Beautiful, magic metal, finding glory in the light
MMetals are a river that flows through our history. Bronze Age horsemen from Asia’s steppe brought the mysterious stuff to the near-eastern “Cradles of Civilization.” Gold and silver drove Spanish New World exploration and conquest. And now titanium’s use in aerospace and racing has made that element synonymous with the highest performance.
Titanium, sought for its combination of high strength, low weight, and extraordinary corrosion and fatigue resistance, became available in commercial quantities only after 1953. Although common in the earth’s crust, titanium is difficult (read: expensive) to extract from its ore. It was therefore the rivalries of the Cold War that bankrolled its large-scale production. The Soviets became massive producers, making entire lightweight submarines of the stuff. Aerospace-grade titanium currently sells for $20 to $25 a pound, and 15 percent of the empty weight of Boeing’s 787 Dreamliner is titanium.
The word “titanium” has taken on near-magical meaning; it has become a fashion color (shall we call it pale straw?), and like “turbo” has been used to imply special properties in many completely unrelated commercial products. Is there any titanium in a Titanium Edition Ford, for example?
Iron, the basis of steel, has a density of 7.8 times that of water, while that of titanium, 4.5, is just 58 percent as much. This light weight is attractive in any application that requires rapid acceleration. Steels of extreme performance can be stronger than any titanium alloy but only at greater weight. Steels can reach tensile strengths more than 300,000 psi, but titanium’s lightness, even at its lower ultimate strength, gives it the edge in strength-to-weight.
This is the basis for titanium’s use in high-performance motorcycles, mainly in the forms of fasteners, exhaust plumbing, valves, and connecting rods. Titanium’s lower stiffness can make it undesirable as a material for axles and chassis, though Italian titanium specialist NCR successfully use special alloys for both currently. In 1966, BSA, seeking to extend its success in 500cc European motocross, created a titanium chassis, but associated problems made it unsuccessful.
A complete contrast has been the use of titanium in bicycle frames, where its lower stiffness reduces ride harshness, earning the description “magic ride.”
In 1956, the well-connected AJS engineer and former TT rider Jack Williams (father of Peter Williams of Norton fame) showed that connecting rods of high-strength
titanium alloy could reduce bearing loads and therefore friction loss in internal-combustion engines. Boeing pioneered titanium-machining techniques in producing the B-52 bomber in the early 1950s. In the 1960s, Bob Nichols, who worked 25 years at Douglas’ mile-long plant in Santa Monica, California (now empty), introduced titanium con-rods to the open-wheel Champ car community.
It is mainly in dynamic applications such as valves and connecting rods that titanium has made a place for itself in high-performance engines. Even with the necessity of protecting reactive titanium valve stems from seizure with anti-friction coatings, and providing hardened seating surfaces and hard stem caps, its lightness has enabled engines to reliably reach higher revs because its lower weight can require lower valve spring pressures than do steel valves. In the later 1970s, racing motorcycles began to use titanium intake valves, but titanium exhausts soon followed. When Honda decided to re-enter US AMA roadracing in 1980, early team manager Steve Mclaughlin (some call him “the father of Superbike”) flamboyantly ordered thousands of dollars’ worth of titanium valves and rods from Jet Engineering.
During the 500cc two-stroke era of Grand Prix racing, engineers gradually substituted titanium for the steel traditionally used to make exhaust pipes, starting with the pipes farthest from the bike’s roll axis. As specialist shops acquired the tooling to work titanium, four-stroke pipes were made of the light metal, resulting in complete four-cylinder systems as light as 7 pounds.
Yamaha introduced titanium springs to motocross for the obvious reason: weight; titanium springs cut weight 30 percent but cost at least eight times more than steel. Several years ago, when I was given a tour of the Honda/ HRC Supercross transporter, I was shown a drawerful of titanium footpeg assemblies—at $2,600 each. The benefits are that light weight improves nearly all aspects of performance.
Titanium’s high cost comes from the need to process or weld titanium in either vacuum or an inert atmosphere. This protects the metal from absorbing gases that can render it brittle and prone to cracking.
Why is titanium light and strong? Because at the smallest level, this metal’s atomic radius is fairly large, giving the solid a lower density, and its room-temperature hexagonal close-packed crystal structure puts every atom in contact with 12 others. Metals are ductile rather than brittle because, with few outer-shell electrons, solid metal is effectively an array of atomic nuclei filled by a “gas” of loosely bonded electrons. Metals bend rather than snap because this electron gas lets interatomic bonds stretch, break, and then re-form with new partners. The high mobility of the electron gas is also responsible for the electrical and thermal conductivity of metals.
Titanium’s exceptional fatigue strength owes much to the metal’s reactivity, which instantly forms a powerfully protective surface layer of titanium oxide. Whereas exposure of steel and aluminum to weather inevitably produces tiny corrosion pits that combine with cyclic stress to produce eventual fatigue failure, titanium’s protective layer greatly slows this process.
This self-protection gives pure titanium its ability to be accepted by the human body in the form of dental implants, artificial replacement joints, and the plates and screws used to speed the healing of broken bones.
The rainbow colors surrounding the welds in titanium exhaust systems are created by imperfect weld conditions. Ideally, titanium welding takes place in a “glove box” (visually similar to a bead blast cabinet) that is purged and filled with inert argon gas, but sufficient oxygen remains to form surface oxide layers on the work that appear colored. These thin layers act as interference filters in the same way as do thin films of oil, floating on water.
A titanium production scheme using less energy than the present Kroll process might in time allow price reductions, making the light metal more attractive for wider use in production vehicles.
The romance of titanium in the motorcycle world began when we could see the metal’s special gleam on factory racebikes. Seeing that, who could regard the standard production zinc-plated steel fasteners as anything other than advertisements for excess weight?
The beauty changes the closer you get. Titanium is nearly unassailable when facing environmental factors that lead other metals to oxidize, corrode, and eventually fail.
NCR titanium custom frame can be tuned for flex based on riding style, varying wall thickness, and diameter of tubing. Welds are perfect.