EVALUATION OF TWO TITANIUM FORGING ALLOYS
UNITED TECHNOLOGIES CORP STRATFORD CT SIKORSKY AIRCRAFT DIV
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Ti-6Al-6V-2Sn and Ti-13V-11Cr-3Al both solution heat-treated and aged were evaluated. Both small-size specimens and full-size helicopter components were tested. Small-size specimens were tested for resistance to fatigue crack initiation, resistance to fatigue crack propagation, and fracture toughness. Fatigue crack initiation tests included tension-tension tests both of unnotched specimens and of joints. Helicopter main rotor cuffs were evaluated in fatigue crack initiation and fatigue crack propagation tests with expanded holes and with reamed holes. The titanium alloy cuff test results were compared to those for Ti-6Al-4V annealed and 4340 steel heat-treated to a 125-ksi minimum ultimate tensile strength cuffs and to small-size specimen tests. Tensile test data, chemical analysis and forging parameters are also presented. The crack initiation resistance of Ti-6Al-6V-2Sn was found to be superior to that of Ti-13V-11Cr-3Al. Axial tension-tension fatigue results showed 50 higher fatigue strengths for Ti-6Al-6V-2Sn than for Ti-13V-11Cr-3Al. Joint fatigue tests also showed higher strength values for the Ti-6Al6V-2Sn alloy. Fracture toughness results were comparable for both alloys. Joint fatigue test evaluations were made for reamed, shot peened, and expanded holes. The highest fatigue strength values were associated with specimens having expanded holes. The Ti-6Al-6V-2Sn cuffs with both reamed and expanded cuff-to- spar attachment holes showed higher fatigue crack initiation strength values than those of the Ti-13V-11Cr-3Al.
- Metallurgy and Metallography
- Fabrication Metallurgy