There are many different ways that carbide wear parts can fail. Unfortunately, there is not a single best grade of carbide that will work for all applications. In fact, using one grade in place of another may very well decrease the chances of one type of failure, but will typically increase the chances of another failure all together.
Usually, carbide grades chose in a way that the mode of failure and the life of the carbide wear parts are somewhat predictable. This way disruptive unscheduled assembly outages, including the carbide component, can be avoided. Therefore, replacement of the parts can be performed before a failure.
Erosion or Abrasive Wear
Erosion or abrasive wear attacks the working surface of the component. This causes a progressive loss of material in this area because of gases that contain solid particles or a stream of liquid at a high velocity flowing across or directed onto the carbide surface. It can also be caused by the rubbing or sliding of a work material or mating component over the component surface.
The rate of the wear will depend on the on the amount of pressure or force that is being inflicted on the surface of the carbide wear parts. The progressive wear that is caused by the erosion or abrasion is the most preferred type of failure because it typically does not cause complete stoppage or total breakdown of operations due to a failed component.
Leaching or Corrosion
When there is an electrochemical or chemical reaction between the environment and the carbide surfaces, the result is corrosion wear. Such reactions typically affect the metallic binder matrix, which is the nickel or cobalt. It generally does not affect the tungsten carbide grain. However, the loss of the metallic binder matrix at exposed surfaces will cause the mechanical bond that holds the carbide grains to be lost.
Acidic liquids are especially corrosive. It is also important to note that nickel is far less susceptible to leaching than cobalt. Therefore, cobalt should be avoided in environments that are moderate to highly corrosive. There is seldom data available on the rate of corrosion in a specific situation and must be determined by observation only.
The life of carbide wear parts depends on several factors, such as the geometry of the carbide component, the properties and composition of the carbide and the assembly design. The operation environment of the carbide is a factor as well. Changes in any of these factors can affect the service life of the component.
