Coating technology has been proven to improve diamond and cubic boron nitride (CBN) tool
performance by improving crystal retention in the bond and protecting the crystal from chemical
attack during tool fabrication. Coating methods include chemical vapor deposition (CVD), physical
vapor deposition (PVD), and electroless and electrolytic wet chemical methods. Design of the coating
for the proper bond system and application, and proper design of the coating process itself, is critical
to obtaining the desired tool performance. For example, poorly designed high-temperature CVD
coating processes are likely to significantly degrade the fracture toughness of the diamond even before
they are subjected to the thermal cycle associated with tool fabrication. This has potentially severe
consequences for tool performance. In this paper, we analyze the effects of coatings processes, which
display similar chemical signatures and morphological characteristics, but whose underlying diamond
substrate is affected differently. In addition, scanning electron microscopy (SEM) and energy
dispersive x-ray spectroscopy (EDS), coupled with analysis of processed tools, are used to classify
commercially available diamond coatings as a function of the requirements of relevant applications.
Conclusions
The potential benefits of coatings in superabrasive sawing, drilling and grinding operations
are enormous. However, it is critical to distinguish between coatings that are likely to provide
measurable improvement to the tool and those that inflict damage and reduce the utility of the
substrate superabrasive crystal.
Electroless and electrolytic coatings are suited for bonds processed at lowtemperatures.
The thick and textured coatings when deposited properly provide retention
benefit with little coating-associated crystal degradation.
Of the high-temperature coating processes, PVD coatings with their shell-like
structure are seen to be not very compatible with traditional metal bond tools. In fact, it is
likely that the long deposition times induce unwanted damage in the crystals.
CVD coatings can provide demonstrable advantages in tool performance. However,
not all CVD coatings are alike. Coatings from different vendors may possess similar chemical
compositions but will behave differently in identically processed bond systems. Differences
in the coating processes, including inappropriate process control, between different vendors
are shown to leave the crystals vulnerable to severe degradation. Fortunately, by utilizing
methods to assess compatibility, wetting, adhesion and crystal degradation, the potential
usefulness of various coatings can be evaluated relatively quickly before investing in field
trials.