1. Abhishek Barat Research Assistant
Effect of Polishing and Surface Roughness on the performance of coatings in Fretting Wear 
Abhishek Barat
Research Assistant

2. Outline Personal Background
Motivation and Background
Objective
Fretting Wear Test Rig
Description of experiment
Results
Future work
Personal Background
Joined Mechanical Engineering Tribology Laboratory, (METL) – August 2013
Worked as Scientist – Gas Turbine Research Establishment, India (December, 2009 – July, 2013)
B.Tech (Hons) in Mechanical Engineering from National Institute of Technology, Bhopal

3. Background and Motivation
Fretting is the oscillatory tangential relative movement between two contacting surfaces due to small amplitude vibration. (Waterhouse R. B)
Initial surface roughness has a significant effect on friction and wear rate
High surface roughness leads to low friction coefficient and a higher wear rate (Kubiak et.al)
Thermal sprayed coatings - improve wear resistance and decrease friction coefficient under sliding conditions. (Picas A. J)
CrC-NiCr coatings used to counter wear at high temperatures
Surface morphology in engineering applications: Influence of roughness on sliding and wearing dry fretting; K.J. Kubiak, T.W.Liskiewicz , T.G.Mathia
Interface roughness effect on friction map under fretting contact conditions; K.J. Kubiak, T.G. Mathia, S. Fouvry
The influence of heat treatment on tribological and mechanical properties of HVOF sprayed CrC–NiCr coatings; Josep A. Picas, Miquel Punset, Sergi Menargues, Manel Campillo, M. Teresa Baile, Antonio Forn

4. Objective
Experimentally investigate effect of polishing on fretting wear resistance of surface coatings
Study the fretting wear behavior of polished and unpolished surface coated samples, at different load conditions
Compute wear volumes and compare the wear coefficients
Develop a numerical model and validate with experimental results

5. Fretting Wear Test Rig Contact configurations Flat-on-Flat
Counterweight
Contact configurations
Flat-on-Flat
Ball-on-Flat
Crossed Cylinder
Testing capabilities
In situ contact point observation
Friction and fretting wear measurement
Lubricated and un-lubricated environments
Elevated temperatures
Loading Arm
Upper Loading Weight
Stationary Test Specimen
Linear Actuator

6. Description of Experiment
Experimental setup – Flat on Flat Configuration
Specimens to be tested at 3 different levels of surface roughness:
Unpolished - Ra = 4.87µm
Polished - Ra = 0.2µm
Finely Polished - Ra = 0.01µm
Experiment variables
Total time of experiment: 36 hours
Displacement Amplitude: 30 µm
Frequency: 20 Hz
Load/Normal force (kg): 4, 6, 8, 10
Slip regime: Gross Slip
Polished Specimen
Unpolished Specimen
Amplitude
Partial Slip
Friction force
Fretting loop
Data Acquisition System
Gross Slip

7. Fretting Loop (Polished)
Results
Wear Scars
Wear Scars
Raw scan of the worn regions, as observed under a microscope
Surface Maps
Surface map of the wear scars and surrounding unworn region obtained using a surface profilometer. Used to calculate the worn volume
Profile
A cross section of the surface, showing depth of wear scar relative to the unworn surface
Fretting Loop
Plot of friction force vs displacement amplitude . Used to calculate the total dissipated energy
𝑽 𝒘 =𝜶 𝑬 𝑫
Where 𝛼 is the dissipated energy wear coefficient (Fouvry, 1997)
Raw scan of the worn regions, as observed under a microscope
Wear Scars – 2D map
Surface map of the wear scars and surrounding unworn region obtained using a surface profilometer. Used to calculate the worn volume.
Wear Scars
Profile
A cross section of the surface, showing depth of wear scar relative to the unworn surface
Displacement (𝜇𝑚)
Fretting Loop
Surface Maps
Plot of friction force vs displacement amplitude . Used to calculate the total dissipated energy
Profile
Fretting Loop (Polished)
Unpolished
Polished
Wear analysis in fretting of hard coatings through dissipated energy concept; Siegfried Fouvry, Philippe Kapsa, Hassan Zahouani, LEO Vincent

8. Future Work Extend the study to more materials and coatings
Analyze the effect of displacement amplitude and frequency on the polished and unpolished coating performance
Study wear scars under SEM to evaluate the underlying wear mechanisms
Study the contact evolution by observing the contact area in situ
Build a FEA model of fretting wear with surface roughness