Stronger than some steels, but almost 45% lighter….. Twice as strong as aluminium, but just about 60% heavier….. That’s titanium for you! Titanium is a lustrous, silver-coloured metal, and incredibly strong, while being very light. It has the distinction of having very high corrosion resistance (even in sea water and chlorine), and the highest strength, relative to its density, compared to any other metal.
Did you know? Titanium was originally discovered in Great Britain, in 1791, and is named after the Titans from Greek mythology.
Titanium is typically combined with iron, aluminium, molybdenum and vanadium, to form alloys. These alloys are strong and tough, light in weight, highly resistant to corrosion and can withstand extremely high temperatures. The most commonly used titanium alloy is the Ti-6Al-4V. Some call it the Cadillac of the titanium alloy industry while some call it the workhorse alloy!
Ti6Al4V, Ti-6Al-4V or Ti 6-4, also called a grade 5 titanium alloy is so called because it is made of 6% aluminium (Al) and 4% vanadium (V), along with about 0.25% iron and 0.2% oxygen, with the remainder being titanium (Ti). It is also called an alpha-beta alloy (since it contains aluminium, which is an alpha stabiliser and vanadium, which is a beta stabiliser) and can undergo heat treatment.
Despite its alluring properties, the high cost of titanium limits the use of titanium alloys to military applications, spacecraft, aircraft, and expensive sports cars, electronic goods, and sports equipment.
Properties and Applications of Ti-6Al-4V
Let’s examine what material properties make this alloy so alluring to many industries:
High corrosion resistance: The Ti 6-4 alloy is highly resistant to corrosion, mainly because of a continuous and consistent layer of oxide that forms spontaneously when exposed to oxygen. This property helps it withstand the harshness of sea water and makes it an ideal choice for underwater and marine applications like submarines, and offshore oil and gas operations equipment, as well as applications in the chemical industry.
High tensile strength and light weight/low density: The military and the aviation and aerospace industries have long benefited from these properties of Ti-6Al-4V. It is used in the structural components of aircraft, hydraulic systems, engine components, helicopter rotor blades, rockets and spacecraft. Its high strength-to-weight ratio is particularly useful in race cars and is used in several components including gear boxes. The military uses it in the manufacture of missiles and artillery.
The alloy’s high strength also means that it can be used for dental implants – titanium screws are fused to the jawbone to replace a deformed or missing tooth, which looks natural and lasts a lifetime.
Heat treatable, easy weldability and fabricability: Ti-6Al-4V can withstand extremely high temperatures (up to 750 °F) and can be easily welded and fabricated, which makes it particularly attractive for the automotive industry, for various engine components, gear boxes etc.
Excellent biocompatibility: One of the amazing properties of Ti-6Al-4V, because of which it has become a wonder alloy for the medical domain, is its biocompatibility – it does not react with body fluids, surrounding tissues or bones and helps with osseointegration. Porous structures made from the alloy allow vascularisation and adherence of the tissue to the implant, thereby speeding up recovery in patients who have undergone hip replacement and knee replacement surgeries. The alloy is also used in prosthetics, bone plates and rods.
Non-magnetic: Ti-6Al-4V is non-magnetic, which means that a person with this implant in the body, can safely undergo X-ray, MRI and others scans. Ti-6Al-4V is used in medical equipment and surgical devices like needles, tweezers, forceps, clamps, scissors, drills etc.
Disadvantages/drawbacks of Ti-6Al-4V
This alloy is truly a wonder alloy, but has a few drawbacks, just like any other:
Poor shear strength: Ti-6Al-4V has poor shear strength and surface wear properties, because of which it tends to slip or seize when in contact with sliding parts. In order to overcome this, oxidizing and nitriding treatments are employed.
Corrosive to strong acids: Though generally resistant to corrosion, the Ti-6Al-4V alloy is not suitable for use with strong acids like hydrochloric or sulphuric acids, as they cause a breakdown of the protective oxide layer on the alloy, upon contact.
The Ti-6Al-4V has proved to be an amazing material that finds applications in a wide variety of industries – the amount of its use in our daily lives is tremendous, and will only continue to grow with advancement in technology and discovery of new uses for its properties.