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Study of solid lubrication with MoS2 coating
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Study of solid lubrication with MoS2 coating

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  • 1. Study of solid lubrication with MoS2 coating in the presence of additives
  • 2. Space Applications • Gassing under the vacuum • High temperature conditions Food and Textile industries • Contamination of product
  • 3.  Low, constant and controlled friction between the two surfaces.  Chemically stable and inert over the required temperature range.  Adhere strongly to one or both the surfaces.  Sufficient resistance to wear.  Non toxic and economical.
  • 4.  Very low volatility.  Chemical inertness.  Stable to radioactivity.  Oxidises to molybdic oxide (MoO3) at higher temperatures, a fair lubricant itself.  Good load carrying capacity (hexagonal layer-lattice structure).  Doesn’t depend on presence of adsorbed vapors to act
  • 5. VERTICAL SLIDE • Applies dead weight • Mounts the load cell HORIZONTAL SLIDE • Scratching the specimen 3mm diameter steel ball bonded to holder Material selected: EN8 steel of size 20 X 20 X 10mm thick Normal Load applied: 30N Stroke length: 8mm Slider velocity: 2mm/s Test conditions: Ambient temp. 20-35ºC, Humidity 50-90% Failure criteria: Coefficient of friction > 0.2  Number of cycles v/s Friction force plots are made for each sample
  • 6. 1. Experiments were carried out to study the dry friction characteristics of the rubbing surfaces of steel specimen having roughness, Ra = 0·19μm. The initial coefficient of friction was around 0·13 and attained a value of 0·5 within 20 cycles. 2. Similar tests were conducted on the specimen having Ra = 0·39μm. The initial coefficient of friction was around 0·15 and attained a value of 0·5 within 20 cycles. RESULT: The coefficient of friction between two steel surfaces is greater than 0·5 under non- lubricated conditions. TEST 1. Scratch test under “dry sliding conditions” between steel specimen and steel ball
  • 7. TEST 2. Scratch test between MoS2 coated steel specimen and steel ball Heating prepared specimen to around 80ºC (to evaporate the moisture) Applying MoS2 by brush (2-3 coats) Heating and curing the specimen at elevated temperature depending on composition (additives,binders, etc.) Removing loose powder from surface Burnishing the specimen for 15 minutes using ball tumbler  Binding Material: Sodium Silicate (Na2SiO3)
  • 8. UNBURNISHED BURNISHED  Phosphate coating provides good base for lubrication.  Being “micro porous”, traps lubricant into interstices.  Larger surface area for lubricant.  Excellent protection against corrosion. RESULT:  Unburnished specimen withstood 105 cycles.  Burnished specimen (30 min) withstood 45 cycles.  “Poor adhesion” between specimen and lubricant.
  • 9. TEST 3. Scratch test between phosphated steel specimens coated with MoS2 and steel ball RESULT: In both the cases above, wear rate was around 0.023 μm/cycle.  Unburnished specimen withstood 250 cycles  Burnished for 15 min., specimen withstood 300 cycles Zinc Phosphate base specimen  Unburnished specimen withstood 190 cycles, Burnished for 15 min., specimen withstood 260 cycles. Manganese Phosphate base specimen
  • 10. TEST 4. Scratch test between MoS2 coated phospated steel specimen with zirconia as an additive, steel ball ZIRCONIA: • Ceramic material which offers high resistance to wear. • Exists in both tetragonal and monoclinic crystal structure. • During scratching, metastable tetragonal converts into monoclinic by strain induced structural transformation. • More % of tetragonal structure would give better result as lubricant RESULT:  In Mn-phosphate base, 8% zirconia as additive failed at 730 cycles, wear rate brought down to 0.014 μm/cycle.  In Zn-phosphate base, 8% zirconia as additive failed at 1400 cycles, wear rate brought down to 0.014 μm/cycle.  Initial friction coefficient more than 0.1 in each case.
  • 11. TEST 5. Scratch test between MoS2 coated phosphated steel specimen with zirconia and graphite as additives and steel ballGRAPHITE: • Good natural low-friction behavior when contaminated with vapors. • Good load bearing ability along with lubricating action • Reduces the friction value which was increased by additive zirconia. RESULTS: On addition of 8% zirconia and 25%graphite; • Zn-phosphated specimen withstood 1250 cycles, with friction crossing 0.1 after 600 cycles! • Average wear rate was 0.01 μm/cycle. • Mn-phosphated specimen withstood
  • 12. Zinc Phosphate base specimen containing zirconia 8% Zinc Phosphate base specimen containing zirconia 8% and graphite 25%
  • 13. TEST 6. HIGH TEMPERATURE SCRATCH TESTS 1. Reciprocating Scratch test at 200ºC. • Test carried for 5500 cycles • Friction as low as 0.05 even after 5500 cycles. • No sign of failure, because all moisture has been evaporated. 2. Reciprocating Scratch test after 90minutes of cooling to room temperature from 200ºC. • Specimen withstood 3000 cycles. • Sufficient time not given to absorb moisture completely. 3. Reciprocating Scratch test after two days of cooling to room temperature 200ºC. • Specimen failed at 600 cycles. • Result coherent with ambient conditions, as moisture had been absorbed to saturation level. RESULT: Humidity affects the adhesion component of friction and therefore the intercrystallite forces, wear rate also increases as more moisture is absorbed.
  • 14. •The addition of zirconia and graphite into the lubricant improves its properties in terms of both friction and wear. • The moisture present in air also plays an important role in reducing friction and wear rate. As the moisture reduces, coating performance of the film is enhanced.