Directed energy deposition and characterization of high-carbon high speed steels

Directed energy deposition (DED) of two high-carbon high speed steel alloys Fe-bal-C-Cr-Mo-V and Febal-x-C-CrMo-V-W-x was performed by using a 4 kW Nd:YAG laser source. The purpose of additive manufacturing was design and evaluation of thermally stable - high temperature wear resistant alloys. High temperature (500 degrees C) pin-on-disc tests were conducted to investigate the effect of carbides phase fraction on friction and wear. Strain scanning of the powder and additively manufactured materials was carried out by Neutron diffraction. Microstructures of both alloys consisted of a martensitic matrix with networks of primary and eutectic carbides. Micro-hardness (0.5 HV) measurement of all multilayer laser deposits, showed a micro-hardness greater than 700 HV, with no detrimental effect of repetitive laser thermal cycling. Febal-x-C-Cr-Mo-V-W-x showed a better high temperature wear resistance due to greater phase fraction of VC and Mo2C carbides. Fracture surfaces of post-heat treated tensile samples of Fe-bal-C-Cr-Mo-V and Febal-x-C-Cr-Mo-V-W-x revealed brittle failures with minimal plasticity. Neutron strain mapping of the metal powders and the additively manufactured materials resulted in a weak diffraction signal and peak widening effect. These results could be explained either by an effect of strong crystallographic texture in the bulk or by the presence of nano- or semi-crystalline phases.