Spark Plasma co-Sintering of hot work and high speed steel powders for fabrication of a novel tool steel with composite microstructure

The capability to produce a hybrid tool steel with properties that can be modulated on the base of the specific application was investigated. Powder metallurgy (PM) offers the possibility to blend and co-sinter different powders to produce a hybrid material which combines the properties of the base materials. With the aim of producing a new steel with high hardness and good toughness, a hot work tool steel (HWTS) and a high speed steel (HSS) powder were selected. Four blends with different composition (HWTS-HSS: 20%–80%, 40%–60%, 60%–40%, 80%–20%) were produced by spark plasma sintering (SPS) and thermally treated. The influence of composition, particle size distribution and oxygen content was evaluated by the means of density, hardness and apparent fracture toughness of the blends. By selecting powders with a small size and narrow particles size distribution near full dense blends with good mechanical properties can be sintered. Large particles hinder the efficient co-sintering due to the different densification kinetics of the powders. High oxygen content in the base powders does not significantly influences the final density but negatively affects the consolidation process, strongly reducing toughness, particularly of the HWTS.