Tribological Properties of Si3N4-hBN Composite Ceramics Bearing on GCr15 under Seawater Lubrication

This paper concerns a comparative study on the tribological properties of Si3N4-10 vol% hBN bearing on GCr15 steel under seawater lubrication and dry friction and fresh-water lubrication by using a pin-on-disc tribometer. The results showed that the lower friction coefficient (around 0.03) and wear rate (10−6 mm/Nm) of SN10/GCr15 tribopair were obtained under seawater condition. This might be caused by the comprehensive effects of hydrodynamics and boundary lubrication of surface films formed after the tribo-chemical reaction. Despite SN10/GCr15 tribopair having 0.07 friction coefficient in the pure-water environment, the wear mechanismsits were dominated by the adhesive wear and abrasive wear under the dry friction conditions, and delamination, plowing, and plastic deformation occured on the worn surface. The X-ray photoelectron spectroscopy analysis indicated that the products formed after tribo-chemaical reaction were Fe2O3, SiO2, and B2O3 and small amounts of salts from the seawater, and it was these deposits on the worn surface under seawater lubrication conditions that, served to lubricate and protect the wear surface.

Effect of Heat Treatment Temperature and Lubricating Conditions on the Fretting Wear Behavior of SAF 2507 Super Duplex Stainless Steel

Super duplex stainless steel (SDSS) has excellent mechanical properties and corrosion resistance. However, currently, there are few researches conducted on its fretting wear performance. This paper studies the influence of different heat treatment temperatures and medium environment on the fretting wear performance of SAF 2507 SDSS. Results show that the combined effect of the sigma phase and seawater lubrication can significantly improve the wear resistance of SAF 2507 SDSS. After treated with different heat treatment temperatures, different contents of sigma phases are precipitated out of SAF 2507 SDSS, which improves the wear resistance of the material to different degrees. In addition, the fretting wear performance of SAF 2507 SDSS also relates to the lubrication medium. In air, the friction and wear performance of SAF 2507 SDSS is poor, while in seawater, solution and corrosion products that acted as a lubricant dramatically improve the wear resistance of the material. Under the combined action of heat treatment and seawater lubrication medium, the friction coefficient and wear reduce by 70% and 91%, respectively.

Tribological behavior of various ceramic materials sliding against CF/PTFE/graphite-filled PEEK under seawater lubrication

In order to select appropriate antifriction and wear resistance material combinations for key frictional pairs in seawater hydraulic components, tribological characteristics of SiC, Si3N4, Al2O3, and ZrO2 ceramics sliding against carbon fiber/polytetrafluoroethylene/graphite-filled polyetheretherketone composite lubricated with seawater were comparatively investigated with a ring-on-ring test rig. The results show that the nonoxide ceramics (Si3N4 and SiC), especially the Si3N4 ceramic, exhibited lower friction coefficients and smaller wear rates than those of oxide ceramics (Al2O3 and ZrO2). And the tribological behaviors of polyetheretherketone/Si3N4 tribopair under dry friction, pure water, and seawater lubrications are further comparatively studied to explore the effect of lubricating medium on the tribological characteristics of Si3N4 ceramic. It is found that the lubricating effect of SiO2 and Si(OH)4 films generated by tribo-chemical reaction between Si3N4 and water is the main factor for the relatively low friction coefficient and wear rate of polyetheretherketone/Si3N4 tribopair under aqueous lubrication. Under seawater lubrication, the Mg(OH)2 and CaCO3 deposition layers caused by the chemical reaction of Mg2+ and Ca2+ in seawater could inhibit the generation of SiO2 and Si(OH)4 films and increase the counterface roughness. As a result, the tribological behaviors of polyetheretherketone/Si3N4 tribopair are worse under seawater lubrication than that of pure water lubrication.

Influence of SiO2/MoS2/graphite content on the wear properties of PTFE composites under natural seawater lubrication

The polytetrafluroethylene (PTFE) mixed with different particles, such as SiO2, MoS2, and graphite, were prepared by using cold briquetting and hot sintering technologies. In order to investigate the influence of different mixture ratios of particles on the wear properties of PTFE composite under natural seawater lubrication, 10 different samples were designed through orthogonal test table and evaluated using an MMU-5 G wear tester. For comparison, the wear experiments of pure PTFE were also carried out under the same conditions. Moreover, the 3D profiles and depth variations of wear scars of PTFE composites were observed by a laser scanning confocal microscope. Results showed that the addition of SiO2, MoS2, and graphite can greatly improve the wear resistance of PTFE under seawater lubrication. In particular, 10% SiO2, 15% MoS2, and 15% graphite filled with PTFE composite possesses the best wear resistance. And a synergistic effect is found for the combination of SiO2, MoS2, graphite, and seawater, which effectively prevents the slipping of PTFE from matrix, increases the adhesion resistance, decreases the friction energy, further results in lower wear rate and little damage on the surface of the PTFE composites.