Control of exaggerated tungsten carbide grain growth at the diamond–substrate interface of polycrystalline diamond cutters (PDC)

Exaggerated tungsten carbide grain growth is common at the interface between the diamond table and the cobalt-cemented tungsten carbide (WC–Co) substrate in polycrystalline diamond cutters (PDC). The exaggerated WC grains at the interface can grow as large as 50 μm with an aspect ratio of 50:1. These large grains can also grow as clusters. The presence of large WC grains/clusters creates weakness at the diamond–substrate interface and impairs the strength of the PDC tool. In the present investigation, we tried to understand the root cause of exaggerated WC grain growth at the interface. Our findings show that WC grain growth at the interface decreases with a decrease in the carbon/tungsten (C/W) ratio. By adding 5 wt.% pure tungsten powder to the diamond, the C/W ratio decreased and we found no WC grain growth. By adding fully stoichiometric WC, which has 6.13 wt.% carbon, grain growth was reduced but still observed. Sintering on a substrate having η-phase (carbon deficient phase) also decreased the C/W ratio, and we did not observe WC grain growth.

Research Highlights
► Exaggerated WC grains grow at the diamond–substrate interface in PDC.
► Lowering the C/W ratio at the interface prevents exaggerated WC grain growth in PDC.
► Adding tungsten powder in the diamond table can lower the C/W ratio.
► Using a carbon deficient WC–Co substrate can lower the C/W ratio.