Failure Modes of Tungsten Carbide Cutters Ⅲ

In part 2 we know that corrosion/ leaching wear is one of the most common failure modes of tungsten carbide cutters, while involving only the metallic binder matrix instead of tungsten carbide particles inside, and therefore a moderate or highly corrosive working environment shall be carefully avoided for carbide cutters. In this part we will talk about chipping/fracturing wear as another failure mode.

3. Chipping/Fracturing Wear

Except at relatively high temperatures, tungsten carbides cutters undergo little plastic deformation prior to failing by brittle fracture. Carbide grades vary widely in tensile strength and toughness and premature failure by chipping or fracture occurs whenever the carbide component lacks the toughness to withstand service conditions that include mechanical shock or impact. Sharp, unprotected edges of tungsten carbide cutters are particularly vulnerable to chipping. Cracks generally initiate in areas associated with high stress concentrations and, once moving, propagate rapidly through the carbide component to produce failure by fracture. Carbides have relatively high compressive strengths, however, and any change in either part geometry or operating conditions that converts tensile stresses to compressive stresses reduces the probability of failure by fracture. Design considerations that reduce the risk of failure by chipping or fracture include the use of protective edge chamfers and radii, avoiding sharp inside edges and other stress-inducing features, increasing the wall thickness of tubes and wear sleeves, and improving surface finishes. In certain instances chipping or fracture occurs as a result of the increased stresses associated with a badly worn carbide component. When this is the case, wear is the primary cause of failure even though catastrophic failure by fracture or breakage may mask it.

(To be continued. This article is divided into 9 parts and this is part 3, for part 2 please refer tohttp://news.chinatungsten.com/en/tungsten-information/79330-ti-10138)

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