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

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

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

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

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

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

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

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