Evaluation of wear mechanisms in additive manufactured carbide-rich tool steels

Advances in additive manufacturing present the opportunity to design tool steels with higher carbon contents than previously possible with conventional manufacturing. A new class of carbide-rich tool steels with 8%, 20% and 25% volume fraction carbides has been developed using electron beam melting. Reciprocating ball-on-plate dry wear tests were performed to investigate the macro tribological performance of these materials. In-situ scratch wear tests were also performed to assess wear degradation effects at a more fundamental level. The main macro wear mechanism was oxidation with adhered iron oxide islands in all carbide-rich tool steels and the sliding of oxide particles caused three body abrasive wear in the lowest carbide containing material. Surface material removed from the counterbody and formed adhesive iron oxide islands over the oxidized carbide-rich tool steel surface. The compacted oxide islands initially formed at the edges of embedded carbides and then evolved to encompass the entire wear scar. The wear damage was assessed quantitatively through laser profilometry. The lowest wear damage was observed in the 20% carbide tool steel which also had the lowest coefficient of friction on moving average of 0.52 +/- 0.01 compared to the 8% and 25% carbide tool steel having on moving average 0.66 +/- 0.03 and 0.61 +/- 0.03 respectively. In-situ scratch wear tests revealed the potential plastic deformation mechanism of the matrix underneath the oxide film. The deformed matrix of 20% carbide tool steel generated limited wear debris at the interface of the tribo-system and this is surmised to provide better wear and friction performance among the materials considered.