Cryogenic Fracture Toughness Improvement for the Super Lightweight Tank's Main Structural Alloy

NASA/TM-211547, Chen*, P.S. and Stanton, W.P., Cryogenic Fracture Toughness Improvement for the Super Lightweight Tank's Main Structural Alloy, George C. Marshall Space Flight Center Marshall Space Flight Center, AL 35812, National Aeronautics and Space Administration Washington, DC 20546-0001, Prepared for the Engineering Directorate, Materials, Processes, and Manufacturing Department * IIT Res, February 2002, pp. 20, Format(s): PDF 4650k

View PDF - Requires Adobe Acrobat Reader or other PDF viewer.

Marshall Space Flight Center has developed a two-step (TS) artificial aging technique that can significantly enhance cryogenic fracture toughness and resistance to stress corrosion cracking (SCC) in aluminum-copper-lithium alloy 2195. The new TS aging treatment consists of exposures at 132 C (270 F)/20 hr + 138 C (280 F)/42 hr, which can be readily applied to flight hardware production. TS aging achieves the same yield strength levels as conventional aging, while providing much improved ductility in the short transverse direction. After TS aging, five previously rejected lots of alloy 2195 (lots 950M029B, 960M030F, 960M030J, 960M030K, and 960M030L) passed simulated service testing for use in the super lightweight tank program. Each lot exhibited higher fracture toughness at cryogenic temperature than at ambient temperature. Their SCC resistance was also enhanced. All SCC specimens passed the minimum 10-day requirement in 3.5-percent sodium chloride alternate immersion at a stress of 45 KS. The SCC lives ranged from 57 to 83 days, with an average of 70 days.

Keywords:	multi step heating rate-controlled (msrc) aging treatment, two-step aging treatment, cryogenic fracture toughness (cft)
Subjects:	Chemistry and Materials: Metals and Metallic Materials: Metallurgy
ID Code:	591
Deposited On:	12 January 2004