Titanium (Ti) is a grey transition metal which is strong, light and resistant to corrosion. Titanium is as strong as steel, but the density is 60% lower. It is the 9th most abundant element on earth. Titanium is often used in an alloy with these elements: iron, aluminum, vanadium and molybdenum. Casting of titanium is very hard, just because it is so strong. And due to its rarity it is expensive compared to other metals.
*A transition metal is a chemical element that contains valence electrons (electrons that form a chemical bond) in two valence shells, instead of one. Transition metals can be found in the middle of the periodical system. Please consult the Encyclopaedia Britannica for more detailed information. (https://www.britannica.com/science/transition-metal)
The advantages of titanium
Titanium is strong in relation to its mass. The density is 60% higher than aluminum, while it is twice as strong. The melting point is higher than 1650 °C. At temperatures above 430 °C titanium starts to lose strength. Titanium and titanium alloys oxidate immediately when they come in contact with oxygen. But at room temperature a layer of titanium oxide is formed as a kind of coating, thereby protecting the inner metal. The favorable properties of titanium lend itself for usage in airplanes, spacecraft, ocean-going vessels, rockets and armoring. In most of these uses it is used as an alloy with aluminum, zirconium and nickel. Approximately two thirds of titanium that is produced in the world is used for the manufacturing of airplane engines and fuselages. The (petro)chemical industry benefits from the durability of titanium by using it in pipelines, valves and storage tanks.
The human body doesn’t reject titanium and is therefore considered biocompatible. In the medical industry titanium implants are used in the hip joints, the wrist and jaw.
The physical properties of titanium:
- Density: 506 g/cm³ at 20 °C
- Brinell hardness: 716 – 2770 Mpa
- Tensile strength: 434 MPa
- Melting point: 1668 °C
- Molar heat capacity: 060 J/mol x K)
Machining titanium
The characteristics of titanium that make it such a strong and high-quality material also make it hard to machine. In some cases, up to 90% of the original piece has to be removed to achieve an end product. Titanium has a low value for Young’s modulus, meaning that the metal is not very stiff. The consequence when machining is that the mill can easily start vibrating and damage the surface of the workpiece. During the machining process splinters are released that can hinder the cutter. Serially and automatically CNC machining of titanium is a complex undertaking.
Utilizing high quality work tools is of vital importance. The chisel, drill, tap or cutter has to be coated in cemented carbide (which is a composite of tungsten, titanium and tantalum carbide). With this composite the chisel can withstand the stickiness and splintering of titanium alloy. The coating also protects the tool from overheating. Other than that, it is advisable to orient the cutting tool in such a way that the chisel turns with the direction of the machining, not against it. So the cutting edge will touch the titanium at the widest point, and the metal chips stay behind the cutter and do not interfere with it. Utilizing this technique ensures manageable temperatures and smooth sailing for the cutter.
The worldwide titanium industry
Titanium was discovered by Englishman William Gregor in 1791. To extract titanium from natural ore is a laborious and costly endeavor. To do it, one must reduce the raw material to a kind of ‘sponge’ of porous form and then melting this sponge to a bar. About 95% of all titanium ore is refined to titanium dioxide that is used in the manufacturing of paint, paper, toothpaste, cement, jewelry, tennis rackets, fishing rods, golfclubs and all kinds of plastic. Titanium alloys are used in architectural applications like armoring, airplane landing gears, helicopter exhausts and hydraulic systems. Two thirds of all titanium is destined for airplane engines and fuselages. The three biggest producers of titanium in the world are China, Japan and Russia.