short representation of friction and wear&tribology

1. NATIONAL INSTITUTE OF TECHNOLOGY, HAMIRPUR
TRIBOCHEMICAL POLISHING

2. CONTENTS
1. Corrosive wear and oxidation wear
2. Tribochemistry
3. Tribochemical polishing
4. Conditions

3. CORROSIVE WEAR AND OXIDATION WEAR
 Corrosive and oxidative wear occur in a wide variety of situations both
lubricated and unlubricated.
The fundamental cause of these forms of wear is a chemical reaction between
the worn material and a corroding medium which can be either a chemical
reagent, reactive lubricant or even air.
Corrosive wear is also known as chemical wear.

4. These wear occurs when sliding takes place in the corrosive environment,
air is the most dominant corrosive medium is oxygen.
 These wear requires both chemical reaction (corrosion) and rubbing , so in
the absence of sliding there will be no corrosive wear.
 These wear are important in number of industries such as mining ,
mineral processing , chemical processing and handling.

5.  Chemical corrosive occurs because of chemical and electrochemical
intersection of interface with the environment.
Chemical corrosion occurs in a highly corrosive environment and in high
temperature and high humidity environment.
 Electrochemical corrosion is a chemical reaction accompanied by the passage
of an electric current for the occurrence of potential difference between two
regions.

6. Fig no.1 Models of interaction between a corrosive agent and a worn surface

7. The first process is dominated by the formation of durable lubricating films. If
such films are prevail then worn contacts are well lubricated and corrosive wear
does not occur.
 The second process is related to the formation of a sacrificial or short lifetime
corrosion product film under sliding contacts.
 The third process relates to wear in highly corrosive media.
 In the forth step rapid corrosion occurs on the exposed surface.

8. Fig no.2

9. TRIBOCHEMISTRY
 Chemistry dealing with the modification of chemical reaction by friction or
mechanical energy is called turbo chemistry.
 It is also defined as the chemical reactions between the surface and the
lubricant molecules inside a sliding contact under boundary lubrication
conditions.
These reactions controls the lubrication processes.
They determine the reliability and durability of moving parts in machines.

10.  The wear controlled by this reaction as called as Tribochemical wear.
 The mechanism by which friction increases the rate of chemical reaction are:-
 Heat produced at contacting asperities.
 Removal of product scale resulting in fresh surfaces.
 Accelerated diffusion.
 Mechanochemical excitation of surface bonds.

11. TRIBOCHEMICAL POLISHING
 The corrosive wear is not always an entirely destructive process.
 Corrosive wear can be utilized to produce very smooth surfaces where the
component is polished in a moderately active chemical reagent or water. This
technique is known as tribochemical or chemo-mechanical polishing.
 Tribochemical polishing has been used to generate very smooth surfaces on
silicon nitride, silicon and silicon carbide.

12. Tribochemical polishing (TCP) is a new technique for polishing
materials that is based on the friction‐stimulated dissolution of material in a
liquid.

13. Fig no. 3 Mechanism of tribochemical polishing

14. STEPS OF MECHANISM
 Chemical reaction between worn surface and corroding medium.
 Preferential removal of successive layers of oxide at asperity peaks.
 Worn surface becomes very smooth after initial wear.

15. Tribochemical polishing is effective only when the following
conditions are satisfied:
 Friction at the asperities is sufficient to generate tribocorrosion
products.
 Mechanical stresses are low to avoid any surface deformation or
fracture.
Corrosive medium is not too aggressive to cause corrosion outside the
frictional contact.

16. ADVANTAGES
High hardness.
High thermal conductivity.
Service life increases.
 Reliability increases.

17. Fig. 4 Tribochemical polishing of sic

18. THANK YOU