**3. Development status of diamond composite hardbanding materials**

At present, mechanical properties and wear resistance of hardbandings have been dramatically advanced. Although such improvements have been made, hardbandings and casings still suffer from friction and wear issues. The materials of existing hardbanding products are mostly iron-base alloy materials, so the problem of wear and tear is always unavoidable because of the pairwise similarity of elements. Therefore, if nonmetallic materials with high wear resistance are used to produce hardbandings, the wear problem will be greatly solved.

Polycrystalline diamond (PCD) is widely used in oil and mining explorations due to the advantages of homogeneous hardness, good toughness, and easy processing. And furthermore, PCD has a high wear resistance and low friction coefficient. Even in a high-temperature environment, it can also maintain its excellent performance. Thus PCD is obviously an ideal hardbanding material which could accomplish the optimum balance of drill string improvement and casing wear reduction [29].

Zhang et al., of the China University of Petroleum, Beijing, has developed a new hardbanding material (shown in **Figure 3**), called PCD reinforced WC matrix composite (PCD composite for short), which is a kind of homogeneous composite material of fine property [30]. This hardbanding material has a strong resistance to wear, which can be very good to prevent the drilling pipe joint wear in the strong abrasive formation. Because of the extremely weak wear of the iron foundation material, the casing can be well protected with small friction factor and friction resistance.

In order to understand the relationship between the raw material's properties and its tool performance, the material properties and drill pipe hardbanding performance of this PCD composite were investigated [29]. We find that the

*Research Progress of the Drill String Hardbanding Materials DOI: http://dx.doi.org/10.5772/intechopen.90013*

**Figure 3.** *Schematic description of PCD composite hardbanding.*

excellent anti-friction property and reasonable hardness of this PCD composite hardbanding are the primary reasons for its enhanced tool performance. Besides, a height difference was found at the border between the PCD part and the WC matrix part, which is advantageous to form lubricant film to improve the lubricating performance. To better understand its performance, the friction and casing wear properties of PCD composite hardbanding were also investigated. The results indicate that as the applied load and sliding speed steadily increase, the friction coefficients of PCD composites decrease. In addition, the casing wear rates increase with increasing load but decline with sliding velocity. The dominant wear mechanism of the PCD composite is the micro-cutting wear, accompanied by adhesive wear [31].

Due to the poor thermal stability of PDC, the performance will be affected in high-temperature geothermal wells and deep wells [32]. In many polycrystalline diamond composites, the thermally stable polycrystalline (TSP) diamond can exhibit excellent anti-friction and good anti-abrasion, which also can be achieved in an environment of high temperature and super high pressure and thermally stable up to 1200°C. Thus, in order to improve the thermal stability, the TSP was used to replace the PCD to produce this hardbanding. By proving experimentation, TSP composites could satisfy the requirements of protecting the casing and the drill pipe at the same time when drilling deep holes. This perfect performance is dependent on the adsorbed lubricating liquid on the rubbing surface and the formation of height difference between the TSP part and the WC matrix part [33].

The overall results demonstrate that the PCD composite series hardbandings are extremely promising for drill pipe hardbanding applications.
