Titanium is split into three different structural types.
Alpha Alloys are non-heat treatable and are generally very wieldable. They have quite a low strength, fairly tough and possess very good mechanical properties at cryogenic temperatures.
Alpha-Beta alloys are heat treatable and most are wieldable. They have a quite high strength level; their forming qualities are good.
Beta alloys is very heat treatable, it has a very high strength range, but only intermediate temperatures.
Beta-Type alloys have a good combination of properties in sheet, springs and heavy pieces.
Titanium is used in many different ways all over the world and its many properties all help to favour this excellent metal. Titanium is used widely in aerospace as over 50% of the titanium-produced worldwide is used for aerospace parts. This is due to the fact that it is light and has a high melting point of nearly 1668.C*
Titanium is also very resistant to corrosion and is therefore used in many Chemical plants. Because titanium does not corrode it can be used in tubing and be as thin as 0.5mm and never have to be replaced. Usage of titanium in the chemical, nuclear and fossil plants make up over a third of the world production. Many titanium alloys are also used due to the fact that they are non-magnetic, excellent fire resistance and have a short radioactive half-life.
Titanium is also used in many operations as it has a excellent resistance to corrosion and erosion, high heat transfer efficiency. The biocompatibility and the strength of titanium make it a perfect choice for dental and other prosthetics. Bone naturally adheres to the surface oxide of titanium without the need of additional coatings.
However there are some drawbacks with titanium as it is very brittle and very hard to work with. It is also very expensive and quite hard to get hold of.
The SR-71 Blackbird:
Titanium is used widely in the construction of the SR-71 Blackbird as it has very high melting points which allows the plane to fly at a high altitude at very fast speeds. The average speed of the SR-71 is Mach 3. This is over 3 times faster than the speed of sound, which is 761 mph at sea, level.
This new plane required a metal that would be able to cope with the high temperature that would be produced on the surface of the airplane and a material that would be strong enough to be able to withstand the high aerodynamic forces.
The surface temperatures would reach as high as 800C*, which means that they could only use steel or titanium as they are the only metals that can cope with such high temperatures. They chose to use titanium as its density is much less and therefore it will reduce the weight of the plane. The designers of the SR-71 used a rare form of titanium, which would account for 93% of the airframe of the plane.
They had some problems with titanium such as it reacts with other metals especially at very high temperatures; this was a big problem, as the plane would mainly be flying at very fast speeds, which would increase the temperatures.
The other main problems that they had with the titanium was the availability and they found It quite hard to get hold of the metal so they had to import it from the former Soviet Union, which is ironic as the plane was built to spy on the Soviet Union. Titanium also reacts with cadmium-plated tools. The cadmium was used on the tools and then would be used on the plane and when the titanium touched the cadmium it would start to react and therefore make the plane unstable.
Another problem that they had was that the drill tools that they used would often break because of the hardness of the titanium.
They solved this problem by using special drill bits and using special drilling angles and lubricants. They also changed the number of drilled holes from 30 to 120. The last problem that they had to solve was that when the titanium heated up it started to expand and this would cause unevenness in the wings. They solved this by corrugating the wing skin, which allowed the wing skin to expand at a different rate compared to the wing spars. This involves Young Modulus which is stress divided by strain. For example a material with a large strain for little stress is flexible and easy to stretch, where as a material with little strain for a large stress is stiff and hard to stretch. The Young Modulus is large for a stiff material and is small very a flexible material.
Overall titanium was used for the Blackbird SR-71 for a number of reasons and was chosen because of its unique properties that make it stand out from all other metals.
