Fracture toughness of a hot work tool steel-TiC composite produced by mechanical milling and spark plasma sintering

The effect of the processing route and the addition of 20 vol% TiC particles on the fracture toughness of the hot work tool steel AISI H13 was investigated. To this end, as-atomized, mechanically milled and mechanically alloyed powders were consolidated by spark plasma sintering. Nearly dense materials were produced. The fracture toughness was measured with modified disk-shaped compact tension specimens. Acoustic emissions and the fracture surfaces were analyzed to study the damage evolution. The consolidation of the as-atomized powder resulted in the highest relative density and fracture toughness. In contrast, relatively low fracture toughness was achieved for the mechanically milled powder which was attributed to the lower relative density after sintering. The lowest fracture toughness was achieved for the steel-TiC composite material that also exhibited the lowest density. Furthermore, crack path deflection was lowest for this material. This was attributed to the TiC particles which served as a weak crack path. Early cleavage fracture due to stress concentration at TiC particles/agglomerations was proved by means of acoustic emission analysis.