1 INTRODUCTION

After a component is manufactured, all or parts of its surfaces may have to be processes further or coated in order to impart certain properties and characteristics. Surface treatment may be necessary to:

1. Improve resistance to wear, erosion, and indentation (slide ways in machine tools, wear surfaces of machinery, and shafts, rolls, cams and gears).
2. Control friction (sliding surface on tools, dies, bearings, cam, and machine ways)
3. Improve lubrication (surface modification to retain lubricants).
4. Improve corrosion and oxidation resistance (sheet metals for automotive or outdoor uses, gas turbine components, and medical devices).
5. Improve stiffness and fatigue resistance (bearings and multiple-diameter shafts with fillets).
6. Rebuild surface on worn components (worn tools, dies, and machine components).
7. Impart decorative features, colour
8. Improve surface roughness (appearance, dimensional accuracy, and frictional characteristics).
9. Reduce adhesion (electrically contacts).