The evaluation of various cladding materials for down-hole drilling applications using the pin-on-disk test

Eleven different hard-face claddings were evaluated for banding deep-hole drilling shafts to minimize friction and wear with the well casings. Friction forces were measured using 4140 pins on disks clad with both current commercial alloys and several developmental alloys. These were lubricated with simulated “mud” slurry consisting of bentonite clay and silica powder mixed in water. Loads and speeds were varied to determine the sensitivity of friction with operating conditions. The friction coefficients varied between 0.3 and 0.4 for all cases. Although the range is relatively narrow, differences of this magnitude could still be important in reducing the energy required to drill. Higher rotational speeds resulted in slightly lower friction coefficients, but the effect of loads between 2 and 5 N were not significant. The results were also evaluated with respect to alloy composition, oxide film composition, surface hardness and surface roughness, all variables which could have an effect on the friction coefficient. The lower alloy content iron based compositions seemed to produce lower friction coefficients, possibly due to the production of iron oxide flakes which could act as a solid lubricant. Although the hardness of the claddings varied over a wide range, there was no apparent relationship to friction as was also the case for the surface roughness. The microstructures of higher friction claddings had finer and more homogeneous features than lower friction claddings.