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Tests have shown that the Ti-6Al-4V alloy performs best under impact-fatigue loading conditions. This type of test best simulated actual loading conditions in many components in electro-mechanical devices. While the desired impact-fatigue performance is obtained with Ti-6Al-4V, the tendency of the alloy to gall and seize in wear indicated the desirability of some means of surface treatment for improved wear resistance. The combination of improved or unimpaired fatigue performance, along with improved wear, are not necessarily complementary results of surface treatment. Three basic types of surface treatments were investigated: (1) nonmetallic compound or gaseous diffusion coatings, (2) intermetallic-compound coatings, and (3) diffused metal coatings. After eliminating a number of surface treatments on the basis of hardness testing and microstructural examination, the following were selected for impact-fatigue and wear testing: (1) nitriding, (2) heat treatable titanium-chromium alloy layer, (3) heat treatable titanium-chromium alloy layer plus nitriding, and (4) oxygen-saturated alpha-titanium layer. The impact-fatigue testing showed that it is possible to obtain a surface treatment which results in improved fatigue life of Ti-6Al-4V. The results of all impact-fatigue testing will be presented, along with a discussion of subsequent wear testing of each surface treatment.
titanium alloys, fatigue, wear, surface treatment
Senior associate engineer, Rochester, Minn.
Manager, Materials Laboratory, Rochester, Minn.