1. Introduction to Wear and corrosion
In machine design, wear and corrosion are major causes of material degradation and failure.
- Wear: Gradual removal of material from surfaces in contact due to relative motion
- Corrosion: Deterioration of material due to chemical or electrochemical reactions with the environment
Designing against these effects improves life, reliability, and efficiency of components.
2. Types of Wear
(a) Adhesive Wear
- Occurs due to metal-to-metal contact
- Micro-welding and tearing of surfaces
(b) Abrasive Wear
- Caused by hard particles or rough surfaces
- Types:
- Two-body abrasion
- Three-body abrasion
(c) Surface Fatigue Wear
- Repeated loading → cracks → pitting
(d) Corrosive Wear
- Combination of chemical attack + wear
3. Factors Affecting Wear
- Load and contact pressure
- Sliding velocity
- Surface roughness
- Material properties
- Lubrication condition
- Temperature
4. Design Against Wear
(1) Material Selection
- High hardness
- Good wear resistance
- Examples:
- Alloy Steel
- Cast Iron
- Ceramics
(2) Surface Hardening
- Case hardening
- Nitriding
- Carburizing
- Induction hardening
(3) Proper Lubrication
- Reduces friction and wear
- Forms protective film
(4) Surface Finish Improvement
- Smooth surfaces reduce wear
- Use grinding, polishing
(5) Reduce Contact Stress
- Increase contact area
- Proper design geometry
(6) Use of Coatings
- Anti-wear coatings (e.g., TiN, DLC)
- Surface plating
5. Types of Corrosion
(a) Uniform Corrosion
- Even material loss over surface
(b) Galvanic Corrosion
- Occurs between dissimilar metals
(c) Pitting Corrosion
- Localized holes → dangerous
(d) Crevice Corrosion
- Occurs in confined spaces
(e) Stress Corrosion Cracking
- Combined effect of stress + corrosion
6. Factors Affecting Corrosion
- Environment (moisture, chemicals)
- Temperature
- Material composition
- Surface condition
- Presence of electrolytes
7. Design Against Corrosion
(1) Material Selection
- Corrosion-resistant materials:
- Stainless Steel
- Aluminium
- Titanium
(2) Protective Coatings
- Painting
- Galvanizing
- Electroplating
(3) Cathodic Protection
- Sacrificial anode method
- Impressed current method
(4) Design Modifications
- Avoid crevices
- Ensure drainage
- Avoid sharp corners
(5) Corrosion Allowance
- Extra thickness provided
(6) Environmental Control
- Use inhibitors
- Control humidity
8. Combined Wear and Corrosion
- Occurs in harsh environments
- Example: marine applications
- Requires:
- Special materials
- Coatings
- Lubrication
9. Applications
- Marine structures
- Pipelines
- Automotive parts
- Industrial machinery
- Chemical plants