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W. Lengauer, D.S. Janisch, A. Eder, K. Dreyer, K. Rödiger, H.-W. Daub, D. Kassel, H. van den Berg:
"Nitridation sintering of WC-Ti(C,N)-(Ta,Nb)C-Co hardmetals";
International Journal of Refractory Metals & Hard Materials, 36 (2013), 36; 22 - 30.

Gradient sintering ofWC-Ti(C,N)-(Ta,Nb)C-Co hardmetals in vacuumand nitrogen atmospherewas investigated
via interrupted sintering experiments and evolving gas analysis. Reduction of surface oxides with corresponding
gas evolution was followed by spreading of the binder, shown with coercivity measurements. With low carbon
balance, η phases were formed during the intermediate stages of sintering. By introducing nitrogen gas at a
later stage all of the η phases could be decomposed again and a graded near-surface microstructure could be
formed. If nitrogen is introduced at an early stage when porosity is still open, the TiC powder particles are nitrided,
leading to a considerable uptake of nitrogen. Carbon released by this reaction must be balanced by addition ofW
metal.Wand Co binder promote the reaction of TiC with N, whereas TaC and NbC do not. The concept of reaction
sintering hardmetal by bulk nitridation was applied on two hardmetal grades and was found an effective way of
introducing the nitrogen into such hardmetals.

Gradient sintering ofWC-Ti(C,N)-(Ta,Nb)C-Co hardmetals in vacuumand nitrogen atmospherewas investigated
via interrupted sintering experiments and evolving gas analysis. Reduction of surface oxides with corresponding
gas evolution was followed by spreading of the binder, shown with coercivity measurements. With low carbon
balance, η phases were formed during the intermediate stages of sintering. By introducing nitrogen gas at a
later stage all of the η phases could be decomposed again and a graded near-surface microstructure could be
formed. If nitrogen is introduced at an early stage when porosity is still open, the TiC powder particles are nitrided,
leading to a considerable uptake of nitrogen. Carbon released by this reaction must be balanced by addition ofW
metal.Wand Co binder promote the reaction of TiC with N, whereas TaC and NbC do not. The concept of reaction
sintering hardmetal by bulk nitridation was applied on two hardmetal grades and was found an effective way of
introducing the nitrogen into such hardmetals.

Hardmetal, Sintering, Nitrogen, Gradient, Eta Phase

http://dx.doi.org/10.1016/j.ijrmhm.2011.12.013