I have done an experiment using lubricant on a pin on disk apparatus. I have added some solid additives to the lubricant. To my surprise when we weighed the tested pin, the weight of the pin after test was found to be higher than the initial pin. The hardness of pin is 12HRc and disk hardness is 58HRc.SEM images clearly indicates wear has taken place in the pin. The experiment was repeated several times but same results i.e weight of pin after test is more than initial pin.
First I would clean the pin after test because it may absorb solid additives. Second, soft pin may not be worn without removal of metal, i.e. it may suffer plastic deformation which is also wear but to be detected only by pin's height reduced. Third reason may be metal transfer film which sticks alternatively either to pin or counterbody surface.
Dear Tarasov,thankx for your reply. But EDS result shows that no solid additives have been deposited. Pin is 12Hrc and disc is 58Hrc, will 58HRc stick on 12HRc?
what are the materials of the pin, disk and solid additives and the load and speed at which you are running the test.
Can you observe the wear track on the disc ?
I think you should check the composition of the pin surface after testing.
Normally softer or softened material sticks to harder one but it depends on the sliding conditions and mainly on the temperature within the contact areas. The harder materials which I presume is quenched steel here may be both thermally and deformationally softened. So this structural instability would lead to seizure and transfer of metal from harder to softer material.
The harder material is EN 31 and softer is EN 21. We did the test with two different additives. In one additive we got the negative weight loss while with the other we got positive wear loss.
The harder material is EN 31 and softer is EN 24. We did the test with two different additives. In one additive we got the negative weight loss while with the other we got positive wear loss.
I think you will get your answer from careful examination and analysis of the tested pin surface
Hi Shubrajit
I think the gain in the weight of the pin might be due to the oxidative wear of the pin. Due to the severe test conditions (depending on the load and the speed), the temperature at the asperity contacts might be much higher than the bulk temperature of the tribo-couple. This can lead to the oxidation of the pin/substrate material at the asperity contacts. If the oxidation products form a stable passive layer at the pin, it will increase the weight of the pin. An EDX analysis of the pin surface will give a good idea if this is the case or not. For more on the oxidative wear u can refer to my publication: A Tewari. Load dependence of oxidative wear in metal/ceramic tribocouples in fretting environment. WEAR (2014) 289, 95-103.
Best regards
Abhishek
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