| 其他摘要 | The study on nanocrystalline (NC) material now mainly focuses on the sample preparation and structure characterization, while few papers reports wear and friction properties of NC samples deduced usually by single experimental results. It should be indicated that this method could not evaluate tribological behavior of material preciously. In this dissertation surface nanocrystallization is realized by many kinds of NC technologies, the tribological behavior of NC and microcrystalline (MC) sample will be investigated systemically to discuss their applied area. It is helpful to the application of NC material and NC technology.
1. Tribological behaviors of Armco iron by severe rolling
Bulk NC Armco iron was produced by severe rolling (SR). The wear resistance of SR sample in dry sliding such as reciprocating, erosion and fixed abrasive wear was less than that of conventional rolled (CR) sample, and SR sample showed the lower plough resistance in impacting and sound emission scratch tester. The friction and wear properties of SR sample were improved after annealing, but also less than that of CR one. In LP lubricating, the wear loss of SR sample with/without annealing was less than or close to that of original one, and the coefficient of friction (COF) of NC sample was less than that of CR and annealed SR. NC sample by severe rolling displayed the better anti-friction and anti-wear properties than CR and annealed SR ones when additive of ZDDP or oleic acid was added into LP. The content and depth of activated element on the worn track of SR sample was higher than that of CR one by EDS and AES. The COF of NC sample decreases at elevated temperature of the LP lubricant with ZDDP, which should be ascribed to the better capacity to react with additive duo to high surface activity of NC grain, but CR one with low surface activity shows the contrary tendency.
2. Tribological behaviors of NC surface by supersonic fine particles bombarding (SFPB)
Surface nanocrystallization was realized on pure iron and carbon steels, while not realized on gray iron after SFPB treatment. In dry sliding, the wear rate of SFPB sample was about three times as that of original one, and the wear rate of polished SFPB sample was less than that of original one, while COF of SFPB sample was less than that of the others. In LP lubricating, the wear rate and COF of three samples decreased and their sequence was consistent to that in dry sliding. Only in LP+ZDDP lubricating, was the wear rate of SFPB sample less than that of original one, and the wear rate of polished SFPB sample decreased drastically compared with that of original one, and three samples had the same COF by and large (about 0.10). The content and depth of Zn, S absorption or reaction film on the NC sample was higher than that on original one, this exhibited the high activity of NC grain. Pure iron in four Fe-C alloy got best surface NC effect deduced from the wear rate in different medium.
3. Tribological behaviors of NC surface of Q235 steel by high energy peening (HEP)
NC layer with many delves on the surface was fabricated on the Q235 carbon steel using HEP. The wear loss and COF of HEP sample in dry sliding were higher than that of original one, while the consequence of wear loss of two samples in LP lubricating was contrary and the COF was consistent to each other (about 0.11-0.12). When ZDDP was added into LP, the discernment extent of wear loss of HEP was higher than that of original compared with that in LP lubricating. Only in LP+ZDDP lubricating, could polished HEP sample display excellent wear resistance, and the content and deepness of Zn, S on its worn tracks was higher than that of original one, which accorded with the NC effect of SFPB technology. The wear loss and COF of original sample rubbed on sand by hand was lowest in different medium.
4. Electroless Ni-P- (NC) PTFE composite coating and its tribological behaviors
MC and NC PTFE particles were dispersed into distilled water and formed latex using cationic (fluidizer) and non-ionic surfactant by ultrasonic homogenizer. After (MC or NC) PTFE latex was added into plating solution, the electroless Ni-P- (MC) PTFE, Ni-P- (NC) PTFE composite coating with different volume content could be produced through the adjustment of PTFE concentration. Sample was placed vertically in plating solution containing nano PTFE particles, while in MC PTFE electroless plating solution the sample was placed horizontally. The experiment result indicated the good anti-frictional effect was achieved when (MC or NC) PTFE content reaches to 25% (by vol.), and the COF was about 0.11-0.15 (sliding with stainless steel ball). The anti-friction properties of above PTFE composite coatings are studied in a pin-on-disc tester (the velocity is about 0.46 m/s). The wear loss and frictional coefficient of MC Ni-P/PTFE composite coating at load of 2～4N was lower than that of NC Ni-P/PTFE composite coating. When the load exceeded 6N, the wear and friction properties of MC Ni-P/PTFE composite coating turned bad, while NC Ni-P/PTFE composite coating could endure the higher load which reached to 21N.
5. Discuss of tribological behaviors of NC surface of carbon steel by severe plastic deformation
The NC samples prepared by severe plastic deformation could not be suit to dry sliding due to its cold working, defect, surface roughness, and disability to plastic deformation of NC grain. The good tribological properties of NC sample could be displayed in LP, especially in LP+ZDDP lubricating, which should be ascribed to the better ability to absorb or react with additive duo to high surface activity of NC sample. |
修改评论