Indo-Turkey Tripartite Program – Visit to IIT Kanpur Shri Awadesh Kumar Mallik Scientist Gr IV (1) Central Glass & Ceramic Research Institute, CSIR India
Fretting Wear Tester
Fretting Test Conditions - linear relative reciprocatory displacement sliding Ball-on-Flat configuration Normal Load 8 N constant Stoke Length – 100 μm Frequency – 6 Hz No. of Cycles – 45000 Sliding Distance – 9 m Reciprocating Velocity – 1.2 mm/sec Unlubricated Temperature 23-25 oC Relative Humidity 50%-52% 8N 100 μm, 6 Hz, 45000 cycles
Types of Counterbodies B 0.8 + 18% SiC Flat High Temperature Pressure Less Sintering SiAlON Flat 6 mm diameter Al2O3 balls 10 mm diameter Al2O3 balls 10 mm diameter Si3N4 balls
Properties of Counterbodies
Roughness before Fretting
Friction Curves – SiC Composite 6 mm Al2O3 Running-in Period 400-700 cycles 6 mm Al2O3 10 mm Al2O3 10 mm Si3N4
Friction Curves - HTPLS Running-in Period 400-700 cycles 6 mm Al2O3 10 mm Al2O3 10 mm Si3N4
3D profile of worn surfaces – SiC Composite 10 mm Al2O3 10 mm Si3N4
3D profile after fretting – HTPLS 10 mm Al2O3
2D profile after fretting SiC Composite 6 mm Al2O3 10 mm Al2O3
2D profile after fretting – SiC Composite 10 mm Si3N4 - SiC
Steady state Average COF Wear & Friction Values Sample Steady state Average COF Wear Volume mm3 Wear Rate mm3N-1m-1 SiC vs 6 mm Al2O3 0.55 7.25 Χ 10-4 1.003 Χ 10-5 SiC vs 10 mm Al2O3 0.15 -.20 6.1 Χ 10-4 8.472Χ 10-6 SiC vs 10 mm Si3N4 0.30-0.35 3.1 Χ 10-4 4.305 Χ 10-6 HTPLS vs 6 mm Al2O3 0.69 1.452 Χ 10-3 2.016 Χ 10-5 HTPLS vs 10 mm Al2O3 0.15-0.25 1.247 Χ 10-3 1.731 Χ 10-5 HTPLS vs 10 mm Si3N4 1.636 Χ 10-4 2.272 Χ 10-6
Optical Images of Wear Scar – SiC Composite 6 mm Al2O3 6 mm Al2O3 10 mm Al2O3 10 mm Si3N4
Optical Micrograph of Wear Scar of HTPLS 6 mm Al2O3 6 mm Al2O3 10 mm Al2O3 10 mm Si3N4
SEM Images of Wear Scars – Least Worn SiC composite against 10 mm Si3N4 balls Tribo-islands Sliding direction Wear debris inside tribo-island Grain Pull-out
Oxygen rich triboislands Possible Chemical reaction under stress & temperature 2 SiAlON + 2.5 O2 = 2 SiO2 + Al2O3 + N2 SEM images with EDAX Element Weight % Weight % σ Atomic % Carbon 9.726 1.524 16.801 Oxygen 35.956 0.752 46.628 Sodium 0.387 0.102 0.350 Aluminum 3.605 0.115 2.772 Silicon 43.629 0.824 32.230 Potassium 0.372 0.059 0.197 Calcium 0.487 0.061 0.252 Gallium 0.094 0.182 0.028 Samarium 4.171 0.249 0.576 Gold 1.574 0.305 0.166 Abrasive Grooves Oxygen rich triboislands Element Weight % Weight % σ Atomic % Carbon 5.451 0.766 9.225 Nitrogen 32.904 1.039 47.756 Oxygen 3.618 0.457 4.597 Aluminum 2.390 0.091 1.801 Silicon 49.328 0.892 35.705 Calcium 0.292 0.057 0.148 Gallium 0.071 0.179 0.021 Samarium 4.194 0.248 0.567 Gold 1.752 0.306 0.181
Highest Worn SiC Composite vs 6 mm Al2O3 ball Sliding direction Crack Propagation & Fragmentation of Tribo-islands Spalling of tribolayer and wear debris
Oxygen rich triboislands Possible Chemical reaction under stress & temperature 2 SiAlON + 2.5 O2 = 2 SiO2 + Al2O3 + N2 SEM with EDAX Abrasive Grooves Element Weight % Weight % σ Atomic % Carbon 1.721 1.011 2.915 Oxygen 51.630 0.663 65.654 Sodium 2.308 0.116 2.042 Aluminum 8.621 0.168 6.500 Silicon 29.702 0.416 21.516 Potassium 1.578 0.080 0.821 Samarium 2.925 0.220 0.396 Gold 1.515 0.298 0.156 Oxygen rich triboislands Element Weight % Weight % σ Atomic % Carbon 3.710 0.762 6.169 Nitrogen 34.832 0.892 49.673 Oxygen 4.906 0.487 6.125 Aluminum 2.293 0.086 1.697 Silicon 50.435 0.822 35.870 Gallium 0.000 Samarium 2.448 0.221 0.325 Gold 1.377 0.300 0.140
Wear Mechanisms Formation of scattered oxygen rich Tribo-islands Abrasive wear grooves along sliding direction Wear particles on abrasive grooves Crack propagation causing fragmentation of tribolayers Spalling of Tribo-island Wear debris in and around tribo-islands Grain Pull-out Oxidation of abrasive wear particles
Low Friction due to Higher Hertzian Contact for bigger balls Hertzian Contact Pressure Po, Where Po = (3/2) Pm = (6WE *²/π³R²) The initial Contact Diameter is given by, a = (3WR/4E*)⅓ W is the applied load E* is effective Elastic modulus & R is the radius of the ball For a given load 8 N as the ball diameter increases from 6 mm to 10 mm initial contact diameter increases which thereby reduces Hertzian contact pressure Po and hence lower resistance to motion (COF)
SEM of Unworn Surfaces