Laser metal deposition of self-lubricating alloys on selective laser melting maraging tools for the high temperature forming of aluminium

Abstract

Selective laser melting (SLM) is an additive manufacturing technique that allows the layer-by-layer fabrication of metallic components with high dimensional tolerances, being also particularly suitable for implementing complex geometries such as cooling channels in hot forming tools. However, high temperature forming processes pose severe conditions that often require additional surface protection and functionality. The present work proposes to increase the lifetime and endurance of SLM tools using self-lubricating coatings deposited by laser metal deposition (LMD). To this end, 3D printed samples made of maraging steel prepared by SLM are functionalized with self-lubricating coatings applied by LMD. Two different metallic alloys are deposited, a nickel-based alloy containing metal sulphides and silver, and an iron-based alloy containing graphite. The resulting microstructure after the hybridization of both additive manufacturing techniques has been thoroughly analysed in terms of the microstructural changes. Afterwards, the functionalized 3D printed tools are investigated for prospective high temperature sheet metal forming of aluminium alloy AA6082 using a ring compression test rig at 300 °C, using a reference hot work tool steel as reference. The results show that the use of Ni-based self-lubricating coatings contributes to a more stable frictional behaviour, independently of the dilution of the externally added lubricant. These results serve as example for the enormous potential for the combination of laser metal deposition with selective laser melting for tool functionalization.