A new surface vibration extrusion process for surface densification and improvement of properties in powder metallurgical steel

Selective surface densification (SSD) can greatly improve the mechanical properties of powder metallurgical (P/M) parts with low additional costs. This work proposes a new surface vibration extrusion process to make up for some drawbacks of the existing SSD processes as far as possible. The surface densification effect and mechanism, as well as mechanical properties of the surface extruded P/M Fe-Mo-Cu-C steel with and without vibration assistance, are comparatively investigated. Following a small surface extrusion processing via a simple extrusion die, the surface of the vibration extruded P/M steel is more thoroughly and uniformly densified under a lower extrusion load when compared with the directly extruded P/M steel. This can be attributed to the vibration assistance facilitating the dislocation motion and metal flow. The high surface-densified layer is achieved, with depth up to 530 lm slightly superior to some commercial SSD parts. Moreover, approximately twice the surface hardness is obtained compared with the hardness before the extrusion. Lastly, superior friction and wear properties are achieved. Results indicate that surface vibration extrusion can be used as a promising process for the surface densification of P/ M parts. (c) 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

Selective surface densification (SSD) can significantly improve the mechanical properties of powder metallurgical (P/M) parts at low additional costs. This study proposes a new surface vibration extrusion process that enhances surface densification by facilitating dislocation motion and metal flow. The vibration-assisted extrusion results in a more thorough and uniform surface densification with lower extrusion load compared to direct extrusion. The high surface-densified layer achieved has a depth of up to 530 μm, slightly surpassing some commercial SSD parts, with approximately twice the surface hardness and superior friction and wear properties. Overall, surface vibration extrusion shows promise as a process for surface densification of P/M parts.