In this article, Everloy, a manufacturer of cemented carbides, provides an expert’s perspective on cemented carbide corrosion and its countermeasures.

What is cemented carbide corrosion?

Cemented carbide is composed of either WC-Co or WC-Ni as the main component.
In neutral or acidic solutions, corrosion of cemented carbide occurs when Co or Ni elutes into the solution.
As a result, the area where Co or Ni are eluted loses binder that supports the WCs, thus making the cemented carbide extremely brittle, making it prone to breakage and premature wear.

The difference in concentration of dissolved oxygen amount in the water,
adhering to cemented carbide, creates a local cell reaction which leads to elution of Co binder as metal ions.

Corrosion reaction:  Ｃｏ＋ ½ O₂＋H₂O→Ｃｏ²⁺＋２ＯＨ^－

Anode reaction:  Ｃｏ→Ｃｏ²⁺＋２ｅ^－

Cathode reaction:  ½Ｏ_２+Ｈ₂Ｏ+２ｅ^－→２ＯＨ^－

In addition, when a metal with a electrical higher potential than WC-Co alloy (e.g., stainless steel, etc.) is in contact with the solution, a local cell reaction is created between the different metals due to the potential difference, and the rate of corrosion (galvanic corrosion) will increase in the carbide alloy on the anode side.
As WC-Ni alloy has higher potential than the WC-Co alloy, it is said that corrosion is less likely to occur. Furthermore, if small gaps (pores, etc.) are present on the surface, oxygen amount will decrease in the gaps causing concentration of anodic reaction, which leads to eluted metal ions lowering the pH of the solution in the gaps. This will increase the corrosion rate (crevice corrosion).

Countermeasures against corrosion of cemented carbide

Although depending largely on the usage environment, using NI as metallic binder or adding metals with passive layer such as Cr generally improves corrosion resistance. With the know-how accumulated over many years, we provide excellent cemented carbide that has both performance and corrosion resistance.
It is also possible to propose materials after evaluating the condition of the parts which the customers are using.

We will handle it

Did you understand the corrosion of cemented carbide?
We have a wide variety of cemented carbides in our lineup.
If you have any concerns about cemented carbide, please feel free to contact us.