High diamond content wear-resistant inserts
While it seems obvious that wear resistance is proportional to the diamond content of the diamond insert, there are a number of limitations that make it necessary to optimize the diamond content.
Diarotech has therefore studied the effect of the diamond content of its inserts on their wear resistance, in order to provide them with the best cost-performance ratio.
General information on cutting and wear resistance
Diamond is the element that gives diamond tools their cutting and wear-resistance capability.
For cutting, it can be good to reduce the diamond content in order to increase the aggressiveness of the tools (to the detriment of its lifespan).
The graph above shows the change in the rate of penetration (ROP) according to the diamond content by volume for a given rock and binder under identical working conditions.
It shows that a reduction in the diamond content considerably improves the rate of penetration.
We will generally work with higher diamond content for applications requiring good wear resistance. Indeed, an increase in the diamond content by volume results in an increase in the diamond surface area and therefore a decrease in the metal surface area (the matrix) in contact with the rock. This has the effect of limiting the wear of the matrix and limiting the friction coefficient between the tools and the drilled wall. This suggests a non-linear (exponential) relationship between diamond content and wear resistance.
While it is therefore tempting to want to maximize the diamond content in the tools, several limitations appear.
First, there is a geometric limit to the diamond content permitted in a tool. Indeed, if we consider that the diamonds are spherical and are optimally stacked (referred to as “face-centered cubic stacking”), a limit of 74% Vol appears. In practice, the limit is around 67%.
However, such diamond content by volume leads to major weakness in the tools. Indeed, these compact stacks can only be created if the diamonds are in contact with each other. The diamonds in contact therefore form preferential fracture planes. In practice, these diamond-to-diamond contact points increase significantly above a content of 50% by volume.
Finally, the last technological limit explaining, among other things, the increase in the cost of these high diamond content inserts, is the wear of the pre-formation matrices which is found to increase considerably from 29% Vol. This limit, beyond which the contact between the diamond and matrix increases, is highlighted in the below graph by geometric demonstration and where R is the diamond content by volume
Optimum content discovered
Taking all these limits into account, it appears that the diamond content by volume that maximizes the cost-performance ratio is 40%!
Indeed, this volume content makes it possible to control the wear of the matrices within acceptable ranges while ensuring excellent wear resistance and guaranteeing good resistance to breakage.
Indeed, as shown by the wear facies below. This volume content gives a very large surface coverage of diamonds while avoiding diamond to diamond contact points.
Assessment of wear resistance
In order to best assess the wear resistance of its inserts, Diarotech has developed an in-house test bench for rapid and reproducible characterization, the results of which match those in the field.
In fact, standardized tests (G65 ASTM, G99ASTM, etc.) are not suitable for the characterization of composite materials and give results that are not consistent with observations in the field. This can be mainly explained by test conditions that differ greatly from the actual conditions (WOB, RPM, fluid flow rate, fluid load rate, etc.). The test bench developed integrates all these aspects and allows real-time wear measurement through laser displacement measurement.
Finally, the above graph shows the results of wear tests carried out on the major anti-wear standards in the oil drilling sector. It highlights the definite benefit of Diarotech’s wear-resistance solution, which offers 4,000 times greater wear resistance than a carbide insert, 400 times greater compared to a TSP insert and 10 times greater compared to an insert impregnated with 25% diamond content by volume.