The friction and wear of various hard-face claddings for deep-hole drilling

Hard-face claddings are used for banding drill shafts that rotate against well casings while lubricated by drilling mud. This tribosystem should have the lowest friction possible in order to minimize drilling power requirements, and the lowest total system wear to maximize component life. Blocks representing a variety of hard-face claddings were slid against rotating rings of AISI 4140 casing material and lubricated by simulated drilling mud that consisted of a slurry of silica sand, clay, and water. The cladding specimens included currently used alloys and several candidate compositions. There was an excellent correlation between the friction coefficient and the wear, by weight loss, of both the cladding and the casing alloys. There was also a good direct correlation between the wear of the cladding and the wear of the casing. Claddings with finer grain sizes and finer, more uniformly distributed hard carbides had higher hardness and produced lower wear on both the cladding and the casing counter-face. The complex mechanisms involved with three-body wear and friction in interfaces lubricated by slurries present a challenge for further study.