Ji, The Hagon mono came out around 1977. The first ti frame that I know of was the works BSA Victor 1966. Lars Larsson rode a ti Husky in the 1971 season. Below is Ed Youngbloods description of the bike.
In 1971, Torsten Hallman commissioned Pro-Fab to build a small number of titanium frames. One was built to house Husqvarna's tried and true four-speed “egg engine,” and the others were built for the new five-speed engine. Using a 400cc version of the four-speed engine, Lars Larsson barnstormed the support class of the Inter-Am that year, winning four of the six rounds. Modern Cycle (January 1972) reported the project under the headline, “Titanium, the Racer's Latest Secret Weapon.” The machine struck fear into the American racing community, resulting in the 1972 AMA rule book declaring, "Titanium frames will not be allowed in AMA comptition (page 45)." It was believed that titanium would radically increase the cost of racing. This was a fair concern since, during the Cold War era, titanium was considerably more expensive than it is today. Because Larsson has restored this motorcycle with a 250cc engine, it weighs a few pounds less than it did when raced in 1971.