Analysis of PDC Cutters Wear Mechanism

PDC is a superhard material composed of diamond and tungsten carbide composite substrate. The diamond crystals in the diamond compact are arranged in a disordered, isotropic manner, combining the high hardness of diamond, low friction coefficient, and the good impact toughness of tungsten carbide, high thermal conductivity, low thermal expansion rate. Its application mainly leverages its superior cutting and abrasion resistance performance. Therefore, studying its cutting and wear mechanisms aims to effectively control and prevent wear, which has significant theoretical importance for guiding the production of high-performance PDC.

The wear modes of PDC cutters differ from traditional tools, mainly exhibiting abrasive wear, adhesive wear, fatigue wear, and diffusion wear.

PDC Cutters Wear: Abrasive Wear

There are often tiny particles with extremely high hardness in the processed materials, which can create grooves on the surface of PDC cutters, resulting in abrasive wear. Abrasive wear is present on all surfaces, most notably on the rake face. It can occur at various cutting speeds; however, at low cutting speeds, because the cutting temperature is relatively low, other causes of wear are less significant, making abrasive wear the main reason. Additionally, the lower the hardness of the tool, the more severe the abrasive wear.

PDC Cutters Wear: Adhesive Wear

Adhesive wear occurs when the surfaces in relative motion adhere to each other at the microscopic contact points due to molecular attraction. When the adhesion strength exceeds the internal bonding strength of the material, adhesive junction points shear and fracture due to the adhesive effect, causing the sheared material to detach as wear debris or transfer from one surface to another. This phenomenon is called adhesive wear.

When machining metal matrix composites with PCD tools, the main failure modes are adhesive wear and micro intercrystalline cracks caused by diamond grain defects. In processing high hardness, high brittleness materials, the adhesive wear of PCD tools is not significant; in contrast, when processing materials with low brittleness (such as carbon fiber-reinforced materials), the wear of PDC cutters increases, and adhesive wear becomes the dominant factor.

PDC Cutters Wear: Fatigue Wear

Fatigue wear arises when friction surfaces in rolling or rolling and sliding motion form pits due to material fatigue flaking under cyclic contact stress. This type of wear is collectively known as surface fatigue wear or contact fatigue wear.

PDC Cutters Wear: Diffusion Wear

During high-temperature cutting, chemical elements from the workpiece and the tool diffuse into each other in the solid state, changing the composition and structure of the tool, which weakens the outer layer of the tool and accelerates its wear. The diffusion phenomenon always maintains a continuous diffusion from a body with a high depth gradient to one with a low depth gradient. When cutting steel and iron materials with PDC cutters at temperatures above 800°C, carbon atoms in the PDC cutters will intensely diffuse to the workpiece surface, forming new alloys and graphitizing the surface of PDC cutters.

The wear process of PDC cutters involves the micro cleavage and fragmentation of diamond particles, resulting from the generation and expansion of microcracks under stress. Therefore, its wear resistance and damage resistance can be improved from the following aspects:

Firstly, improving the microstructure of the polycrystalline diamond layer to enhance its macroscopic performance can reduce initial micro-cracks, voids, and other defects, increasing density. The main reason for the instability of polycrystalline composite performance may be the unstable control of the sintering process, with many defects in the polycrystalline diamond layer. To improve the impact resistance of the composite, using smaller diamond grain sizes is recommended. Smaller diamond grain size and spacing help to improve bonding strength and uniform diamond particle distribution, thereby enhancing the macroscopic performance of the composite. During the sintering process, the diamond must undergo sufficient deformation to generate intersecting twin bands, preventing cracks from penetrating the entire particle and preventing large-scale diamond fractures. Secondly, reasonable process parameters must be chosen to minimize the impact load on the composite during cutting.