Effect of filler behavior on nanocomposite SU8 photoresist for moving micro-parts (original) (raw)
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SU8 nanocomposite coatings with improved tribological performance for MEMS
Surface & Coatings Technology, 2006
The increasing interests in micro-electro-mechanical systems (MEMS) has raised the requirement for photoresist materials with improved friction and wear properties for mechanically loaded 3D shaped microstructures. In this work, SU8 photoresist layers reinforced with different amounts of silica nanoparticles were produced and thermally treated. Dry sliding tests indicate that SU8 composite epoxies produced in the form of thin films exhibit similar or even better tribological properties than bulk epoxies. The SU8 nanocomposites exhibit reduced wear rates and frictional coefficient compared to the un-reinforced material. Further, nanoparticle content, heat treatment and nature of the sliding counter piece were found to affect wear and friction. The tribological behaviour was discussed in terms of mechanical properties and contact pressures.
Different concentrations of graphite powder (particle size < 20 µm) were added for the enhancement in mechanical and tribological properties of SU-8 polymer. The materials were studied as thick coatings with thickness in the range of ~ 35-40 µm on glass substrate. SU-8 and SU-8/graphite composite properties were examined using atomic force microscope (for nanoindentation test) and pin-on-disc tribometer (for friction and wear). The surface characteristics were studied using Optical Microscope, Goniometer and 3D Profilometer. At 10 and 20 wt% graphite concentration, it was found that several properties were enhanced such as elastic modulus ~ 2.2 times, marginal increment in hardness and approximately same water contact angle and same surface free energy (SFE) as compared with those of pure SU-8. More importantly, 10 wt% graphite concentration has given two-times lower steady-state coefficient of friction and ~ 10 times more wear life compared to those of pure SU-8. The 20 wt% composite gave higher coefficient of friction but lower wear rate than the 10 wt% composite.
Tribology Online, 2016
Different concentrations of graphite powder (particle size < 20 µm) were added for the enhancement in mechanical and tribological properties of SU-8 polymer. The materials were studied as thick coatings with thickness in the range of ~ 35-40 µm on glass substrate. SU-8 and SU-8/graphite composite properties were examined using atomic force microscope (for nanoindentation test) and pin-on-disc tribometer (for friction and wear). The surface characteristics were studied using Optical Microscope, Goniometer and 3D Profilometer. At 10 and 20 wt% graphite concentration, it was found that several properties were enhanced such as elastic modulus ~ 2.2 times, marginal increment in hardness and approximately same water contact angle and same surface free energy (SFE) as compared with those of pure SU-8. More importantly, 10 wt% graphite concentration has given two-times lower steady-state coefficient of friction and ~ 10 times more wear life compared to those of pure SU-8. The 20 wt% composite gave higher coefficient of friction but lower wear rate than the 10 wt% composite.
Tribology - Materials, Surfaces & Interfaces, 2016
SU-8, an epoxy-based negative photoresist polymer, is highly suitable for making micro-electromechanical systems (MEMS) structures. Despite fabrication advantages, its bulk mechanical and tribological properties are the main limitations for application as MEMS material. Carbon filler materials such as graphene, graphite and multi-walled carbon nanotube (MWCNT) are added to SU-8 for tribological and mechanical property enhancements. SU-8/(5 wt%) graphite composite has performed better for the steady-state coefficient of friction at all loads including for the speed effect. SU-8/(5 wt%) MWCNT has shown excellent wear resistance. At 10 wt% graphite content, SU-8/graphite is superior in tribological performance to other composites tested.
Lubrication Mechanism of SU-8/Talc/PFPE Composite
Tribology Letters, 2017
SU-8, a very promising structural polymer for the next-generation 3D fabrication of micro-electromechanical systems (MEMS), has extremely poor tribological properties. The improvement in tribological properties has been recently addressed by developing SU-8/talc (30 wt%) /perfluoropolyether (PFPE) (30 wt%) composite. This composite showed wear durability approximately five orders of magnitude greater in comparison with that of pure SU-8. This drastic increment was found to be because of the in situ lubrication mechanism provided by the PFPE liquid droplets present in the composite. In this present investigation, the lubrication mechanism for SU-8/talc (30 wt%)/PFPE (10, 20 and 30 wt%) composites was further investigated by varying sliding speed (0.1-1.0 m/s) and normal load (2 N and 4 N) using silicon nitride ball of 4 mm diameter as the counterface. The data show that the coefficient of friction and interfacial shear strength follows linear relations with the logarithm of the sliding velocity. Normal load has effect on marginally reducing the coefficient of friction.
