The Delamination Theory of Wear
Annual progress rept. May 1973-June 1974
MASSACHUSETTS INST OF TECH CAMBRIDGE MATERIALS PROCESSING LAB
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The delamination theory of wear and the supporting experimental evidence are presented. The theory is valid when there is no significant temperature rise at the surface to induce any phase transformation and thermally activated diffusion of elements. It is shown that at low sliding speed the wear of metals occurs by subsurface deformation which induces void and crack nucleation and subsequent crack propagation parallel to the surface. The cracks eventually propagate to the surface producing thin wear sheets. This phenomenon has been observed on a variety of metals from soft cadmium to fully hardened AISI 4340 steel. The delamination theory of wear predicts that the best method of preventing wear is to use a material without large second phase particles or inclusions. For example, annealed zone refined iron has 13 the wear rate of AISI 1020 steel. Another prediction of the theory is that a thin layer of a soft metal on a hard substrate should reduce the wear rate because the dislocations are not stable in the thin layer. It is shown that a 0.1 micrometer cadmium coating on both contacting surfaces of AISI 1018 steel reduces wear by three orders of magnitude over the unplated steel. This coating is effective in an inert atmosphere, inert oil, but is not effective in an oxidizing atmosphere.
- Metallurgy and Metallography