| Water-based lubrication is an effective method to reduce energy consumption and it's environmentally friendly.In water-based lubrication,the separation between the friction pairs is in nanoscale and the friction coefficient is in super-low regime.With the rapid development of advanced manufacturing technology,water-based lubrication shows the applied potentials in the lubrication of transportation equipment and ultraprecision machining elements.In this dissertation,two polysaccharides compounds were selected as lubricant additives and their lubrication properties were investigated.Sodium alginate(SA)and hydroxyethyl cellulose(HEC)were extracted from nature plants and shows excellent properties of bioeompatibility.They are green materials and easily degradable.The lubrication behaviors of them were explored to reveal the lubrication mechanism.The work will provide fundamental insights for application of water-based lubrication.The main works are as follows:(1)By analyzing the tribometer theoretically,two sources of measurement error were discovered.They are the displacement between the contact point and the rotating center and the misalignment between the wear surface and the horizontal plane.Based on the results of designed test,the measurement error caused by the displacement would be as low as 5%if the friction force was less than 0.85 N.And a lower friction force caused a lower measurement error.By force analysis,the misalignment angle between the wear surface and horizontal plane should be regulated below 0.02g ° to guarantee the measurement error below 5%if the magnitude of the friction coefficient is as low as 0.01.To solve these problems,a high precision regulating device was developed and the measurement error reduced to 3.1%.(2)The highly polished quartzes were assembled as flat-contact tribopairs.The effect of concentration,speed,load and surface roughness on the tribological properties of sodium alginate was studied.The results showed that the friction coefficient of sodium alginate stably lasted for more than 12 h.The 4.00 wt.%SA solution showed the lowest friction coefficient(??0.002)and the friction coefficient became larger if the concentration was lower or higher than 4.00 wt.%.The friction coefficient decreased with rotational speed and the effect of load on the friction coefficient was studied at low-speed and high-speed conditions.The friction coefficient decreased weakly with increasing loads.The tribopairs adhered together if the surface roughness of upper and lower pairs were the same.To achieve stable and low friction coefficient,the surface roughness of upper and lower pairs should be rationally selected.(3)The lubrication properties of four celluloses were investigated under flat contact.Under the same test condition,the lubrication of methyl cellulose solution and hydroxypropyl cellulose solution was not stable and the friction pairs would adhere together.The carboxymethyl cellulose solution showed a stable friction behavior and a high value of friction coefficient.The hydroxyethyl cellulose solution possessed the most stable lubrication property and the lowest friction coefficient.The effects of speed,load and concentration on the lubrication properties of hydroxyethyl celluloses were studied.The friction coefficients of four HEC solutions showed no obvious reflect to the rotational speed.When the load increased from 1 N to 9 N.the friction coefficients decreased rapidly from 0.005 to 0.001.The higher load resulted in more stable friction behavior.The 1.00 wt.%solution showed the lowest friction coefficient(??0.001).If the concentration was larger or lower than 1.00 wt.%,the friction coefficient became larger than 0.001.For 3.00 wt.%solution,the viscosity took the leading function.thereby the load showed a weak impact on its lubrication property.(4)The friction behavior of HEC was studied by the point contact of Si3N4 ball and Ti-6A1-4V disk.During the running-in stage,the friction coefficient kept decreasing and the stable friction coefficient was about 0.005.The running-in stage can be divided into two stages:during running-in stage I,the high friction coefficient kept decreasing;during running-in stage ?,the friction coefficient behaved in fluctuation and it could reach 0.01 for a very short time.When the concentration increased from 0 to 1.00 wt.%.the friction coefficient reduced from 0.053 to 0.005.When the concentration was larger than 1.00 wt.%,the friction coefficient increased with increasing concentration.If the concentration was between 0.50 wt.%?2.00 wt.%,super low friction coefficients(<0.01)were achieved.The friction coefficient decreased when the speed increased from 80 r/min to 410 r/min.If the speed was larger than 410 r/min.the friction coefficients increased with increasing speed.When the speed was between 300 r/min?630 r/min.super low friction coefficients(<0.01)were achieved.(5)Laser surface texturing(LST)was used to improve the lubricating property of HEC and three line-like patterns(grid line,parallel line,radial line)were selected.The surface topographies and element contents were detected.The friction coefficient and wear loss of polished surface were the largest.The friction coefficient was 0.043 and the wear loss was 6.7 g.The friction coefficient of radial-line surface was 0.028 and the wear loss was 4.0 g.For the surfaces textured with same texture,the higher surface texture density resulted in the lower friction coefficient and wear loss.The resulting wear tracks were examined and some unworn part were detected on the Si3N4 ball against the textured surfaces.The ratio of film thickness and surface roughness was calculated,which indicated that the lubrication regime of radial-line surface transformed from boundary lubrication to mixed lubrication while other surfaces worked in boundary lubrication condition.(6)The synergistic effect of coupling agent APTES can improve the lubrication property of HEC solutions in radial-line texture surface.The friction coefficients of HEC and APTES solutions were between 0.03?0.04.Contrastively,the friction coefficient of HEC-APTES solution decreased from 0.029 to 0.017 after running-in stage.When the quantity of APTES increased from 0 to 6.00 wt.%.the friction coefficient and wear loss of mixture solution decreased.When the speed was lower than 520 r/min,the friction coefficient decreased with rotational speed.The friction coefficient increased with rotational speed when the speed was larger than 520 r/min.Based on the analysis of the worn surfaces,two contact status included asperity contact condition and plough/lubricant contact condition.The scatter map of element was detected and it indicated that the hydrated HEC chains adhered onto the Ti-6A1-4V surface by synergistic effect of APTES.A lubrication model for HEC-APTES tested against textured surface has been established. |
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