Cupaloy

The Westinghouse Time Capsules are two time capsules prepared by the Westinghouse Electric & Manufacturing Company: "Time Capsule I" was created for the 1939 New York World's Fair and "Time Capsule II" was created for the 1964 New York World's Fair. Both are buried 50 feet below Flushing Meadows–Corona Park, the site of both world's fairs; the 1965 capsule was placed ten feet north of the 1939 capsule. The capsules are to be opened at the same time in the year 6939, five thousand years after the first capsule was sealed.

The time capsules are bullet-shaped, measure 90 inches (2.3 m) in length, and have an exterior casing of about 8.75 inches (22.2 cm) in diameter. Time Capsule I weighs about 800 pounds (360 kg), while Time Capsule II weighs about 400 pounds (180 kg).

Time Capsule I was made of a non-ferrous alloy called Cupaloy, created especially for this project. Designed to resist corrosion for 5,000 years, the alloy was made of 99.4% copper, 0.5% chromium, and 0.1% silver. Westinghouse claims that Cupaloy has the same strength as steel, yet will resist most corrosion over thousands of years because it becomes an anode in electrolytic reactions, receiving deposits instead of wasting away like most iron-bearing metals. Time Capsule II was made of a stainless steel metal called Kromarc, supplied by U.S. Steel. Westinghouse Research Laboratories determined, with extensive chemical testing, that this new super-stainless steel alloy would resist corrosion, much like the alloy used for Time Capsule I. Invented by Frederick Charles Hull,> Kromarc 55 stainless steel is composed of 52.60% iron, 21.24% nickel, 15.43% chromium, 8.20% manganese, 2.15% molybdenum, 0.22% silicon, 0.05% carbon, 0.013% phosphorus, and 0.012% sulfur.

...
Wikipedia