A study of abrasive wear mechanisms using diamond and alumina scratch tests

Scratch tests using alumina (Al₂O₃) abrasive particles and Vickers diamond pyramids were employed to study material removal mechanisms in the abrasion of cobalt-base powder metallurgy alloys 6 and 19. The alloys were specially prepared to produce either fine or coarse carbides in order to study the effects of carbide size. Scanning electron microscopy was used to analyze the scratch grooves, the scratch tools and the wear debris particles.

Comparison of scratch tests with Al₂O₃ and diamond pyramids shows that many features produced by the extremely hard regularly shaped diamond tools are different from those produced by irregular Al₂O₃ particles. Except for differences produced by tool wear, multiple-pass Al₂O₃ scratch tests provide excellent reproduction of the material removal processes which occur in low stress Al₂O₃ abrasion. Al₂O₃ scratches produced both chip-like and fine irregular debris particles similar to those extracted from spent abrasive used in wear testing.

Material removal in the fine carbide alloys is facilitated by the direct removal of entire carbides within the volume of micromachining chips removed from the scratch groove. In coarse carbide alloys, machining chips from large carbides are observed, but the depth of cut in the carbide phase is less than that in the f.c.c. matrix and this leads to a decrease in the volume of material removed. Direct comparison of chips removed from fine and coarse carbide alloys by the same Al₂O₃ particle shows larger chips from the fine carbide material.

The effects of subsurface deformation and surface irregularities on material removal were studied by carrying out scratch tests on specimens subjected to prior abrasion and by investigating multiple-pass scratches in the same scratch groove.