In the case of tool wear, diffusion occurs at the ______ causing the tool surface to become depleted of the atoms responsible for its hardness.

Concept:

The mechanisms that cause wear at the tool-chip and tool-work interfaces in machining are

• Abrasion: Mechanical wearing action caused by hard particles in the work material gouge and removing small portions of the tool. Abrasive action occurs in both flank wear and crater wear. It is a significant cause of flank wear. 
• Adhesion: When two metals are forced into contact under high pressure and temperature, adhesion occurs between them. These conditions present between the chip and the rake face of the tool. As the chop flows across the tool, small particles of the tool are broken away from the surface, resulting in attrition of the surface.
• Diffusion: This is a process in which an exchange of atoms occurs at the tool-chip boundary, Tool surface becomes depleted of the atoms responsible for its hardness. Diffusion is believed to be a principal mechanism of crater wear.
• Chemical reactions: The high temperatures and clean surfaces at the tool-chip interface in machining at high speeds result in chemical reaction oxidation, on the face of the tool. The oxidized layer being softer than the parent tool material is sheared away, exposing new material to sustain the reaction process.
• Plastic deformation: The cutting forces acting on the cutting edge at high temperatures cause the edge to deform plastically, making it more vulnerable to the abrasion of the tool surface. Plastic deformation contributes mainly to flank wear.

Types of wear 

• Flank wear
• Cater wear
• Chipping