1. Mechanical surface structural transformation treatment

Mechanical surface treatment by attrition is of great interest in the field of tool steels. This treatment consists in plastically deforming a metal surface at very high speed and under repeated impact by ultrasonic vibration of metal balls a few millimeters in diameter. The surface to be treated is placed in a vacuum chamber in which the balls are vibrated, producing energetic impacts (1 to 20 m.s ^-1 ) in random directions. The most notable differences between this type of treatment and conventional shot peening are the random projection of the beads onto the surface and the size of the metal spheres (2 to 5 mm). Table 1 compares this severe plastic deformation process with shot peening. The main feature of mechanical attrition treatment is a dramatic reduction in grain size in the...