In the pursuit of the perfect cutting tool, the Rapid Cooling (RC) process is a dual-edged sword. While it is essential for engineering a Cobalt-depleted functional gradient to enhance coating adhesion, it also creates a high-stakes environment for carbon management.

Recently, we analyzed a set of technical feedback that perfectly illustrates the "Problem -> Analysis -> Solution" cycle in advanced sintering.

Two issues were identified in the test samples:

• The Appearance of η-phase (Co3W3C): Making the inserts extremely brittle and unusable for metal cutting.
• Increased Porosity: Compared to high-pressure HIP samples, these showed higher micro-voids, affecting overall structural strength.

A. The "Carbon Deficit" caused by Surface Engineering

To achieve a Cobalt-depleted surface, we must create a carbon gradient that "pumps" liquid cobalt from the surface into the core.

• The Hidden Consumption: Modern, high-efficiency RC furnaces have stronger atmosphere circulation and higher vacuum capabilities. This environment is "carbon-hungry"—it aggressively strips carbon from the surface.
• The Threshold: If the process consumes more carbon than the initial powder mix provides, the surface drops below the critical carbon limit. The result? Instead of just moving the cobalt, the lack of carbon forces the Tungsten and Cobalt to bond into the brittle η-phase.
• Technical Feedback: As our technical team concluded, the appearance of η-phase is a direct signal of a Carbon Deficit.

Porosity in these samples is a matter of pure physics.

• The Gap: Standard RC units typically operate at a pressure of 9.8 bar. While excellent for many inserts, it cannot match the "brute force" of a Sinter-HIP furnace (60–100 bar) in closing sub-micron pores.
• The Fix: This necessitates an even tighter control over the Liquid Phase Sintering (LPS) duration and temperature uniformity to ensure full densification.

Based on these findings, we've refined our approach to mastering the "Carbon-Pressure" balance:

• Adjusting the Carbon-to-Tungsten Ratio: Since the RC process and new furnace environments "consume" more carbon, we must pre-emptively increase the carbon addition in the initial powder mix. This "over-fueling" ensures there is enough carbon to drive the cobalt migration without triggering decarburization.
• Precision Temperature Tuning: We've fine-tuned the final sintering temperature to maximize densification within the 9.8 bar limit.

Conclusion: Quality is not just about the equipment; it's about the synergy between chemistry and physics. By understanding how the RC process "spends" your carbon, you can compensate for it at the source to produce tools that are both tough and perfectly coated.