JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech IV SURFACE ENGINEERING Previous Question Paper (July/August - 2022 - R18)

Mechanical surface treatments are processes used to alter the topography, surface integrity, and mechanical properties of a component's surface layer. Grinding involves the removal of material using a rotating abrasive wheel. It is primarily used to achieve high dimensional accuracy and superior surface finish by removing irregularities left by previous machining operations. Machining, such as turning or milling, uses cutting tools to remove bulk material to reach specified dimensions. While it shapes the component, it often introduces residual stresses and surface roughness that may require subsequent finishing. Blasting, including shot peening or sandblasting, involves propelling abrasive media at high velocity against the surface. This process cleans the surface, removes contaminants, and, importantly, induces compressive residual stresses that significantly enhance the fatigue life and resistance to stress corrosion cracking of the material.

Surface modification significantly alters the performance characteristics of materials by changing the properties of the surface layer relative to the bulk. Key properties influenced include:

• Hardness and Wear Resistance: Modification techniques like nitriding or hard facing increase surface hardness, which directly improves resistance to abrasive, adhesive, and erosive wear.
• Corrosion Resistance: By creating a chemically inert barrier or modifying the surface composition (e.g., through galvanizing or anodizing), the surface becomes less susceptible to oxidation and environmental degradation.
• Fatigue Strength: Processes like shot peening induce compressive residual stresses, which inhibit crack initiation and propagation, thereby extending the fatigue life of components subjected to cyclic loading.
• Friction and Lubrication: Surface treatments can alter the coefficient of friction and improve the retention of lubricants, reducing energy loss and preventing galling in sliding contacts.
• Adhesion and Wettability: Modifications can increase surface energy or create specific topographies to improve the bonding strength of coatings, adhesives, or paints applied to the surface.