Polycrystalline diamond (PCD) used in down-hole tool applications is ideally suit for harsh environments such as drilling at circulation break and poor lubrication, in which the water molecules of physical and chemical adsorption can severely affect the tribochemistry effect across cutting interface. Here, tribological behaviors of PCD are studied in a controlled humid atmosphere (5%-50% RH). The friction coefficient is ~ 0.04 under 5% RH condition, which is significantly increased to ~ 0.11 under 50% condition.The run-in period and wear rate of PCD decrease while increasing RH levels during the tribotest. Such an ultra-low friction coefficient regime is explained coincide with the formation of efficient carbonaceous transfer films in the run-in periods through ex situ, micro-laser Raman spectroscopy and Atomic Force Microscope (AFM) measurements.Abstract graph: This paper highlights an intimate relationship among RH levels, dangling bonds passivation, run-in periods, transfer films formation and tribological behaviors.3 bits due to its extremely high wear resistance, high hardness and excellent toughness.Among these applications, fluids such as water, drilling mud and gas, are always required to lubricate the surfaces and interfaces of PCD in down-hole applications and its counter frictional pair. 1-4 Previous works have focused on that diamond rubbing against diamond in the presence of oil and water based drilling fluids had a coefficient of friction between 0.05 and 0.08. 5 Sexton et al. 6 investigated the bearing wear rates in laboratory testing and results showed that PCD thrust bearings provide a long-lasting bearing solution for down-hole drilling tools. Knuteson et al. 7 reported that the friction coefficient values of PCD thrusting bearing decreased in the lubrication regime moving from boundary to mixed-mode and may even become hydrodynamic. Mehan et al. 8 measured the wear rates of PCD and pointed out that wear mechanism of PCD was the result of diamond particles falling off in pin-on-disk tribometer experiments. However, the above works only concentrated on the mechanical aspects of wear performance and have not addressed the role of service environment factors on the friction coefficient, wear and ultimate failure wear of PCD. Considering the operating conditions such as high speeds, high loads, run-in period, frequent starting and stopping, cyclic fluctuating loads and extreme conditions such as drilling at circulation break and poor lubrication, the PCD contact surfaces cannot be ensured keeping in liquid lubrication condition all the time. We have confirmed from tribological behaviors of PCD under different relative humidity (RH) that friction coefficient, wear and adhesion behaviors are significantly affected by the adsorbed water molecules which can have distinct impacts on physical and chemical properties of solid surfaces. Understanding the effects of the relative humidity on sliding interface would be 5 formation of a transfer layer, possibly graphitic in nature. 19 Transfer films are known t...
In this paper, the tribological behavior of 316L stainless steel with heterogeneous lamella structure (HLS), prepared through 85% cold rolling technology and subsequent annealing treatment (750 °C, 10 min), were conducted on a ball-on-disc tribometer under different normal loads in dry ambient air conditions. The morphologies, structures, and compositions of the raw and worn surfaces were analyzed by 3D surface profilometer, XRD, SEM, EDS and TEM. Based on this, the results showed that the HLS 316L stainless steel samples exhibited lower and more steady friction coefficients than coarse-grained samples, especially under higher loads, which can be attributed to the existence of numerous oxidative particles across sliding interfaces. However, the wear resistance of HLS 316L stainless steel sample was a little weakened compared to that of the coarse-grained sample under a normal load of 5 N. When the load increases up to 15 N, an obviously decreased wear resistance was found for the HLS of the 316L stainless steel sample, which was 50% lower than that of coarse-grained sample. This can be ascribed to the more severe oxidative and abrasive wear performance of HLS 316L stainless steel sample under dry sliding conditions.
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