Experimental Analysis and Modeling for Reciprocating Wear Behavior of Nanocomposite Coatings
2018
This paper presents the study of wear responses of nanocomposite coatings with a steel ball under oscillatingreciprocating state. Nanocomposite coatings for this study include: Nickel-Alumina (Ni/Al 2 O 3), Nickel-Silicon Carbide (Ni/SiC), Nickel-Zirconia (Ni/ZrO 2) and Ni/Graphene. Ni/ZrO 2 exhibited maximum wear rate followed by Ni/SiC, Ni/Al 2 O 3 and Ni/Graphene respectively which was also assured by Scanning Electron Microscopy (SEM) micrographs, grain sizes, hardness, porosity, surface stresses, frictional coefficients behaviours and "Ushaped" wear depth profiles. The "U-shaped" profiles were utilised to calculate the energy distribution (Archard factor density) along the interface. A novel mechano-wear model incorporating the energy distribution equations with the mechanics equations was developed for analysing the effects of intrinsic mechanical properties (such as grain sizes, hardness, porosity, surface stresses of the nanocomposite coatings) on the wear response. The predictions showed close agreement with the experimental results. In conclusion Ni/Graphene exhibited better anti-wear properties compared to other nanocomposite coatings. The high anti-wear behaviour of Ni/Graphene composite is due to enhanced strengthening effects in the presence of graphene. The importance of this work is evident from various industrial applications which require reliable modelling techniques to predict coatings failures due to wear. This work will bring significant impact to precision manufacturing, wind turbine industries, automotive, locomotive and aerospace in overcoming critical wear failures.
Experimental analysis and modelling for reciprocating wear behaviour of nanocomposite coatings
Wear
This paper presents the study of wear responses of nanocomposite coatings with a steel ball under oscillatingreciprocating state. Nanocomposite coatings for this study include: Nickel-Alumina (Ni/Al 2 O 3), Nickel-Silicon Carbide (Ni/SiC), Nickel-Zirconia (Ni/ZrO 2) and Ni/Graphene. Ni/ZrO 2 exhibited maximum wear rate followed by Ni/SiC, Ni/Al 2 O 3 and Ni/Graphene respectively which was also assured by Scanning Electron Microscopy (SEM) micrographs, grain sizes, hardness, porosity, surface stresses, frictional coefficients behaviours and "Ushaped" wear depth profiles. The "U-shaped" profiles were utilised to calculate the energy distribution (Archard factor density) along the interface. A novel mechano-wear model incorporating the energy distribution equations with the mechanics equations was developed for analysing the effects of intrinsic mechanical properties (such as grain sizes, hardness, porosity, surface stresses of the nanocomposite coatings) on the wear response. The predictions showed close agreement with the experimental results. In conclusion Ni/Graphene exhibited better anti-wear properties compared to other nanocomposite coatings. The high anti-wear behaviour of Ni/Graphene composite is due to enhanced strengthening effects in the presence of graphene. The importance of this work is evident from various industrial applications which require reliable modelling techniques to predict coatings failures due to wear. This work will bring significant impact to precision manufacturing, wind turbine industries, automotive, locomotive and aerospace in overcoming critical wear failures.
In Situ Lubrication of SU-8/Talc Composite with Base Oil (SN150) and Perfluoropolyether as Fillers
Tribology Letters, 2016
In this paper, pure SU-8 and SU-8/talc (30 wt%) composite were filled with two liquid lubricants, hydrocarbon base oil (SN150) and perfluoropolyether (PFPE) in different weight percentages (2, 10, 20 and 30 wt%). The composite coatings in the thickness range of *150 lm were prepared on glass substrate using spin-coater. Pure SU-8 and its self-lubricated composites were examined using pin-on-disk tribometer, 3D optical profilometer, optical microscope, micro-hardness tester, thermogravimetric analyzer and goniometer. From tribological tests, it was observed that the coefficient of friction reduced by *9-10 times after adding lubricant fillers and the wear life was [4 9 10 5 cycles for the SU-8/talc (30 wt%) with 30 wt% PFPE at 6 N normal load and 0.28 m/s sliding speed compared with zero life for without PFPE. The corresponding specific wear rate was 6.4 9 10-8 mm 3 /N-m. From surface characterization, it was observed that the surface changed from hydrophilic to hydrophobic in nature after adding PFPE, but SN150 oil-filled composite shows hydrophilic nature at higher wt%. The wear mechanism for SN150-filled composite was by delamination at high load and higher wt% of the liquid, whereas for PFPE-filled composite, it was of abrasive type. There were improvements in the elastic modulus, hardness and thermal decomposition temperature for SU-8 composites with liquid fillers over pure SU-8, and the benefit was more for composites that also contained 30 wt% of talc.
An in-situ heating effect study on tribological behavior of SU-8+PFPE composite
Wear, 2013
SU-8 polymer is an emerging structural material for micro-fabrication of MEMS/NEMS devices using photolithography process. However, poor tribological properties of SU-8 restrict its wide applications as a very reliable MEMS material. In our earlier work [1], we have developed SU-8 composites which reduced friction and enhanced wear life of SU-8 by more than four orders of magnitude. The improvements in the properties were attributed to the self-lubricating nature of the composite by continuous supply of the lubricant into the worn areas, the lubricious nature of the filler lubricant perfluoropolyether (PFPE), and possible chemical bonding between SU-8 and PFPE. In this current work, we further investigated the effect of in-situ heating on the tribological performances of the SU-8þ PFPE composite. In-situ heating from room temperature (25 1C) to 100 1C showed a strong effect on the tribological behavior of SU-8þPFPE composite by reducing its initial and steady-state friction coefficients by $ 2 and $ 7 times, respectively. Wear life (n) increased by more than three times due to in-situ heating. Greater surface area coverage by the spreading of PFPE lubricant and migration of PFPE from the bulk to surface are found responsible for this superior tribological performance of the composite at high temperatures.