloys and Co-based alloys used for implants, but many deliberately contain a considerable void content. The heterogeneity of the non-fully dense powder products, the void content, and the possibility of having elemental copper in the matrix makes preparing specimens difficult. Unlike fully dense metals and alloys, which are typically easier to examine than their wrought equivalent due to their greater homogeneity, additional steps are required to reveal the correct void content and size.