Tailoring hardness and toughness gradients in functional gradient hardmetals (FGHMs)

The microstructure of hardmetals in the near-surface area can be optimised for increased productivity in metal cutting operations. This was performed by diffusional processes induced by a reactive gas phase within the production cycle. This treatment also influences the various parameters important in hardmetal production such as sintering shrinkage and phase composition so that the starting formulation has to be adjusted to this process. The hardness and toughness can be tailored in such a way so as to smoothly increase or decrease towards the surface depending on the formation of hard phase particles. Hence, a graded microstructure is obtained which has favourable response to wear. Two principally different functional gradient hardmetals (FGHMs), one with an increased surface hardness and a decreased toughness and one with a decreased hardness and an increased toughness were prepared, and scaled up into industrial production and tested. The FGHMs were found to outperform conventional hardmetals.