Colloquia

Summary

Tungsten carbide–cobalt composites are widely used for their combination of extreme hardness and reasonable toughness. Traditionally, performance improvements in these tools have focused on compositional adjustments during powder processing and sintering. 

However, increasing industrial demands have sparked renewed interest in post-sintering surface modifications, such as gas-phase carburization, to create hardness gradients without compromising processability or introducing brittle defects. Despite this potential, little systematic work has been done to optimize the gas-phase carburization process for tungsten carbides.

To fill this research gap, a full-factorial Design of Experiments was conducted, testing the influence of methane flow rate, carburization time, and diffusion time on a fine-grain WC-Co grade with 13% cobalt content. Statistical modeling and desirability-based optimization were used to evaluate the effects of these parameters on surface hardness, case depth, free carbon formation, and porosity, with a focus on balancing performance gains against structural reliability. Beyond optimizing performance and reliability, the research also evaluates process homogeneity within the custom-designed multi-layer batch furnace used for the experiments.

Key findings showed that while surface hardness and carburization depth can be effectively optimized at the layer level, structural integrity remains highly sensitive to carburization time and methane flow. Experimental validation confirmed strong agreement between predicted and measured results at a layer but revealed significant batch-level variation linked to furnace design and geometric complexity. 

This research highlights that successful industrial implementation of carburization for WC-Co parts requires not only parameter optimization but also hardware redesign, improved process monitoring, and geometry-driven design adaptations.