Tribochemical wear is the most complex wear mechanism [MARI04, RABI95]. It includes a reaction between body, counter body and environment [DIN79, HABI80]. A large reactive surface or friction heat accelerate these reactions.
Beads of molten workpiece material give evidence of the high temperatures during the cutting action. For example, Mfiller [MULL01, p. 57] found beads of molten workpiece material (bearing steel) on SiC grits after single grit scratch tests. Reactions of the workpiece surface, the grit or bond material are promoted by grinding process heat. Possible reactions of the abrasive grits were explained in Chap. 2 “Abrasives”.
6.4.2 Grit Splintering or Breakage
In brittle materials, such as grit materials, it is hard to differentiate between microscopic breakage processes, or wear by abrasion [WILK91]. This is because the grooves and small chips, which generally help to detect abrasion, are missing in brittle materials due to their low tensile yield point [WILK91].
In monocrystalline diamonds, breakage occurs along the cleavage planes. Polycrystalline diamonds break along the crystal boundaries. Wear by micro-chipping occurs at friable diamond [BAIL99]. When machining hard, brittle, short chipping workpiece materials with the more friable diamonds, the grinding forces tend to be lower and surface roughness smaller [BAIL99].
Alternating thermal or mechanical load lead to elastic and plastic deformation, change of material hardness (softening or hardening), crack formation and crack propagation [GAHR87, RABI95, PEKL57, p. 86 ff]]. Surface shattering is a fatigue mechanism occuring at impact load [DIN79, HABI80]. Grain boundaries or cleavage planes open and the cracks start at or near the surface [GAHR87].