Improvement of Reliability and the Mechanical Properties of Titanium Alloy Forgings.

摘要

A series of fabrication and heat treatment sequences were evaluated to develop processing cycles that optimized property levels in Ti-6246 and Ti-38644 hand forgings. Die forgings were then produced using the optimum process for each alloy to demonstrate that reliable and consistent property levels could be obtained in airframe structural parts. The Ti-6246 optimum process consisted of forging at 1725 F, heat treating 4 hours at 1685 F, solution treating 4 hours at 1525 F, and aging 8 hours at 1100 F with an air cool after each operation. Consistent strengths and ductilities were obtained throughout 4 to 10-in. cross sections which were higher than currently available in other alpha-beta titanium systems. Good combinations of fatigue endurance limits, stress corrosion cracking thresholds, fracture toughness, thermal stability, and resistance to cyclic crack growth rate were also developed. The Ti-38644 optimum process consisted of forging at 1500 F, heat treating at 1500 F, and aging 4 to 12 hours at 950 to 1150 F with an air cool after each operation. Excellent transverse ductilities and good fracture toughness values were obtained at high yield strengths. Fatigue endurance limits, stress corrosion cracking thresholds, and resistance to cyclic crack growth rate were equivalent to or higher than other beta alloy systems. These property levels make the Ti-6246 and Ti-38644 systems excellent candidates for thick section airframe applications. (Author)