FRICTION AND WEAR OF ION-IMPLANTED METALS - REVIEW

A review is given of the current status of friction and wear testing with ion-implanted metals, mostly centred on ferrous materials. The changes in coefficients of friction measured under low speed conditions are ascribed to the modification of oxidation properties and to decohesion below the implanted layer due to implantation-induced damage. Wear tests carried out under pin-on-disc and crossed-cylinder geometries show that high doses (above 1017 cm-2) of nitrogen and other ions reduce the mild wear rate on steels by a factor of at least 10. The beneficial effects of ion implantation continue beyond the original range of the implanted ions. This is consistent with a mechanism by which dislocations acting as traps for nitrogen and carbon provide wear resistance. Continued effectiveness against wear may arise from thermal or stress-induced migration of implanted atom-defect complexes below the contact region. High dose nitrogen implantation also leads to nitride formation and so hardness increases can be accounted for directly. For inhomogeneous materials such as cemented tungsten carbide it is more difficult to account for the improvements in wear properties. Nitrogen and carbon implantation is thought to reduce the plastic flow of cobalt and hence to decrease the wear rate of the composite carbide. © 1979.