Ultrahard coatings are being deposited on the exterior surfaces of rock bit cutters and other downhole tools for increased wear and erosion resistance. Processing entails hypersonic spray Processing entails hypersonic spray deposition of carbide containing coatings and subsequent fusion using high powered lasers. These coatings are put on finished components within a matter of minutes without damage to the cutting elements. Field tests conducted on 7 7/8 F27 and F17 type bits have indicated above average performance of the coatings. These hard coatings dramatically decrease fluid erosion of cutter surfaces, leading to improved insert retention and the potential for increased bit performance. potential for increased bit performance. Implementation of this state of art technology on entire families of downhole tools will be discussed. Introduction In the quest for increased rates of penetration, drillers are constantly penetration, drillers are constantly subjecting drilling bits to higher weights and rotary speeds, far in excess of design limits. Bit manufacturers are looking for means to increase bit performance by design methods, without sacrificing bit diameter or structural integrity of cutters. The bit designer is looking for increased cutting tool extension, without insert loss, often trading cutter extension for adequate grip area, so that insert loss does not occur. The bit body itself must withstand a variety of changing formations and severe wear and erosion under downhole conditions. The presence of high pressure drilling mud and presence of high pressure drilling mud and cuttings impinging on the bit body causes severe erosion not encountered in other engineering applications or disciplines. Over the years, a variety of design and material processing methods have been investigated to retard downhole wear and erosion. Design approaches have included milling of slots and contours that can act as channels or ways that will allow the high pressure mud and debris to egress away from the cutters. Metallurgical approaches have included putting a hard carburized case on the cone shell. Bit manufacturers have implemented carburizing as a means for increasing surface hardness over the last several decades. However, this process has its limitations. The traditional methods of carburizing cutter heads include a profile operation that removes most of the case around inserts, to facilitate drilling and pressing inserts. Thus, most rock bits have a negligible carburized layer around inserts, rendering little protection against downhole wear and erosion. Increasing core hardness of rock bit cutters themselves to values beyond about 40 Rockwell C cannot be carried out, since increased hardness leads to lower fracture toughness and eventual cutter breakage or very severe peeling of the cone-shell steel. P. 49
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