WEAR PROTECTION OF A PRESSURE-LOADED TITANIUM ALLOY BY LUBRICATED ELECTROLESS NICKEL COATINGS

Specimens of 8%-Mn-Ti alloy, plated with heat-diffused electroless nickel alone or plated and coated with a MoS2 containing solid film lubricant, were worn using an extreme pressure 4-ball type wear tester in which the conventional 3 stationary balls were replaced by flat specimens. Wear damage was expressed in terms of wear scar volume. Wear time or load were kept constant and respectively, load or time was varied. Thickness of the Ni coating was varied in the range between 0.5 and 4.0 mil. (0.0005 and 0.004 in). Wear protection by nickel plating alone or by covering the Ti surface with only the solid lubricant was slight. However, it became very significant when the Ni coating was combined with the solid film lubricant. Corresponding results were obtained with the Falex wear tester. In the range of applied loads approaching a 100 kg limit, the wear life of specimens covered with solid lubricant impregnated Ni coatings, increased with the thickness of the Ni layer. When applied loads exceeded the 100 kg limit, wear was controlled by load and wear time, not by thickness of the lubricated Ni coating. Wear behavior of the titanium alloy, when mated with balls of different compositions, was also studied. It was found that wear damage was decreased with increasing hardnesses of the mating materials. Microscopic examination indicated that formation of layers, apparently produced by interaction of softened nickel with decomposition products of the solid lubricant, are involved in the process of wear protection. Generation of frictional heat at higher loads was indicated by a phase transformation in the alpha-beta titanium alloy. Finally, Hertz stresses in the area of contact between the spherical body and the flat surface were calculated. © 1969.