One of the trickiest problems for the additive manufacturing industry is the manufacture of hardmetal tools, inserts and wear parts of all shapes, sizes and degrees of intricacy.

The case for AM-HM is almost self-evident. Hardmetal objects are difficult and expensive to manufacture but often replaced when only a tiny fraction has been worn away. Much could be saved in weight and material costs, if the least stressed volumes could be replaced by closed voids or if more shaping could take place before sintering. However, unlike most other AM materials, like metals and biological constituents, hardmetals are a combination of a very hard high melting-point ceramic (generally WC) and a tough metal binder (usually Co) with comparatively low melting (and boiling) points.

When processed by conventional liquid-phase PM sintering, a small part of the WC dissolves in the metal binder as the temperature is raised, forming a eutectic. As the temperature is lowered, carbide is reprecipitated, the compact contracts and virtually all porosity is eliminated. None of this works with regular 3D printing. In simple terms, if we apply high-speed laser melting to the metallic binder, there’s insufficient time for liquid-phase sintering. Raise the temperature to melt the hard component and much or all of the binder metal will evaporate.

These and allied problems have been attacked by numerous researchers. In this feature we discuss the current state of art, as disclosed at a special session of the EPMA’s recent Bilbao Congress. The four papers presented orally at that session are reviewed here in order of presentation.

This article appeared in the May–June 2019 issue of Metal Powder Report. Log in to your free materialstoday.com profile to access the rest of the article.

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