Study of Friction and Wear Behavior Based on Different Lubricants and Materials
Type of DegreePhD Dissertation
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Tribology is the study of friction, wear, and lubrication between the contacting bodies and requires a deeper understanding of multiple disciplines. This study was mainly focused on two main areas: the tribological study of additively manufactured parts and bio-based lubricants (first, second and third generation of biomass) as alternatives to conventional base oils. First, additively manufacturing parts of 17-4 precipitation hardening (PH) stainless steel (SS) were made using laser-based powder beam fusion (LB-PBF), and wrought conventional parts were also made. Both samples were tested using a tribometer under dry and lubricated conditions at 10N and 30N applied loads. The wear rate for both dry and lubricated conditions were found to be proportional to the load under the same loading condition. LB-PBF 17-4 PH SS has a slightly higher hardness value (417 ± 21 HV) than the CM 17-4 PH SS (392 ± 24 HV) due to the finer microstructure produced as a result of a higher cooling rate. This variation in hardness number results in less wear in the LB-PBF sample than the conventional wrought sample. Wear results tested in the dry condition had more adhesive wear while the mechanism changed to abrasion during the lubricated condition. The surface roughness of the LB-PBF specimens was measured to be 1.93 µm, while it was 0.88 µm for the CM ones. Asperities were more likely to be in contact for the LB-PBF samples during the lubricated condition. This could be the reason for variation in the wear rate for the lubricated condition where conventional wrought had lower wear than the LB-PBF samples. There was a difference in the friction between each test condition, but not between the conventional wrought and LB-PBF samples. The average dry coefficient of friction (COF) at 30 N is 0.9 while the dry COF at 10 N is 1.15. SEM and optical images confirmed that the dominating mechanism for wear during the dry condition was due to adhesion whereas abrasion was the dominant mechanism during the lubricated condition. Secondly, the importance of sustainable lubricants is very important and several vegetable-based oils with different oleic content were compared with a standard mineral base oil for friction, wear, and chemical properties. A ball-on-disk tribometer test was performed to analyze the tribological properties of the oil under 50 N of applied load and at varying speeds. The viscosity of the conventional soybean oil increased as the temperature increased past approximately 100oC and could be the result of the heavier molecular fraction of the oil. Plenish and Vistive had lower viscosities than the mineral base, even at 100oC. The Plenish oil samples’ wear areas were comparable to the mineral oil samples with 0.25% of a conventional additive package. This demonstrates the potential of the renewable source as a base lubricant that may not require as many additives as mineral oils. The presence of higher oleic content oils had C=O as a functional group identified from a Fourier Transformation Infrared (FTIR) test. This C=O bond helped to attract oil toward the metal surface to form a film layer. Vegetable oils have a lower COF as compared to mineral oil in the boundary lubrication regimes. The presence of oxygenates in the vegetable oil reacts with the surface and improves the lubricity of the oil. Similar to the previous study, abrasion was found to be the dominant wear mechanism and was identified due to directional grooves on the metal surfaces. Similarly, second and third generation biomasses were used to make bio-oils from fast pyrolysis (using poultry and pine), gasification (“gasitar” using pine), and hydrothermal liquefaction processes (using Scenedesmus and Nannocholoropsis). The friction and wear tests were conducted using a ball on the disk tribometer test. The results showed that the COFs were around 0.02 for both gasitar and Scenedesmus bio-oil; whereas, catalytic and non-catalytic pyrolysis oils had COFs around 0.1. Wear results indicated that catalytic pyrolysis bio-oil had a lower wear cross-sectional area compared to all other tests. The chemical analysis of bio-oil samples indicated that gasitar had lower oxygen and higher hydrocarbon composition, pyrolysis bio-oil had higher oxygenates, and algal bio-oils had a higher nitrogenates composition. The study showed that catalytic pyrolysis bio-oil and gasitar have good prospects to be used as lubricants, however, catalytic pyrolysis bio-oil chemical analysis indicated the presence of oxygenating groups which could have a cascading effect at an elevated temperature. Optical images indicated that for algal and poultry bio-oil scuffing was the dominant wear mechanism where abrasive wear was more dominant for the other bio-oils.