Join Date: Aug 2005
Location: San Francisco California
Bikes: Waterford 953 RS-22
Mentioned: 12 Post(s)
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Titanium alloys, like steel alloys, have a definite fatigue limit (also called endurance limit). Basically, materials with a fatigue limit can experience an infinite number of load cycle stresses below the fatigue limit without failing. For materials that have no fatigue limit (like aluminum and magnesium alloys) every stress, regardless of how miniscule, weakens the material and eventually will lead to failure.
For an excellent introduction to the pros and cons of various bicycle frame materials, read Scot Nicol's series of seven articles Metallurgy for Cyclists
(links to each chapter is along the left side of the web page).
Titanium won't weaken with age unless there are repeated stress excursions beyond the fatigue limit of the alloy, which is highly unlikely in normal use. One area where early titanium frames had failures is in the welds at tubing joints. Welding titanium and titanium alloys must be performed with special precautions because these materials are highly reactive to contamination from atmospheric gases; it is important that during the welding process, the area of the weld is shielded from air by performing the welding either in a vacuum or in an enclosure containing an inert gas. Weld failures are now very rare as the frame manufacturers have learned how to prevent contamination.
A well made titanium frame should last a lifetime or longer.